Abstract
The turbulent characteristics of flow separation induced by trapezoidal prisms subjected to uniform flow are studied using particle image velocimetry (PIV). The streamwise aspect ratios (upper length to lower length) were AR1.0_2.5, AR2.0_2.5, and AR2.0_4.0. The Reynolds number (based on freestream velocity and body height) was Reh = 10000 and the results were analyzed in terms of the mean velocities, Reynolds stresses, and proper orthogonal decomposition. Recirculation bubbles formed in the wake region are asymmetric about the prism centerline, and the lower bubble is smaller than the upper one. Contours of the streamwise Reynolds normal stress exhibit two peaks in the wake of the prisms, and an additional peak over the upper surface of the prism. The peak magnitude of streamwise Reynolds normal stress in the upper and lower wake region are identical. A single peak in the vertical Reynolds normal stress is observed near the centerline of the prism within the wake region. Proper orthogonal decomposition was used to characterize the energetic vortical structures of the flow field around the prisms. The results show that the first two POD modes capture similar relative energy content, regardless of aspect ratio, while the wavelength of the POD decreases as the aspect ratio increases.
