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Turbulent near wake of an Ahmed vehicle model

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Abstract

The lasting high fuel cost has recently inspired resurgence in drag reduction research for vehicles, which calls for a thorough understanding of the vehicle wake. The simplified Ahmed vehicle model is characterized by controllable flow separation, thus especially suitable for this purpose. In spite of a considerable number of previous investigations, our knowledge of flow around this model remains incomplete. This work aims to revisit turbulent flow structure behind this model. Two rear slant angles, i.e., α = 25º and 35º, of the model were examined, representing two distinct flow regimes. The Reynolds number was 5.26 × 104 based on the model height (H) and incident flow velocity. Using particle image velocimetry (PIV), flow was measured with and without a gap (g/H = 0.174) between the vehicle underside and ground in three orthogonal planes, viz. the x–z, x–y and y–z planes, where x, y, and z are the coordinates along longitudinal, transverse, and spanwise directions, respectively. The flow at g/H = 0 serves as an important reference for the understanding of the highly complicated vehicle wake (g/H ≠ 0). While reconfirming the well-documented major characteristics of the mean flow structure, both instantaneous and time-averaged PIV data unveil a number of important features of the flow structure, which have not been previously reported. As such, considerably modified flow structure models are proposed for both regimes. The time-averaged velocities, second moments of fluctuating velocities, and vorticity components are presented and discussed, along with their dependence on g/H in the two distinct flow regimes.

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Acknowledgments

YZ wishes to acknowledge support given to him from Research Grants Council of HKSAR through grant GRF 531912 and from Natural Science Foundation of China through Grant 50930007.

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Authors and Affiliations

  1. Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

    X. W. Wang, Y. Zhou, Y. F. Pin & T. L. Chan

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  1. X. W. Wang
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  3. Y. F. Pin
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  4. T. L. Chan
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Correspondence to Y. Zhou.

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Wang, X.W., Zhou, Y., Pin, Y.F. et al. Turbulent near wake of an Ahmed vehicle model. Exp Fluids 54, 1490 (2013). https://doi.org/10.1007/s00348-013-1490-x

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