Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session RD: Turbulence Simulations VII |
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Chair: James M. McDonough, University of Kentucky Room: Long Beach Convention Center 102B |
Tuesday, November 23, 2010 3:05PM - 3:18PM |
RD.00001: Simulations of the wake of an accelerating body Matthew de Stadler, Sutanu Sarkar When a body moving under its own power maneuvers, momentum is transferred to the surrounding fluid. This transfer of momentum, even for relatively small values, is thought to significantly affect the wake dynamics. Direct Numerical Simulation (DNS) in a spatially evolving frame, a first study of this kind, in addition to the commonly used temporal approximation, was used to evaluate this hypothesis. The main objective is to characterize the time evolution of the self-propelled wake dynamics in the presence of a momentum imbalance in a stratified fluid. Statistics of interest include the defect velocity, wake dimensions, vortex dynamics, the presence or lack thereof of large eddies in the late wake, wake lifetime, internal wave dynamics and mean and turbulent kinetic energies and their associated budgets. Results from the spatially evolving case are compared with data from a temporally evolving case with excess momentum. [Preview Abstract] |
Tuesday, November 23, 2010 3:18PM - 3:31PM |
RD.00002: Turbulent Flow Past Projectiles: A Computational Investigation Igbal Mehmedagic, Donald Carlucci, Liam Buckley, Pasquale Carlucci, Siva Thangam Projectiles with free spinning bases are often used for smart munitions to provide effective control, stability and terminal guidance. Computational investigations are performed for flow past cylinders aligned along their axis where a base freely spins while attached to and separated at various distances from a non-spinning fore-body. The energy spectrum is modified to incorporate the effects of swirl and rotation using a parametric characterization of the model coefficients. An efficient finite-volume algorithm is used to solve the time-averaged equations of motion and energy along with the modeled form of transport equations for the turbulence kinetic energy and the scalar form of turbulence dissipation. Computations are performed for both rigid cylinders as well as cylinders with free-spinning bases. Experimental data for a range of spin rates and free stream flow conditions obtained from subsonic wind tunnel with sting-mounted spinning cylinders is used for validating the computational findings. [Preview Abstract] |
Tuesday, November 23, 2010 3:31PM - 3:44PM |
RD.00003: LES study of aero-optical distortions over a cylindrical turret with passive flow control Kan Wang, Meng Wang Large-eddy simulations are carried out for compressible flow over a cylindrical turret with a flat optical window to study the aero-optical distortions and their mitigation by passive control devices in the upstream boundary layer. The control devices consist of long and thin pins as in an experiment conducted at the University of Notre Dame. A comparison with the experimental data for the baseline case without pins shows overall agreement in terms of velocity statistics and the optical distortion magnitude. The root-mean-square of optical path difference (OPD$_{rms}$) caused by the separated shear layer above the optical window is found to be five times as large as that caused by the attached boundary layer upstream of the turret. Simulation results for the passive-control case confirm key experimental observations. A second shear layer above the main shear layer is observed, which reduces the turbulence intensity of the main shear layer and widens the turbulence region over the optical window. The combined effect of the two shear layers leads to slightly reduced optical distortions compared with the uncontrolled flow with a single strong shear layer. Control strategies for reducing optical distortions without suppressing flow separation will be discussed. [Preview Abstract] |
Tuesday, November 23, 2010 3:44PM - 3:57PM |
RD.00004: Application of Immersed Boundary Method to DNS of Stratified Flows Narsimha Rapaka, Sutanu Sarkar An immersed boundary method is implemented in a Navier-Stokes solver that uses a mixed RK3-ADI time integration scheme with the viscous terms treated implicitly. A predictor-corrector algorithm is used to solve the momentum equations on a collocated grid arrangement. Simulations are performed for flow past a sphere and the results, including separation angle, separation length, the vortex core position and the Strouhal frequency, agree closely with the literature. The present focus is on the numerical behavior of the solver in problems involving nonlinear internal tides on a model topography. Physical quantities of interest include the turbulent kinetic energy, turbulent dissipation rate, buoyancy flux as well as the energy flux and spectra associated with the propagating internal waves. [Preview Abstract] |
