Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session M01: Flash Oral Presentations: Turbulence 
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Chair: Mark Glauser, Syracuse University Room: 6a 
Monday, November 25, 2019 3:20PM  3:21PM 
M01.00001: Deep Learning the Advection in Eulerian Hydrocodes Peter Yeh, Ki Tae Wolf, Samuel Bowie, Carianne Martinez, Kevin Potter, Charles Snider, Matthew Smith, David Hensinger, John Korbin In Eulerian and arbitrary LagrangianEulerian (ALE) hydrocodes, the timestep usually contains two parts. The first is a Lagrangian step, during which the local material cell or element is incrementally deformed. The second step is the remap step or advection step, which computes the material transport between the local elements. This remap step typically relies on heuristic algorithms that depend on neighboring solution variables. Recent developments in deep learning have shown great promise in applications or alternatives to traditional computational engineering methods. In this work, we explore the possibility of a deep learning model to mimic the remap function. Our deep neural network is trained on the nodal velocities of a structured mesh before and after the remap step in our Eulerian hydrocode. We show that our deep learning model can accurately reproduce the remap function to acceptable accuracy, and we compare speeds between our DNN and the existing remap function. This work continues to demonstrate that deep learning models can enhance numerical predictive capabilities. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DENA0003525. [Preview Abstract] 
Monday, November 25, 2019 3:21PM  3:22PM 
M01.00002: Complex Nozzle Optimization Techniques using Machine Learning Dom DiDominic, Jonathan Fitzgerald, Emma Gist, Mark Glauser Advances in the aviation industry have led to the expanded use of complex nozzles on nextgenerationplus aircraft that allow for seamless integration in the airframe. Complex nozzles, such as MultiAperture Rectangular Single Expansion Ramp Nozzle (MARS Nozzle) used in this study, primarily focus on reducing generated noise while preserving the efficiency of the nozzle. This study explores the use of optimization through a trained deep neural network as the design process of an aft deck plate, representing nozzleaircraft integration, to minimize the effective sound pressure level of the nozzle. This is accomplished by the neural net acting as a surrogate model to predict sound levels based on aft deck geometries and flow conditions. Two nongradient based optimization schemes were chosen to minimize the sounds levels: NelderMead (traditional method) and Particle Swarm Optimization (evolutionary algorithm). Results from the optimization model are validated with experimental particle image velocimetry (PIV) results as well as computational simulations to verify the fidelity of the neural networks. [Preview Abstract] 
Monday, November 25, 2019 3:22PM  3:23PM 
M01.00003: Towards a machine learning method for simulating turbulenceshockwave interactions Ben Stevens, Tim Colonius In recent years, machine learning has been used to create datadriven solutions to problems for which an algorithmic solution is intractable, as well as fine tuning existing algorithms. This research applies machine learning to the development of an improved finitevolume method for turbulenceshockwave interactions. Shock capturing methods make use of complicated nonlinear functions that are not guaranteed to be optimal. Because data can be used to learn complicated nonlinear relationships, we train a neural network to improve the results of WENO5. We also postprocess the outputs of the neural network to guarantee that the method is consistent. The training data is generated using integrable functions that represent the waveforms we would expect to see while simulating a PDE, which gives us an exact mapping between cell averages and interpolated values. We demonstrate our method on linear advection of a discontinuous function, the inviscid Burgers equation, and the 1D Euler equations. Specifically, we examine the ShuOsher problem, a toy problem for turbulenceshockwave interactions. We also show preliminary results for dynamically trained models. [Preview Abstract] 
Monday, November 25, 2019 3:23PM  3:24PM 
M01.00004: Reinforcement learning enabled control of chaotic dynamics Sumit Vashishtha, Siddhartha Verma We illustrate the utility of Deep Reinforcement Learning (RL) for controlling chaotic systems. A deep RL policy network, based on proximal policy optimization, is employed to stabilize the unstable fixed points and periodic orbits embedded in the chaoticattractor of the Lorenz system. Previous attempts to control the underlying chaotic trajectories have relied on linearization of the dynamics around the targeted solutions, or on timedelayed feedback based on the output variables. However, there are certain caveats associated with these control approaches such as, requiring an a priori understanding of the chaotic system to be controlled, and difficulty in stabilizing certain classes of periodic orbits. These issues are overcome in the RL enabled control, especially when long term correlations are accounted for using layers of Long Short Term Memory (LSTM) cells in the policy network. [Preview Abstract] 

M01.00005: ABSTRACT WITHDRAWN 
Monday, November 25, 2019 3:25PM  3:26PM 
M01.00006: RealTime Reduced Order Modeling Using Time Dependent Subspaces Michael Donello, Hessam Babaee We present realtime reducedorder models for deterministic/stochastic systems constructed by projection of the fulldimensional dynamics onto a timedependent basis. To this end, we leverage a scalable algorithm to extract time dependent modes from highly transient data sets. We will present two case studies for the reducedorder modeling of: (1) transient instabilities in KuramotoSivashinsky equation, and (2) transient flow over a bump. The results will be compared to a reducedorder model constructed using static (i.e. time invariant) POD modes. [Preview Abstract] 
Monday, November 25, 2019 3:26PM  3:27PM 
M01.00007: POD analysis of the unsteady behavior of the wake under the influence of laminar to turbulent transition in a compressor cascade Lei Shi, Hongwei Ma, Lianpeng Zhao For low incidence angle and Reynolds number, the transition region is usually located closer to the trailing edge, which leads to a strong interactions of the vortex shedding of the laminar separation bubble and the wake flow. In this paper, particle image velocimetry (PIV) measurements have been performed in order to analyze the unsteady flow field in a compressor cascade. The instantaneous snapshots have been postprocessed by means of proper orthogonal decomposition (POD). The first mode pair allows the application of a correlationbased method to correctly sort each PIV instantaneous image in the wake period. For all the time steps, according to the extent of the deviation between the timeaveraged flow field and the phaseaveraged counterpart, the flow field can be divided into three regions associated with the LSB vortex shedding, the wake flow and the interaction between the former two dynamics. The triple decomposition of the velocity fluctuations enables the quantification of the contribution associated with the three coherent motions as well as the stochastic motions to the overall velocity fluctuations. [Preview Abstract] 
Monday, November 25, 2019 3:27PM  3:28PM 
