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 M02: Flash Oral Presentations: Geophysical Flows |
Hide Abstracts |
Chair: Karan Venyagamoorthy, Colorado State University Room: 6b |
Monday, November 25, 2019 3:20PM - 3:21PM |
M02.00001: Passive vortical flows enhance mass transfer in a coral colony. MD MONIR HOSSAIN, ANNE STAPLES Corals are sessile and rely on the surrounding ocean flow to obtain nutrients and carry out their other physiological functions. Recent studies have shown that corals in low flow conditions can stir the water column, creating vortical flows that enhance mass transfer rates by up to 400{\%} (Shapiro et al., PNAS, 2014). Here, we perform three-dimensional immersed-boundary simulations of the flow through a single \textit{Pocillopora meandrina} colony under high flow conditions. We demonstrate that the passive geometric features of the branching colony produce highly vortical internal flows. This enhances mass transfer at the interior of the colony and compensates almost exactly for flow speed reductions there of up to 64{\%}, resulting in the advection time scale remaining roughly constant throughout the colony. We further compute the transport of a passive scalar from the surface of the colony under idealized sinusoidal oncoming flow conditions and find a double-peaked concentration profile in the interior of the colony. [Preview Abstract] |
Monday, November 25, 2019 3:21PM - 3:22PM |
M02.00002: Investigation of the mechanism in the formation of power-law spectrum of internal waves Yulin Pan, Brian Arbic, Arin Nelson, Dimitris Menemenlis, Richard Peltier We consider the formation of power-law spectrum of internal waves in a stratified ocean. The collection of field measurements have shown considerable variability of the spectral slopes compared to the high-wavenumber high-frequency part of the Garrett-Munk spectrum. Theoretical explanations on the spectral slopes have been developed in the context of the stationary solution of the kinetic equation. Depending on the properties of the collision integral (divergence or convergence at two ends), different power-law solutions can be found, resulting from different mechanisms of nonlinear interactions. In this work, we study the mechanism in the formation of power-law spectrum of internal waves in a realistic ocean, utilizing the numerical data from high-resolution ocean modeling. We show that the model captures the power-law spectrum in a broad range of scales (e.g., almost two decades in frequency). The nonlinear interaction is studied using a bi-coherence analysis and a new approach for a direct evaluation of the collision integral. The results show that the integral is dominated by the non-local interactions involving the low-frequency modes, implying the importance of induced diffusion mechanism. This is consistent with the spectral slopes observed in the model. [Preview Abstract] |
Monday, November 25, 2019 3:22PM - 3:23PM |
M02.00003: Azimuthal Instability of a Vortex Ring in a Liquid CO$_{\mathrm{2}}$ Drop Rising in the Deep Ocean. Louis L. Steytler, Arne J. Pearlstein Risk analysis for sub-seafloor storage of liquid CO$_{\mathrm{2}}$ requires assessment of the fate of liquid drops that escape as a result of loss during injection, passage though natural fissures, and seismic activity. Key issues in assessing the fate of escaped CO$_{\mathrm{2}}$ drops include the rate at which they rise through and dissolve in seawater, and how those rates depend on drop size. At typical depths, the density of liquid CO$_{\mathrm{2}}$ is slightly less than the density of seawater, and its viscosity is approximately one-tenth that of seawater. For this combination of physical properties, the flow internal to the drop is significantly more complex than the flow external to the drop. We report a three-dimensional numerical simulation of a 6 mm CO$_{\mathrm{2}}$ drop rising isothermally through seawater, neglecting compressibility effects, mass transfer, and hydrate formation. Starting from rest, a recirculating vortex ring develops internal to the drop, and as the result of a nonaxisymmetric instability, leads to transition from a relatively simple internal flow to a highly complex one. Comparison to results for the classical azimuthal instability of free vortex rings reveals several similarities. By reducing internal mass transfer resistance, the complex flow internal to the drop is expected to enhance dissolution of CO$_{\mathrm{2}}$ into seawater. [Preview Abstract] |
Monday, November 25, 2019 3:23PM - 3:24PM |
M02.00004: Determining surface divergence in free-surface flows: convergence and solution of a nonlinear Volterra-type integral equation Tianyi Li, Andrew Szeri, Lian Shen The transport of scalar quantities underneath a free surface is of interest to many interfacial transfer applications. While surface thermal quantities such as temperature and heat flux are relatively easy to measure, the interfacial flux of dissolved gases is much more challenging to quantify Deducing the fluid motions from the data of surface thermal quantities may offer new physical insights into the correlation between free-surface turbulent flows and scalar transport dynamics and can also provide a powerful method for measuring and modeling interfacial gas flux. In this study, we analyze a nonlinear singular Volterra-type integral equation proposed by Szeri (J. Geophys. Res. Oceans, 122, no. 4 (2017): 2781-2794) for calculating surface divergence based on surface temperature and heat flux. We prove the local linear convergence of the corresponding Picard iteration method and derive the rate of convergence explicitly. Numerical examples are provided to validate the convergence performance of the method. [Preview Abstract] |
Monday, November 25, 2019 3:24PM - 3:25PM |
M02.00005: Hydrodynamic X-Waves James N. Steer, Alistair G. L. Borthwick, Miguel Onorato, Amin Chabchoub, Ton S. Van Den Bremer Stationary wave groups exist in a wide range of nonlinear dispersive media: optics, Bose-Einstein condensates, plasma, and hydrodynamics. Unidirectional hydrodynamic stationary groups have been widely investigated. However, in two-dimensional propagation, the observation of stationary wave groups becomes more difficult because of dispersion, diffraction, and nonlinear effects. Here, we report experimental observations of nonlinear gravity-driven X-waves, i.e., X-shaped wave envelopes that propagate with constant form on the water surface. These can be constructed and described within the framework of higher-dimensional nonlinear Schr\"odinger equations (NLSEs). The 2D+1 NLSE predicts wave stability and balance between dispersion and diffraction when the envelope consisting of the arms of the X travel at an angle of $\pm {\rm atan}(1/\sqrt{2}) \approx \pm 35.26\si{\degree}$ to the direction of travel of the carrier wave. Moreover, we analyse in detail the single crossed-wave component and find that group dispersion decreases to a minimum at the nondispersive crossing angle of approximately $\pm 35.26\si{\degree}$. Our results may motivate investigations in other physical media, governed by weakly nonlinear evolution equations and improve understanding of extreme event lifetime. [Preview Abstract] |
Monday, November 25, 2019 3:25PM - 3:26PM |
