Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session PC: Turbulence Simulations VII |
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Chair: Andrew Ooi, University of Melbourne Room: 101C |
Tuesday, November 24, 2009 11:40AM - 11:53AM |
PC.00001: Numerical studies of the flow past a rotating sphere at \textit{Re} = 500 Eric Poon, Gianluca Iaccarino, Andrew Ooi, Matteo Giacobello The flow past a rotating sphere is of interest in many engineering applications. A number of numerical studies have been performed to investigate the flow past a streamwise and transversely rotating sphere in the laminar flow regime (\textit{Re} $\le $ 300, where \textit{Re} is the Reynolds number based on freestream velocity, $U_{\infty }$, and sphere diameter, $d)$. In order to extend the understanding of a sphere's trajectory due to the rotating motion of the sphere, the flow past a rotating sphere is investigated for \textit{Re} = 500. This Reynolds number sits in the unsteady asymmetric regime for a stationary sphere. The non-dimensional rotation rates, 0 $\le \quad \Omega ^{\ast}$ $\le $ 1, are considered. The sphere rotation axis is orientated in two of the principle axis directions, namely streamwise and transverse directions. The effect of the rotation axis and $\Omega ^{\ast}$ on the flow structures and the aerodynamic forces of a rotating sphere will be presented. [Preview Abstract] |
Tuesday, November 24, 2009 11:53AM - 12:06PM |
PC.00002: Direct numerical simulation of turbulent flow over a backward-facing step Michal A. Kopera, Christopher Cantwell, Robert M. Kerr, Dwight Barkley, Hugh Blackburn Turbulent flow in a channel with a sudden expansion(backward-facing step) is studied by direct numerical simulation (DNS) of incompressible Navier-Stokes equations. Initial results are presented for a 3D DNS of a backward-facing step flow with Reynolds number 6000, based on average bulk upstream velocity and step height. The expansion ratio is 2. Turbulent inflow is provided by regeneration of velocity and pressure fields from a plane downstream from the inflow. Simulations are made using the Semtex DNS spectral element solver. The goal is to generate hi-resolution DNS data of a high Reynolds number flow over a backward-facing step for LES comparisons. [Preview Abstract] |
Tuesday, November 24, 2009 12:06PM - 12:19PM |
PC.00003: Numerical Simulations of Turbulent Rayleigh-Benard Convection Janet Scheel The results from numerical simulations of three-dimensional, fully turbulent Rayleigh-Benard convection will be presented. These results are compared to experiments and theoretical stochastic models, particularly the scaling of heat transport and thermal/viscous boundary layers with Rayleigh number. The orientation and strength of the large-scale circulation has also been measured. The orientation of this large-scale circulation exhibits diffusive meandering in addition to chaotic, abrupt switches. [Preview Abstract] |
Tuesday, November 24, 2009 12:19PM - 12:32PM |
PC.00004: Direct Numerical Simulation of Spiral Turbulence S. Dong, X. Zheng Spiral turbulence in the Taylor-Couette setting is one of the most fascinating phenomena of fluid dynamics, where intertwined helical turbulent and laminar patterns propagate between counter-rotating concentric cylinders. It is characterized by spatiotemporal intermittency and the co-existence of turbulent and laminar domains in space and time. We report a direct numerical simulation of spiral turbulence in the Taylor-Couette geometry over a range of Reynolds numbers at which well-defined turbulent/laminar spiral patterns are observed. The statistical features of turbulent spirals are characterized with a conditional averaging technique. [Preview Abstract] |
Tuesday, November 24, 2009 12:32PM - 12:45PM |
PC.00005: Direct Numerical Simulation of Turbulent Pipe Flows subjected to Transverse Oscillations Mark Czajkowski, Olivier Desjardins Fundamental effects of transverse oscillations on a turbulent pipe are being studied using direct numerical simulations (DNS). Previous studes of pipes subjected to oscillations around their central axis have shown a reduction in pressure drop. This study is a generalization of previous work to the case of an oscillation around an axis parallel to but not coinciding with the pipe centerline.The role of oscillation frequency, amplitude, and radius on the statistics of turbulent pipe flows, as well as bulk properties like pressure drop are investigated. Two key non-dimensional numbers are identified. The first relates the oscillation amplitude to a turbulent length scale (Taylor micro-scale); and the second number, a Strouhal number, compares the oscillation frequency to a turbulent time scale. These non-dimensional numbers, along with oscillation radius, are varied over a range of values, and DNS were performed using the arbitrarily high order accurate code NGA [Desjardins, et al., JCP 2008]. The resulting turbulent flows were analysed using a variety of turbulent statistics and compared to stationary and pipes rotating around their central axis. [Preview Abstract] |
Tuesday, November 24, 2009 12:45PM - 12:58PM |
