Trapped vortex cell for aeronautical applications: flow analysis through PIV and Wavelet transform tools.

Abstract Results of the application of a trapped vortex cell to an airfoil with the aim of improving the aerodynamic performances are presented for two complementary experiments arranged at CIRA and at Politecnico di Torino. In the CIRA experiments, PIV measurements on a simplified configuration were carried out to characterize the trapped vortical structure and its effect on the separating flow downstream of the cell. In the experimental investigation at Politecnico di Torino, static pressure distributions were measured around a complete airfoil model, to yield lift and pitching moment coefficients. Wake surveys were also carried out to measure the drag. To study the unsteady phenomena inside the cavity pressure fluctuations signals were also investigated using Kulite sensors. In both experiments, the angle of attack of the airfoil and the Reynolds number were varied. It is shown that the flow inside the cell is highly unsteady with significant shedding of flow structures downstream. This phenomenon results in a large region of separated flow, in higher drag and lower lift. By contrast, the cell flow is considerably stabilized and regularized by applying distributed suction over the cell wall. As a result, the flow downstream of the cell reattaches and lower drag and larger lift are observed.