M02.00006: The Cooling Box Problem: A Freezing Lake in the Lab Jason Olsthoorn, Kyle Gerrard, Edmund W. Tedford, Gregory A. Lawrence Recent field measurements have demonstrated that inland waters are warming rapidly and that seasonally ice-covered lakes are warming faster than those that do not. With limited field studies of lakes in harsh winter conditions, the impact of this changing environment is not clear, particularly from an ecological perspective. Similarly, the physical processes responsible for the warming within these cold-water bodies have not yet been identified. Our research focuses on the surface cooling processes occurring prior-to and immediately after ice formation, with a particular interest in the transport of heat. We model a cooling box problem, similar to the Rayleigh-Bernard problem. However, the nonlinear equation of state of freshwater complicates the traditional Rayleigh-Bernard analysis. We demonstrate that the nonlinear equation of state fundamentally alters the classical results of the Rayleigh-Bernard problem. Using a combination of linear stability analysis, numerical simulation and laboratory experiments, we quantify the mixing within the water column and the resultant surface heat transfer. Modified scaling laws for heat transport and energetics agree well with our data. [Preview Abstract] |
Monday, November 25, 2019 3:26PM - 3:27PM |
M02.00007: ABSTRACT WITHDRAWN |
(Author Not Attending)
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M02.00008: Local flow and turbulence at a tidal energy conversion installation near a pier of an estuarine bridge Martin Wosnik, Kaelin Chancey Estuarine bridges could serve as ideal locations to deploy marine hydrokinetic (MHK) energy conversion systems. The hydrokinetic resource is typically strong at these narrow locations, the bridge piers can serve as supporting structure for both the bridge and turbines, and synergies exist in the permitting processes. The “Living Bridge Project” installed a hydrokinetic turbine on a floating platform at Memorial Bridge in Portsmouth, NH. The location is well-suited as a tidal energy test site, reaching tidal current speeds greater than 2.5 m/s during spring ebb tides. In tidal estuaries the currents can vary significantly in space and time. Measurements were conducted with two acoustic Doppler current profilers (ADCP), mounted on the bow and stern of the platform, and with two acoustic Doppler velocimeters, mounted in various locations. The ADCPs indicated higher maximum current velocities and mean kinetic power density than prior nearby resource assessments. The ADV measurements yielded turbulence time and length scales consistent with estuary scales, e.g., width of the river and distances between the bridge piers. The tidal flow turbulence characteristics, such as the size and occurrence of coherent structures, affects the loading on the tidal turbine. [Preview Abstract] |
Monday, November 25, 2019 3:28PM - 3:29PM |
M02.00009: Duffing equation describes sloshing experiments Kerstin Avila, Bastian B\"auerlein In nature and in engineering, periodic forcing leads often to nonlinear resonances which are challenging to model and predict. The Duffing equation ($ \ddot x + \delta \dot x + \beta x + \alpha x^3 = F \cos \omega t$) is the simplest and most widely studied model describing such phenomena and is thus used in introductory courses to nonlinear dynamics. Despite numerous analytical and numerical studies across disciplines investigating its properties and dynamics, laboratory experiments exhibiting its dynamics are very scarce and, to our knowledge, all of them have been constructed to behave as a Duffing oscillator. We show that sloshing of water in a rectangular container driven by harmonic horizontal excitation is accurately described by the Duffing equation. The choice of the setup combined with automated flow visualizations and PIV-measurements allow it to reproduce key features of the Duffing oscillator experimentally. Besides the characteristic resonance curve we observe a hysteresis which increases with the driving amplitude and features transitions at exactly $90^\circ$-phase-lag, as well as period-three-motion. The experiments reach from linear and nonlinear dynamics fully described by the Duffing oscillator, up to highly nonlinear effects with e.g. breaking surface waves. [Preview Abstract] |
Monday, November 25, 2019 3:29PM - 3:30PM |
M02.00010: Effect of spring non-linearity on vortex-induced vibration of a circular cylinder Rahul Mishra, Rajneesh Bhardwaj, Mark Thompson The vortex-induced vibration (VIV) of a circular cylinder subject to nonlinear structural support has been studied computationally for fixed mass ratio ($m^* = 2.546$) in the two-dimensional Reynolds number regime. Unlike for the classic case for which the structure support consists of a spring and damper in parallel, this study considers a system composed of two springs and one damper, where the two springs are in parallel and the damper is in series with one of the springs. The arrangement of the springs and damper is similar to the Standard Linear Solid (SLS) model used for modelling the behavior of a viscoelastic material. The spring in series with the damper is linear and that parallel to the damper provides a non-linear force. The non-linear structural system is governed by the following three parameters: (a) the ratio of the spring constant (R), (b) damping ratio ($\zeta$), and (c) non-linearity strength ($\lambda$). The focus of the present study is to examine the response of the cylinder to VIV subject to changing $\zeta$ and $\lambda$. The main feature of this non-linear system is its ability to sustain vibration for a greater range of flow velocity; potentially useful for vibratory energy extraction. [Preview Abstract] |
Monday, November 25, 2019 3:30PM - 3:31PM |
M02.00011: The flow surrounding fire whirls Adam D Weiss, Prabakaran Rajamanickam, Wilfried Coenen, Antonio L Sanchez, Forman A Williams Despite significant research efforts, our current understanding of the flow structure and dynamics of fire whirls, including the reasons for their dramatic flame-lengthening effect and increased burning rate, is far from complete. The present study contributes to the needed understanding by investigating the steady axisymmetric structure of the cold outer flow surrounding fire whirls developing over localized fuel sources lying on a horizontal surface. Consideration is given to the three distinct flow regions arising from the disparity of length scales present in the problem, namely, an outer rotational inviscid region driven by the buoyant turbulent plume of hot combustion products that develops above the fire, a near-wall boundary layer, and a near-origin non-slender region where the radial inflow of the boundary layer collides. The resulting description, and in particular the terminal boundary-layer structure as the axis is approached, may be useful in future numerical computations of fire whirls. [Preview Abstract] |
Monday, November 25, 2019 3:31PM - 3:32PM |