M01.00008: Sparse Identification of Nonlinear Dynamics in 2D Chaotic Electrohydrodynamic Convection Igor Novosselov, Yifei Guan, Steven Brunton This study focuses on developing a reducedorder model for the chaotic electrohydrodynamic (EHD) convection flow between two parallel electrodes with unipolar charge injection. A Lattice Boltzmann Method with tworelaxation times solver [1] is used to obtain a numerical data set for electroconvective instabilities. Under strong charge injection and high electrical Rayleigh number, the system transitions from structured electroconvective vortices to chaotic motion. The chaos in this system is related to the standard Lorenz model obtained from RayleighBenard convection, although this model system exhibits a more complex threeway coupling between the fluid, the charge density, and the electric field. Fluid coherent structures are extracted from the temporally and spatially resolved chaotic system via proper orthogonal decomposition (POD). A nonlinear model is developed for the chaotic time series of these POD coefficients with the sparse identification of nonlinear dynamics (SINDy) algorithm [2]. The resulting sparse nonlinear model captures a similar phase portrait and the dominant chaotic dynamics of the original system. References: [1] Y. Guan and I. Novosselov, Two Relaxation Time Lattice Boltzmann Method Coupled to Fast Fourier Transform Poisson Solver: Application to Electroconvective Flow, Journal of Computational Physics (accepted for publication) (2019). [2] S. L. Brunton, J. L. Proctor, and J. N. Kutz, Discovering governing equations from data by sparse identification of nonlinear dynamical systems, Proceedings of the National Academy of Sciences 113, 3932 (2016). [Preview Abstract] 
Monday, November 25, 2019 3:28PM  3:29PM 
M01.00009: Waveletbased Data Compression for Threedimensional Fluid Flow Simulations on Regular Grids Dmitry Kolomenskiy, Ryo Onishi, Hitoshi Uehara Highperformance computational fluid dynamics can produce large volumes of output data. Even though data reduction may be performed during the course of computation to store only the quantities of interest such as statistical moments, it is often necessary to store full threedimensional fields for purposes including simulation restart, timeresolved visualization and exploratory analyses. In this talk, I will present a waveletbased method for compression of numerical simulation data on regular structured grids. It is inspired by image compression, and it consists of discrete wavelet transform, quantization adapted for floatingpoint data, and entropy coding. I will discuss different aspects of these numerical techniques, present an opensource software WaveRange, and show example numerical tests, ranging from idealized configurations to realistic global weather simulation data. [Preview Abstract] 
Monday, November 25, 2019 3:29PM  3:30PM 
M01.00010: Data Compression for Turbulence Databases Using SpatioTemporal SubSampling and Local Resimulation Charles Meneveau, Tamer Zaki, Zhao Wu The size of datasets from numerical simulations of turbulent flows has been growing roughly at the rate expected from Moore's law. However, storing the rapidly growing amounts of numerical simulation data is very challenging. Motivated by specific data and accuracy requirements for building numerical databases of turbulent flows, data compression using spatiotemporal subsampling and local resimulation is proposed. The DNS data are aggressively subsampled in space and time during the simulation, and a local resimulation is to be performed later when the data are needed. Numerical resimulation experiments for decaying isotropic turbulence based on subsampled data are undertaken. The results and error analyses are used to establish parameter choices for sufficiently accurate subsampling and subdomain resimulation. It is found that the numerical algorithms of the resimulation have to match the original simulation exactly to reproduce errorfree results: any mismatch between the two is found to lead to surprisingly large errors. By carefully controlling the resimulation parameters, resimulation errors close to singleprecision machine accuracy can be achieved under stringent conditions. [Preview Abstract] 
Monday, November 25, 2019 3:30PM  3:31PM 
M01.00011: Temporal evolution and statistical characteristics of uniform momentum zones using datainformed resolvent hierarchies Angeliki Laskari, Beverley McKeon Experimental data from timeresolved planar particle image velocimetry in streamwisewallnormal planes of a turbulent boundary layer are used for the determination of temporal evolution and statistical characteristics of uniform momentum zones. Specifically, the temporal variation of both the probability density function (pdf) of the streamwise velocity and the instantaneous number of zones is assessed. Statistically important patterns observed in the experimental data are then used to guide the selection of modes on a selfsimilar resolvent hierarchy. Although the full range observed for the instantaneous number of zones is not recovered with the use of this restricted number of modes, it is shown that the largest variation observed is due to the modes located in the middle of the logarithmic region. Additionally, results indicate that a single resolvent hierarchy can reproduce a prominent semiperiodic behaviour observed in the experimentally constructed temporal pdf of the streamwise velocity. It is further shown that this behaviour is directly related to the wavenumber of the modes closest to the edge of the logarithmic region. [Preview Abstract] 
Monday, November 25, 2019 3:31PM  3:32PM 
M01.00012: Resolvent analysisbased models of nonlinear Taylor vortex flow Benedikt Barthel, Xiaojue Zhu, Beverley McKeon Taylor vortices have recently garnered renewed attention as an analogue for the selfsustaining process (SSP) in wall bounded shear flows. An instability of the mean flow leads to streamwise rolls which form streaks, which in turn become unstable and feedback to the rolls. We seek to shed light on the SSP by first understanding the dominant nonlinear interactions which sustain Taylor vortices. Here we use the resolvent formulation of McKeon and Sharma to treat the nonlinearity not as an inherent part of the governing equations but rather as a triadic constraint which must be satisfied by the model solution. We exploit the low rank linear dynamics of the system to calculate an efficient basis for our solution, the coefficients of which are then calculated through an optimization problem where the cost function to be minimized is the triadic consistency of the solution with itself as well as with the input mean flow. We compare our results to DNS of Taylor Couette flow for a range of Reynolds numbers (Zhu et al., Comp. Phys. Comm., 2018). Our model solution replicates both the flow structures as well as the turbulent statistics observed in the simulations. [Preview Abstract] 
Monday, November 25, 2019 3:32PM  3:33PM 
M01.00013: A TimeSpectral Analysis for Summed Linear and Product Signals with Applications to Fluid Mechanics and Chaotic Systems Chien C. Chang, ShengSheng Lu, YenLiang Lee, JenJen Lin There are time signals of general interest put in the form: Time signal = trend with time + periodic components + residual or randomness. It is of great importance to identify the periodic components whose frequencies and amplitudes may be varying with time. In the past, we have seen excellent works on timefrequency analysis of a signal such as shorttime Fourier, wavelet, HilbertHuang transforms among others. Yet there are still critical and fundamental issues to be addressed. Notably all the previous analysis (tacitly) assumes that the signal concerned is a linear superposition of its decomposed components no matter whether a base set of functions or no base is employed. Moreover, a common query is that the signal may often be overdecomposed that the analysis with respect to individual modes does not catch the essential features of the signal’s spectral content. In this study, we propose to develop a principal frequency analysis suitable for general summed linear signals and product signals (beats/wavepackets). As an illustration, this approach of analysis is first applied to several basic examples and then to timedependent drag in fluid mechanics and signals of a chaotic Rosseler system. [Preview Abstract] 
