Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session G5: Computational Fluid Dynamics IV |
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Chair: Andrew Cook, Lawrence Livermore National Laboratory Room: 24A |
Monday, November 19, 2012 8:00AM - 8:13AM |
G5.00001: Large-eddy simulations of coherent vortices embedded in an impinging jet Wen Wu, Ugo Piomelli Large-eddy simulations of impinging jets with embedded ring vortices are carried out to study the interaction between the axisymmetric wall jet generated away from the impingement region and the vortex rings. After the primary vortex interacts with the wall, a secondary vortex (with opposite-sign vorticity) is formed from the lifted wall vorticity, which is stretched and wrapped around the primary one. The instability of the secondary vortex dramatically increases the three-dimensionality of the vortex pair. Turbulence statistics reveal a very strong interaction between the two, and intense turbulence generation. The liftup of wall turbulence also results in the generation of rib-like vortices that roll around the primary vortex ring. A three-dimensional, sinusoidal instability of the main vortex is also observed, as well as the generation of near-wall streamwise vortices, which may be related to the striations observed when vortex rings impinge on a sand bed. The stretching and dissipation eventually cause the destruction of the coherent structures of the vortices. [Preview Abstract] |
Monday, November 19, 2012 8:13AM - 8:26AM |
G5.00002: Numerical simulation of supersonic water vapor jet impinging on a flat plate Kazuto Kuzuu, Junya Aono, Eiji Shima We investigated supersonic water vapor jet impinging on a flat plate through numerical simulation. This simulation is for estimating heating effect of a reusable sounding rocket during vertical landing. The jet from the rocket bottom is supersonic, M=2 to 3, high temperature, T=2000K, and over-expanded. Atmospheric condition is a stationary standard air. The simulation is base on the full Navier-Stokes equations, and the flow is numerically solved by an unstructured compressible flow solver, in-house code LS-FLOW-RG. In this solver, the transport properties of muti-species gas and mass conservation equations of those species are considered. We employed DDES method as a turbulence model. For verification and validation, we also carried out a simulation under the condition of air, and compared with the experimental data. Agreement between our results and the experimental data are satisfactory. Through this simulation, we calculated the flow under some exit pressure conditions, and discuss the effects of pressure ratio on flow structures, heat transfer and so on. Furthermore, we also investigated diffusion effects of water vapor, and we confirmed that these phenomena are generated by the interaction of atmospheric air and affects the heat transfer to the surrounding environment. [Preview Abstract] |
Monday, November 19, 2012 8:26AM - 8:39AM |
G5.00003: A New Formulation for Volume-of-Fluid Simulations of Drops on Solid Surfaces: Inclusion of Adhesion Force C. Chang, A. Criscione, S. Jakirlic, C. Tropea, Alidad Amirfazli The capillary forces acting on a sessile drop placed on a solid surface has two basic components: (1) the Laplace pressure (LP) due to the curvature of the liquid-gas interface, and (2) the Surface Tension Force (STF) as a concentrated force acting at the three-phase contact line. STF can be thought of adhesion force for a drop placed on a solid surface. To date, Volume-of-Fluid (VoF) simulations of drops on solid surfaces have only considered LP, and ignored the STF. Ignoring the STF can lead to incorrect description of the physics for systems involving sessile drops (e.g. shedding of a drop from a surface) especially when capillary and external (e.g. inertial) forces are of the same order of magnitude. Continuum Surface Force (CSF) method is widely used in VoF to model the LP. By modifying the CSF implementation at the contact line, we have added the STF to the VoF formulation. Two case studies, i.e. water drops on an inclined surface and a sessile drop exposed to a shearing airflow are considered. When the STF was ignored, a drop placed on an inclined surface moved at an unrealistically low inclination (e.g. 1 degree for a system with considerable contact angle hysteresis of 10-30 deg.). Same unrealistic motion for the drop was observed when exposed to very low air velocities. Inclusion of the STF corrected both of these unphysical outcomes. A discussion of various systems with different wettabilities (adhesion force values) for each of the two case studies will be provided and comparisons with experiments will be presented. [Preview Abstract] |
Monday, November 19, 2012 8:39AM - 8:52AM |
G5.00004: ABSTRACT WITHDRAWN |
Monday, November 19, 2012 8:52AM - 9:05AM |
G5.00005: Turbulent Flows Over Three-Dimensional Shark Skin Aaron Boomsma, Li Wen, George Lauder, Fotis Sotiropoulos Shark skin is covered with thousands of small tooth-like structures called denticles. It has long been hypothesized that denticles act as riblets do in a turbulent boundary layer and help reduce friction drag and enhance shark swimming efficiency. We employ the Curvilinear Immersed Boundary (CURVIB) method (Ge and Sotiropoulos, J. Comp. Physics, 2008) to carry out high-resolution large eddy simulations of turbulent flow past a series of anatomically realistic shark denticles mounted on a flat plate. The denticle shapes used in our simulations were obtained by scanning Mako Short Fin shark skin with micro-CT. The computed results are analyzed to elucidate the three-dimensional structure of the flow past the denticles and identify possible drag reduction mechanics. Drag measurements obtained in a laboratory flume for various denticle spacings and arrangements are also reported and analyzed in tandem with the LES results to explore similarities between shark skin and engineered riblets. [Preview Abstract] |
Monday, November 19, 2012 9:05AM - 9:18AM |
