Bulletin of the American Physical Society
74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021; Phoenix Convention Center, Phoenix, Arizona
Session Q22: Turbulence: Shear layers, Jets and Wakes-II |
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Chair: Charles Meneveau, Johns Hopkins Room: North 222 AB |
Tuesday, November 23, 2021 8:00AM - 8:13AM |
Q22.00001: A simple similarity scaling model for the axisymmetric turbulent jet Clara M Velte, Preben Buchhave The literature contains numerous descriptions of similarity scaling laws for the axisymmetric turbulent jet. These descriptions are often based in some way on empirical results. Thus, no models have been found by the authors that are based only on basic physical principles. This is the aim of the current work. From a simple model for the jet, we derive some predictions for the axisymmetric turbulent jet [1]. These predictions are backed by carefully conducted laser Doppler anemometry measurements acquired using our in-house processor [2]. The measurements are carried out on an air jet with a confinement large enough so that the jet can be considered free to a good approximation. The measurement quality is high enough to provide reliable second and third order statistics even in the outer parts of the jet and far downstream. The one-parameter law resulting from the simple model derivation and the measurement results agree even in the higher order statistics. |
Tuesday, November 23, 2021 8:13AM - 8:26AM |
Q22.00002: Scalings of the temporally developing turbulent planar jet and its turbulent/non-turbulent interface Sarp Er, John C Vassilicos, Jean-Philippe Laval We start with a first principles theoretical analysis of the temporally developing self-similar turbulent planar jet using mass, momentum and energy conservation laws which shows that the mean flow scalings are the same for equilibrium and non-equilibrium dissipation scalings in this very particular flow. The wake width, Taylor and Kolmogorov lengths all grow as the square root of time which makes this flow quite exceptional. The turbulent/non-turbulent interface (TNTI) propagation velocity and the mean centerline velocity vary in time in the same way, i.e. as inverse square root of time, but the TNTI velocity is also proportional to the global Reynolds number to a power which is inversely proportional to the fractal dimension of the interface. This fractal dimension remains constant in time during the self-similar regime, but depends on enstrophy threshold and therefore varies across the small TNTI thickness. The TNTI propagation velocity is observed to be lower at the highly contorted inner part of the TNTI and higher at the smoother outer edge of the TNTI in agreement with flux conservation. |
Tuesday, November 23, 2021 8:26AM - 8:39AM |
Q22.00003: A Stationarized Lagrangian Jet Bianca Viggiano, Thomas Basset, Laurent Chevillard, Charles Meneveau, Mickaël Bourgoin, Raúl B Cal Limitations of the applicability of universality in turbulence, as it was introduced by Kolmogorov in 1941, are often observed, especially in non-homogeneous flows deviating from idealized conditions, e.g. jets, wakes, canopies, etc. The study of such turbulent flows from a Lagrangian perspective gives insights into mixing and transport from the viewpoint of the fluid element as it experiences the flow field, but the lack of statistical stationarity poses challenges for analysis and modeling. In 1957, Batchelor proposed a method to “stationarize” the trajectories of flow fields which are spatially inhomogeneous, if they are also self-similar. An extension of such a transformation is herein applied to experimental data from a turbulent jet. Analysis of the stationarized jet Lagrangian statistics is performed and results are compared to trends observed in homogeneous, isotropic and stationary turbulence to validate the methods presented. |
Tuesday, November 23, 2021 8:39AM - 8:52AM |
Q22.00004: Modeling jet--plate interactions using large-eddy simulation Nikhil Tamhane, Sijie Huang, Jeonglae Kim Aircraft propulsion systems such as the ultra high bypass ratio turbofan engine, by virtue of their design, impose a constraint on engine installation below the wing, causing jet-wing interactions. Similar interactions are encountered when a jet-powered aircraft takes off on airport runway or aircraft carrier deck. High-speed jet flow near a solid surface shows markedly different turbulence characteristics compared with free jet, attachment of jet flow and development of non-equilibrium turbulent boundary layer downstream. Pressure fluctuations on the surface tend to be more unsteady and stronger, leading to increased vibration affecting aircraft cabin noise and modified jet noise radiation. Large-eddy simulation (LES) is useful to characterize turbulent jet flows over a solid surface as well as wall pressure distribution to promote physical understanding and modeling studies. We perform LES in a simplified configuration of jet-plate interaction, with the jet-plate distance fixed at 2D, where D is the nozzle-exit diameter. For jet Mach number of 0.7, LES is performed using the dynamic Smagorinsky model on an unstructured grid. Comparisons with the corresponding experiments are encouraging including turbulence statistics and spectra. |
Tuesday, November 23, 2021 8:52AM - 9:05AM |
Q22.00005: Dynamics of vortical structures in compressible mixing layers through tracking and graph-based geometrical analyses Jonas Buchmeier, Ivan Bermejo-Moreno We present a numerical study of the geometrical evolution of vortical structures identified by the Q-criterion in compressible temporally evolving mixing layers of varying convective Mach number (Mc = {0.3, 0.7, 1.1}, Reω,0 = 640, Reθ,0 = 160) and uniform initial density. The structures are extracted from the flow field by iso-surfacing and individually tracked from instantaneous snapshots obtained throughout the direct numerical simulation. The temporal evolution and interactions among vortical structures are mapped onto a graph data structure, which is queried to conduct the geometrical analysis. |
Tuesday, November 23, 2021 9:05AM - 9:18AM |
