柔性壁面湍流边界层相干结构控制的实验研究

本文利用热膜测速技术对刚性壁面和柔性壁面湍流边界层的流向速度分量进行了实验测量,首先研究了柔性壁面对平均速度分布和湍流度分布的影响,结果表明:柔性壁面的边界层速度分布在对数律层向上有所平移,缓冲层加厚,具有一般的壁面减阻特征;而柔性壁的湍流度比刚性壁的湍流度要低,分布也更为平坦。然后综合运用自相关法和条件采样技术研究了湍流近壁区的相干结构,结果表明:刚性壁自相关曲线的第二峰值出现的时间比柔性壁的短,柔性壁的猝发频率比刚性壁的低许多。实验结果表明柔性壁面具有一定的减阻作用。

The Experimental Investigation of Coherent Structure Control in Turbulent Boundary Layer Over Compliant Wall

The hot film anemometer is introduced in this paper to measure the longitudinal component of velocity in turbulent boundary layer over rigid flat and compliant coating respectively. Experimental study was first carried out to investigate the influence of compliant wall on the mean velocity profile and the distribution of turbulence intensity level across turbulent boundary layer. Measurement was carried out at the same position of the rigid and compliant walls. And the mean velocity profile and the distribution of turbulence intensity have been nondimensionalized by inner scale. The result shows that, in boundary layer of turbulent flows over a compliant wall, compared with that over a rigid wall, the velocity profiles in log law region is extended further away from the wall and in thickening buffer region, which is characteristic of drag reduction. Furthermore, the maximum turbulence intensity was found at y~ =10~20 and the peak value of the compliant wall was smaller than that of the rigid wall while the distribution is getting flat. After this the methods of self-correlation and conditional sampling have been performed to analyze the coherent structures in the near wall region of turbulence. The result shows that, the second peak of the self-correlation curve of the rigid wall which represents mean burst period appears earlier than that of the compliant wall and the existence of the compliant wall reduces bust frequency. The experimental results confirm the effect of drag reduce for compliant coating surface of turbulent boundary layer.