Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session T02: Convection and Buoyancy-Driven Flows: Thermal Instability (8:00am - 8:45am CST)Interactive On Demand
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T02.00001: Thermoelectrohydrodynamic convection under dielectric heating conditions in parallel plate capacitors Harunori Yoshikawa, Innocent Mutabazi The stability of stationary dielectric fluid layers subject to transversal electric fields in parallel plate capacitors is investigated by a linear perturbation theory in microgravity and horizontal configurations. Internal heating due to dielectric loss is shown to induce convection in both gravitational environments. In microgravity, the convection is driven by the thermal dielectrophoretic force, which is assimilated as a thermal buoyancy force in an electric effective gravity field $g_e$. The convection develops when a Rayleigh number $Ra_e$ based on $g_e$ exceeds a critical value. Critical modes consist of two-layered convection rolls. In the horizontal configuration, destabilizing and stabilizing effects of the Archimedean buoyancy in the upper and lower half fluid layers enrich the behavior of the fluid system. The critical condition varies significantly with the variation of Rayleigh number $Ra$ because of the competition of $g_e$ and Earth's gravity. With increasing $Ra$, the structure of critical modes changes from two- to single-layered convection. The mechanism of instabilities will be discussed from a consideration on the energy transfer from base to perturbation flows. [Preview Abstract] |
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T02.00002: On the prediction of saturation states for flows in a corrugated channel with functionally graded heating Mohammad Zakir Hossain, S.J. Sherwin Functionally graded heating (FGH) is a type of heating where temperature of a surface is spatially distributed. Presence of FGH is ubiquitous in nature (e.g., atmospheric boundary layer as surfaces of different colours heat up at different rates – forests/lakes combination in rural environments and roofs/streets in urban environments), and in engineering (e.g., discrete heat sources - systems of localised fires, computer chips, heating wires, etc.). FGH generates structured convection. To understand the character of this convection, a spectral/hp element algorithm is developed to solve the incompressible Navier-Stokes and advection-diffusion equations along with a flowrate forcing constraint. The flow bifurcation process is investigated using a linear stability analysis based on the time-stepper Arnoldi algorithm. The saturation states of the baseflow are identified by direct numerical simulation (DNS) where desired forms of disturbances are imposed into the baseflow. It is observed that the two-dimensional disturbances saturate to an oscillatory state whereas the three-dimensional disturbances saturate to a steady non-oscillatory state. [Preview Abstract] |
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T02.00003: Thermomagnetic instability of a ferrofluid confined between two concentric cylinders Antoine Meyer, Innocent Mutabazi, Marie-Charlotte Renoult, Romain Canu The stability of a ferrofluid confined between two coaxial differentially heated cylinders of infinite length is investigated through a linear stability analysis. A vertical current flux at the center of the cylindrical annulus creates a radially dependent magnetic field in the gap. The differential magnetisation of the ferrofluid due to stratification of the temperature and of the magnetic field produces the Kelvin's body force which can be seen as a buoyancy generated by a magnetic gravity. The centripetal magnetic gravity can destabilize the flow leading to three-dimensional vortices. The stability conditions as well as the spatial and temporal properties of these instabilities are given for different radius ratios and different fluid properties. An energy analysis complet this investigation in order to evaluate the contribution of thermomagnetic coupling at the onset of convective flows. [Preview Abstract] |
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T02.00004: Computational Fluid Dynamics Benchmark Validation Experiment of Plenum-to-Plenum Flow through Heated Parallel Channels Austin Parker, Barton Smith Computational Fluid Dynamics (CFD) is an economic alternative to experiments and is becoming increasingly more important for safety, design, and regulatory licensing in complex systems. Benchmark validation experiments provide input and output measurements necessary for a computationalist to determine the uncertainty of their calculations. Sufficient experimental inputs are not normally provided in publications for determining CFD model uncertainty. This project is a CFD benchmark validation experiment of plenum-to-plenum flow through heated parallel channels. The experiment was carried out in a new, triple-channel wind tunnel test section in an existing wind tunnel. The focus is on thermal mixing due to convection in the upper plenum. This flow feature has physics relevant to phenomena found in High Temperature Gas Reactors. Buoyantly driven flows such as these are challenging for CFD models because the physics are highly coupled. For instance, velocity is highly dependent on temperature and mixing downstream indirectly affects the mass flow through the channels. The result of this experiment is a published dataset of tabulated boundary conditions and system response quantities that is vital to understand model uncertainty in computations of similar fluid flows. [Preview Abstract] |
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