Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session M34: Convection & Buoyancy Driven Flows: Numerical Simulations |
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Chair: Yogesh Jaluria, Rutgers University Room: Georgia World Congress Center B406 |
Tuesday, November 20, 2018 8:00AM - 8:13AM |
M34.00001: Transient Flow in a Wall Plume and its Application to Solve an Inverse Problem Yogesh Jaluria, Ardeshir Bangian Tabrizi The transient buoyancy-induced flow generated by a line heat source on a vertical surface is investigated. The transient characteristics of this wall plume are of particular interest in wall fires and electronic systems. The nature of the flow as the leading edge effects move downstream and the flow gradually approaches steady flow is studied in detail. These results are then applied to solve an inverse problem, where the temperature variation downstream is known but the boundary conditions, in terms of heat input and source location, are not. The method presented here is a search and optimization algorithm developed to approach the inverse two-dimensional wall plume flow using only transient data. The data are taken at particular locations on the wall rather than at arbitrary locations. In the forward problem, downstream locations experience a peak in the temperature before attaining the steady state temperature. Here, the time when the peak temperature is achieved is determined at selected points. Then, an interpolation function is presented to relate these peak times with source strength and location. A system of equations is solved to find these. Particle swarm optimization is then applied to solve for the unknown source strength and location with minimum uncertainty. |
Tuesday, November 20, 2018 8:13AM - 8:26AM |
M34.00002: Solving coupled Stefan-flow problems using Immersed Boundary Smooth Extension Jinzi Mac Huang, David Stein, Michael John Shelley Natural convection accompanies many Stefan problems such as the dissolution and melting of solid objects in fluid. Gravity driven flows are responsible for many land-forming processes, for example the formation of Karst landscapes and the "stone forests" of China and Madagascar. Smaller structures, like iceberg "scallops", are also a consequence of natural convection. Recent experimental results show that even much simpler cases of dissolution or melting of initially spherical solids can lead to very nontrivial pattern formation. In this talk, we will present a numerical study of fluid-coupled Stefan problems, based on a high-order Immersed Boundary Smooth Extension method for evolving the boundaries of soluble solids immersed in a fluid. The method yields solutions with high regularity across boundaries, which allows us to evolve the geometry with high order of accuracy. An efficient spectral method reduces the computational cost and allows for high resolution. We demonstrate the efficacy of our approach with examples of melting and dissolution that produce high Grashof number flows. |
Tuesday, November 20, 2018 8:26AM - 8:39AM |
M34.00003: Large eddy simulations of turbulent thermal convection using renormalized viscosity and thermal diffusivity Sumit Vashishtha, Mahendra K Verma We use renormalized viscosity and thermal diffusivity to construct a subgrid-scale model for large eddy simulations (LES) of turbulent thermal convection. This model is based on the observations [1, 2] that the behavior of turbulent thermal convection is similar to that of hydrodynamic turbulence. Therefore, for LES, we add renormalization viscosity, νren ∼ Π1/3(π/Δ)-4/3, which is similar to that obtained for hydrodynamic turbulence, to the kinematic viscosity; here Π is the kinetic energy flux in the inertial range of wavenumbers and Δ is the grid spacing. The subgrid thermal diffusivity is assumed to be equal to subgrid viscosity; i.e. turbulent Prandtl number is assumed to be unity. We present a comparison between results - fluxes and spectra of temperature and velocity fields, time series of different quantities, temperature isosurfaces, scaling of Nusselt number with Rayleigh number - obtained using LES on a 1283 grid and DNS on a 5123 grid. A good agreement between LES and DNS results is obtained. [1] M.K. Verma, A. Kumar, and A. Pandey, New J. Physics 19, 025012 (2017). [2] A. Kumar, A.G. Chatterjee, and M.K. Verma, Phys. Rev. E 90, 023016 (2014)
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Tuesday, November 20, 2018 8:39AM - 8:52AM |
M34.00004: Simulating Low-Mach Compressible Flow at Large Prandtl Numbers with a High-Order Fully-Implicit All-Speed Flow Solver Brian Weston, Amanda Braun, Robert Nourgaliev, Jean-Pierre Delplanque We present a high-order, fully-implicit fluid dynamics solver for simulating very low-Mach compressible flow. The work is motivated by the development of large-scale simulations of high-explosive cookoff, which requires modeling multi-species/multi-phase reactive flow at high Peclet numbers. The governing equations are discretized in space up to 5th-order with a reconstructed Discontinuous Galerkin method and integrated in time with L-stable fully implicit time discretization schemes. The resulting set of non-linear equations is converged using a robust physics-block based preconditioned Newton-Krylov solver, with the Jacobian-free version of the GMRES solver. We implement the low-Mach version of the AUSM+-up Riemann solver, which correctly mimics the pressure fluctuations of an incompressible flow solver in the asymptotic limit of small Mach number. We demonstrate that our fully-implicit flow solver is able to robustly converge compressible flow calculations with Mach numbers less than 1.e-5. Furthermore, thin thermal boundary layers at high Prandtl numbers are easily resolved with a high-order discretization scheme. |
