Suction Controlled Topological Transition in Laminar Juncture Flows

The effect of suction on the topological transition in juncture flow is studied experimentally and numerically. A number of combinations of the positions, where suction is applied, and the flow rates are investigated and their effect on the topological transition of laminar juncture flow is assessed. It is observed that for any particular case, a combination of suction hole positions and volume flow rates can transform the most upstream surface singular point of the horseshoe vortex (HSV) system from a saddle of separation to a saddle of attachment. The topological transition at low suction rates is achieved, when the suction holes are placed close to the separation region. A better HSV control is achieved, when suction is applied close to the juncture at high suction rates. A previously proposed separation/attachment prediction method based on the mass conservation is also confirmed by analyzing the simulated results of suction-controlled and originally-generated wall saddles. The results suggest that the topological transition (separation/attachment) at each wall saddle can be accurately estimated according to the sign of a discriminant coefficient C_S/A comprised of the local shear stress τ_w on the wall and stream-tube width n near the saddle.