Q22.00006: Compressiblity, curvature and variable density effects on turbulent shear layers Kristen Matsuno This work is the first of several steps in addressing the challenge of characterizing the behavior of turbulence in retropropulsive jet plumes. Most prior simulation studies focused on turbulent mixing have been limited to a single turbulence mechanism; limited work with multiple turbulence mechanisms has been pursued. The primary goal of this work is to improve the understanding of turbulent mixing layers affected by variable density, rotation and curvature by considering a planar, constant-density and low-Mach mixing layer, then systematically including the aforementioned effects. The CFD solver OVERFLOW is used to compute a suite of high resolution simulations across a range of convective Mach numbers, free-stream density ratios, and radii of curvature. Turbulent stress anisotropy, mass fluxes, and pressure-strain correlations are used to assess how each of the parameters effects turbulent mixing and to provide comparison with previously published planar shear layer statistics. Using the database, it will also be evaluated if rotation/curvature, compressibility, or density variations dominate turbulent mixing characteristics in particular configurations. |
Tuesday, November 23, 2021 9:18AM - 9:31AM |
Q22.00007: Velocity–Pressure-Gradient tensor measurements in a turbulent shear layer flow impinging on a cavity trailing corner by Time-Resolved Tomographic PIV Jose R Moreto, Xiaofeng Liu The velocity–pressure-gradient measured by time-resolved tomographic PIV for a turbulent shear layer flow over an open cavity at a Reynolds number of 40,000 will be presented. The velocity–pressure-gradient is decomposed into the pressure diffusion and the pressure-rate-of-strain tensors, with the latter term necessary for the characterization of the intercomponent turbulence fluctuation energy transfer in both the shear layer and the impingement regions around the cavity trailing corner. We acquired 138,000 Tomo-PIV images at a sample rate of 4500 frames per second and a 42mm × 11mm field of view with a 7mm depth of the measurement volume. The pressure gradient is obtained from the pseudo-Lagrangian tracking based on the consecutive time-resolved three-dimensional velocity fields, and it is further integrated using the rotating parallel ray Omni-directional integration method to obtain the pressure field. The quality of the measurements is ensured by evaluating the curl-free property of the measured pressure gradient and the divergence-free property of the velocity field. The quality of the measured pressure-related terms is also cross-checked with the balance of the Reynolds stress transport budget. The three-dimensional measurement of the pressure-related turbulence terms by time-resolved Tomo-PIV will be used to verify the conjectures raised by Liu and Katz (2018, https://doi.org/10.2514/1.J056168) regarding the magnitude of the spanwise intercomponent energy transfer based on their planar PIV data. |
Tuesday, November 23, 2021 9:31AM - 9:44AM |
Q22.00008: The Dynamics of Coherent Structures in a Turbulent Wake behind a Body of Revolution at ReD=5000 Fengrui Zhang, Yulia T Peet The study on coherent structures gives intuitive understanding of turbulent flows. This work focuses on the dynamics of coherent structures that are formed in the wake past an axisymmetric body at ReD=5000. The data used is gathered over 790 vortex shedding cycles from a direct numerical simulation. Characteristic motions of the wake, such as vortex shedding, bubble pumping, precession of wake barycenters, etc., are related to coherent structures by the dominant frequencies that can be cast in a non-dimensional form by Strouhal scaling StD=fD/U∞. Power spectra analysis, azimuthal Fourier analysis and modal analysis are employed to identify the frequencies and visualize the corresponding coherent structures. |
Tuesday, November 23, 2021 9:44AM - 9:57AM |
Q22.00009: Insights into second-moment closure modelling performance for stratified wakes from DNS ensembles Naman Jain, Xinyi Huang, Xiang Yang, Robert F Kunz Wake flows in the environment, usually characterized by high Re and Fr, require large computational resources, prohibiting the use of DNS/LES. RANS based models are more practical, but the inherently complex dynamics render RANS eddy-viscosity modelling inappropriate. RANS Second-Moment Closure (SMC) modelling is more suitable, and here we study their performance for stratified towed and momentumless wakes. 11-equation based modelling is used, and a range of sub-model complexity is employed for diffusion, pressure strain/scrambling, and dissipation terms. These sub-models are evaluated in terms of how well DNS represents them in comparison to exact Reynolds averaged terms. Statistically converged DNS results for direct comparison are obtained by an ensemble average of 100 realizations. These highlight important inconsistencies in model performance, such as non-negligible pressure-diffusion and dissipation anisotropy, as presented by the authors in an earlier study of stratified shear layers. Some mean flow elements are captured well for stratified wakes, but the flow dynamics are inaccurately predicted. Simple corrections to model shortcomings are being studied and tested. |
Tuesday, November 23, 2021 9:57AM - 10:10AM |
Q22.00010: Comparison of Shear Layer Dynamics in Reacting and Non-Reacting Bluff Body Flows Samuel Whitman, James G Brasseur, Peter E Hamlington We investigate the dynamical impacts of variable temperature, density, and viscosity on the shear layers and recirculation zones created by non-reacting and reacting flow around three-dimensional triangular prism bluff bodies. Both heated and non-heated bluff bodies are studied for the non-reacting cases to examine thermofluidic variations separately from fluid and flow variability due to combustion. All simulations are performed using adaptive mesh refinement (AMR) to locally resolve physics of interest, resulting in the most highly resolved high Reynolds number bluff body simulations to date. We find a resolution-dependent effect of heat transfer on mean flow statistics, including the recirculation zone length, in the non-reacting cases, reminiscent of observations for bluff body stabilized flames. Strong gradients along the boundary and shear layers, which affect the dynamical significance of different terms in the vorticity transport equation, are analyzed to understand the impacts of vortical structures in the shear layer. These results highlight the importance of capturing strong gradients in simulations of bluff body flows, enabled here by the use of AMR. |
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