Distribution of turbulent eddies under wave-current coexisting flow over hemispherical rough bed

This experimental study examines the distributions of turbulent eddies across three distinct rough beds with emphasis on positions such as upstream, downstream, crest, and cavity of the roughness elements. Three different roughness spacing with p/r = 4, 6, and 8 with roughness elements arranged in a regular pattern (where p and r denote the patch distance and roughness height, respectively) were explored for three distinct flow scenarios: current-only flow as well as two combined wave-current flows with wave frequencies of 1 Hz and 2 Hz. The surface waves propagated in the direction of flow. Furthermore, experiments were conducted for two different flow Reynolds numbers: 62,000 and 46,500. The effect of surface waves with different frequencies on the time-averaged turbulent properties (relevant to the eddy structure) of steady current is investigated, and the comparative results are described for two different flow submergences. Results indicate significant differences in the sizes of eddies for different tested scenarios, including that for different flow submergence cases. The quantitative findings regarding the different length scales of turbulence (Integral, Taylor, Kolmogorov) in the context of different flow submergence are investigated. Furthermore, these results are connected by the quantitative outputs of time-averaged velocity, production, and dissipation rates of turbulent kinetic energy. For a fixed time window, the change of eddy scales against the water depth at each considered location is evaluated by the wavelet decomposition of the instantaneous velocity signal. Results indicate that the frequency of the occurrence of larger eddies increases with the increase in wave frequency for at the outer zone.