The effect of spanwise modulated DBD plasma forcing on flow development in a laminar separation bubble

The effect of spanwise modulated disturbances on flow development within a separation bubble formed over a flat plate is investigated experimentally using two-component Particle Image Velocimetry. Spanwise uniform and non-uniform forcing are considered using novel surface mounted dielectric barrier discharge (DBD) plasma actuators. Characterization of the disturbances is performed, showing that the actuators produce streamwise jets within the active regions and no significant momentum elsewhere, thus enabling spanwise forcing at the desired wavelengths. When subjecting the separation bubble to these disturbances applied at the frequency matching that of the most unstable mode in the baseline flow, the bubble height reduces and mean reattachment shifts upstream with decreasing spanwise wavelength, which is a likely consequence of higher momentum coefficients for these cases. However, significant changes in the flow topology are shown to arise for relatively large wavelengths, and hence low momentum coefficients. These modifications are linked to changes in the development of the dominant coherent structures induced by the spanwise modulated perturbations.