方背Ahmed模型非定常尾迹的实验研究

范亚军; 夏超; 葛典典; 杨志刚

doi:10.11729/syltlx20190112

方背Ahmed模型非定常尾迹的实验研究

doi: 10.11729/syltlx20190112

范亚军^{1, 2,},
夏超^{1, 2, ,},
葛典典^{1, 2},
杨志刚^{1, 2, 3}

1.
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
2.
同济大学上海地面交通工具风洞中心, 上海 201804
3.
北京民用飞机技术研究中心, 北京 102211

基金项目:

上海地面交通专业技术服务平台项目 19DZ2290400

上海市重点实验室项目 18DZ2273300

详细信息

作者简介:
范亚军(1994-), 男, 安徽黄山人, 硕士研究生。研究方向:汽车空气动力学。通信地址:上海市嘉定区曹安公路4800号同济大学嘉定校区(201804)。E-mail:fanfan1021@tongji.edu.cn

通讯作者:
夏超, E-mail: chao.xia@tongji.edu.cn

中图分类号: U461
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- 被引次数: 0
出版历程
- 收稿日期: 2019-08-21
- 修回日期: 2019-09-24
- 刊出日期: 2019-12-25

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

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

摘要

摘要: 方背Ahmed模型是一种简化的商用车类车体模型，气流在尾部发生分离形成回流区，使背部产生负压继而带来较大的气动阻力。利用风洞实验对1/4缩比的方背Ahmed模型的非定常尾迹进行了精细测量和统计分析，实验雷诺数为9.2×10⁴。背部压力、粒子图像测速（PIV）和热线测量结果表明方背Ahmed模型的非定常尾迹呈现出3种流动特征的相互耦合：左右涡结构不对称分布的双稳态特征、水平以及垂直方向的涡脱落和回流区的周期性抽吸。其中双稳态现象在非定常尾迹中占主导作用，表现出2种稳定状态（水平不对称）的交替出现（转换概率P_转换=0.149），且每种稳定状态可维持较长的时间尺度（平均维持时间约为6 s），其频谱特性满足-2次幂律分布；水平和垂直方向剪切层振荡引起的涡脱落频率分别为Sr_H=0.13和0.17；回流区周期性抽吸的频率为Sr_H=0.07。3种流动结构共存并相互作用，从而使方背Ahmed模型的非定常尾迹呈现复杂的三维湍流特性。
- 方背体模型 /
- 非定常尾迹 /
- PIV测量 /
- 双稳态现象 /
- 涡脱落
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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图 1 实验设置

Figure 1. Experimental setup

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图 2 时均流场

Figure 2. Time-averaged flow field

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图 3 背部两对称点压力测量结果

Figure 3. Pressure result of two symmetrical points on the back

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图 4 背部垂直方向测点瞬时压力系数变化

Figure 4. Instantaneous C_p of three pressure taps in the vertical direction on the back

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图 5 压力梯度随时间的变化

Figure 5. Variation of pressure gradient over time

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图 6 尾迹区横截面z/H=0.67处的瞬时涡量场及流线:(a)、(b)和(c)及条件平均速度场和流线:(d)、(e)和(f)

Figure 6. Instantaneous vorticity field and streamline at the z/H=0.67 plane of the wake region: (a), (b), (c); and conditional average velocity field and streamline: (d), (e), (f)

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图 7 尾迹区横截面x/H=1.5处的瞬时速度场及流线:(a), (b)和(c)及条件平均速度场和流线:(d), (e)和(f)

Figure 7. Instantaneous velocity field and streamline at the x/H=1.5 plane of the wake region: (a), (b), (c); and conditional average velocity field and streamline: (d), (e), (f)

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图 8 尾迹区纵截面y/H=0处3个不同的瞬时时刻的涡量场和流线图

Figure 8. Three different instantaneous vorticity field and streamline of the y/H=0 plane in the wake region

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图 9 热线对称测点频谱图

Figure 9. Hot-wire symmetric point spectrum

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参考文献(12)

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