A Study on the Aerodynamic Characteristics and the Flow Separation of a Circular Cylinder with Longitudinal Ridges

Any buff body subjected to a flow experiences flow separation. This flow separation occurs due to loss of momentum in the boundary layer as the flow progresses over the body. One main consequence of this flow separation is the retarding aerodynamic force called ‘Drag.’ Drag is the penalty for achieving the optimum aerodynamic performance of any object subjected to airflow; thus, it is of utmost importance to reduce drag, and this can be achieved by delaying the flow separation. Flow separation can be delayed using an active or a passive flow control device. In this experiment, we have used ridges, a passive flow control device, on a circular cylinder subjected to airflow in the subsonic wind tunnel at a wind speed of 30 m/s corresponding to the Reynolds number of 1.015 × 105. Ridge ratios of 0.12, 0.16, and 0.20 are used in the investigation. The ridges (tubes) were placed symmetrically on the top and bottom hemispheres at varying angular locations starting from 75° to 105° (measured from the stagnation point) in the range of 15°. The pressure distribution over the circular cylinder before and after placing the ridges was obtained from the simultaneous ethernet-based scanivalve pressure scanner. The variation of the coefficient of pressure was plotted for various test cases. The angles of flow separation and the coefficients of drag were obtained for all the cases considered (varying diameters and varying angular locations). It was observed that the maximum drag reduction occurs when the ridge is placed at 105°. It was also observed that the coefficient of drag was least for the 6-mm ridge placed at 105° among all the other modified cases.