Changes in Turbulent Flow Structure under Combined Wave-Current Motions

Abstract

The horizontal, lateral, and vertical velocity components in a recirculating channel were measured to study changes in the turbulent intensity, Reynolds stress, and velocity distributions due to the interaction between a current and gravity waves. These physical quantities for waves following and opposing a current were obtained by analyzing the velocity data taken during 250 wave cycles. The phase-averaged RMS values of horizontal and vertical turbulent intensities for the larger waves seem to decrease from those for the smaller waves at most elevations above the bed, although the analyzed data are scattered in the measured range. The direction of wave propagation to the current mostly influences the essential features of the resultant Reynolds stress and the general characteristics of the horizontal and vertical velocities. In this situation for the following waves, the mean velocities for the larger waves increase more rapidly from the bed to the mid-depth but decrease still more in the outer region. In contrast, the situation for the opposing waves reverses in the whole depth. The physical aspects from these measured horizontal velocities could be well described using the Eulerian mean velocity equation. Phase-averaged water surface variations for a combined wave and current motion are similar to those for the associated wave-alone motion, regardless of the relative directions of wave and current. The surface waves have sharp crests and long troughs when wave height is larger or water depth is shallower. The distributions of mean velocity components and turbulent quantities, including the lateral and vertical turbulence intensities and the corresponding Reynolds stress, were derived from the velocity data in a lateral plane. The presence of the waves amplifies the magnitude of lateral turbulent intensities considerably near the sidewall but does not cause marked changes in their vertical profiles close to the center of the channel.