Monday, November 25, 2019 3:33PM  3:34PM 
M01.00014: Bioinspired flows in unsteady environments. Part I: highly unsteady ambient flows Meilin Yu, Naresh Poudel, John Hrynuk Autonomous underwater vehicles (AUVs) and unmanned aerial vehicles (UAVs) usually need to carry out tasks in unstructured and dynamic flow environments. This poses a number of challenges that cannot easily be addressed by approaches developed for highly controlled environments, such as uniform flows frequently used in experiments and numerical simulation This work studies the impact of highly unsteady ambient flows on the performance of flapping wings/fins at relatively high Reynolds numbers (i.e., 12,000 based on the foil chord length). The unsteady flow environment is generated by an array of incline small cylinders or three arrays of staggered ones placed upstream of the flapping wing/fin. A highorder accurate flux reconstruction flow solver with moving/deforming bodyfitted unstructured meshes is used to perform the numerical simulation. We find that highly unsteady flow environments dominated by small eddies can always enhance timeaveraged thrust generation, no matter how the foil location is changed within the ambient chaotic flows; the effect of environmental unsteadiness on lift production seems to be random. The effects of wing/fin kinematics and the size of cylinders are also studied. [Preview Abstract] 
Monday, November 25, 2019 3:34PM  3:35PM 
M01.00015: Turbulent flow structure associated with interacting 3D bedforms Nathaniel Bristow, Gianluca Blois, James Best, Kenneth Christensen Barchan dunes are threedimensional, crescentshaped bedforms, and while most commonly associated with aeolian environments, recent observations have shown them to form in subaqueous and extraterrestrial environments as well. As barchans migrate in the direction of the flow, they interact with their neighbors, typically by way of a collision. The morphodynamics of such collision processes are complex, where the role of the turbulent flow structure is strongly coupled to that of the sediment transport and morphological change. Here we study the flow structure in a decoupled manner through measurements of the turbulent flow over fixedbed models of barchan dunes in various configurations involved in a barchan collision process. Particle image velocimetry is used to measure the flow in a refractiveindex matched flume environment that enables access to the whole flow field around these geometrically complex bedforms. Presented herein are results from planar PIV measurements in several measurement planes, including the crossplane, showing the dynamics of turbulent flow structures associated with barchan dunes which are hypothesized to drive the morphodynamics of the dune interaction. [Preview Abstract] 
Monday, November 25, 2019 3:35PM  3:36PM 
M01.00016: Application of the OneWay NavierStokes (OWNS) equations to hypersonic boundary layers Omar Kamal, Georgios Rigas, Matthew T. Lakebrink, Tim Colonius Prediction of linear instability and amplification of disturbances in hypersonic boundary layers is challenging due to the presence and interactions of TollmienSchlichting, Mack, and entropic modes. While DNS and global analysis can be used, the large grids required make the computation of optimal transient and forced responses very expensive, particularly when a large parameter space is required. At the same time, parabolized stability equations (PSE) are unreliable for multimodal interactions. In this work, we instead apply a newly developed technique, the OneWay NavierStokes (OWNS) equations, which are based on a rigorous parabolization of the full equations of motion. OWNS removes disturbances with upstream group velocity using a highorder recursive filter. We extend the original algorithm by considering bodyfitted curvilinear coordinates incorporating full compressibility and real gas effects. We validate the results by comparison with DNS. We present preliminary results for the optimal growth of disturbances in flatplate and conical boundary layers. This work has been supported by the Boeing Company through a Strategic Research and Development Relationship Agreement CTBAGTA1. [Preview Abstract] 
Monday, November 25, 2019 3:36PM  3:37PM 
M01.00017: Turbulence drag modulation by combined effect of solid particles injection and synthetic roughness Carlos DuqueDaza, Jesus RamirezPastran The combined effect of prescribing geometrical perturbations at one of the walls and injecting spherical solid particles on the behaviour of an incompressible turbulent channel flow at low friction Reynolds number ($Re_{\tau}=180$) was investigated through numerical simulations. The effect of the presence of spherical solid particles was explored from the perspective of the particlesmassfraction (PMF), whereas spanwise ribslike and cavitylike geometrical alterations were prescribed as synthetic large scale roughness elements in one of the walls. Values of particlevolumetricfraction (PVF or $\phi_v$) and particle to fluid density ratio of $\phi_v=10^{3}$ and $\frac{\rho_f}{\rho_p}=2700$, respectively, were employed to allow the use of a twoway coupling approach between the particles and the carrier phase. It is shown that, regardless of the type of geometric perturbation prescribed, the injection of solid particles exhibited a strong attenuating effect of the turbulent intensity of the flow, as well as a turbulent skin friction drag reduction. These findings reinforce the concept of a selective stabilising effect induced by the solid particles. In this case, the PMF played an important role on the seemingly selective modulation of the turbulent activity. [Preview Abstract] 
Monday, November 25, 2019 3:37PM  3:38PM 
M01.00018: Modification of Turbulent Boundary Layer in the Homogeneous Polymeric Dag Reduced Flow Yasaman Farsiani, Zeeshan Saeed, Brian Elbing Polymer induced drag reduction in turbulent flows has drawn significant scientific attention, not only due to their potential to improve relevant economies, but also because recent findings have challenged the classical views on how they modify the nearwall mean velocity profiles in the high DR regime (\textgreater 40{\%}). Observed modifications suggest that they are dependant on polymer and flow properties, but being based on mean statistics, they cannot reveal details of the intermittency of the nearwall events and coherent structures. The momentum exchange processes in a TBL depend on the turbulence structure and this is also true in drag reduced flows, making the changes in the instantaneous velocity fluctuations and their correlations with polymeric flows important for understanding the DR mechanism. In this presentation, mean and fluctuating velocity profiles, with controlled polymer and flow properties are compared with their Newtonian counterparts. Furthermore, twopoint correlations of the fluctuating velocities are used in elaborating on the dominate coherent structure configurations such as inclination angles, length scales and frequencies within the given region of the TBL. This can potentially explain the modification in mean velocity profiles. [Preview Abstract] 
Monday, November 25, 2019 3:38PM  3:39PM 
