Separated Flow Response to Single Pulse Actuation

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Separated Flow Response to Single Pulse Actuation

Albrecht, Thomas / Weier, Tom / Gerbeth, G. / Monnier, Bruno / Williams, David R.

The response of a separated flow over a two-dimensional wing to short-duration disturbances from a Lorentz force leading-edge actuator is presented. At a chord Reynolds number of $R e = 10^{4}$ and an angle of attack of $α = 16 \deg$ , the flow is initially laminar but undergoes transition within the separated shear layer.The transient flow structures and lift force measurements were obtained with varying actuator pulse duration, pulse amplitude, and direction of actuation. The peak amplitude of the lift is shown to depend on the pulse duration when the pulse duration is less than 0.5 convective times, after which it saturates. Saturation of the lift amplitude also occurs when the effective actuator pulse amplitude exceeds $C_{μ} = 0.05 %$ . Detailed flow structures that develop in the separated shear layer were identified using the finite-time Lyapunov exponent method. The direction of the actuator pulse has a significant influence on the initial development of the shear layer, but the larger-scale envelope of the separated flow has essentially the same response, irrespective of the direction of actuation. A reconstruction of the velocity field using only three proper orthogonal decomposition modes is sufficient to reproduce the dominant features of the flow response to a single pulse. The second proper orthogonal decomposition mode correlates with the transient lift signal.