﻿ 车尾水平收缩气动减阻的规律及机理
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 同济大学学报(自然科学版)  2017, Vol. 45 Issue (9): 1377-1382, 1389.  DOI: 10.11908/j.issn.0253-374x.2017.09.018 0

### 引用本文

ZHU Hui, ZHENG Zihao, YANG Zhigang. Regulation and Mechanism of Aerodynamic Drag Reduction by Horizontal Tail Contraction[J]. Journal of Tongji University (Natural Science), 2017, 45(9): 1377-1382, 1389. DOI: 10.11908/j.issn.0253-374x.2017.09.018.

### 文章历史

1. 上海地面交通工具风洞中心，上海 201804;
2. 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;
3. 广州汽车集团股份有限公司汽车工程研究院，广东 广州 511434

Regulation and Mechanism of Aerodynamic Drag Reduction by Horizontal Tail Contraction
ZHU Hui1,2, ZHENG Zihao3, YANG Zhigang1,2
1. Shanghai Automotive Wind Tunnel Center, Shanghai 201804, China;
2. Shanghai Key Laboratory of Vehicle Aerodynamics and Vehicle Thermal Management Systems, Shanghai 201804, China;
3. Guangzhou Automobile Group Co. Ltd., Automotive Engineering Institute, Guangzhou 511434, China
Abstract: Based on wind tunnel test and numerical simulation, the regulation of horizontal tail contraction on aerodynamic drag reduction was studied. The results indicate that tail contraction raises pressure level of tail surface and reduces aerodynamic drag. On the basis of the reliable numerical simulation results, the changes of wake structure were studied. The research indicates that the contraction provides additional kinetic energy for the dead zone behind tail, which suppresses formation and development of trailing vortex pair, therefore, the flow energy loss of wake and aerodynamic drag reduces.
Key words: aerodynamic drag reducing    horizontal tail contraction    flow mechanism

1 模型风洞实验及结果

 图 1 车尾收缩角方案 Fig.1 Scheme of tail contraction design

α取值为0°、4°、10°和16°，皆为1:12缩比模型，各模型长、宽和高皆一致，分别为347 mm、135 mm和118 mm，材料为工程代木.为避免贴片式测压法对流场的干扰，采用非对称布置测压孔法[13]，测压孔坐标不随车尾收缩而变化并在分析数据时作镜像处理.模型车头距离喷口125 mm[14]，阻塞比为10.4%，设车头地面投影中心为测量坐标原点，具体如图 2所示.

 图 2 实验布置 Fig.2 Arrangement of wind tunnel test

 图 3 阻力系数 Fig.3 CD of test

 图 4 截面位置 Fig.4 Location of sections

 图 5 后风窗表面压力系数分布 Fig.5 CP distribution on back windshield

 图 6 车尾表面压力系数分布 Fig.6 CP distribution on tail

 图 7 车侧表面压力系数分布 Fig.7 CP distribution on side

 图 8 尾部上翘角表面压力系数分布 Fig.8 CP distribution on rear diffuser
2 数值仿真及实验验证

 图 9 数值仿真阻力系数 Fig.9 CD of simulation

 图 10 截面4处表面压力系数分布 Fig.10 CP distribution on Section 4

 图 11 截面5处表面压力系数分布 Fig.11 CP distribution on Section 5

3 基于流场特征的机理分析

 图 12 尾流场结构对比 Fig.12 Comparison of near wake structure

20°模型Fc沿后风窗收缩趋势向后流动，抑制Tc的形成及发展；Fsh沿收缩角先上升后下沉，从车尾侧进入尾流场且气流翻卷趋势减弱；Fsl同样从车尾侧进入尾流场并抑制Tsl的形成和发展；受下洗气流及尾部侧气流的作用，Fl在横截面上扩散范围减小.整个区域流动顺畅，结构清晰.

 图 13 后风窗表面油流 Fig.13 Oil streamline on back windshield
 图 14 后风窗表面分离区 Fig.14 Separation zone on back windshield

Fsh可细分为上层Fsh′及下层Fsh″，如图 15所示.收缩前Fsh″较晚到达车尾上平面并自下而上翻卷而出.收缩后Fsh′在新侧棱Sv之前到达上平面，绕过Sv进入收缩角区域后，Fsh′在Z方向压力梯度作用下再次下沉到车尾侧，使得Fsh″无法向上流动，翻卷趋势减弱.

 图 15 车尾侧上半部油流 Fig.15 Oil streamline on upper tail side

 图 16 车尾侧下半部油流 Fig.16 Oil streamline on lower tail side

 图 17 尾部涡结构对比 Fig.17 Comparison of tail vortices structure

0°模型尾迹区纵向涡结构主要由TcFsh翻卷形成的涡TshTsl形成，见图 18.Tsh在尾后1 000 mm处与Tc融合；发展到7 000 mm后Tsl消失，此时尾迹区主要的涡结构为以Tc为核心的拖曳涡对.

 图 18 0°模型尾后流线 Fig.18 Streamline after tail of 0° model

20°模型尾迹区纵向涡结构如图 19所示，Tc只短暂出现在近尾端-150 mm~100 mm处，Fs引起的纵向涡消失.下洗气流在1 240 mm处形成近地面涡Tg.Tg与0°模型经充分发展后的Tc相比其涡量显著下降，因此气动阻力显著减小，如图 20所示.

 图 19 20°模型尾后流线 Fig.19 Streamline after tail of 20° model
 图 20 尾后X=2 000 mm处涡量 Fig.20 Vorticity on X=2 000 mm after tail
4 结论

(1) 随着水平面车尾收缩角的增大，气动阻力显著减小；

(2) 车尾收缩抑制车尾展向涡的发展并提高车尾端面压力水平，因而减小压差阻力；

(3) 随着车尾收缩角增大，车尾侧气流向上、下翻卷趋势被抑制，使尾部拖曳涡强度减弱，能量耗散减小，整车获得较低的气动阻力；

(4) 伴随车尾收缩而形成的后风窗收缩使侧风窗气流越过C柱向对称面流动的趋势被减弱，抑制了C柱附近涡系的发展，进而抑制了尾迹区拖曳涡对的发展，故有效降低了气动阻力.

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