M01.00019: Analysis of VaryingPhase Opposition Control with Spatial Scale Restriction Simon Toedtli, Beverley McKeon This study considers a generalized version of the opposition control scheme (Choi et al, J Fluid Mech, 1994) from a Fourier domain perspective. Recent work (Toedtli et al, PRF, 2019) has shown that the effectiveness of the controller strongly depends on the relative phase between sensor measurement and actuator response, but an understanding of the underlying physics proves difficult so long as the controller simultaneously acts on a large number of spatial scales. We therefore consider here controllers with spatial scale restrictions and show that such controllers are capable of substantially altering the flow structure and drag. We first focus on the adverse scenario, where control leads to a pronounced drag increase, and use a combination of numerical simulation and modal analysis to shed light on the mechanisms underlying the change in drag. Insights obtained from the dragincreasing scenarios may help guiding the search for scalerestricted controller parameters that lead to drag reduction, which would be an important step towards a practical implementation of the control scheme. [Preview Abstract] 
Monday, November 25, 2019 3:39PM  3:40PM 
M01.00020: Control of a Turbulent Boundary Layer Separation Bubble by Shortfin Mako Shark Skin Amy Lang, Leonardo Santos, Andrew Bonacci, Jacob Parsons It has been demonstrated that samples of real shortfin mako shark skin can control turbulent boundary layer separation due to the passive actuation of the scales in the presence of reversing flow. Unlike vortex generators, this passive flowactuated mechanism functions locally at the point where there flow needs to be controlled and this study demonstrates that shark skin is capable of controlling the flow even downstream of the point where separation is already occurring. As in previous studies, shark skin specimens were mounted to a flat plate and placed in a tripped turbulent boundary subjected to an adverse pressure gradient induced by a rotating cylinder. DPIV experiments were conducted in a water tunnel facility for three different Reynolds numbers (on the order of 10\textasciicircum 5) with different strengths of adverse pressure gradient to measure the control the presence of the shark skin had on the flow separation when the skin was placed on the downstream half of a quasisteady turbulent separation bubble. Results confirm that the shark skin is able to control the flow by impeding the reversing flow near the surface. Furthermore, wall skin friction was calculated showing that the presence of the skin lowered the skin friction to the near zero vicinity but prevented it from going significantly negative as on the smooth wall cases. [Preview Abstract] 
Monday, November 25, 2019 3:40PM  3:41PM 
M01.00021: Effect of mass transfer on aeroheating in hypersonic chemically reacting boundary layers Mona Karimi, Joseph Schulz, Nagi Mansour At atmospheric entry hypersonic speeds, ablation as well as surface catalycity will impact boundary layer aeroheating. Outgassing occurring from an ablative surface in planetary entry environment introduces a rich set of problems incorporating thermodynamic, fluid dynamic, and material pyrolysis. Although it is established that mass injection diminishes the wall heat transfer via convective blockage, understanding the underlying physical mechanism of the mass injectioninduced boundary layer turbulence is still unresolved. To properly characterize the aerothermal environment and the required protection system, it is important to investigate gassurface interaction models that inherently couple material response and boundary layer physics. The present study examines the aeroheating budget in hypersonic boundary layer with mass transfer produced material pyrolysis that reacts with the boundary layer environment. A coupled simulation of a chemically reacting viscous NavierStokes solver of the boundary layer over a pyrolyzing material is analyzed. [Preview Abstract] 

M01.00022: ABSTRACT WITHDRAWN 
Monday, November 25, 2019 3:42PM  3:43PM 
M01.00023: Comparison of turbulent/nonturbulent interfaces in an adverse and zero pressure gradient turbulent boundary layer Jongmin Yang, Jinyul Hwang, Min Yoon, HYUNG JIN Sung The turbulent/nonturbulent interfaces of the zero pressure gradient (ZPG) and adverse pressure gradient (APG, $\beta \quad =$ 1.45) turbulent boundary layers (TBLs) are explored using the direct numerical simulation data (Re$\tau \quad =$ 830), where $\beta $ is the Clauser pressure gradient parameter. The interfaces are extracted by the method based on the enstrophy magnitude. Depending on the enstrophy, the outer boundary layer flow can be classified into free stream, boundary layer wake, and intermittent flow regimes. In addition, we can analyze the behavior of the intermittent flow regime by changing the threshold. The fractal dimension is obtained by using the boxcounting algorithm. The fractal dimensions in the APG and ZPG TBLs are constant over the long range of the box size. The interfaces of the APG and ZPG TBLs show the monofractal behaviors. The geometric complexity of the interfaces in the APG and ZPG TBLs can be represented by the genus, which is defined by the number of handles in the geometric object. The genus in the APG TBL is larger than that in the ZPG TBL. The geometric complexity of the intermittent flow regime is increased in the APG TBL. In addition, we examine the projection area and the volume of the genus and the pockets to analyze the entrainment process in the APG and ZPG TBLs. [Preview Abstract] 

M01.00024: ABSTRACT WITHDRAWN 
Monday, November 25, 2019 3:44PM  3:45PM 
M01.00025: Influence of Splitter Plate Geometry on a MultiStream Jet Nozzle Emma Gist, Cory Stack, Dominic DiDominic, Tyler Vartabedian, Seth Kelly, Datta Gaitonde, Mark Glauser Current and future aircraft designs are focusing on the integration of propulsion systems into the airframe to maximize efficiency and provide a stealth profile. This integration has led to different nozzle configurations such as the MultiAperture Rectangular Single Expansion Ramp Nozzle (MARS) where the nozzle has a primary and secondary bypass. This examination focuses on the reintroduction of the secondary subsonic bypass with the supersonic core flow and their mergence behind a splitter plate. The two streams differ from each other in all aspects, including the velocity, pressure and density. LargeEddy simulations (LES) have shown that splitter plate thickness affects the formation and evolution of largescale structures in the presence of the shock and expansion wave system. This also impacts the acoustics as well as the mechanical loading due to the unsteady fluctuations in the flow. This study focuses on using thinner splitter plates and the introduction of passive control by a geometric change on the end of the splitter plate where the streams coalesce. This study aims to provide insight into the physics associated with the complex merging flows and how a splitter plate can be used to manipulate the flow to reduce noise without compromising performance. [Preview Abstract] 
Monday, November 25, 2019 3:45PM  3:46PM 
M01.00026: Computational Study of Film Cooling Performance of a Gas Turbine: An application of the Transverse Jets German SierraVargas, Carlos DuqueDaza Film cooling technology based on transverse jets is employed to provide and control a protective film that remains attached to the surface and therefore to reduce the heat transfer from a high temperature main flow to the surface to be protected. Aiming to assess the impact of the jettocrossflow velocity ratio on the film cooling effectiveness, a number of numerical experiments were performed using four jettocrossflow velocity ratios over a NACA 4412 cascade vane. A computational model based on finite volume discretization, employing a WALE turbulence model, was prescribed to solve an incompressible flow on a 3D structured mesh. A passive scalar was included in the model to simulate temperature and transport of energy. $Y^+$ values and Courant number were limited, in order to ensure convergence. Comparisons were made between the jet trajectory and the friction coefficient, evidencing how the midline of the cooling jet yields regions of boundarylayer separation and reattachment. Analysis of the boundarylayer behavior indicates a relation with the local convective coefficient increments. Moreover, the results showed how the film cooling decreased the heat transfer at the region near the injection, but increased detrimentally the heat flux at the end of the vane. [Preview Abstract] 
