Experimental investigation of the unsteady wake of the square-back Ahmed model

Fan Yajun; Xia Chao; Ge Diandian; Yang Zhigang

doi:10.11729/syltlx20190112

Volume 33 Issue 6

Dec. 2019

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Article Navigation > Journal of Experiments in Fluid Mechanics > 2019 > 33(6): 84-89

Fan Yajun, Xia Chao, Ge Diandian, et al. Experimental investigation of the unsteady wake of the square-back Ahmed model[J]. Journal of Experiments in Fluid Mechanics, 2019, 33(6): 84-89. doi: 10.11729/syltlx20190112

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Experimental investigation of the unsteady wake of the square-back Ahmed model

doi: 10.11729/syltlx20190112

Fan Yajun^{1, 2
,},
Xia Chao^{1, 2
,
,},
Ge Diandian^{1, 2},
Yang Zhigang^{1, 2, 3}

1.
Shanghai Key Lab of Vehicle Aerodynamics and Vehicle Thermal Management Systems, Shanghai 201804, China
2.
Shanghai Automotive Wind Tunnel Center, Tongji University, Shanghai 201804, China
3.
Beijing Aeronautical Science &Technology Research Institute, Beijing 102211, China

Received Date: 2019-08-21
Rev Recd Date: 2019-09-24
Publish Date: 2019-12-25

Abstract

Abstract

The square-back Ahmed model is a simplified commercial vehicle body model. The flow separates at the tail to form a recirculation region, leading to the negative pressure on the back and large aerodynamic drag. The unsteady wake of the 1/4-scale square back Ahmed model were finely measured and statistically analyzed via the wind tunnel test. The experimental Reynolds number was 9.2×10⁴. The results of the back pressure measurement, particle image velocimetry (PIV) and hot-wire measurement show that the unsteady wake pattern of the square back Ahmed model basically consists of three flow characteristics: the bi-stable behavior (random asymmetry between the left and right vortex structures), vortex shedding in the horizontal and vertical direction, and pumping of the recirculation region periodically. Among them, the bi-stable phenomenon plays a dominant role in the wake. It shows the alternating occurrence of two stable states (the transition probability is 0.149). Each stable state can maintain a long time scale (the average duration is about 6 s), and its spectral characteristics satisfy the -2 power law distribution; the corresponding frequency of the periodic pumping oscillation is Sr_H=0.07; and the vortex shedding frequencies corresponding to the oscillations in the horizontal direction and the vertical direction are Sr_H=0.13 and Sr_H=0.17, respectively. The interaction among these structures exists, and thus the unsteady wake of the square back Ahmed model presents complex three-dimensional features.
- square back model,
- unsteady wake,
- PIV measurement,
- bi-stable behavior,
- vortex shedding

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References(12)

References

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