Tuesday, November 20, 2018 8:52AM - 9:05AM |
M34.00005: A Numerical Study of Turbulent Thermal Convection in a Cavity with Evaporation at the Free Surface William Hay, Miltiadis V. Papalexandris Evaporation from an air-water interface is controlled by interfacial temperature and hence vapour pressure, but influenced also by gas and water side convection and the means of heat addition. Currently however, our understanding of the effect of turbulence on evaporation rate at a free surface heated from below is far from complete. |
Tuesday, November 20, 2018 9:05AM - 9:18AM |
M34.00006: Abstract Withdrawn
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Tuesday, November 20, 2018 9:18AM - 9:31AM |
M34.00007: Laminar Natural Convection from Two Vertically Attached Horizontal Cylinders Immersed in Unconfined Power-Law Fluids Subhasisa Rath, Sukanta K. Dash Natural convection have emerging potential applications in non-Newtonian fluids. The apparent viscosity of a Power-law fluid exhibits a measurable variation with shear rates. Thus, the coupled velocity and thermal fields are further accentuated in Power-law fluids. Owing to the pragmatic significance, free convection from two vertically attached cylinders has been investigated numerically to elucidate the shear-thinning and shear-thickening behavior of a Power-law fluid using a modified Power-law model. Average Nusselt number shows a positive dependence on both Grashof and Prandtl numbers, whereas it shows an adverse dependence on Power-law index. Overall, shear-thinning behavior enhances the convection whereas shear-thickening behavior impedes it with reference to the generalized Newtonian fluids. Two competing mechanisms determine the resulting heat transfer: decreasing driving force due to preheating of the fluid by the lower cylinder and the mixed convection contribution due to the flow induced by the lower cylinder. As a result, the heat transfer from the upper cylinder has been strongly influenced by the plumes from the lower cylinder. Owing to the interaction of plumes, the heat transfer was found to decrease for both the cylinders compared to that of a single cylinder. |
Tuesday, November 20, 2018 9:31AM - 9:44AM |
M34.00008: Heat Transfer in Wall-bounded Flows at Transcritical Conditions Jack Guo, Xiang Yang, Werner M. Ihme Despite the prevalence of fluids at transcritical conditions in engineering applications, the structure of the thermo-viscous boundary layer and heat transfer in wall-bounded flows are only incompletely understood. To address this, DNS of a channel flow at transcritical conditions is performed, in which a temperature differential at the bottom and top walls is prescribed so that the thermodynamic state of the fluid crosses the Widom line and the density varies by a factor of 18. The DNS is analyzed with the specific focus on examining the thermo-viscous boundary layer structure and testing the scaling relations. It is found that the canonical van Driest transformation performs well in describing the logarithmic wall layer region, and the observed scaling behavior of the streamwise energy spectrum provides support of the attached-eddy model at transcritical conditions. |
Tuesday, November 20, 2018 9:44AM - 9:57AM |
M34.00009: New model for turbulent heat transfer accounting for radiation convective coupling in RANS framework Simone Silvestri, Dirk Roekaerts, Rene Pecnik In high temperature participating flows, radiation tends to be the most relevant heat transfer mechanism. Radiative heat transfer differs from conduction due to its peculiarity of being non-local. This non locality causes counter intuitive interactions with turbulent temperature field and conductive heat transfer. While some theoretical knowledge has been gathered regarding the mechanism underlying these interactions, standard models have not yet been adapted to these recent findings. In particular, solving the RANS equations relies on the modeling of unclosed terms, one of which is the turbulent heat transfer. This quantity is severely modified by the presence of radiative heat transfer, leading to erroneous temperature predictions if standard models are employed. Therefore, this work provides the inclusion of radiative convective coupling in the modeling of the turbulent heat transfer. The proposed model consists in a first order approximation of the fluctuating radiative field which is expressed as a linear function of temperature fluctuations. This concept is applied to modify the existing standard two equation model and tested against various DNS cases. The results show very good agreement both in terms of average temperature and turbulent heat transfer. |
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