Monday, November 25, 2019 3:46PM  3:47PM 
M01.00027: MultiJet Impingement Array Performance Escalle Thibaud, David Helmer, Michael Benson Impinging jets are frequently used in applications requiring cooling, and the design of such arrays requires understanding of both fluid dynamics and convective heat transfer. While impinging jet arrays have been extensively studied historically, there remain relatively few combined velocity and heat transfer datasets. This report presents such coupled measurements for an impinging jet array, including threedimensional, threecomponent velocity measurements acquired using Magnetic Resonance Velocimetry, as well as fullfield heat transfer measurements acquired with steadystate IR thermography with a jouleheating boundary condition. The goal of this measurement is to provide a benchmark dataset against which future experiments and especially simulations can be validated in detail. [Preview Abstract] 
Monday, November 25, 2019 3:47PM  3:48PM 
M01.00028: Viscous elastic fluid jets induced by sudden acceleration Yoshiyuki Tagawa, Andres FrancoGomez, Hajime Onuki, Yuichiro Nagatsu Modern interest for 3Dmanufacturing applications requires controlled ejection of liquids with viscous nonNewtonian properties, such as polymer solution and molten resin. In this study, we compare jet evolutions of two viscous polymer solutions with different elasticity but similar shearthinning properties (i.e. elastic and inelastic). Both jets are ejected by using our novel jet generation system employing an impulsive force (Onuki {\&} Tagawa, Phys. Rev. Applied, 2018). The inelastic solution jets eventually pinchoff into droplets. In contrast, remarkably, jets of the elastic solution completely retract after ejection, even though the initial velocity of the jet is high (\textgreater 10 m/s). We rationalize these behaviors by considering high elongational rate of liquids, which is beyond an explored range of existing studies. This contribution may open a new door for developing new additiveprinting systems. [Preview Abstract] 
Monday, November 25, 2019 3:48PM  3:49PM 
M01.00029: Eddy viscosity for resolvent analysis of turbulent jets Ethan Pickering, Georgios Rigas, Oliver Schmidt, Denis Sipp, Tim Colonius Resolvent modes of turbulent jets have shown striking qualitative agreement with datadeduced modes, found via spectral proper orthogonal decomposition (SPOD), of highfidelity, largeeddy simulations (LES), however, quantitative comparisons are still lacking. The discrepancy is linked to the presence of spatially colored noise inherently contained within SPOD modes but absent in resolvent analyses. Considering SPOD presents the optimal basis to describe statistical variability of turbulent flows, we present an optimization that aligns resolvent analysis towards SPOD through the introduction of an eddyviscosity model to the resolvent operator. The optimization is applied to Mach 0.4, 0.9, and 1.5 round, isothermal, turbulent jets, using five eddyviscosity models: linear damping, a spatially constant eddyviscosity field, a turbulent kinetic energybased viscosity field, a RANS derived viscosity field and a fully optimized field. Alignments between modes substantially increase ($>90$\% for many cases) in the most energetic region of frequencywavenumber space ($St=01, m=02$) across all Mach numbers. Additionally, we find optimal alignments are relatively insensitive to the choice of eddyviscosity model, rather, the inclusion of an eddyviscosity model is the critical choice. [Preview Abstract] 
Monday, November 25, 2019 3:49PM  3:50PM 
M01.00030: Transport Mechanisms Governing the Strength of Delta Wing LeadingEdge Vortices James Buchholz, Kevin Wabick, Aadil Manazir, Brian Snider The flow physics of nonslender delta wings are complex and relatively poorlyunderstood in comparison with their slender counterparts. The leadingedge vortices on nonslender delta wings can exhibit strong interactions with the surface of the wing, and often exist in systems of multiple vortices. The vortices are sustained primarily by a balance between fluxes of vorticity within the shear layer separating from the leading edge, threedimensional flow induced by the free stream, and the diffusive flux of vorticity generated on the suction surface due to the strong pressure gradients created by the vortices. These contributions are measured in a water tunnel, at Reynolds numbers on the order of $10^4$, for regions spanning the suction surface of a delta wing with leadingedge sweep angle of 50 degrees. It is found that the balance depends on the chordwise position along the wing, with the shear layer contributing to LEV growth primarily near the apex of the wing, and transport further downstream dominated by flow threedimensionality and interaction with the surface. Understanding these interactions provides a foundation for the design of flow control strategies and the prediction of aerodynamic loads and their fluctuations due to exogenous inputs. [Preview Abstract] 
Monday, November 25, 2019 3:50PM  3:51PM 
M01.00031: Fluid forces and flow transitions for a NACA0012 hydrofoil at low Reynolds numbers Siddharth Gupta, Jisheng Zhao, Mark Thompson, Atul Sharma, Amit Agrawal, Kerry Hourigan A study has been conducted to investigate the effect of angle of attack ($\alpha$) on the hydrodynamic performance and wake structure of a static NACA0012 hydrofoil in a freestream flow at low Reynolds number (\textit{Re}). The investigation employed waterchannel experiments and inhouse numerical simulations (based on an immersed interface method) over the angle of attack range of $0^o \le \alpha \le 90^o$ and the Reynolds number range of $2000 \le Re \le 10,000$. The angle of attack of a foil is an important parameter affecting the fluid dynamics and fluidstructure interaction; however, this problem has been poorly understood at low Reynolds numbers and particularly at large angles of attack, despite its importance in numerous applications, such as fishlike locomotion, autonomous underwater vehicles, birdinsect flights, microair vehicles, and wind turbines. The present findings showed that there exist different flow regimes and transitions over the $\alpha$ and \textit{Re} ranges investigated: e.g., a laminar flow regime is observed for $0^o \le \alpha \le 5^o$, followed by a transition regime prior to three distinctly different vortex shedding modes I, II and III for higher angles of attack. More details will be presented at the Division of Fluid Dynamics Meeting. [Preview Abstract] 
Monday, November 25, 2019 3:51PM  3:52PM 
M01.00032: Jacobi polynomial solution technique for the unsteady aerodynamics of porous airfoils Rozhin Hajian, Peter J. Baddoo, Justin W. Jaworski Recent research has uncovered analytic solution forms for the flow field past a thin airfoil with an arbitrary porosity distribution. However, efforts to extend this work to unsteady flows or airfoil motions fail due to the presence of extra terms in the singular integral equation that are not readily treated analytically. To circumvent this issue, the bound vorticity along the chord is expanded as a series of weighted Jacobi polynomials. Analytic expressions for the parameters of the Jacobi polynomials are derived via asymptotic analysis. This approach is shown to be valid for static airfoils in steady flows with either continuous or discontinuous porosity distributions. A numerical validation is presented that demonstrates the spectral convergence of the scheme. The mathematical method is then extended to consider the unsteady motions of porous airfoils where the classical singular integral approach breaks down. [Preview Abstract] 