M02.00012: Potential Fluid Mechanisms for Low Frequency Sound from Tornadoes Brian Elbing, Christopher Petrin, Matthew Van Den Broeke Tornado-producing storms have been observed to emit infrasound (sound at frequencies below human hearing) up to 2 hours before tornadogenesis. Weak atmospheric attenuation at these frequencies allows for long-range detection. Hence, passive infrasonic monitoring could be a method for long-range studying of tornadogenesis as well as tornado characterization. Identifying the fluid mechanism(s) that produce the infrasound is critical to enable such capabilities. However, there are insufficient detailed observations to test potential mechanisms. This presentation will provide an overview of potential mechanisms as well as comparisons against recent observations. These will include preliminary analysis from the 2019 tornado season, which has produced numerous severe storms within the range of an infrasound array deployed at Oklahoma State University. [Preview Abstract] |
Monday, November 25, 2019 3:32PM - 3:33PM |
M02.00013: Uncertainty Quantification of Models for Ocean Surface Boundary Layer Turbulence Gregory Wagner, Raffaele Ferrari, Andre Souza The atmosphere and ocean communicate through the ocean's turbulent surface boundary layer (OSBL), and accurate models of OSBL turbulence are necessary for accurate climate prediction. In this talk we use a suite of Large Eddy Simulations of OSBL turbulence in a range of physical scenarios to optimize and estimate the uncertainty of free parameters in models for OSBL turbulent mixing designed to be embedded in ocean general circulation models. We evaluate deficiencies in the structure of several different OSBL turbulence models by comparing the dependence of optimal parameters on the targeted physical scenario. Our ultimate goal is to choose a ’best’ OSBL turbulence closure for implementation in a new Earth System Model being developed as part of the “Climate Machine” (CliMa) project. [Preview Abstract] |
Monday, November 25, 2019 3:33PM - 3:34PM |
M02.00014: Coupled-mode flutter in wind turbine blades -- numerical prediction and experimental evidence. Yahya Modarres-Sadeghi, Todd Currier, Pieter Boersma, Bridget Benner, Xavier Amandolese We present a model to predict the onset of couple-coupled flutter in wind turbine blades as well as the post-instability behavior of the blade. While linear models to predict the onset of wind turbine blade instabilities have been around for a while, nonlinear models are lacking. Besides, experimental results to show these instabilities and to validate the models for wind turbine blades do not exist. We discuss a nonlinear model to predict these instabilities and present experimental results at two different scales to validate the model: one set with blades of around 40 cm in length and the other set with blades of around 200 cm in length. In both series of experiments dynamic instabilities are observed. The larger-scale tests enable us to observe the coupling of two blade modes in a coupled-mode response, as well as oscillations purely in the torsional direction at higher wind speeds. The coupled-mode flutter is also predicted in the nonlinear numerical model. [Preview Abstract] |
Monday, November 25, 2019 3:34PM - 3:35PM |
M02.00015: Effects of Land Cover on Wind Profiles: Case Study at Kirkwood Iowa. Robert Ahlman, Wei Zhang, Corey D. Markfort The atmospheric boundary layer serves as the incoming flow and kinetic energy source for wind turbines and remains a particularly challenging flow to study in fluid dynamics research. The difficulty lies in not only the wide range of spatial and temporal turbulent scales that need to be resolved but also the effects of the underlying surface. In particular, it is not well understood how wind velocity profiles respond to complex terrain and variations in atmospheric thermal stability. This research aims to characterize wind profiles in the surface layer and assess the accuracy of commonly used metrics for various terrain and thermal stability conditions. Data sets were recorded by various instruments mounted on a 106-meter tall meteorological tower at the Kirkwood Community College in Cedar Rapids, Iowa. Vertical profiles of wind speed and temperature, filtered by the direction of the incoming wind, for an entire year have been analyzed. Standard metrics and well-established formulations were assessed for their ability to accurately describe the wind profiles for a variety of different conditions. This work helps to provide insights into the effects of complex terrain and the atmospheric thermal stability on wind profiles, crucial to onshore wind resource assessment. [Preview Abstract] |
Monday, November 25, 2019 3:35PM - 3:36PM |
M02.00016: Effect of the Instabilities in the Overlying Atmospheric Boundary Layer on the Street Canyon Ventilation Tadeu Mendonca Fagundes, Neda Yaghoobian, Juan Ordonez Human health and air quality in urban areas are important problems that are linked to the pollution dispersion and ventilation capacity of urban streets. The ventilation mechanism and transfer process within urban streets is in strong connection with the instabilities in the overlying atmospheric boundary layer. In this study, we aim to use computational modelling to investigate the coupling between the flow within three-dimensional urban canyons and the turbulent structures in the above canyon flow. The state of the atmospheric boundary layer over an idealized urban area is controlled by the condition of the upstream topography. The transport phenomena in urban canyons is examined under different upstream conditions to reveal the ventilation mechanism in urban areas. [Preview Abstract] |
Monday, November 25, 2019 3:36PM - 3:37PM |
M02.00017: Wake recovery in collocated wind plants Raúl Bayoán Cal, Hawwa Kadum, Mike Quigley, Gerard Cortina, Marc Calaf Large eddy simulations approach is used to investigate the power production enhancement mechanisms in collocated wind plants in which twelve clusters of vertical axis wind turbines are collocated with a 3x4 horizontal axis wind turbine array. Three cases are studied: 1.) a standard wind plant ($SWP$), 2.) an aligned collocated wind plant ($CWP_{al}$), and 3.) a staggered collocated wind plant ($CWP_{st}$). A control volume analysis is employed to examine the energy balance and relevant terms for the various characteristic compounded wakes. The results show that collocated configurations have an averaged 48.5\% higher power than the standard wind plant due to the faster wake recovery and improved vertical transport of mean kinetic energy. The collocated plants spatial heterogeneity is found to play a significant role in mean kinetic energy vertical transport advancement by increasing the dispersive stress with an average of 37.5\% increase in the vertical kinematic shear stress from the standard wind plant, consequently reinforcing the mean kinetic energy flux which is the lead term in mean kinetic energy budget. This arrangement resulted in 4\% higher power production for the aligned configuration than the staggered even though the latter has faster wake recovery. [Preview Abstract] |
Monday, November 25, 2019 3:37PM - 3:38PM |
M02.00018: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 3:38PM - 3:39PM |
