Passive Separation Control on a Body at Transonic Speed

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The present paper proposes a new approach to control flow separation around a body. Flow separation is controlled by inserting simple tabs inside the separated region to suppress the reverse flow action. This is expected to increase the pressure in the base region of the body, thus reducing drag. Moreover, flow instability is also expected to decrease because of change in the wake profile. The cases considered in the present investigation are flows around a circular cylinder at M=0.6 and 0.73. Tabs having lengths of 10% and 20% of the cylinder diameter were used. The results show that the base pressure of the cylinder can be increased when these tabs are inserted inside the separated region. The smallest drag on the cylinder/tab body was achieved when the two pairs of tabs were installed on both sides of the cylinder at angles of ±120° and ±140°, measured from the front stagnation point of the cylinder. Compared to the plain cylinder, drag was reduced by 32% at M=0.6 and by 18% at M=0.73. Schlieren photography reveals that the vortex formation length is increased when the tabs are installed. Moreover, the tabs greatly suppress the level of pressure fluctuations on the cylinder surface. This can be attributed to change in the wake profile that is associated with drag reduction. Furthermore, the frequency of the Karman vortex street is also increased. The analysis of the results was assisted by numerical calculations based on Large Eddy Simulation (LES). From these results, five significant effects of the tabs were identified: restriction of the reverse flow action, trapping of vorticity in the region upstream of the tabs, suppression of the shear layers’ movement, more rapid vortex roll-up downstream of the body, and reduced strength of the downstream vortices.
社団法人日本航空宇宙学会の論文
2002-02-04

Passive Separation Control on a Body at Transonic Speed

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