Monday, November 25, 2019 3:52PM  3:53PM 
M01.00033: Confinement effects on the development of the tip vortex of an elliptical hydrofoil Praveen Kumar, Krishnan Mahesh Tip vortices are widely studied due to their relevance to many engineering applications. In many cases, e.g. ducted propulsors, tip vortices evolve under confinement. The effects of confinement on the development of tip vortex is the subject of the present work. Large eddy simulations are performed for flow over a confined elliptical hydrofoil at an incidence angle of 12 degrees and a Reynolds number of 0.9 million based on root chord length and freestream velocity. Two different cases of tip gap, i.e. the perpendicular distance between the hydrofoil tip and the bottom wall, are simulated and compared to the experiments of Boulon et al. (J. Fluid Mech. (1998), 390: 123), who studied confined effects on tip vortex cavitation. Instantaneous and timeaveraged flow fields are analyzed to understand the evolution of tip vortex under confinement. [Preview Abstract] 

M01.00034: ABSTRACT WITHDRAWN 

M01.00035: ABSTRACT WITHDRAWN 
Monday, November 25, 2019 3:55PM  3:56PM 
M01.00036: Analysis of the StreamwiseOscillating Cylinder Wake: Interplay Between QuasiSteady and Unsteady Dynamics Maysam Shamai, Scott Dawson, Igor Mezic, Beverley McKeon The flow around a cylinder oscillating (surging) in the streamwise direction with a frequency, $f_f$, much lower than the shedding frequency, $f_s$, has been relatively less studied than the case when these frequencies have the same order of magnitude. We combine particle image velocimetry and Koopman Mode Decomposition to investigate the cylinder wake for nominal parameters $f_f/f_s \sim 0.040.2$ and mean Reynolds number, $Re \approx 900$. The amplitude of oscillation is such that the instantaneous Reynolds number is far from the critical value. Characterization of the wake reveals a range of phenomena associated with nonlinear interaction of the two frequencies, including amplitude and frequency modulation. We perform analyses in multiple frames of reference to motivate use of the cylinderfixed frame. Utilizing this frame, we present a scaling parameter and associated transformation in order to relate the unsteady, or forced, dynamics to that of a quasisteady, or unforced, system. Implications for Koopman analysis of the flow around a moving body will be discussed. This work is supported under ARO grant W911NF1710306. [Preview Abstract] 
Monday, November 25, 2019 3:56PM  3:57PM 
M01.00037: On the Wake Dynamics of a Freely Vibrating Sphere at Moderate Reynolds Number Amir Chizfahm, Rajeev Jaiman Fluidstructure interaction of an elasticallymounted sphere exhibits a wide range of complex flowinduced vibration (FIV) regimes. Unlike a vast amount of literature available on the vortexinduced vibration of an elasticallymounted circular cylinder, such studies on a sphere are limited. We aim to understand the fundamentals of new vortexshedding modes and coupled dynamics pertaining to the FIV response of a freely vibrating sphere in all three spatial directions, using a bodyfitted finiteelement based fluidstructure interaction framework. To predict and analyze the vortex synchronization regimes and the wake patterns, the FIV response of the sphere at a low mass ratio is investigated over a broad range of reduced velocity and Reynolds number. We find that the sphere begins to move along a linear trajectory with hairpin vortexshedding mode, finally transforming into a circular trajectory with spiral mode in its stationary state. We systematically examine these mode transitions and motion trajectories in the three degreesoffreedom for the Reynolds number up to 30,000 which has not been studied in detail in the literature. [Preview Abstract] 
Monday, November 25, 2019 3:57PM  3:58PM 
M01.00038: Erosion of a Sharp Density Interface by Homogeneous Isotropic Turbulence Blair Johnson, Joel Lagade, Jr. An experimental study is performed to quantify mixing across a stably stratified density interface subject to turbulence in the absence of mean shear. Driven by a spatiotemporally varying array of 256 synthetic jets suspended above a water tank, high Reynolds number (Re$_{\mathrm{\lambda }}$ \textasciitilde 300) horizontally homogeneous isotropic turbulence is generated with negligible mean flow. A dense layer comprised of a mixture of sugar, Rhodamine B dye, and water is initially stationary at the base of the tank. Simultaneous particle image velocimetry (PIV) and laserinduced fluorescence (LIF) measurements are used to characterize the nearinterface flow velocity structures and density evolution, respectively. From PIV data, statistical metrics such as turbulence intensities, turbulent kinetic energy, spectra, dissipation, and integral length scales can be found. Using LIF data, entrainment is quantified based on techniques presented in Zhou et al. (2017), in which an effective turbulent diffusivity is calculated directly from instantaneous spatial buoyancy gradients. This study presents preliminary results of the dependence of mixing on imposed turbulence levels, initial density gradient, and depth of the dense layer, to determine under what conditions erosion, sharpening, and mixing of the layers occurs. [Preview Abstract] 
Monday, November 25, 2019 3:58PM  3:59PM 
M01.00039: What is a ``Length Scale" in Variable Density Turbulence? Dongxiao Zhao, Hussein Aluie A ``length scale'' in a fluid flow does not exist as an independent entity but is associated with the specific flow variable being analyzed. While this might seem obvious, we often discuss the ``inertial range'' or the ``viscous range'' of length scales in turbulence as if they exist independently of a flow variable, which in incompressible turbulence is the velocity field. How should we analyze ``length scales'' in flows with significant density variations, such as across a shock or in multiphase flows? A choice can be made according to the socalled \emph{inviscid criterion}. It is a kinematic requirement that a scale decomposition yield negligible viscous effects at sufficiently large ``length scales.'' Recently, we proved that a HesselbergFavre decomposition satisfies the inviscid criterion, which is necessary to unravel inertialrange dynamics and the cascade. We present numerical demonstrations of those results, where we also show that other commonly used decompositions can violate the inviscid criterion and, therefore, are not suitable to study inertialrange dynamics in variabledensity turbulence. [Preview Abstract] 
Monday, November 25, 2019 3:59PM  4:00PM 
M01.00040: Homogeneous variabledensity turbulence with asymmetric initial density distributions Denis Aslangil, Daniel Livescu, Arindam Banerjee In most natural and engineering applications, turbulent mixing occurs between unbalanced amounts of two or more miscible fluids of different densities. For example, during RayleighTaylor and RichtmyerMeshkov instabilities, the mole fraction percentages of the pure fluids change from zero to unity from edge to edge within the mixing layer. In this study, we investigate the effects of differential amounts of mixing fluids on the evolution of HVDT by using highresolution direct numerical simulations (up to 2048\textasciicircum 3) for two different density ratios 1.1:1 and 7:1. Three cases with different initial compositions characterized by an initial composition ratio ($\chi =$mole fraction of heavy fluid/ mole fraction of heavy fluid) was chosen for each density ratio; a heavy fluid dominated case (HF) with $\chi =$3, a light fluid dominated case (LF) with $\chi =$1/3 and the classical HVDT case where $\chi =$1. It is found that at large density ratios, upon increasing the initial amount of the pure light fluid, the turbulence kinetic energy generation is enhanced, whereas upon increasing the initial amount of the pure heavy fluid, the turbulence generation is suppressed. In addition, it takes longer for turbulence to disperse into the regions of heavy fluid compared to regions of light fluid. [Preview Abstract] 
