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ACTIVE CONTROL OF TURBULENT FLOW OVER A MODEL VEHICLE FOR DRAG REDUCTION

Haecheon Choi
Department of Mechanical & Aerospace Engineering Seoul National University 1, Gwanak-ro, Gwanak-gu, Seoul 08826, Korea

Jeonglae Kim
School of Mechanical and Aerospace Engineering Seoul National University Seoul 151-742, Korea

Seonghyeon Hahn
Center for Turbulence and Flow Control Research Institute of Advanced Machinery and Design Seoul National University Seoul 151-742, Korea

Dong-kon Lee
School of Mechanical and Aerospace Engineering Seoul National University Seoul 151-742, Korea

Jin Choi
School of Mechanical and Aerospace Engineering Seoul National University Seoul 151-742, Korea

Woo-Pyung Jeon
Center for Turbulence and Flow Control Research Institute of Advanced Machinery and Design Seoul National University Seoul 151-742, Korea

Resumo

The objectives of the present study are to examine the applicability of the distributed forcing (Kim and Choi 2002) to flows over bluff bodies having a fixed separation and thus to evaluate the universality of the distributed forcing. Therefore, both the large eddy simulation (LES) with a dynamic model for subgrid-scale stress components and wind-tunnel experiment are carried out for flow over a model vehicle. LES is performed at the Reynolds number of Re = uh/ν = 4200, whereas two different Reynolds numbers of Re = 20,000 and 40,000 are considered in the experiment, where u is the free-stream velocity and h is the body height. In LES at Re = 4200, a significant amount of the base-pressure recovery is obtained with the in-phase distributed forcing, while the out-of-phase one leaves the base pressure almost unchanged. Furthermore, the in-phase distributed forcing substantially suppresses vortex shedding, whereas the out-of-phase one does not seem to influence vortex shedding very much. The power spectra of the velocity fluctuations and the spatial distribution of the Reynolds shear stress also show that the in-phase distributed forcing considerably enhances the three dimensionality of the wake behind the model vehicle. Similar results are also obtained from the in-phase forcing in the experiment at higher Reynolds numbers and thus it is believed that the distributed forcing is applicable to a broad class of two-dimensional bluff bodies for drag reduction in a wide range of the Reynolds number.