To this end, a novel flow configuration has been devised to investigate synthetic jet based separation control in canonical flows using DNS/LES. The configuration consists of a 5% thick flat plate with elliptic leading edge and blunt trailing edge at zero incidence in a free-stream. A separation bubble of prescribed size is created on the top surface of the plate at a desired location by applying blowing and suction on the top boundary of the computational domain. This flow is characterized by at least three distinct time scales corresponding to the instabilities in the shear layer, the separation zone and the wake; therefore the resulting flow field can be considered as a canonical separated airfoil flow.
Two-dimensional direct simulations of this flow at a chord Reynolds numbers of 60,000 subject to zero-net mass-flux perturbation of the boundary layer at different characteristic time scales are investigated. Results indicate that at a Reynolds number of 60,000, the entire system composed of the shear layer, the separation zone, and the wake is locked onto a single frequency. Forcing the ZNMF device close to this lock-on frequency or its first super harmonic is found to result in optimal control of the mean separation bubble. On the other hand, results from the simulation of the same configuration at a Reynolds number of 100,000 indicate that the instabilities of the shear layer and the separation zone are decoupled from the wake instability and exist as harmonics.
The stability characteristics of the different mean flows resulting from ZNMF forcing at different frequencies are evaluated in terms of local linear stability theory based on the Orr-Sommerfeld equation. The numerical results are also Fourier analyzed in time and compared to theoretical results. Some results from the ongoing large-eddy simulations of this flow configuration will also be presented.