Monday, November 25, 2019 4:00PM  4:01PM 
M01.00041: A variational level set methodology without reinitialization for predicting equilibrium interfaces over arbitrary textured surfaces Karim Alame, Sreevatsa Anantharamu, Krishnan Mahesh A robust numerical methodology to predict equilibrium interfaces over arbitrary solid surfaces is developed. The kernel of the proposed method is the distance regularized level set equations (DRLSE) with techniques to incorporate the nopenetration and massconservation constraints. In this framework, we avoid reinitialization typically used in traditional level set evolution algorithms. The method is secondorder accurate and requires only central difference schemes. The application of the method, in the context of Gibbs free energy minimization, to obtain liquidair interfaces is validated against existing analytical solutions. The capability of our current methodology to predict equilibrium shapes over both structured and realistic rough surfaces is demonstrated. [Preview Abstract] 
Monday, November 25, 2019 4:01PM  4:02PM 
M01.00042: Investigation of Mixing Law Efficacy for Hydrodynamic Simulations and Associated Compressibility Implications Caleb White, Humberto Silva III, Peter Vorobieff A computational simulation of various mixing laws for gaseous equations of state (EOS) using planar traveling shocks for multiple mixtures in three dimensions (3D) is analyzed against nominal experimental data. Numerical simulations utilize the Sandia National Laboratories (SNL) shock hydrodynamic code CTH and other codes including the SNL thermochemical equilibrium code TIGER and the uncertainty qualification (UQ) and sensitivity analysis code DAKOTA. The mixtures are: a 1:1 and a 1:4 molar mixture of helium (He) and sulfur hexafluoride ($\text{SF}_6$). The mixing laws to be analyzed are the ideal gas law, Amagat's Law, and Dalton's Law. Examination of the experimental data with TIGER revealed that the shock strength should not be strong enough to turn the mixture nonideal as the compressibility factor, $z$, was essentially unity ($z \approx 1.02$). Strikingly however, experimental results show that neither Dalton's nor Amagat's Law are able to accurately predict the properties of the shocked mixture. A methodology is being developed to possibly optimize the various mixing laws with computational results for the data set investigated. Lastly, a framework for future sensitivity and uncertainty quantification analysis will be established. [Preview Abstract] 
Monday, November 25, 2019 4:02PM  4:03PM 
M01.00043: Effect of countergradient subgridscale transport on turbulent mixing Sidharth GS, Raymond Ristorcelli The present work explores the effect of subgridscale models on the statistics of turbulent mixing of passive and active scalars. We compare the commonly employed gradient diffusion model against the nonlinear gradient model (related to Clark model/ Finitescale equations). The aim is to investigate the consequence of isotropic eddy viscosity/ scalar diffusivity versus a tensorial viscosity and diffusivity that permits countergradient transport of resolvedscale variables. For an isotropic turbulent flow, unlike the gradient diffusion model, the nonlinear gradient model can be shown to preserve the combined supergrid and subgrid scalar variance to the leading order in filter width. Therefore, the effect of the two classes of models on the evolution of the scalar variance (passive and active) is contrasted. Furthermore, in the active scalar case (variabledensity mixing), we compare the turbulence and mixing statistics in the Reynolds versus Favrefiltered representation of largescale velocity and scalar variables (Sidharth GS and Candler JFM (2018)). The role of variabledensity subgrid acceleration on the dynamics of subgrid velocity variance is of particular interest and compared with the wellstudied specificstress based production term. [Preview Abstract] 
Monday, November 25, 2019 4:03PM  4:04PM 
M01.00044: Topological classification of recurrences in turbulent flows Nazmi Burak Budanur, G\"okhan Yaln\i z, Bj\"orn Hof In recent years, numerical discoveries of unstable timeperiodic solutions in various shear flow simulations have sparked hopes of developing a chaos theoretic understanding of turbulence. For many cases of interest, however, the standard tools of chaos theory, such as Poincar\'e sections, were insufficient for uncovering a complete picture of turbulent dynamics due to its high dimensionality. As a result, the discoveries of periodic orbits in turbulent flows have remained at an illustrative level with no obvious paths toward their utilization in turbulence modeling and control. One simple question one might ask is whether the turbulent dynamics transiently approximate periodic solutions, and if so, how frequently? We argue that a systematic study of this problem requires a method for unsupervised identification of geometric similarities between periodic orbits and turbulent trajectory segments in the system's state space. We will demonstrate with examples that topological data analysis methods can be employed for this purpose. [Preview Abstract] 
Monday, November 25, 2019 4:04PM  4:05PM 
M01.00045: Probe into the gas leakage dynamics from the bubbly wake of a ventilated supercavity Siyao Shao, Jiarong Hong Understanding the liquidgas interface instability and associated gas leakage mechanisms is critical for developing new strategies for sustainable ventilated supercavitation in practical applications. However, despite recent effort from Wu et al [JFM, 2019, 862, 11351165], to directly characterize the gas leakage through the cavity internal flow measurement is challenging, particularly across a broad range of cavity regimes. Here we probe into the gas leakage mechanism by investigating bubbly wake generated from a ventilated supercavity with various closure modes including reentrant jet, twin and quad vortex closures. The size and shape of bubbles and their 3D distribution in the wake are captured using a high speed digital inline holography (DIH). The instantaneous gas leakage rate, estimated from the size and velocity of bubbles at each time instant, shows a strong intermittent behavior while the average gas leakage from DIH agrees well with the ventilation input under all experimental conditions. In addition, the detailed spatial and temporal characteristics of bubble distribution in the wake are found to vary under different closure conditions, connecting strongly with the interface instability and bubble breakup mechanism at the closure of the supercavity. [Preview Abstract] 

M01.00046: ABSTRACT WITHDRAWN 
Monday, November 25, 2019 4:06PM  4:07PM 
M01.00047: Breakup and reconnection of two coaxial counterrotating helical vortices Alessandro Capone, Fabio Di Felice, Alessandro Maiocchi, Jais Mohamed, Francisco Alves Pereira Our experiments examine the interaction between two coaxially aligned helical vortices induced by two counterrotating propellers of slightly different diameters operating in a water tunnel. We observe the interaction between the two coherent structures through highspeed visualizations performed in low pressure conditions that trigger the onset of cavitation in the vortex cores, thus enabling their imaging. We document the observations with PIV measurements at different phase angles between the two helical systems and for different ratios between the upstream flow and the rotation speed. The results show that the two helical systems merge and breakup in the region of closest distance and strongest vorticity. This event is followed by a reconnection process that bridges the broken parts, resulting in the formation of isolated vortex rings advected by the accelerated flow from the propeller system. These periodically generated vortex rings, spatially organized in an alternating pattern, have a sawtooth appearance and show evidence of entrainment, stretching and rollup due to the velocity gradients along the radial direction. Residual vorticity threads are also observed that intermittently bridge consecutive rings, as a result of momentum transfer. [Preview Abstract] 