M02.00019: On the near-wake characteristics of a tidal current turbine model in a sheared turbulent inflow Ashwin Vinod, Arindam Banerjee Tidal current turbines deployed in tidal flows can be anticipated to encounter sheared and turbulent flow environments. Therefore, a thorough understanding of the implications of such operating conditions would be valuable in optimizing the performance and operational life of the installed turbines. The ongoing experimental work at Lehigh University aims to improve the understanding of tidal turbine performance, and the mechanism of momentum transfer in its near-wake in a controlled, sheared, turbulent inflow. A 1:20 laboratory-scale tidal turbine model with a rotor diameter of 0.28m is used in the experiments. An active grid type turbulence generator consisting of a series of five stepper motor-controlled horizontal winglet shafts is employed to generate a vertically sheared, turbulent inflow. To better control the shear profile, winglets with different sizes/solidities are utilized in the active grid. All flow measurements were carried out using an acoustic doppler velocimeter. In addition to performance metrics, and mean, turbulent wake characteristics, contributions of the different terms in mean momentum and kinetic energy equations are also examined to better capture the process of wake re-energization. [Preview Abstract] |
Monday, November 25, 2019 3:39PM - 3:40PM |
M02.00020: Low-order modelling of wake meandering behind turbines Vikrant Gupta, Minping Wan Far-wake regions behind tidal or wind turbines usually have low-frequency oscillations, referred as wake meandering, that cause an increase in turbulence level and thus adversely affect the performance of the downstream turbines in an energy farm. We propose a Ginzburg--Landau equation based low-order model for the far-wake region. The model reproduces the main qualitative features of wake meandering: (i) its origin via amplification of upstream structures, (ii) dependence of oscillation frequency on the upstream disturbance amplitude (higher amplitudes lead to lower frequencies), and (iii) shift towards lower frequencies as the wake flow evolves in the streamwise direction. Additionally, the model also predicts the increase in the meandering amplitude and an advancement in its onset with increasing thrust coefficient. To our knowledge, this is the first low-order dynamical system in the literature that models wake meandering. The model coefficients are obtained from the mean flow local stability results that we show correctly account for the changing operating conditions and thus pave way for the prediction of wake meandering features. Its low-order makes it suitable to use inside an energy farm design model, where it can help to mitigate the adverse effects of wake meandering. [Preview Abstract] |
Monday, November 25, 2019 3:40PM - 3:41PM |
M02.00021: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 3:41PM - 3:42PM |
M02.00022: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 3:42PM - 3:43PM |
M02.00023: Gravitational Effects in Turbulent Two-Phase Heat Transfer in Horizontal Channels Ilyas Yilgor, Pramod Bhuvankar, Sadegh Dabiri Present work explores heat transfer in horizontal turbulent bubbly flows. High fidelity direct numerical simulations (DNS) are conducted using finite volume and front-tracking methods to analyze the turbulent two-phase heat transfer between two parallel walls with Dirichlet boundary conditions at different temperatures for E\"otv\"os and Archimedes numbers ranging from 0.03-0.6 and 500-10000, respectively. Non-condensable bubbles are present in the flow with a void fraction of 3\% and Reynolds numbers ranging from 3000 to 5000. Two-phase simulations are compared to the corresponding single phase simulations with the same flow rate. The improvement in Nusselt number relative to single phase flow is quantified. A critical region where the improvement in heat transfer due to the presence of bubbles equals the convection heat transfer loss due to a reduced flow rate for a constant pressure gradient is documented. Change of void fraction distributions with gravity, flow rates, average Nusselt numbers and shear stresses are also presented. A range of parameters yielding optimum heat transfer are given. [Preview Abstract] |
Monday, November 25, 2019 3:43PM - 3:44PM |
M02.00024: Temporal dynamics and mode transition in a turbulent Rayleigh-Bénard Convection in a cylindrical domain with a moderate aspect ratio Yulia Peet, Philip Sakievich, Ronald Adrian The current study focuses on dynamics and evolution of large-scale motions in a turbulent Rayleigh-Bénard convection in a cylindrical domain with a moderate aspect ratio of 6.3. We perform Direct Numerical Simulations of the problem with a spectral-element code, and analyze the temporal dynamics of the azimuthal Fourier modes associated with the large-scale motions. Focusing on the first several modes, we document the processes that govern their evolution and interactions, including the in-mode processes, such as fast and slow rotations, as well as inter-mode interactions associated with the mode cessations and transitions. Time scales associated with these processes are analyzed. [Preview Abstract] |
Monday, November 25, 2019 3:44PM - 3:45PM |
M02.00025: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 3:45PM - 3:46PM |
M02.00026: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 3:46PM - 3:47PM |
M02.00027: Curvature of magnetic field in plasma turbulence Yan Yang, Minping Wan, Riddhi Bandyopadhyay, William Matthaeus, Yipeng Shi, Tulasi Parashar, Quanming Lu, Shiyi Chen Magnetic field lines undergo stretch-twist-fold processes in the presence of turbulence. The curvature field, measuring the tangling of the magnetic field lines, is studied in detail here, using both simulations and observations. The probability distribution function (PDF) of the curvature has distinct power-law tails for both high and low limit values. A central finding is that high curvature co-locates with low magnetic field, which gives rise to the power-law tail of PDF at high curvature. The curvature drift term that converts magnetic energy into flow and thermal energy, largely depends on the curvature field behavior, a relationship that helps to explain particle acceleration due to curvature drift. This adds as well to evidence that turbulent effects most likely play an essential role in particle energization since turbulence drives stronger tangled field configurations, and therefore curvature. [Preview Abstract] |
Monday, November 25, 2019 3:47PM - 3:48PM |
M02.00028: Shear and buoyancy effects in the spatial organization of Stratocumulus clouds Monica Zamora Zapata, Jan Kleissl The convective nature of Stratocumulus (Sc) clouds involves the motion of updrafts and downdrafts, driven by cloud-top radiative cooling and surface heat fluxes. Spatially, updrafts reach thicker cloud regions, while downdrafts are found at the thinner or cloud free regions. The balance of surface shear and buoyancy changes the coherent structures (Moeng and Sullivan, 1997). Surface rolls appear with stronger shear, and cells appear when buoyancy dominates. While stronger surface shear increases the cloud fraction of Cumulus clouds (Park et al., 2016), the shear effect on Sc clouds is unknown. Moreover, shear can also occur at the cloud top, where it erodes the Sc cloud from the top (Wang et al., 2012), but the effect on the horizontal spatial properties (aspect and cloud fraction) is unclear. In this work, we study the spatial organization of Sc clouds as a function of shear and buoyancy. We vary the heat flux and wind speed in Large Eddy Simulations (UCLA-LES) of the DYCOMS II RF01 reference case. Cells and rolls are observed at the surface depending on the heat flux and wind speed conditions, with clouds aligning in the direction of the wind for strong surface rolls. On average, the cloud base is more flat and cloud fraction is larger for stronger surface buoyancy. [Preview Abstract] |
