大尺度类波形壁面湍流边界层TR-PIV实验研究

TR-PIV Experimental Investigation of Turbulent Boundary Layer over a Large-Scale Wave-Like Wall

针对传统波形壁面因尺度微小所引发的加工困难、维护费用昂贵等问题,设计了一种大尺度的类波形壁面.对虎鲸的皮肤嵴结构进行放大和形貌改良,得到的大尺度类波形壁面可以更好地适用于工程实际;研究了大尺度类波形壁面对湍流边界层的影响,分析了其减阻效果及减阻机理.采取高时间分辨率粒子图像测速(TR-PIV)技术,对光滑壁面和振幅与波长之比分别为2a1/λ=0.033、2a2/λ=0.050、2a3/λ=0.066的3种大尺度类波形柔性壁面湍流边界层流场进行了实验测量,对流场中的时空相关函数进行计算.分析一个波长范围内流向、法向速度及压力分布,发现波形结构下坡段附近的逆压梯度使得流动减速,爬坡段附近的顺压梯度则加速了流动,减速效果最强位置位于波谷,加速效果最强位置位于波谷始末,流场中的速度在两个极值内变化.对不同工况下类波形壁面末尾凹槽下游紧邻平板区域各阶统计量进行了对比,结果表明3种类波形壁面的平均速度剖面于对数区表现出不同幅度的抬升,近壁区平均速度均有不同程度增大;近壁区流场雷诺切应力具有明显的降低,近壁区湍流脉动被抑制,雷诺应力的峰值相对壁面略有外移;3种类波形壁面均具有一定减阻效果,最大减阻率为23.0%.

A large-scale wave-like wall was designed to overcome difficult processing and expensive maintenance caused by the small scale of a traditional wavy wall.By enlarging and improving the skin ridge structure of killer whale,the large-scale wave-like wall can be better suitable for engineering practice.The influence of the large-scale wave-like wall on the turbulent boundary layer was studied,and its drag reduction effect and drag reduction mechanism were analyzed.To experimentally measure the turbulent boundary-layer flow fields on smooth walls and three large-scale wave-like walls with the amplitude-to-wavelength ratios of 2a1/λ=0.033,2a2/λ=0.050,and 2a3/λ=0.066,the time-resolved particle image velocimetry(TR-PIV)technique was adopted.After calculating the spatiotemporal correlation functions in the flow field and comparing the flow velocity,normal velocity,and pressure distribution in a wavelength range,it was observed that the difference in the morphological parameters does not affect the existence of pressure gradients within the turbulent boundary layer of the new large-scale wave-like wall;the inverse pressure gradient near the downhill section decelerates the flow,whereas the compliant pressure gradient near the climbing section accelerates the flow,with the strongest deceleration effect at the trough and the strongest accel-eration effect at the beginning and end of the trough,and the velocity in the flow field hovers within two extreme values.Comparison of the order statistics in the plate area immediately behind the last spreading notch of the new wave-like wall for different operating conditions shows that the average velocity profile of the three new wave-like wall surfaces in the logarithmic region shows different magnitudes of elevation;and the average velocity of the near-wall area have different degrees of increase.Further,the near-wall area flow field Reynolds shear stress significantly reduced;near-wall area turbulent pulsation is suppressed;peak Reynolds stress is slightly outward relative to the wall surface.Three types of wave-like wall surface have a certain effect on drag reduction,with the maximum drag reduction rate of 23.0%.