Monday, November 25, 2019 4:07PM  4:08PM 
M01.00048: Kelvin wave generation on vortices in BoseEinstein condensates Scott Strong, Lincoln Carr Understanding the dynamics of a single line of concentrated vorticity is an open and fundamental problem in the study of superfluid turbulence. The local induction approximation, or LIA, is a straightforward integrable model of curvature induced flow. Here, the curvature and torsion evolve under a cubic focusing nonlinear Schr\"odinger equation whose wealth of conservation laws are thought to artificially constrain interactions between helical modes. Our work describes LIA as the lowestorder approximation in a fully nonlinear expansion of curvature induced motion honoring arclength conservation present in the Hamiltonian formulation of inviscid fluid dynamics. These higherorder corrections are accurate at scales where LIA is not, and accounts for nonlocally induced flows and contributions due to the vortex core. Our fully nonlinear model predicts that traveling waves of localized curvature seek to transport bending along the vortex. Simulations show dynamics similar to those seen postreconnection in vortices generated by obstacles and cavitation in classical flows. In ultraquantum turbulent tangles, energy transfer between helical Kelvin modes of vortex lines permits free decay and our relaxation of bending via Kelvin wave generation may be its most primitive manifestation. [Preview Abstract] 
Monday, November 25, 2019 4:08PM  4:09PM 
M01.00049: A formation time scale for vortex rings generated by pulsed planar jets Ben Steinfurth, Tim Geffke, Julien Weiss The flow field of a pulsed planar jet emitted from an outlet of high aspect ratio is studied experimentally. Considering that the effectivity of various flow control applications is determined by largescale coherent vortex structures, the objective of this study is to shed some light upon the generation mechanisms of these vortices. First, flow visualizations are conducted with pulsed jets issued into a steady water tank, verifying that the concept of an optimal generation time scale ensuring the exclusive generation of a leading vortex ring exists. Then, quantitative measurements are performed employing particle image velocimetry. Based on the derivation of flow diagnostics and additional extensive hotwire measurements, the following main conclusion can be drawn: increasing the pulse width, i. e., the amount of ejected fluid of a pulsed planar jet results in saturation of the leading vortex ring in terms of its dimensions and entrainment characteristics. Beyond a certain pulse width, a trailing structure with properties similar to a steady planar jet occurs. The shear rates of this trailing jet are well below those observed inside the vortex ring. Thus, jet modulation with the identified optimal pulse width may be beneficial from a flow control perspective. [Preview Abstract] 
Monday, November 25, 2019 4:09PM  4:10PM 
M01.00050: SemiLagrangian Lattice Boltzmann Method for Compressible Flows Dominik Wilde, Andreas Kraemer, Holger Foysi The lattice Boltzmann method (LBM) is an established tool for the simulation of weakly compressible flows. However, in the field of compressible flows the LBM is still lacking a widely accepted framework, which is why it is an active field of research. On the one hand, traditional LBM solvers with an exact propagation of the distribution function values usually require large velocity sets. On the other hand, Eulerian solvers like finite volume or finite difference LBMs suffer from high computation costs. We propose a semiLagrangian streaming step allowing for unstructured grids and for nonintegerbased velocity sets. This procedure effects small numerical dissipation, while the spatial order of convergence can be increased by the use of highorder interpolation polynomials in combination with an appropriate choice of support points. The semiLagrangian LBM circumvents the costly application of explicit time integration in Eulerian schemes. Instead, from an algorithmic point of view, the semiLagrangian LBM is still close to the original LBM formulation. Simulations of a Sod shock tube, a 2D Riemann problem, a shockvortex interaction, and a 2D airfoil confirm the newly introduced semiLagrangian LBM to be appropriate for the calculation of compressible flows. [Preview Abstract] 

M01.00051: ABSTRACT WITHDRAWN 
Monday, November 25, 2019 4:11PM  4:12PM 
M01.00052: Princeton High Reynolds Number Supertank facility Konstantinos Steiros, Marcus Hultmark Characterizing the aerodynamic behavior of large structures presents a major challenge in many engineering fields, including modern wind engineering, architecture, and urban planning research. The combination of enormous Reynolds numbers, relatively small Mach numbers, and unsteady or periodic events, render such flow measurements practically impossible in a conventional test facility. To address this issue, we present a novel recirculating wind tunnel facility, the Supertank, where the gauge pressure will be varied from 0 to 80 bar, enabling the testing of a large range of Reynolds numbers. The novelty of this facility lies in its large size, allowing a test section of 0.88 X 0.88 m$^2$ cross section and 7.5 m length, and in its easily accessible design. In that manner, series of wind turbines and even small wind farms will be able to be characterized at high Reynolds numbers, and it will serve as an ideal facility to evaluate numerical models and simulations. Several technical details of the facility will be discussed, along with the potential that this facility will unlock for applied and fundamental research. [Preview Abstract] 
Monday, November 25, 2019 4:12PM  4:13PM 
M01.00053: Leverage the Capability of Princeton Superpipe Liuyang Ding, Alexander Pique, Simeret Genet, Daniel Hoffman, Marcus Hultmark, Alexander Smits The Superpipe facility at Princeton utilizes compressed air as the working fluid to obtain highReynoldsnumber turbulence. It comprises a recirculating pressure vessel that can hold up to 220 atm, and a test pipe of 200 diameter long inside the pressure vessel. The range of bulk Reynolds number achievable is 81x10$^{\mathrm{3}}$ to 6x10$^{\mathrm{6}}$. Previous measurements in the Superpipe have only employed hot wires and only investigated equilibrium flows. We now report our progress in maximizing the capability of Superpipe towards optical measurement of nonequilibrium turbulence at high Reynolds numbers. We designed a new traversing system with a miniature rail mounted inside the test pipe, which allows test models to travel over a large axial distance. The blockage ratio of the rail is 0.6{\%} of the pipe cross section. A linear driving stage is placed in the diffuser section and is 16 diameters downstream of where the flow is sampled. We will present preliminary hotwire data of turbulence past a streamlined body of revolution, and compare it with PIV measurement of the same flow in a water pipe. In addition, the design of a new PIV system for the Superpipe will be presented. Details regarding imaging and illumination with optical fibers, calibration procedure, and seeding method will be discussed. [Preview Abstract] 
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