Session: 03-09-02 Turbulent Flows (2/3)

Paper Number: 87640

87640 - The Effects of Aspect Ratio on Turbulence Wake Flow Over Right Trapezoidal Prism 

Flow separation and reattachment around bluff bodies immersed in a uniform flow have received much attention in the fluid community. However, extensive research efforts have been devoted to the study of flow separations induced by symmetrical shapes like square or rectangular prisms. In the present study, the right-angled trapezoidal prism is used as a canonical asymmetrical geometry to investigate the effect of streamwise aspect ratio on the separated shear layers and the near wake region of the asymmetrical bluff bodies. The experiments were conducted in an open recirculating water channel using a high-resolution particle image velocimetry. The water level was maintained at 0.43 m and the free-stream velocity was kept constant at 0.49 m/s. The tested trapezoidal prisms were machined with constant angle 45°, vertical height, h = 0.03 m, the fixed bottom length 0.03 m and variable bottom length, L = 0.03 m and 0.12 m. The resulting streamwise aspect ratios are, AR (= L/h) = 1 and 4, respectively. The Reynolds number based on the prism height and freestream velocity was 14700. The corresponding Froude number based on the free-stream velocity and the water level was calculated as 0.24, which implied that the free surface had negligible influence on the flow dynamics over the test prism. Two side-by-side cameras were simultaneously used to capture images at a frame rate of 3 Hz.

Preliminary results show that the primary vortex of the AR1 trapezoidal prism starts from the leading edge, along the top surface and extends into the wake region. However, the primary vortex of the AR4 trapezoidal prism is above the prism. Mean reattachment is observed in the AR4 case but no reattachment occurred on the AR1 prism. Two wake vortexes were observed in the AR4 case as expected, however, the upper one is considerably larger than the lower one. Furthermore, the levels of Reynolds stresses are an order magnitude higher in the AR1 case compared to the AR4 case. The contours of streamwise Reynolds normal stress show double peaks in the near wake region of both prisms. The vertical Reynolds normal stress peak locations were observed in the near wake region for both cases.

In the final paper, a detailed literature review and a complete description of the test facility and measurement procedures will be presented. The flow topological differences between the two aspect ratios will be analyzed through one-dimensional profiles and contours of the mean velocities, Reynolds stresses and higher-order turbulence statistics. Furthermore, the quadrant analysis method will be employed to show the effects of aspect ratio on the separated shear layers and the near wake region of right-angled trapezoidal prisms.

Presenting Author: Jinhao Kang University of Manitoba