2 Experimental results and analysis
The instantaneous velocity vector field data were averaged over time, and the mean square of the flow velocity and normal pulsation velocity were obtained. The flow pulsation intensity and normal pulsation intensity were as follows:
In the formulas, and indicate the fluctuation intensity of the flow and normal pulsation intensities, respectively; and represent the flow instantaneous velocity and normal instantaneous velocity at a certain position (x.y) at a certain time t, respectively, that are acquired by PIV in the flow field; N is the period of PIV acquisition; and C is the number of acquisitions in the PIV field of view.