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 S08: Flow Instability: General I |
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Chair: Bud Homsy, University of British Columbia Room: 212 |
Tuesday, November 26, 2019 10:31AM - 10:44AM |
S08.00001: Investigation on Chemical Garden Pattern in Hele-Shaw cell by Interfacial Rheology Taro Maeda, Yuichiro Nagatsu Chemical garden is an experiment with precipitation reaction. Precipitation is formed by placing a metal salt such as cobalt chloride in an aqueous solution of sodium silicate. In recent years there have been several reports on pseudo 2D chemical garden experiments in Hele-Shaw cell. We also experimentally investigate the influence of concentration of CoCl$_{\mathrm{2}}$ on chemical garden patterns in Hele-Shaw cell. As the displaced fluid, 3.13 M sodium silicate solution is used, while 0.10\textasciitilde 6.25 M cobalt chloride solution is used for injection liquid. Filament pattern is observed at high concentration, spiral pattern is confirmed at middle concertation and flower pattern is emerged at low concentration. These results are the same as those previously reported. So far, the convincing explanation on the dependence of the patters on the concentration is lacking. We consider the difference originates from the viscoelastic properties of the interfacial solution phase including the precipitation. Therefore, we analyze such influences by performing some interfacial rheological experiments. We find that the result of interfacial LAOS (large amplitude oscillatory shear) measurement is linked to the selection of formed pattern. [Preview Abstract] |
Tuesday, November 26, 2019 10:44AM - 10:57AM |
S08.00002: Geometrically-weighted Modal Analysis Technique Kourosh Shoele, TsoKang Wang Modal decomposition techniques have been used to analyze complex flow and explore how they can be explained with a low-dimensional model. The data-driven methods such as proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) are used to extract coherent structures in the form of spatial modes. However, the classical data-driven modal decomposition methods have no spatial recognition and are not applicable to time-dependent grids which is common in shape-changing applications. We propose a novel method, the geometrically-weighted modal analysis, utilizing differential geometry mapping techniques to solve this issue. The deforming geometries are transformed into fixed domain based on their geometric characteristics and with the use of divergence-free mapping then the modal analysis is applied. Through different examples, we demonstrate the capability of this method to accurately capture the flow feature and dynamics of complex fluid-structure interaction systems. [Preview Abstract] |
Tuesday, November 26, 2019 10:57AM - 11:10AM |
S08.00003: Experimental Study of Roll-Hydrothermal Wave Coexistence in Convection Driven by Buoyancy and Thermocapillarity Michael Schatz, Brett Tregoning, Joshua Barnett, Minami Yoda, Roman Grigoriev Buoyancy-thermocapillary convective flow in a volatile fluid with a free surface and a horizontal temperature gradient arises in a variety of situations. Previous work examining buoyancy-thermocapillary flow in a rectangular geometry showed that hydrothermal waves are usually found in the limit where the dynamic Bond number approaches zero while a stationary convection roll pattern is found in the limit where the dynamic Bond number is of order unity while the Marangoni number is held as a control parameter. Linear stability analysis predicts a dynamic Bond number regime in between these limits in which static convection rolls coexist in the domain with hydrothermal waves that propagate along the direction of the temperature gradient [Grigoriev and Qin, JFM 838, 248 (2018)]. By probing this regime over a range of dynamic Bond numbers, we examined these predicted dynamics using an experimental cell containing silicone oil imaged with a shadowgraph technique. [Preview Abstract] |
Tuesday, November 26, 2019 11:10AM - 11:23AM |
S08.00004: Stability analysis of supersonic round jet with temperature non-uniformity Monika Chauhan, K. TODD LOWE, Luca Massa We perform parallel and parabolized stability analyses of round supersonic jets supported by the adiabatic expansion in turbulent nozzle. We carry out Reynolds-average Navier-Stokes calculations in two and three dimensions and test various turbulence models to resolve the effects of incoherent turbulence created by the nozzle walls on coherent structures in the shear layer. The computed mean profiles are in reasonable agreement with the experiments using the SST turbulence model and show the presence of a region of low momentum near the axis due to matching of Mach number in the cold and hot streams. After validating the mean profiles against the experimental data, we determine the stability characteristics with axisymmetric injection at the upstream of the throat. We find that the maximum axisymmetric mode is weakened by cold injection at the axis, while the first and second circumferential modes are of similar magnitude but exist for a reduced range of Strouhal numbers. Next, we evaluate the effect of circumferential temperature non-uniformity in the mean profile by calculating the stability of three-dimensional mean-profiles with resonant coupling against the circumferential instability modes. [Preview Abstract] |
