On the interaction of vortical structures and shear layer in turbulent flow around trapezoidal prisms with varying aspect ratios

Abstract

The spatiotemporal dynamics of turbulent flow induced by trapezoidal prisms in a uniform flow are studied using time-resolved particle image velocimetry (TR-PIV). Three prisms with aspect ratios (AR, defined as the ratio between lower surface length and height) of 1, 2, and 3 (denoted as AR1, AR2, and AR3, respectively) were tested at a Reynolds number of 10000 based on the incoming velocity and prism height. In the wake region of the prisms, two recirculation bubbles form. For the AR1 prism, the bubbles are almost symmetric in size, whereas for AR2 and AR3 prisms, the upper bubble is significantly larger than the lower one. The peak values of the Reynolds stresses in the wake region decrease with increasing AR. Quadrant analysis reveals that the strength of sweep and ejection events increases with decreasing aspect ratio, enhancing flow recovery within the recirculation zone. The vertical derivative of Reynolds shear stress plays a major role in the higher flow recovery for AR1, but as the aspect ratio increases to 3, the vertical derivative of tangential momentum becomes the dominant factor. The nondimensional fundamental shedding frequencies for the AR1 and AR2 prisms are 0.13 and 0.11, respectively, whereas dual shedding frequencies of 0.05 and 0.12 are observed for the AR3 prism. Frequency synchronization induced by von Kármán (VK) vortex shedding remains strong from the leading edge to the wake region in the cases of AR1 and AR2 while becoming limited to the wake region for AR3.