Turbulence characteristics of wave-blocking phenomena

Abstract

This study explores experimentally the turbulent flow in a laboratory flume, interacting with waves propagated against the flow. It focuses a region of 'wave-blocking' for which there is a stream-wise location on the water surface, where the wave propagation velocity vanishes. The observations are corroborated by finding a critical wave frequency for a particular discharge above which the waves are effectively blocked; and verified by the dispersion relation of monochromatic wave. The counter-current propagating waves show an evolutionary change in the flow with three segmented regions, viz, flow at the upstream, blocking at the mid-stream and waves in the downstream. The instantaneous velocity data were collected using 3-D Micro-acoustic Doppler velocimeter (ADV) along the flume centerline. This study addresses the changes in the mean flows, Reynolds stresses, eddy viscosity, turbulence kinetic energy fluxes and associated contributions of burst-sweep cycles to the total Reynolds shear stress due to addition of surface waves against a current. The velocity power spectral analysis shows the energy distribution over the whole profile from upstream to downstream. The quadrant analysis is also used to highlight the turbulent event evolutions along the flow; and shows that at the waveblocking and wave dominated regions, the contributions from ejection and sweep to the total shear stress are dominant. The changes in turbulence key parameters due to waveblocking may affect the sediment transport in coastal region.

Development of bedforms due to waves blocked by a counter current

“…Apart from this, the normalized turbulence intensities in the stream-wise and vertical directions above the rigid flat surface agreed well with those of Nezu and Rodi (1986), Clifford (1998), Ojha and Mazumder (2010), and Chatterjee et al (2018), with slight changes of empirical coefficients. The dimensionless stream-wise mean velocity over the flat rigid surface followed the log-law at all the measuring locations.…”

“…Both the experimental and recirculating channels of the flume are of the same dimensions (10 m long, 0.5 m wide and 0.5 m deep). The cross-sections of both inlet and outlet pipes were smaller than the wetted crosssection of the flume (figure 1a of Chatterjee et al, 2018). The water depth is kept constant at H = 25 cm for all experiments and the hydraulic slope of the flume is of the order of 0.001.…”

“…Two different flow discharges (Q = 0.0197 and 0.0322 m 3 /s) with corresponding Reynolds numbers, i.e. Detailed descriptions of the experimental flume with inlet and outlet pipes are available in Chatterjee et al (2018). The data were collected from the lowest level, i.e.…”

“…The effect of wave against flow induces the wave-blocking when the incident wave is diminished by a sufficiently strong current. Recently, Chatterjee et al (2018) experimentally studied the turbulence features of the wave-blocking phenomenon, where the opposing current gradually blocked the primary wave energy, i.e. Hence, a region is created beyond which the waves are absent and only the background flow of fluid remains.…”

“…They studied the energy dissipation due to monochromatic and random wave breaking at or before blocking points. Recently, Chatterjee et al (2018) experimentally studied the turbulence features of the wave-blocking phenomenon, where the opposing current gradually blocked the primary wave energy, i.e. where the wave-propagation velocity vanished.…”