Influence of synthetic jet on uniform momentum zones

Abstract

Based on a set of streamwise-wall-normal experimental databases of turbulent boundary layer (TBL) acquired by time-resolved particle image velocimetry (TR-PIV) system at the Reynolds number Reτ=537, which includes the velocity fields with and without synthetic jet, the influence of the synthetic jet on uniform momentum zones (UMZs) was studied. The turbulent/non-turbulent (T/NT) interface of each instantaneous frame was identified by local turbulent kinetic energy (L-TKE) method and the area below the interface was divided into UMZs by probability density function (P.d.f.) histogram of streamwise velocity. The relationship between the T/NT interface average height EYi and the UMZs number NUMZ is analyzed. The spatial position and velocity of UMZs are extracted by centroid method, and the basic statistical characteristics within UMZs under two working conditions are investigated. After processing the velocity fields corresponding to each NUMZ separately, it is found that NUMZ is highly correlated with Q events. The synthetic jet reduces the streamwise and wall-normal length scales of the fluid induced by Q events, and under the same externa conditions, the two scales are also positively related to the intensity of Q events. The shear stress in the flow field promotes the generation of the forward vortices, which drives the stratification of UMZs. The hairpin vortices generated by synthetic jet result in a large number of forward vortices in the region with y/δ<0.3, and the turbulent kinetic energy (TKE) and Reynolds shear stress are input into the vortex region in varying degrees.