Experiment Investigation On Evolution Of Synthetic Jet Vortex Rings And Its Impinging Onto A Solid Wall

In recent years,synthetic jet,as an active flow control method,has been widely concerned because it does not need additional gas source.The circular synthetic jet is a typical synthetic jet,which generates periodic vortex ring at the orifice through the reciprocating motion of vibrating parts,and forms momentum output at the downstream.The motion and flow field characteristics of synthetic jet vortex ring have great influence on flow control.In addition,it is also a common flow phenomenon that the vortex moves downstream and impinges onto the solid wall.In this paper,the evolution of vortex ring and its impinging onto different types of wall are studied?The following work was mainly carried out:Firstly,the vortex ring evolution of synthetic jet in static fluid was studied.Particle image velocimetry(PIV)and Planar laser-induced fluorescence(PLIF)were used to obtain the velocity and visualization of the flow field,and then the motion law and time-average flow field characteristics of the vortex ring were analyzed.The results show that at low Reynolds number,the motion of vortex ring keeps laminar and has good similarity,and its dissipation is mainly caused by vorticity diffusion and fluid viscosity.At high Reynolds number,the loss of coherence is mainly due to the formation of turbulence.Then,combined with the evolution characteristics of vortex ring,continuous vortex rings impinging onto a flat plate was studied experimentally.The influence of Reynolds number on vortex ring motion was investigated.Through the vortex ring trajectory and time-averaged flow field characteristics,it was found that the primary vortex ring can expand along the wall at high Reynolds number and induce the formation of tertiary vortex,and the opposite jet formed after impinging onto the wall will inhibit the development of the primary vortex ring.Finally,the impinging of the vortex ring onto the spherical wall was studied,and the effects of Reynolds number and spherical diameter on the motion of the vortex ring were considered.For a single vortex ring impinging a sphere,the Reynolds number and the diameter of the sphere have great influence on the induction ability and the expansion distance of the primary vortex ring,respectively.For the continuous vortex ring impacting the spherical surface,the primary vortex ring can continue to expand to dissipation on the wall.In this case,the curvature will drive the boundary layer to separate and generate the secondary vortex with larger circulation.In addition,with the increase of Reynolds number,the coherence of the flow field becomes weak.