Comparative study of two combined blowing and suction flow control methods on pitching airfoils

Abstract

A comparative study of two combined blowing/suction flow control methods was conducted on the pitching airfoil using the unsteady Reynolds-averaged Navier–Stokes (URANS) method. One used leading-edge blowing and trailing-edge suction, which is referred to as a co-flow jet (CFJ), and a conformal slot CFJ (C-CFJ) was adopted. Another used leading-edge suction combined with trailing-edge blowing, which was called reversed CFJ (R-CFJ). The S809 airfoil was used as the baseline as its stall characteristic is suitable for separation flow or stall control research. Aerodynamic coefficients of these two combined blowing/suction methods were compared under no-stall, mild-stall, and deep-stall cases. The net gain of output power was also discussed if CFJ methods were used for wind energy applications. The influence mechanism of these two methods on the flow around the airfoil was revealed. The results showed that the C-CFJ is suitable for the no-stall and mild-stall cases, while the R-CFJ is suitable for the deep-stall case. Leading-edge suction is more stable than leading-edge blowing when suppressing the dynamic stall. The leading-edge jet flow will cause dynamic stalls when it is detached from the airfoil surface, while the detached jet flow can block the development of the separation when it is placed on the trailing edge.