Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session A21: Turbulence: Simulations I - LES Application |
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Chair: Johan Larsson, University of Maryland Room: 316 |
Sunday, November 24, 2013 8:00AM - 8:13AM |
A21.00001: Wall-modeled large eddy simulation of high-lift devices from low to post-stall angle of attacks Julien Bodart, Johan Larsson, Parviz Moin The flow around a McDonnell-Douglas 30P/30N multi-element airfoil at the flight Reynolds number of 9 million (based on chord) is computed using LES with an equilibrium wall-model with special treatment for transitional flows. Several different angles of attack are considered, up to and including stall, challenging the wall-model in several flow regimes. The maximum lift coefficient, which is generally difficult to predict with RANS approaches, is accurately predicted, as compared to experiments performed in the NASA LPT wind-tunnel. [Preview Abstract] |
Sunday, November 24, 2013 8:13AM - 8:26AM |
A21.00002: Wavelet-based adaptive LES of turbulent flow around a square-cylinder Giuliano De Stefano, Oleg V. Vasilyev The incompressible turbulent flow around a two-dimensional bluff body with square cross-section is simulated by using a wavelet-based adaptive LES method. The presence of the obstacle is modeled with the Brinkman volume-penalization technique, which results in modifying the governing equations with the addition of an appropriate forcing term inside the spatial region occupied by the cylinder. The localized dynamic kinetic-energy-based approach (De Stefano et al., PF 2008) is utilized to model the residual stresses term in the wavelet-filtered volume-penalized incompressible Navier-Stokes equations. The filtered momentum and SGS energy equations are numerically solved by means of the adaptive wavelet collocation method, where the time-dependent non-uniform spatial grid is dynamically determined following the flow evolution. The combined volume-penalization/wavelet-collocation approach is successfully applied to the simulation of turbulent vortex shedding flow behind a stationary prism with square cross-section at moderate Reynolds number. The present results are in good agreement with both experimental findings and data from non-adaptive numerical solutions. [Preview Abstract] |
Sunday, November 24, 2013 8:26AM - 8:39AM |
A21.00003: Numerical Study of Impulse Actuated Stall Control Sigfried Haering, Robert Moser Experimental studies have shown that pulse actuated dynamic stall control provides a simple means to significantly increase the performance of lifting surfaces and expand their flight envelope. However, precise information of the complex boundary layer reattachment mechanisms are inaccessible to experimental measurements. Therefore, adequately resolved and validated simulations are necessary to fully understand and utilize this approach. Numerical studies using detached large eddy simulation (DES) of a stalled airfoil with both spanwise-uniform and staggered actuation regions experiencing single pulse actuated flow reattachment are performed. The results of these simulations provide fundamental insight into the stall control mechanisms observed in experiments. Such studies may be extended to design optimal actuator spacing, orientation, and scheduling. [Preview Abstract] |
Sunday, November 24, 2013 8:39AM - 8:52AM |
A21.00004: Dynamic Immersed Boundary Method for Modeling of Turbulent Boundary Layers over Bio-Fouled Surfaces Xiang Yang, Jasim Sadique, Rajat Mittal, Charles Meneveau The growth of large organisms on ship surfaces, i.e. macrobiofouling, is a major contributor to drag, and consequently, fuel consumption. The problem of turbulence over biofouled surfaces may be reduced to that of a developing turbulent boundary layer over a surface with a wide range of roughness length scales. Due to the presence of these scales, direct numerical simulation (DNS) or even wall-resolved large-eddy-simulation (LES) is prohibitively expensive. We address this challenge by developing a dynamic immersed boundary method that does not require the flow field nor the roughness to be fully resolved. The effect of unresolved small eddies are included via an LES sub-grid model. The large-scale roughness elements are resolved by a sharp-interface immersed boundary method and the effect of small (unresolved) roughness elements is incorporated through the use of a wall model that assumes a log-law at the grid point closest to the wall. This computationally efficient method is validated against experiments of developing turbulent boundary layer with multiple-scale roughness elements. We present results from this study and provide a discussion of our findings. [Preview Abstract] |
Sunday, November 24, 2013 8:52AM - 9:05AM |
A21.00005: Computational Analysis of Particle Nucleation in Dilution Tunnels: Effect of Flow Configuration and Tunnel Geometry Satbir Singh, Peter Adams, Ashwin Misquitta, Kyung Lee, Eric Lipsky, Allen Robinson Measurement of fine particle emission from combustion sources is important to understand their health effects, and to develop emissions regulations. Dilution sampling is the most commonly used technique to measure particle number distribution because it simulates the cooling of combustion exhaust with atmospheric air. Experiments suggest that the measured distribution is dependent on the dilution ratio used and the tunnel design. In the present work, computational analysis is performed to investigate the effect of tunnel flow and geometric parameters on H$_2$SO$_4$-H$_2$O binary nucleation inside dilution tunnels using a large-eddy-simulation (LES) based model. Model predictions suggest that the experimental trends are likely due to differences in the level of turbulence inside the tunnels. It is found that the interaction of dilution air and combustion exhaust in the mixing layer greatly impacts the extent of nucleation. In general, a cross-flow configuration with enhanced turbulent mixing leads to greater number of nucleation-mode particles than an axial-flow configuration. [Preview Abstract] |