Monday, November 25, 2019 3:48PM - 3:49PM |
M02.00029: Short-Wave Instability for Low Reynolds Number Flow over an Inclined Spinning Circular Disk at High Tip-Speed Ratios Marcus Lee, Tim Colonius, Beverley McKeon Spin stabilization motivates the study of spinning circular disks for potential application to micro air vehicle design for increased flight robustness. We use a three-dimensional immersed boundary lattice Green's function method (IBLGF) to simulate flow over a spinning circular disk at angle of attack for Reynolds numbers of $O(10^2)$ and tip-speed ratios up to 3. A short-wave instability emerges in the advancing tip vortex for tip-speed ratios greater than about 1.9. This instability is not present in the non-spinning case and can exhibit frequency lock-in behavior either with the rotation of the disk or with the vortex-shedding instability. Spectral proper orthogonal decomposition (SPOD) of the flow field isolates high-energy modes that help to characterize these instabilities and their coupling. [Preview Abstract] |
Monday, November 25, 2019 3:49PM - 3:50PM |
M02.00030: Layering, transport and jet formation in rotating, stratified flows with a thermal wind. Steven Tobias, Adrian Barker, Chris Jones The Goldreich-Schubert-Fricke (GSF) instability may provide an important contribution to angular momentum transport in planets and stars. We investigate the nonlinear development of the instability, in particular noting the tendency for the transport to be affected by the formation of layers. This is perhaps not surprising as the linear and nonlinear evolution of the equatorial axisymmetric instability is formally equivalent to the salt fingering instability. This is no longer the case in 3D, but we find that the 3D equatorial instability behaves nonlinearly in a similar way to salt fingering. We propose and validate numerically a simple theory for nonlinear saturation of the GSF instability and its resulting angular momentum transport. Away from the equator the nonlinear development is more complicated with layers formed, though these are not perpendicular to the direction of gravity. We conclude by discussing the implications for transport of heat and angular momentum in planets and stars. [Preview Abstract] |
Monday, November 25, 2019 3:50PM - 3:51PM |
M02.00031: Evaporation driven Rayleigh-Taylor instabilities in aqueous polymer solutions Endre Mossige, Vinny Suja, Sam Wheeler, Meiirbek Islamov, Gerald Fuller Understanding the mechanics of detrimental convective instabilities in drying polymer solutions is crucial in many applications such as the production of film coatings. It is well known that solvent evaporation in polymer solutions can lead to Rayleigh-Benard or Marangoni-type instabilities. Here we demonstrate another mechanism, namely that evaporation can cause the interface to display Rayleigh-Taylor instabilities due to the build-up of a dense layer at the air-liquid interface. We study experimentally the onset time ($t_p$) of the instability as a function of the initial polymer concentration ($c_0$) and molecular weight. In dilute solutions, $t_p$ shows two limiting behaviors. For high diffusivity polymers (low molecular weight), the pluming time scales as $c_0^{-2/3}$, while in the absence of diffusion, the pluming time scales as $c_0^{-1}$. Above a critical concentration, $\hat{c}$, viscosity delays the growth of the instability, resulting in $t_p$ scaling as $(\nu/c_0)^{2/3}$. These scaling results are not restricted to polymer solutions or evaporation driven instabilities, but are transferable to other binary systems undergoing gravity driven instabilities. [Preview Abstract] |
Monday, November 25, 2019 3:51PM - 3:52PM |
M02.00032: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 3:52PM - 3:53PM |
M02.00033: Chaotic and steady regimes of elasto inertial turbulence in 2D channel flows Fuqian Yin, Jacob Page, Rich Kerswell, Vincent Terrapon, Victor Steinberg Elasto inertial turbulence (EIT) is a non-laminar state of flow occurring in polymer flows in subcritical and supercritical flows. In 2D subcritical channel flows, the drag increases owing organized polymer dynamics which create flow structures through a backward energy transfer between polymer and the flow. Using viscoelastic direct numerical simulation based on the FENE-P model, we find two main regimes of flow: Chaotic and steady regimes with various variations in between these two bounds. Chaotic flows consist of elongated thin sheets of first normal stress with no particularly defined spacing between the sheets. In steady flow, a peculiar structure, dubbed the super core structure (SCS), emerges. Its existence is controlled by the polymer length and its shape varies with the Weissenberg number. The SCS has exceptional persistence and is speculated to be an exact solution of the flow, as well as a possible connection between EIT and elastic turbulence occurring in inertial-less flows. [Preview Abstract] |
Monday, November 25, 2019 3:53PM - 3:54PM |
M02.00034: Sources of flexible wall excitation and wall-pressure fluctuation in turbulent channel flow Sreevatsa Anantharamu, Krishnan Mahesh Structural excitation by turbulent flows result in vibration. We present one-way coupled fluid structure interaction simulations of linear elastic and viscoelastic plates for different material and geometric properties excited by wall-pressure fluctuations generated from Direct Numerical Simulation (DNS) of incompressible turbulent channel flow at $Re_{\tau}$ of $180$ and $400$. Fluid DNS simulation is carried out in a moving frame of reference using the discrete kinetic energy conserving finite volume method of Mahesh et al. (2004) and the solid simulation is performed in stationary frame of reference using the finite element method. The one-way coupled results are analyzed by a novel framework that represents the plate averaged response spectral density as a double integral of the net source wall-normal cross-spectral density computed for both $Re_{\tau}$ using DNS data. The relative magnitude and phase of the cumulative sources for different frequencies is obtained using spectral proper orthogonal decomposition. Similar technique is applied to analyze the wall-pressure fluctuation spectra. The distribution and the properties of the net sources that contribute to the plate averaged response and wall-pressure fluctuation spectra is discussed for both $Re_{\tau}$. [Preview Abstract] |
Monday, November 25, 2019 3:54PM - 3:55PM |
M02.00035: Experimental study of a forced plume in a linearly stratified environment using simultaneous measurements of velocity and density fields. Harish Mirajkar, Partho Mukherjee, Sridhar Balasubramanian We present the results of local small-scale measurements of a vertical forced plume ejecting into a linear stably stratified environment, with a stratification strength of $N$= 0.4$s^{-1}$. High-resolution measurements of velocity and density fields were acquired using simultaneous Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF). The refractive indices of the ambient and the plume fluids were matched to avoid optical aberrations. The energetics of an evolving forced plume were studied by measuring the terms in kinetic energy budget terms, such as mechanical production ($P$), buoyancy flux ($B$), and dissipation ($\epsilon$). The P and $\epsilon$ magnitude decreases with increase in the height, while the magnitude of buoyancy flux, $B$, decreases with height and becomes zero at the neutral buoyant layer ($Z_{s}$). Below the neutral buoyant layer, the buoyancy flux, $B$, shows presence of unstable motions and its sign changes as the plume intrudes into the neutral buoyant layer, indicating stability. The Kolmogorov -5/3 spectral slope is evident in the one-dimensional spatial spectra, indicating the existence of the inertial subrange. [Preview Abstract] |