G5.00006: Three-dimensional simulation of jellyfish by the penalty immersed boundary method Sung Goon Park, Cheng Bong Chang, Hyung Jin Sung The interaction between the motion of a three-dimensional jellyfish and the surrounding fluid was numerically simulated by the penalty immersed boundary method (pIBM). The effects of the vortex formation and the elastic properties on the kinematics of swimming jellyfish were examined. In order to simulate the incompressible fluid motion, the fractional step method was adopted on the Eulerian domain, while the subdivision finite element method was used to describe the solid motion on the Lagrangian domain. Coupling of the fluid motion and the jellyfish motion was realized in the framework of the pIBM. Our results suggest that the starting and stopping vortices, which are respectively induced from a power stroke and a recovery stroke, were formed in the wake of the swimming jellyfish. These two types of vortex interacted with each other, which made the size of vortex larger and caused the augmentation of thrust. Swimming performance of the jellyfish also depended on the elastic properties such as the tension and bending rigidity. It was found that the center velocity of the jellyfish increases with increasing the tension rigidity. [Preview Abstract] |
Monday, November 19, 2012 9:18AM - 9:31AM |
G5.00007: Evaluation of Wind Turbine Wake Interaction Models in a RANS Framework Jordan Wilson, Karan Venayagamoorthy Wind energy produced from horizontal axis wind turbines (HAWTs) remains the most cost effective source of renewable energy production. Computational fluid dynamics (CFD) model studies are widely used as an \textit{a priori} means to study wind farm environments for adequacy of wind resources and optimal configurations. This body of research explores the velocity deficit effect and flow fluctuations created by turbine wakes in a RANS framework for National Renewable Energy Laboratory (NREL) 5MW reference turbines. Various turbine models are explored to determine the most computationally efficient model that accurately captures the physics of interest. While only neutral ABL conditions are simulated in this study, consideration is also given to future work looking at the stable ABL and a full diurnal cycle when selecting a closure model. The objective of this current research is to further understand the development and resolution of turbine wakes for power optimization in neutral ABL conditions with a mind toward fatigue load minimization. [Preview Abstract] |
Monday, November 19, 2012 9:31AM - 9:44AM |
G5.00008: CFD simulation of Urban Environment to study building energy and Urban Heat Island (UHI) implications Negin Nazarian, Jan Kleissl Numerical simulations are used to study the street-scale urban environment investigating air flow and heat transfer that affect Urban Heat Island formation and urban energy use. Simulations are performed based on Reynolds-averaged Navier-Stokes equations and Large Eddy Simulations using ANSYS/FLUENT. Comprehensive simulations of the daytime urban environment are presented accounting for various contributing factors such as building aspect ratio, stability, and radiative properties of surfaces. Buoyancy and co-occurrence of forced and mixed convective flow regimes are accounted for and the local Richardson number inside the canyon and near building surfaces are examined. A three-dimensional regular building array is used for air flow simulation and thermal analysis. Periodic boundary conditions are used in both stream/span-wise directions representing fully-developed flow and wind profile above the canyon and vortex formation inside the street canyon are studied. The simulations are performed on a clear day in southern California and corresponding daytime solar load is applied for heat transfer purposes. Considering the coupled behavior of thermal effects and flow in the urban environment, we examine surface and canopy air temperature versus building energy use. [Preview Abstract] |
Monday, November 19, 2012 9:44AM - 9:57AM |
G5.00009: Large Eddy Simulation of Dilute Sediment Suspension in an Open Channel Flow Getnet Agegnehu, Heather D. Smith Flow and suspended sediment transport in fully developed turbulent open channel flow has been investigated using Large Eddy Simulation. We used a three-dimensional, non-hydrostatic model, OpenFOAM for this study. Pre-evaluation of three existing turbulence closure schemes is performed by comparing the mean flow and turbulent quantities with the direct numerical simulation results of Moser et al. (1999). It is found that the Dynamic Mixed Smagorinsky model underestimates the wall shear stress compared to the Dynamic Smagorinsky and one equation Eddy Viscosity schemes. Moreover, the Dynamic Smagorinsky scheme gives relatively better results in both the mean and turbulent quantities. The advection-diffusion equation is solved for suspended sediment transport and the effect of sediment roughness is included in the momentum equation based on the rough wall formulation proposed by Cebeci and Bradshaw (1977). A pick up function based on van Rijn (1984) is used to determine the sediment erosion. The settling process is taken into account with a settling velocity appearing in the concentration equation. Sediment and flow quantities are validated by comparing with the experimental data of Lyn (1988). The coupled hydrodynamics results are in good agreement with the experimental data. [Preview Abstract] |
Monday, November 19, 2012 9:57AM - 10:10AM |
G5.00010: A three dimensional numerical simulation of current induced sediment processes - A comparison to experimental work Markus Burkow Current driven sediment transport causes the evolution of bedforms like dunes, ripples or scour marks. These bedforms are formed by the interaction of entrainment and deposition of sediment particles. In this study we use a numerical simulation of the three dimensional fluid flow and the simultaneous transport processes to reproduce these processes. To solve the incompressible two-phase Navier-Stokes equations we use NaSt3D as fluid solver for incompressible flow problems in three dimensions. High order schemes are applied for spatial as well as for temporal discretization. Bed load transport as the main agent responsible for building up bed forms is modelled by the Exner equation. The rearrangement of sediment leads to a new sediment surface height which results in new bedforms. To test our model we compare our results to flume experiments concerning scour erosion at obstacles carried out at Department of Geography, University of Bonn. And as a two-phase example experimental results concerning splash-erosion are compared to our simulations. In both examples simulation and experiment are in good agreement. [Preview Abstract] |
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