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

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 acceleration 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%. © 2023 Tianjin University. All rights reserved.