Monday, November 25, 2019 3:55PM - 3:56PM |
M02.00036: Effect of control parameters of traveling-wave blowing and suction on relaminarization phenomenon in fully developed turbulent Taylor-Couette flow Hiroya Mamori, Kohei Ogino, Koji Fukudome, Naoya Fukushima, Makoto Yamamoto Direct numerical simulations of turbulent Taylor-Couette flows are performed to investigate the effect of control parameters of a traveling wave control. A traveling wave-like blowing and suction is imposed on inner or outer cylinder walls. The control is aiming the torque reduction effect. A parametric study is conducted to clarify the range of the control effect. A result shows a range of not only torque reduction but also relaminarization phenomenon of turbulent flow. In the inner wall control case, for example, the relaminarization phenomenon occurs, when the wave travels in corotating direction, the wavelength is long, and a wavespeed is faster than the wall velocity of the inner cylinder. We will also discuss the influence of the traveling wave on the Taylor vortex. [Preview Abstract] |
Monday, November 25, 2019 3:56PM - 3:57PM |
M02.00037: An affine reconstructed discontinuous Galerkin algorithm for diffusion Yang Song, Bhuvana Srinivasan In recent years, the discontinuous Galerkin (DG) method has been successfully applied to solving hyperbolic conservation laws. Due to its compactness, high order accuracy, and versatility, the DG method has been extensively applied to convection-diffusion problems. Reliable DG algorithms for hyperbolic terms are well studied. However, an accurate and efficient diffusion solver still constitutes ongoing research, especially for a nodal representation of the discontinuous Galerkin (NDG) method. An affine reconstructed discontinuous Galerkin (aRDG) algorithm is developed in this work to solve the diffusion operator using unstructured NDG method. The proposed numerical approach is computationally efficient, uses minimal storage, and achieves the same order of accuracy as the conventional DG hyperbolic solver. Convergence studies will be presented along with numerical simulations of Rayleigh-Taylor instability growth in the presence of various diffusive mechanisms. [Preview Abstract] |
Monday, November 25, 2019 3:57PM - 3:58PM |
M02.00038: Analysis of the Flow Over a Sphere Using Direct Simulation Monte Carlo Method in OpenFOAM Tadd Yeager, Douglas Fontes, Michael Kinzel Continuum assumptions are not valid for some flows such those found in cases involving atmospheric reentry. For these kinds of problems, the flow field cannot be solved considering the average physical properties (usually used to describe the effects of molecular interaction). Thus, these molecule-molecule interactions must be solved directly. Rarefied flow is often characterized by the Knudsen number, which is related to the ratio of the flow's Mach and Reynolds numbers. Aiming to study of the effects of these relevant dimensionless parameters as they pertain to flow over a blunt body, this paper presents an analysis of rarefied flow over a stationary sphere modeled using the Direct Simulation Monte Carlo (DSMC) method. In these simulations, high subsonic and supersonic flows of air are to be considered and discussed. These cases are simulated using the dsmcFoam solver from OpenFOAM. The preliminary average results of the surface force density and pressure distribution around the sphere surface are consistent with known physics, as are the velocity and momentum fields. Different particle velocities and particle number density should be evaluated to provide a better understanding of interactions between rarefied free stream flow and blunt solid bodies. [Preview Abstract] |
Monday, November 25, 2019 3:58PM - 3:59PM |
M02.00039: Stability analysis without numerics: analytic approximations to the pseudospectra of linear operators in fluid mechanics Scott Dawson The pseudospectra of a linear dynamical system determine the extent to which, and nature by which, disturbances to the system at a given frequency can be amplified. In practice, pseudospectral analysis (or equivalently, input-output or resolvent analysis) proceeds by computing leading singular values and vectors of the associated discretized operator. This talk will describe a methodology by which the pseudospectra of linear differential operators can instead be closely approximated by prescribed analytic functions. The methodology utilizes results and intuition from wavepacket pseudospectral theory to assume a general form of optimal pseudospectral modes, from which specific mode shapes and growth factors may be obtained by solving a low-dimensional optimization problem for a small number of unknown parameters. This method gives substantial computational savings over standard numerical approaches, and produces accurate results across regimes relevant to real flows. In particular, in such regimes the difference between numerically computed solutions and analytic approximations are typically much smaller than $\epsilon$ for the $\epsilon$-pseudospectrum. We will further discuss connections to other nonmodal stability tools, such as optimal transient energy growth analysis. [Preview Abstract] |
Monday, November 25, 2019 3:59PM - 4:00PM |
M02.00040: Scale dependence of entrainment bubble size distribution in free-surface turbulence Xiangming Yu, Kelli Hendrickson, Dick Yue Air entrainment by free-surface turbulence plays important roles in both natural processes and engineering applications. We consider the size spectrum of surface entrained bubbles under strong free-surface turbulence (SFST) and develop a physical/mechanistic model for the entrainment bubble-size spectrum per unit interface area $\mathcal{N}_e(r)$. The model defines the spectrum dependence on gravity $g$, surface tension $\sigma/\rho$, and turbulence dissipation $\epsilon$, and obtains two distinct entrainment regimes separated by bubble-size scale $r_0$. From the model we show that $r_0=r_c=\frac{1}{2}\sqrt{\sigma/\rho g}$, the capillary length scale, and not the Hinze scale $r_H$ as is generally assumed. For an air-water interface and earth gravity, $r_c \approx 1.5$mm. We confirm the theoretical model by high-fidelity, two-phase, volume-conserving direct numerical simulations (DNS) of a canonical SFST flow. We will present: (1) the respective power-laws of the two regimes; (2) the value $r_0=r_c\ne r_H$; (3) the scaling of $\mathcal{N}_e$ with $g$,$\sigma/\rho$ and $\epsilon$; and (4) confirmation of the $\epsilon-r$ entrainment regime map predicted by the model. [Preview Abstract] |
Monday, November 25, 2019 4:00PM - 4:01PM |
