开口回流式整车风洞风机尾流的流动控制

Flow Control of Fan Wake in the Open-Jet Closed-Circuit Automotive Wind Tunnel

摘要:

对风洞风机尾流进行流动控制，可以提高风机效率、优化流场品质，因此对于回流式风洞必须使用全局模型进行研究。建立风洞全流道仿真模型，并通过现有实测结果对仿真流动结构和速度分布进行对照验证。不同尾锥截断长度流动控制的仿真结果表明：尾流控制存在两种与近壁大涡结构密切相关的机理，一种是垂直背后分离流诱导的小涡结构与大涡相互作用，另一种是改变分离位置影响曲面分离流形成的大涡结构，两者均可影响大涡结构距离尾椎的距离，改变近壁剪切层速度分布，使得剪切层向内侧偏转，导致尾流低速区减小，提高主扩散段出口的总压，提高气流均匀性。引入涡流发生器后，气流绕过涡流发生器产生的小涡结构使得尾流大涡结构改变，主扩散段总压以及气流均匀性进一步改善。

关键词:汽车风洞;风机尾流;流动控制;涡流发生器

Abstract:

The flow control of the fan wake in the wind tunnel can improve the efficiency of the fan and optimize the quality of the flow field. For the closed-circuit wind tunnel， the global model with the entire flow channel must be used to verify the simulated flow structure and velocity distribution against the measurement data. Results show that for different truncated length of the fan tail， there are two mechanisms of wake control that are closely related to the near-wall large eddy structure. One is the interaction between the large eddies and the small ones induced by the separation flow from the vertical base， and the other one is changing the large eddy structure， which formed from the flow separation and can be strongly influenced by the separation positions due to the surface curving. Both mechanisms can affect the distance between the large vortex structure and the tail cone， and change the velocity distribution of the near-wall shear layer， causing the shear layer to deflect inwardly， resulting in a decrease of the low-velocity area of the wake， increasing the total pressure at the outlet of the main diffusion section， and improving the uniformity of the flow field. After the vortex generators are introduced， the small vortex structure generated by the flow passing through can change the large vortex structure of the wake， then the total pressure and the flow uniformity of the main diffusion section are further improved.

Key words:automotive wind tunnel;fan wake;flow control;vortex generators