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.