M02.00041: Investigation of the effect of evaporating ocean spray on the air-sea heat fluxes in high-wind conditions Yevgenii Rastigejev, Sergey A. Suslov We have studied the effect of evaporating ocean spray droplets of typical sizes on air-sea heat fluxes in a marine atmospheric boundary layer (MABL) with various vertical profiles of air temperature and moisture and values of turbulence intensity in high-wind conditions. We have found that the vertical latent and total heat fluxes are strongly enhanced by large spray droplets with radii ~0.5mm because their presence results in steep vertical gradients of moisture and temperature in a MABL. The effect of small droplets on the total heat flux is not as profound: fine spray primarily redistributes thermal energy between its latent and sensible components. We have shown that spray affects the turbulent kinetic energy (and thus the intensity of the vertical turbulent transport) mostly mechanically (by altering the vertical distribution of mass density of the air-spray mixture) rather than thermodynamically (by changing vertical distributions of the air temperature and moisture). We have compared the dependence of the total vertical heat flux on the wind speed produced by the current model with the observation data that show seemingly anomalous growth of the vertical heat flux with the wind speed. We showed that this may be explained by the presence of ocean spray in a MABL. [Preview Abstract] |
Monday, November 25, 2019 4:01PM - 4:02PM |
M02.00042: Clustering and settling of snow particles in atmospheric turbulence Cheng Li, Kaeul Lim, Tim Berk, Aliza Abraham, Michael Heisel, Michele Guala, Filippo Coletti, Jiarong Hong Understanding the turbulence effect on snow settling velocity is critical for accurate modeling of ground snow accumulation during a snowfall. Following the study of Nemes \textit{et al.} [JFM, 2017, 814, 592-613], a systematic investigation on the snow settling velocity upon changing turbulence and snow concentration is conducted using data from four deployments between 2016 and 2019. The snow settling velocity and concentration was measured using field-scale PIV/PTV, the snow particle size and morphology were characterized using digital in-line holography, and the air turbulence was quantified using sonic anemometers. The turbulence and snow conditions from these deployments range from low (\textit{Re}$_{\mathrm{\lambda }}\approx $ 900) to high turbulence (\textit{Re}$_{\lambda }\approx $ 9000), and from weakly-clustered to strongly-clustered snow, respectively. The settling speed ($W_{\mathrm{s}})$ are enhanced for all cases compared to quiescent fall speed ($W_{\mathrm{q}})$. The enhancement ratio ($W_{\mathrm{s}}$/$W_{\mathrm{q}})$ increases with \textit{Re}$_{\lambda \thinspace }$initially, drops after a threshold is reached, and it is maximized when the aerodynamic stopping distance of the snow particles is comparable with the Taylor microscale. The clusters are elongated in the vertical direction. In the case of strong clustering, the settling velocity positively correlates with particle concentration evaluated at different scales. [Preview Abstract] |
Monday, November 25, 2019 4:02PM - 4:03PM |
M02.00043: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 4:03PM - 4:04PM |
M02.00044: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 4:04PM - 4:05PM |
M02.00045: Energy losses induced by channel-spanning brush accumulations Elizabeth Follett, Isabella Schalko, Heidi Nepf Channel-spanning, porous accumulations of instream wood form naturally in some rivers or may be intentionally placed in the river channel in order to increase floodwater storage and infiltration as a natural flood management intervention. The accumulation of instream wood pieces acts as a porous obstruction, so that flow progressing through the structure experiences frictional losses due to drag on wood elements. Using flume measurements of channel-spanning wood accumulations that varied wood diameter, discharge, water depth, and structure porosity, we show that the spatially averaged energy loss occurring due to drag on wood elements can be described by a quadratic drag law proportional to a drag coefficient $C_{D}$, the frontal area per volume $a$ [L$^{\mathrm{-1}}$], and the structure porosity $\phi$, similar to flow through emergent rigid canopies. An additional energy loss occurred, associated with the free falling water exiting the structure, which generated significant turbulence. This loss was dependent upon the magnitude of the water fall height. An energy-based model is developed to predict the backwater rise behind a jam. [Preview Abstract] |
Monday, November 25, 2019 4:05PM - 4:06PM |
M02.00046: Experimental model for visualization of the isotherm patterns conformed in the steam chamber in SAGD oil recovery Ayax H Torres-Victoria, Salomón Peralta-López, Fernando Aragón-Rivera, Abraham Medina-Ovando, Jaime Klapp Steam assisted gravity drainage (SAGD) method was designed to inject steam into a horizontal pipeline to increse the temperature in an oil reservoir. The injected steam conforms a characteristic chamber and finally the previously heated oil, now with low viscosity is recovered by gravity drainage to other horizontal pipeline located below the injection pipeline. An experimental model was designed according to the theoretical model proposed by Higuera & Medina to observe the isotherm patterns conformed into the steam chamber during the SAGD. Their numerical computations were compared with our experimental temperature values obtained from infrared thermography. The experimental model also proved the existence of a thin layer at the boundary of the steam chamber where the condensed water flows into the recovery pipeline. [Preview Abstract] |
Monday, November 25, 2019 4:06PM - 4:07PM |
M02.00047: A Tale of Two Droplets: Wetting Phenomena on Oil-infused Surfaces Ping He, Xianming Dai When a water droplet is in contact with an oil-infused substrate, the oil will climb up the droplet outer contour and form a wetting ridge resulting a hydrophilic or hydrophobic outlook that depends on the competition of three pair-wise surface tensions of water-air, oil-air and water-oil, respectively. The theory of predicting the equilibrium contact angle at different ratios between the droplet size and the oil film depth has been developed in the literature. However, modeling and simulating this dynamic wetting process is not reported in the research field. The main difficulty lies in the numerical representation of the surface tension forces at the tri-phase (water-oil-air) contact line. In this talk, the authors present a novel phase-field method that can accurately compute the tri-phase surface tension forces and precisely predict the equilibrium wetting conditions consistent with the theory. Moreover, the authors present an interesting study of two water droplets interacting on an oil film. The wetting ridges of the two droplets interfere with each other, and drive the droplet-to-droplet motion differed at various initial distances between the two droplets. This study is critically helpful towards understanding the underlying mechanisms in the ridge-ridge interactions. [Preview Abstract] |
Monday, November 25, 2019 4:07PM - 4:08PM |
