Simultaneous measurement of turbulent velocity field and surface wave amplitude in the initial stage of an open-channel flow by PIV

Particle image velocimetry (PIV) was employed to measure the two components of the turbulent velocity field in the initial stage of an open-channel flow in a streamwise-wall-normal plane, and the free-surface level was discriminated from the PIV image. The details of this technique was described and demonstrated by showing the instantaneous velocity field together with the free-surface shape, statistics of velocity field, and the wave-turbulence interaction terms. Preliminary experimental results showed that the turbulence intensity of the streamwise velocity fluctuations (u′) decreased, whereas that of the wall-normal velocity (v′) increased near the bottom wall with downstream distance in the initial stage of an open-channel flow; \(\overline {ug}\) (g is the fluctuation of free-surface level) had a negative value, \(\overline {vg}\) had a positive value near the free surface, and the surface-wave-affected depth deepened with downstream distance.