Spanwise modulation effects of local body force on downstream turbulence growth around two-dimensional hump

Flow characteristics under flow-separation control by the spanwise-modulated body force of a plasma actuator around a two-dimensional hump are numerically investigated. When the Reynolds number is set to Re_h=16000, the incoming flow contains much disturbance and a near-wall streak structure appears around the hump. The local body force induces stable streamwise velocity to form a streak-like profile artificially. Under the forcing, turbulence fluctuations increase downstream, with resulting in early flow reattachment. These changes alter the momentum balance around the hump. Particularly, the wall-normal pressure gradient and velocity fluctuation terms in the momentum equation are modified. This somewhat suggests a relation between increases in wall-normal gradient terms and the flow reattachment profile under the control. In addition, the turbulence growth depends on the spanwise modulation wavelength of the forcing. The most effective wavelength among those tested here is λ_z=0.08, normalized by the hump height, which is λ_z⁺=150 in local viscous wall units. This viscous scale corresponds to that of a streak structure appearing around a two-dimensional hump.