M02.00048: Reduced 1D population dynamics model for inflow size distribution in LES of oil droplet plumes Aditya Aiyer, Charles Meneveau In the context of many applications of turbulent multi-phase flows, knowledge of the dispersed phase size distribution is critical to predicting important macroscopic features. Often the inflow size distribution is unknown and a mono-disperse injection is commonly used. In order to provide an inflow condition for the size distribution in coarse large eddy simulations (LES) of oil jets, we replace the near nozzle region by a reduced 1D model for the downstream evolution of the centerline concentration due to the combined effects of advection, eddy diffusion and breakup. The droplet breakup due to turbulence is modeled by treating droplet-eddy collisions as in kinetic theory of gases. To model drops comparable to the Kolmogorov scale, we extend the droplet breakup kernels using a structure function smoothly transitioning between inertial to viscous ranges. The results from the 1D reduced model are compared to oil jet experiments of \textit{Brandvik et al. (2013)} with good agreement. The size distribution obtained from the 1D model is used as an inflow condition for LES of a turbulent jet including the population dynamics model for the entire drop size distribution. Among others, LES results allow quantifying the variability of the total surface area and the Sauter mean diameter. [Preview Abstract] |
Monday, November 25, 2019 4:08PM - 4:09PM |
M02.00049: Oil Droplet and Sediment Suspension in Laboratory-Scale Stommel Retention Zones Carlowen Smith, Zongze Li, Andres Tejada-Martinez, David Murphy Langmuir supercells are helical wind- and wave-driven circulations in the ocean with alternating regions of upwelling and downwelling that extend to the full depth of the water column. These flows can trap suspended materials in subsurface regions of turbulent vertical motion known as Stommel Retention Zones (SRZs), an effect that can specifically impact oil-particle aggregation following an oil spill. We present a laboratory facility recreating some aspects of SRZs and its characterization using PIV. The experimental facility consists of a 1\texttimes 0.2\texttimes 0.5 m tank in which a shear stress is applied on the side walls using conveyor belts, resulting in a counterrotating vortex pair with either a central downwelling or upwelling region of variable strength and turbulent kinetic energy. Mean up/downwelling flow speeds range from 0.05-0.2 m/s, where turbulent kinetic energy ranges over two orders of magnitude. The facility is used to study oil and particle dynamics within these zones of turbulent retention. Positively buoyant oil droplet and negatively buoyant sediment particle trajectories and spatial concentration fields are quantified, and droplet retention is then compared with sediment suspension, yielding information about the expected efficiency of oil-particle aggregation. [Preview Abstract] |
Monday, November 25, 2019 4:09PM - 4:10PM |
M02.00050: 3D PTV in a spray cloud from wave impact with wind interaction Reyna Ramirez De La Torre, Atle Jensen Marine icing is a phenomenon of growing importance due to the increase of marine traffic in the Arctic sea. An interesting example is the ocean spray freezing on top of vessels. However, its dynamics is still to be understood. These type of studies are important for the safety of people, ships and installations that operate in the Arctic environment. It has been reported that sea spray formation is caused mainly by wave impact and wind. Therefore, an experimental model of this phenomenon was created to describe the trajectories of droplets in the spray cloud generated by wave impact and wind. The experiments were developed in the wave plume of the Hydrodynamics Laboratory in the University of Oslo. Breaking waves were generated, while a fan was used to produce wind on top of the waves. Droplet trajectories were reconstructed by 3D Particle Tracking Velocimetry. Using this setup we studied the dynamics of spray clouds with different wind conditions and compared the experiments with simulations. The overall goal is to develop solutions to reduce the icing of Arctic structures. [Preview Abstract] |
Monday, November 25, 2019 4:10PM - 4:11PM |
M02.00051: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 4:11PM - 4:12PM |
M02.00052: Digital Aerodynamics Flavio Noca, Guillaume Catry Conventional wind tunnels have a limited number of fans. They are generally programmed to all turn at the same speed, thus generating a uniform and permanent flow. We have developed a technology to shape the morphology of wind in space and time. It is based on a large number of fans (wind pixels), which are distributed arbitrarily in space and can be modulated individually in time. We will provide preliminary experimental measurements on the correlation between a given fan-speed distribution and the resulting flow pattern in the test section using PIV and multihole pressure probes. [Preview Abstract] |
Monday, November 25, 2019 4:12PM - 4:13PM |
M02.00053: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 4:13PM - 4:14PM |
M02.00054: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 4:14PM - 4:15PM |
M02.00055: Two-dimensional partially-ionized magnetohydrodynamic turbulence Santiago Benavides, Glenn Flierl Ionization occurs in the upper atmospheres of Hot Jupiters and in the interiors of Gas Giant Planets, leading to Magnetohydrodynamic (MHD) effects which couple the momentum and the magnetic field, thereby significantly altering the dynamics. In regions of moderate temperatures the gas is only partially ionized, which leads to interactions with neutral molecules. To explore the turbulent dynamics of these regions we utilize Partially-Ionized MHD (PIMHD), a two-fluid model -- one neutral and one ionized -- coupled by a collision term proportional to the difference in velocities. Motivated by planetary settings where rotation constrains the large-scale motions to be mostly two-dimensional, we perform a suite of simulations to examine the parameter space of 2D PIMHD turbulence and pay particular attention to collisions and their role in the dynamics, dissipation, and energy exchange between the two species. We arrive at, and numerically confirm, an expression for the energy loss due to collisional heating in both the weakly and strongly collisional limits, and show that, in the latter limit, the neutral fluid couples to the ions and behaves as an MHD fluid. [Preview Abstract] |
Monday, November 25, 2019 4:15PM - 4:16PM |
M02.00056: Multi-lens stereo reconstruction of the free surface waves in wave basin Hua Liu, Qian Wang A Multi-lens stereo reconstruction approach is developed to measure the free surface deformation of water waves in a wave basin. A massive of tiny granule served as the thin film floating on the free surface ensures the function of the common multi-lens stereo imaging technique in reconstructing the wave surface. The granule film and the highbrightness projector produces distinct pattern features on the free surface. The effect of the granule film on the wave propagation is checked which turns out that there is little influence on the wave propagation. Comparing the surface elevation computed from the reconstructed wave surfaces with the wave gauge data, a good agreement is found. The developed multi-lens stereo reconstruction approach is applied in investigating the propagation of a solitary wave over a submerged plate in a wave basin. The 3D deformation of the free surface with the high precision and efficiency for the considerable measuring area will be presented [Preview Abstract] |
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