Sunday, November 24, 2013 9:05AM - 9:18AM |
A21.00006: Coherent eddies in flows over three-dimensional dunes Mohammad Omidyeganeh, Ugo Piomelli We performed large-eddy simulations of the flow over a series of 3D dunes at laboratory scale. The bedform three-dimensionality was imposed by shifting a standard 2D dune shape in the streamwise direction according to a sine wave. The flow structures are discussed for two cases, with the same crestline amplitudes and wavelengths but different crestline alignments: in-phase and staggered. Large-scale, mean streamwise vortices are the primary factor that alters the features of the instantaneous flow structures. Rollers generated in the separated shear layer appear regularly over the lobe, and are shed more frequently than in 2D geometries. Separated vortices in the lobe plane undergo a three-dimensional instability while advected downstream, and rise toward the free surface while developing into a horseshoe shape (similar to the 2D case). When the tip of such a horseshoe reaches the free surface, the ejection of flow at the surface causes boils (upwelling events on the surface). Strong boil events are observed on the surface of the lobe planes of 3D dunes more frequently than in the saddle planes and the corresponding 2D geometry. Boil events occur at higher frequency in the staggered alignment, but with less intensity than in the in-phase alignment. [Preview Abstract] |
Sunday, November 24, 2013 9:18AM - 9:31AM |
A21.00007: LES study of vortical structures and suction peaks on a 3D square cylinder in turbulent boundary layer Tetsuro Tamura, Yoshiyuki Ono Sophisticated LES technique has made it possible to reproduce unsteady flows around a three-dimensional square cylinder in turbulent boundary layer. Various flow patterns such as the separation bubble or vortices in the cylinder wake are sensitively changed depending on the angle of attack. It is well-known that local severe suctions occur in the flow separation regions of the cylinder. The experimental study showed that the local severe suctions on the side of the square cylinder were caused by two types of conical vortices. One was a standing conical vortex at the upper edge of windward corner at glancing angle, which leads to large level of negative pressure. The other was an inversion conical vortex on the lower side of the cylinder when the flow normally attacks. This inversion conical vortex was periodically formed and causes the fluctuation of the pressure near the bottom of windward corner. Here, LES is applied to the flow around a square cylinder in boundary-layer turbulence. Instantaneous large negative pressure peaks are randomly recognized in the present computational results. At the same time, inversion conical vortex and conical vortices are intermittently formed in boundary-layer turbulence. Physical mechanism for occurrence of peak pressures has been elucidated. [Preview Abstract] |
Sunday, November 24, 2013 9:31AM - 9:44AM |
A21.00008: Turbulent Heat Transfer in Curved Pipe Flow Changwoo Kang, Kyung-Soo Yang In the present investigation, turbulent heat transfer in fully-developed curved pipe flow with axially uniform wall heat flux has been numerically studied. The Reynolds numbers under consideration are \textit{Re}$_{\tau} = 210$ (DNS) and 1,000 (LES) based on the mean friction velocity and the pipe radius, and the Prandtl number (\textit{Pr}) is 0.71. For \textit{Re}$_{\tau} = 210$, the pipe curvature ($\kappa )$ was fixed as 1/18.2, whereas three cases of $\kappa $ (0.01, 0.05, 0.1) were computed in the case of \textit{Re}$_{\tau }=$1,000. The mean velocity, turbulent intensities and heat transfer rates obtained from the present calculations are in good agreement with the previous numerical and experimental results. To elucidate the secondary flow structures due to the pipe curvature, the mean quantities and rms fluctuations of the flow and temperature fields are presented on the pipe cross-sections, and compared with those of the straight pipe flow. To study turbulence structures and their influence on turbulent heat transfer, turbulence statistics including but not limited to skewness and flatness of velocity fluctuations, cross-correlation coefficients, an Octant analysis, and turbulence budgets are presented and discussed. Based on our results, we attempt to clarify the effects of Reynolds number and the pipe curvature on turbulent heat transfer. [Preview Abstract] |
Sunday, November 24, 2013 9:44AM - 9:57AM |
A21.00009: Secondary Peak in Nusselt Number for Jet Impinging Flows: LES Study Rabijit Dutta, Anupam Dewan, Balaji Srinivasan Jet impingement heat transfer is widely studied because of its industrial and as well as fundamental relevance. A secondary peak in Nusselt number at some distance away from the stagnation point is observed for both round and slot jet impingement flows at a small nozzle-to-plate spacing. Although various researchers have studied the reason behind this secondary peak, it is still an open question in the literature. We present large eddy simulation (LES) of turbulent slot jet impingement heat transfer to gain further insight into the phenomenon of secondary peak in Nusselt number. Profiles of mean velocities, turbulent fluctuating velocities and Nusselt numbers have been analyzed along the impingement plate. A sudden increase in the wall normal turbulence fluctuations have been observed in the region where the secondary peak in Nusselt number occurs. Further, an analysis of vortex structures of the flow showed that the increase in the wall normal turbulence could be associated with the secondary vortex observed near the impingement wall. [Preview Abstract] |
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