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 同济大学学报(自然科学版)  2017, Vol. 45 Issue (8): 1167-1173.  DOI: 10.11908/j.issn.0253-374x.2017.08.010 0

### 引用本文

CUI Wenshi, YANG Zhigang, WANG Guojun. Influence of Driving Frequency Using Synthetic Jets on Aerodynamic Drag of a Ground Vehicle[J]. Journal of Tongji University (Natural Science), 2017, 45(8): 1167-1173. DOI: 10.11908/j.issn.0253-374x.2017.08.010.

### 文章历史

1. 同济大学 上海地面交通工具风洞中心，上海 201804;
2. 同济大学 上海市地面交通工具空气动力与热环境模拟重点实验室，上海 201804

Influence of Driving Frequency Using Synthetic Jets on Aerodynamic Drag of a Ground Vehicle
CUI Wenshi1,2, YANG Zhigang1,2, WANG Guojun1,2
1. Shanghai Automotive Wind Tunnel Center, Tongji University, Shanghai 201804, China;
2. 2 Shanghai Key Laboratory of Vehicle Aerodynamics and Vehicle Thermal Management Systems, Tongji University, Shanghai 201804, China
Abstract: Based on Large-eddy simulation, influences of driving frequency on aerodynamic drag of a three-dimensional ground vehicle and flow-control mechanism was studied. The results of flow analysis indicate that when synthetic jet array is located at the junction of the roof and the slant, drag reduction is realized with different frequencies. When driving frequency is lower than 90Hz, the aerodynamic drag increases with the driving frequency raise. When the frequency is more than 90Hz, the aerodynamic drag decreases with the frequency increase. While the aerodynamic drag fail to decrease with the frequency 1500Hz. The difference in the recirculation zone and the distribution of Reynolds stress contributes to the variation trend of the aerodynamic drag with different driving frequency. Frequency spectrum analysis reveals that the dynamic attachment flow on the slant is controlled by synthetic jet array with different driving frequency, so that the peak frequency of power spectral density of velocity, surface pressure and aerodynamic drag is related to driving frequency.
Key words: aerodynamic drag    ground vehicle    synthetic jet    large-eddy simulation    driving frequency

1 风洞试验 1.1 合成射流激励器

 图 1 合成射流激励器 Fig.1 Synthetic jet actuator
1.2 车辆模型

Ahmed body模型[1]可有效模拟车辆尾部流场.以0.3倍缩比的Ahmed body模型作为研究对象，如图 2a所示，模型尾部倾角为25°，长、宽、高分别为L=0.322 m, W=0.120 m, H=0.089 m.面y=0，速度和压力测点分布见图 2b.

 图 2 Ahmed body模型风洞试验 Fig.2 Wind tunnel experiment of Ahmed body
1.3 风洞试验

2 数值仿真方法与结果验证 2.1 计算域与网格划分

 图 3 车辆及射流器网格加密区 Fig.3 Refined mesh around Ahmed body and jets
2.2 湍流模型与边界条件设置

 ${V_{{\rm{sja}}}} = {V_0}d/D \cdot {\rm{sin}}\left( {2\pi {f_{\rm{a}}} \cdot t} \right)$ (1)

 ${V_0} = \frac{{\rm{\pi }}}{{Td}}\int_0^{\frac{T}{2}} {\int_0^d {v\left( {y, t} \right){\rm{d}}y{\rm{d}}t} }$ (2)

 ${C_{\rm{ \mathsf{ μ} }}} = N \cdot \left( {{d^2}/W \cdot H} \right){\left( {{V_{{\rm{sja}}}}{\rm{/}}U} \right)^2}$ (3)

2.3 仿真结果验证

 图 4 不同激励下减阻效果 Fig.4 Drag reduction with different driving frequency

 图 5 后垂直背和斜背平均压力系数，面y=0上 Fig.5 Mean pressure coefficient on the slant and rear vertical base, plane y=0

3 结果分析 3.1 气动力比较

 图 6 不同激励频率下平均压力分布 Fig.6 Mean pressure distribution with different driving frequency
3.2 流场比较

 图 7 有无控制下的流场对比 Fig.7 Comparison of natural and controlled flow
 图 8 背部等值面涡量 Fig.8 Isosurface of vortices near the slant
 图 9 不同激励频率下的附着距离 Fig.9 Flow reattachment distance on the slant with different driving frequencies

 图 10 不同激励频率下, 面y=0上雷诺应力分布 Fig.10 Distribution of Renold stress in plane y=0 with different driving frequencies
3.3 频谱比较

 图 11 涡脱落频率分布 Fig.11 Power spectral density of velocity

 图 12 阻力系数功率谱密度 Fig.12 Power spectral density of drag coefficient signal

4 结论

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