2.3 Time-frequency curves of transient velocity
To characterize the development of the flow pulsation characteristics over time for oil containing particles, according to the instantaneous velocity vector of the PIV test, a point (0.9, 0.25) near the center of the test field is randomly selected. Time-frequency analysis of the instantaneous flow velocity and normal velocity at different particle concentrations of 0.65 ppm, 0.97 ppm, 3.00 ppm, 6.58 ppm, and 14.40 ppm is shown in Figs. 4-8, respectively. In Figs. 4-8, (a) shows the time curve of the instantaneous flow velocity of the oil, (b) shows the time curve of the instantaneous normal velocity of the oil, (c) presents the spectrum curve of the instantaneous flow velocity of the oil and (d) presents the spectral curve of the instantaneous normal velocity of the oil.