PIV experimental study on flow characteristics of a low swirl number precessing jet

This study focuses on the flow characteristics of a low swirl number precessing jet at Reynolds number Re=4.5×10⁴ using particle image velocimetry (PIV). The time-averaged streamwise velocity fields, streamwise velocity fluctuation intensity fields and time-averaged vorticity fields at three swirl numbers, i.e., S=0, 0.26 and 0.41, respectively, are compared and analyzed. The experimental results show that as the swirl number increases, the attenuation of the streamwise velocity and its fluctuation intensity increase along the streamwsie direction, the velocity fluctuation intensity on the jet centerline increases, the recirculation zones caused by the confinement move upstream with their scales decreasing, and the streamwise development of the vortex in the outer shear layer decays rapidly, while that in the inner shear layer is almost unaffected. In addition, combining the streamwise velocity spectrum and the characteristics of the transient flow field at a typical time, it can be seen that as the swirl number increases, the precession frequency increases, and the starting position of the precession phenomenon moves upstream, which increases the precession deflection angle.