Effects of Aspect Ratio on Asymmetric Wake Flow Structure Around Right-Trapezoidal Prisms

In this paper, the turbulent flow characteristics around right-trapezoidal prisms with varying streamwise aspect ratios (AR, ratio of upper length to prism height) of AR = 0.6, AR = 2, and AR = 2.5 in a uniform flow were investigated using particle image velocimetry (PIV). The Reynolds number (based on the free-stream velocity and body height) is Reh = 10000, and the results are analyzed in terms of the mean velocities, Reynolds stresses, and probability density function (PDF). The results show that two recirculation bubbles form in the wake region of all prisms. The bubbles are asymmetrical, with the upper recirculation bubble larger than the lower one. For the AR = 2.5, an additional bubble is observed on the upper surface of the prism. Contours of the streamwise Reynolds normal stress show dual peaks, which are located above and below the centerline in the wake region. The magnitude of the peak above the centerline is comparably higher for AR = 2.5 than for AR = 0.6 and 2.0. Conversely, the vertical Reynolds normal stress shows a single peak with increasing magnitude as the aspect ratio rises. Regardless of aspect ratio, the PDF of streamwise fluctuating velocity displays an unimodal distribution, while vertical velocity fluctuation shows a bimodal distribution at the point of maximum vertical fluctuating velocity.