Turbulent characteristics of pulsating flow over hydraulically smooth surface

The mean flow and turbulence characteristics due to the interaction between wave and current is investigated over the hydraulically smooth surface in a wave channel based on measurement of the horizontal, bottom-normal and transverse velocity components in the pulsating fluid using a 3-D micro-acoustic Doppler velocimeter. Pulsations, in the vicinity of the wall are produced by superimposing the surface wave on unidirectional current using plunger type wave-maker. The velocity time series of combined wave-current flow were analysed within the framework of the phase-averaging. Further, to highlight the changes in combined wave-current flow, a comparative study was made between the velocity profiles for current-only flow and those measured for combined wave-current flow. The measured mean stream-wise velocity for waves following a current is reduced towards the free surface when compared with the current-only data. In addition, with an increase in wave height, a further intense reduction of the velocity just below the wave trough occurs. To fully characterize turbulent signals, the joint probability density function of stream-wise and bottom-normal velocity fluctuations is analysed. Spectral analysis was also performed to obtain the oscillation pattern within the flow field that may affect the turbulent properties due to combined wave-current flow.