Turbulence Modification Due to Wave Action at Low Reynolds Numbers in Horizontal Open-Channel Flow

Wave-turbulence interaction was experimentally investigated in turbulent open-channel flows with a shear-free wavy surface using a photochromic dye activation technique. In the experiments conducted, two-dimensional waves of different amplitudes, wavelengths, and frequencies were superimposed on a liquid surface via a mechanical wave maker. The range of Reynolds numbers varied from 3900 to 5000 based on the hydraulic diameter, with the corresponding aspect ratio of the channel width to liquid depth varying from 7.5 to 5.

Within the range of Reynolds numbers investigated, the results showed that the streamwise turbulence intensity increased in the bulk and interfacial regions in comparison to the undisturbed flow.

Furthermore, video sequences of the flow visualization experiments clearly revealed that the spanwise motion of the liquid was significantly suppressed; the traces did not immediately deform in the spanwise direction but retained their shape with increasing wave amplitude and frequency as compared to smooth interface flows. This suggests that waves may have suppressed longitudinal vortices generated near the smooth interface. The suppression of the longitudinal vortices in wavy open-channel flows has been proposed as a mechanism responsible for the turbulence energy redistribution, different from that for smooth open-channel flows.