Tuesday, November 23, 2010 3:57PM - 4:10PM |
RD.00005: Direct Numerical Simulation of a Film Cooling Configuration with a Micro-ramp Vortex Generator Aaron Shinn, S. Pratap Vanka A Direct Numerical Simulation (DNS) of an inclined turbulent jet interacting with a cross-flow in a film cooling configuration is performed. The inclined turbulent jet represents the coolant flow and the cross-flow represents the hot combustion gases. In this configuration, it is known that the coolant jet tends to lift off the wall that is to be cooled, thus decreasing heat transfer effectiveness. The micro-ramp vortex generator is placed downstream of the coolant jet and is used to modify the trajectory of the coolant jet such that it remains closer to the wall, thus enhancing heat transfer. The purpose of this study is to examine the micro-ramp's effect on both the flowfield and heat transfer of the film cooling problem. The coolant jet is inclined at an angle of 35 degrees to the freestream, the blowing ratio is 1.5, and the Reynolds number based on the jet diameter and freestream cross-flow velocity is 8000. The incompressible Navier-Stokes equations are solved numerically using a 3D finite volume solver (CU-FLOW) implemented on a Graphics Processing Unit (GPU). [Preview Abstract] |
Tuesday, November 23, 2010 4:10PM - 4:23PM |
RD.00006: Generalized Velocity Boundary Conditions for Kleiser and Schumann's Influence-Matrix Method Xiaofeng Liu Kleiser and Schumann (1980) introduced a novel influence-matrix method to treat the incompressibility and no-slip boundary conditions when solving the Navier-Stokes equations. They also outlined the related ``tau'' error correction technique which is essential for the high accuracy direct numerical simulation (DNS) of turbulent flows. Werne (1995 proposed a revised ``tau'' correction algorithm on the ``A''-problem level. Both method are correct, though some technical differences exist. Note also that both methods are specific for the no-slip boundary conditions where the odd and even modes of Chebyshev expansion in the wall normal direction decouples. In this talk, the Kleiser and Schumann method will be generalized to treat the Robin type velocity boundary conditions and the related ``tau'' error corrections. This new method will broaden the applicability of the Kleiser and Schumann method to situations where velocity boundary conditions are not limited to no-slip. Three examples (channel flow with a free surface, density current in an open channel, drag reduction in a hydrophobic channel) will be shown with extensive validations using various statistics of turbulent flow. All examples show excellent agreement with data in the literature and the velocity field is divergence free up to machine precision. [Preview Abstract] |
Tuesday, November 23, 2010 4:23PM - 4:36PM |
RD.00007: Microscopic analysis and simulation of check-mark stain on the galvanized steel strip Hongyun So, Hyun Gi Yoon, Myung Kyoon Chung When galvanized steel strip is produced through a continuous hot-dip galvanizing process, the thickness of adhered zinc film is controlled by plane impinging air gas jet referred to as ``air-knife system". In such a gas-jet wiping process, stain of check-mark or sag line shape frequently appears. The check-mark defect is caused by non-uniform zinc coating and the oblique patterns such as ``W", ``V" or ``X" on the coated surface. The present paper presents a cause and analysis of the check-mark formation and a numerical simulation of sag lines by using the numerical data produced by Large Eddy Simulation (LES) of the three-dimensional compressible turbulent flow field around the air-knife system. It was found that there is alternating plane-wise vortices near the impinging stagnation region and such alternating vortices move almost periodically to the right and to the left sides on the stagnation line due to the jet flow instability. Meanwhile, in order to simulate the check-mark formation, a novel perturbation model has been developed to predict the variation of coating thickness along the transverse direction. Finally, the three-dimensional zinc coating surface was obtained by the present perturbation model. It was found that the sag line formation is determined by the combination of the instantaneous coating thickness distribution along the transverse direction near the stagnation line and the feed speed of the steel strip. [Preview Abstract] |
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