Tuesday, November 26, 2019 11:23AM - 11:36AM |
S08.00005: Centrifugal instabilities in curved free shear layers: direct computations in the nonlinear regime Omar Es-Sahli, Adrian Sescu, Mohammed Afsar Curved free shear layers abound in many engineering applications involving complex geometries, such as backward facing step flows, wall injection, the flow inside side-dump combustors, or flows around vertical axis wind turbines. Most of the previous studies involving centrifugal instabilities have been focused on wall-bounded flows, where the so-called Taylor vortices in enclosed geometries or G\"{o}rtler vortices in boundary layer flows on concave surfaces are generated. Centrifugal instabilities in curved free shear layers, however, did not receive sufficient attention partly because these flows are mostly dominated by Kelvin-Helmholtz instabilities. Under certain conditions, however, longitudinal instabilities in the form of G\"{o}rtler vortices can occur, which - alone or in combination with Kelvin-Helmholtz type instabilities - may be susceptible to secondary instabilities and ultimately to turbulence. We study the development and growth of nonlinear G\"{o}rtler vortices evolving inside curved free shear layers in both incompressible and compressible regimes, using direct numerical solution to the Navier-Stokes equations. Results for different flow conditions are reported, along with discussions of challenges associated with simulating these types of flows. [Preview Abstract] |
Tuesday, November 26, 2019 11:36AM - 11:49AM |
S08.00006: Kelvin-Helmholtz shear instability with strong thermal nonequilibrium Myoungkyu Lee, Michael A. Gallis, Jacqueline H. Chen The effect of strong thermal nonequilibrium on the Kelvin-Helmholtz (K-H) instability is studied with the Direct Simulation Monte Carlo (DSMC) method. Transport properties of gases vary with temperature and, in general, are a function of a single temperature, which assumes the translational, rotational, and vibrational energies are locally in equilibrium at macroscopic scales. The local equilibrium assumption is invalid when flows with K-H instability undergo certain conditions whereby the residence time is short compared to thermal relaxation time scales, for example, in reactive turbulent jet flows at high Mach number with strong temperature and/or velocity gradients. The DSMC method models the fluid flows using molecule-simulators, following the probability density functions for different energy modes. First, we demonstrate the validity of the DSMC method by simulating helium-argon flows undergoing K-H instability with DSMC and compare the result with solutions from continuum direct numerical simulation. Next, hydrogen and air are used as working fluids to introduce a strong thermal gradient and nonequilibrium. Finally, we analyze the energy transfer between length-scales as a function of the nonequilibrium ratio, e.g., $\phi_{vib}=3T_{vib}/(T_{tr}+T_{rot}+T_{vib})$. [Preview Abstract] |
Tuesday, November 26, 2019 11:49AM - 12:02PM |
S08.00007: Direct Numerical Simulations of the Span-wise Asymmetric Kelvin-Helmoltz Instability Scott Wieland, David Fritts, Thomas Lund Recent advancements in computational power have allowed the study of more complex fluid interactions, including exploring previously untouched regimes of the Kelvin-Helmholtz instability (KHI). Theory has predicted interesting effects stemming from the introduction of span-wise variations to the perturbations and shear layer of KHI. To investigate this, direct numerical simulations have been carried out using the Complex Geometry Compressible Atmospheric Model. These simulations have been performed at a Reynolds number of 5000 with a Richardson number of 0.05 and have explored both the effects of span-wise asymmetries in the shear layer thickness and the perturbations applied as initial conditions. The results obtained confirm the predicted development of the interactions between misaligned billows as characteristic x-shaped "knots." These knots, though, produce intense events at faster time scales expressed as vorticity and energy dissipation at least an order of magnitude higher than the standard KHI developing in the background. These results will also be compared to observations of similar KHI events obtained from imaging of the polar mesospheric cloud layer and from measurements taken from the Andes LIDAR Observatory. [Preview Abstract] |
Tuesday, November 26, 2019 12:02PM - 12:15PM |
S08.00008: ABSTRACT WITHDRAWN |
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