High-Frequency Fluidic Actuation of a Separation Bubble on a Curved Surface

The unsteady interactions between actuation jets and the vorticity concentration within a separation bubble formed by a subsonic cross flow over a curved surface is investigated experimentally. The nominally 2-D curved surface represents the suction side of a VR-12 airfoil at an angle of attack of 13^o such that its leading and trailing edge stagnation streamlines merge smoothly with the tunnel’s flat side wall. Dissipative (high-frequency) actuation is provided by a spanwise array of fluidic oscillating jets that is located upstream of the separation. The actuation controls the characteristic scale of the separated flow domain and the strength of the trapped spanwise vorticity concentration. The effect of the actuation on both the upstream and downstream edges of the separated bubble are assessed using high-speed particle image velocimetry, and analyzed using modal decomposition to reveal its underlying dynamical and structural characteristics. In particular, empirical mode decomposition (EMD) is used to determine the spectral content of the flow within distinct, characteristic frequency bands that separate between large- and small-scale motions of the separation bubble with specific emphasis on the evolution of the small scales as a result of the actuation.