Abstract
The effect of a triangular wedge upstream of a circular cylinder has been investigated, and the findings are presented herein. The triangular wedge is equilateral in plan form, and the Reynolds number based on the diameter of the main cylinder is approximately 200. Contours of vorticity clearly show that two entirely different wake patterns exist between the wedge and the main cylinder. There also exists a critical spacing ratio and side length ratio at which the wake flow pattern shifts from one within the cavity mode to one within the wake impingement mode. For a relatively small side length ratio of l w / D = 0.20 and 0.27, where the side length refers to the length of one side of the triangular wedge, the drag and lift coefficients decrease monotonically with the spacing ratio. There is a sudden jump of the drag and lift coefficients at larger side length ratios of l w / D = 0.33 and 0.40. This study shows that at a spacing ratio of L/D = 2.8 (where L is the distance between the vertex of the wedge and the center of the cylinder) and a wedge side length of l w / D = 0.40, the reduction of the amplitude of lift and mean drag coefficient on the main cylinder are 71.9% and 60.1%, respectively.
Highlights
Under certain circumstances, a Kármán vortex train is observed in the wake of flow past a bluff body
If the stress level in the bluff body is high, prolonged vibration in the flow field may lead to fatigue
An active control method typically controls flow through constant monitoring of the flow field and structure stress, and exerts external intervention as needed to control the vortex shedding from the main cylinder
Summary
A Kármán vortex train is observed in the wake of flow past a bluff body. Passive control methods control the flow through deliberate selection of the cross-sectional shape of the structure or attaching add-on devices, modifying the flow field, and the vortex formation around the main cylinder. The authors found that the fluctuating lift and drag forces of the main cylinder and control rod are greatly reduced in most flow cases. Lee et al (2004) [12] demonstrated that with the change of gap spacing between the smaller and main cylinder, the wake patterns transform from that of the cavity mode to that of the wake impingement mode Characteristic flow quantities such as pressure and drag force were changed substantially as well. While the control rods serve to modify the flow fields and the lift and drag forces, one may postulate that there could be cases when the main cylinder may lie within the shadow of the wake streams generated by the control rod(s). Refined structured quadrilateral meshes were used near the cylinder surfaces
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