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CSME 2019/12
Volume 40 No.6
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727-731
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Flow Visualization on the Steady and Unsteady Flow Structures around Ahmed Model
Ying-Chao Zhanga, Hui Zhu and Yu Zhoub
aState key laboratory of automotive simulation and control, Jilin University, Changchun, China / Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
bDepartment of Mechanical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong / Institute for Turbulence-Noise-Vibration Interactions and Control, Harbin Institute of Technology, Shenzhen, China
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Abstract:
Ahmed model is a simplified vehicle model for aerodynamic characteristic investigation. To understand the steady and unsteady flow structures, some flow visualization experiments have been carried out to show the flow structures under wake. Ahmed model will with high air drag or low air drag according to the slant surface angle. In low drag regime, the flow above the slant surface is shown by the smoke flow. The flow begins to separate at the upper edge of slant surface and forms a shear vortex of K-H instability due to the velocity difference in wake separation regions and forms a backwards flow and recirculation bubble at the slant surface. In the high drag regime, the presence of the C-pillar vortex is shown by the smoke flow visualizations. Based on the study of K-H instability of low drag model, it is speculated that the formation of C-pillar vortex is accompanied by the existence of shear vortex. Further PIV experiments show that the structure of the C-pillar vortex is studied on a smaller scale, and the vortex of the C-pillar is found. The C-pillar is a steady flow structure, and its sub vortices are unsteady shear vortices. This sub vortex is first report in automotive aerodynamics.
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Keywords: flow structures, Ahmed, steady and unsteady, sub-vortex.
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*Corresponding author; e-mail:
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©
2019
CSME , ISSN 0257-9731
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