Turbulent boundary layer separation is an important issue for a variety of applications, one of which is S-shaped aircraft engine intakes. The turbulent separation at the engine intake causes inlet flow distortion, which can deteriorate engine performance, cause fatigue and reduce engine component life. Various flow control techniques have been applied for turbulent boundary layer separation control, such as vortex generators, vortex generator jets and synthetic jets. The recent advent of dielectric barrier discharge (DBD) plasma actuators can potentially provide a robust method for the control of turbulent boundary layer separation. Compared to other flow control techniques, these new actuators are simple, robust and devoid of moving mechanical parts, which make them ideal for aerodynamic applications. The present work studies the effects of DBD plasma actuators on the suppression of 2-D turbulent boundary layer separation induced by an imposed adverse pressure gradient. First, the flow field with and without actuation in a low-speed wind tunnel is investigated experimentally by Particle Image Velocimetry (PIV) measurements. The results show that plasma actuation can suppress turbulent boundary layer separation in both continuous and pulsed modes. In the pulsed mode, the actuation with an optimal actuation frequency, corresponding to a dimensionless frequency of order one, is found to most effectively suppress the turbulent separation. Moreover, the effects of plasma actuation on the flow is demonstrated and analyzed by using Proper Orthogonal Decomposition (POD). The effect of the actuation is found to be correlated to the second POD mode which corresponds to large flow fluctuations.

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