PC.00006: Numerical Simulation of Flow Over a Savonius Wind Turbine Using a Spectral Element Method Sriharsha Kandala, Dietmar Rempfer A parallel spectral element code, SpecSolve, is developed with the objective of modeling flows in complex geometries. This code supports both structured and unstructured meshes and allows exact representation of boundary surfaces which are particularly useful for modeling turbo machinery flows. In this talk we present the results from 2D Navier-Stokes simulations of flow over a Savonius turbine. The simulation uses a rotating mesh in regions surrounding the blade and a stationary mesh away from the rotor. Results of a 2D Optimization study involving overlap ratio and the number of blades are also presented. These results are compared with experimental data. [Preview Abstract] |
Tuesday, November 24, 2009 12:58PM - 1:11PM |
PC.00007: Numerical Investigation of Base Drag for an Axisymmetric Underwater Vehicle with Bluff Afterbody Min-Jae Kim, Kurnchul Lee The objective of this study is to predict the drag of an axisymmetric underwater vehicle with bluff afterbody. FLUENT, commercial CFD code, is used to simulate high Reynolds number turbulent flows around the vehicle. The computed drag coefficients are compared to available experimental data at various Reynolds numbers. Four widely used two-equation turbulence models are investigated to evaluate their performance of predicting the anisotropic turbulence in a recirculating flow region, which is caused by flow separation arising from the base of the vehicle. The simulations with Realizable k-$\varepsilon $ and k-$\omega $ SST turbulence models predict the anisotropic turbulent flows comparatively well and the drag prediction results with those models show good agreements with the experimental data. [Preview Abstract] |
Tuesday, November 24, 2009 1:11PM - 1:24PM |
PC.00008: Aerodynamics of a Cryogenic Semi-Tanker Jason Ortega, Kambiz Salari The design of a modern cryogenic semi-tanker is based primarily upon functionality with little consideration given to aerodynamic drag. As a result, these tankers have maintained the appearance of a wheeled cylinder for several decades. To reduce the fuel usage of these vehicles, this study investigates their aerodynamics. A detailed understanding of the flow field about the vehicle and its influence on aerodynamic drag is obtained by performing Reynolds-Averaged Navier-Stokes simulations of a full-scale tractor and cryogenic tanker-trailer operating at highway speed within a crosswind. The tanker-trailer has a length to diameter ratio of 6.3. The Reynolds number, based upon the tanker diameter, is 4.0$\times $10$^{6}$, while the effective vehicle yaw angle is 6.1\r{ }. The flow field about the vehicle is characterized by large flow separation regions at the tanker underbody and base. In addition, the relatively large gap between the tractor and the tanker-trailer allows the free-stream flow to be entrained into the tractor-tanker gap. By mitigating these drag-producing phenomena through the use of simple geometry modifications, it may be possible to reduce the aerodynamic drag of cryogenic semi-tankers and, thereby, improve their fuel economy. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Tuesday, November 24, 2009 1:24PM - 1:37PM |
PC.00009: Modeling the Free Surface Penetration of Cylinders and Spheres Samuel Koski, Pavlos Vlachos Free surface penetration is a multiphase flow problem whereby a solid body is translated through a gas penetrating a liquid. The nature of the ensuing fluid dynamics poses a highly complex analytical modeling effort. It is known that for a given surface roughness, body geometry, and velocity, a cavity can be formed aft of the body and maintained for a given distance with traveling from air into water. An analytical model [Dynamics of Transient Cavities, V. Duclaux et al.] of the classical free surface penetration of spheres and cylinders and computational simulations using ANSYS CFX version 12 are preformed and presented. Comparisons of the pinching (closure) and cavity radius as a function of time are considered and the effect of surface roughness is explored. [Preview Abstract] |
Tuesday, November 24, 2009 1:37PM - 1:50PM |
PC.00010: Simulation of Acid-Base Reactions in a Microscale Confined Impinging Jet Reactor Jen Olsen, Lucas Griffith, Michael Olsen, Rodney Fox Numerical simulations were performed of reactive mixing in a microscale confined impinging jets reactor (CIJR). A simple acid-base reaction was modeled and solved for a laminar flow case. Local pH throughout the reactor was determined as a function of hydrogen and hydroxide mixture fraction, and this relationship was used to generate a pH field that could be compared with experimental results. An experimental visualization of the acid-base reaction was performed in the CIJR with phenolphthalein used as a pH indicator. Visualization images of the actual flow were then compared with the predictions of the simulation. Good agreement was observed between the experiment and the simulation. Future work will include adding a turbulence model to the simulation. [Preview Abstract] |
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