Turbulent oscillatory flow along unidirectional current over square ribs

Abstract

The objective of this research is to examine the turbulent flow characteristics over a series of square rib elements under the combined action of surface wave and unidirectional current. The velocity data were analyzed to determine the distributions of the mean velocity, turbulent kinetic energy, Reynolds shear stress, and the contribution of burst-sweep cycles. These were used for the characterization of flow over square rib due to the superposition of surface waves of different frequencies and thereby compare the results with the current-only case. Mean velocity profiles over the rib roughness, illustrate the well-known downward shift from the flat surface data. Also, the thickness of turbulent boundary layer increases with the superposition of surface wave when compared to current-only flow. Particular attention is also given to understand the behaviour of higher-order moments to explicitly account for turbulent momentum transport characteristics over rib roughness under wave-current interactions.

Reply to the discussion by Li and Li on “Turbulence over cube-mounted rough bed using spatiotemporal averaging approach”

“…The developing flow over the cube mounted rough-bed is more akin to the turbulent boundary layer (TBL) beyond 9 m which is similar to the finding of Ojha and Mazumder (2008). This observation is also confirmed recently by Singh et al (2018b). Therefore in the authors' experiment, all the measurements have been performed at 14.3 m from the flume entrance.…”

Effect of d-type rib roughness on the turbulent structure of side wall boundary layer for wave-current combined flow

“…Moreover by critically evaluating the region y/B = 0 to 0.25 in Figure 10(a) to (c), it is reveal that the roughness effects on e + profiles are limited within the roughness sublayer (y/B \ 0.25) for CA, WCC 0.4 and WCC 0.8 and beyond the roughness sublayer (y/B . 0.25) the profiles for smooth and 26 reported in their study that dissipation rate slightly increases for wave-current combined flow compared to current alone flow. From the Table 2, it reveals that the typical roughness scale equivalent sand-grain roughness height in the rough wall bounded turbulent flow increases with the interaction of p/k roughness and wave-current flow compared to that of the interaction of p/k roughness and CA flow.…”

“…Further equal importance over rough boundary has been given from past. Mostly the studies were focused on the bottom roughness such as ripple bed, [23][24][25] series of square rib elements spanning the width of the channel bed surface, 26 5 mm high triangular wooden strips stuck on the bed across the channel width with the spacing between two consecutive strips about 18 mm which corresponded to p/k \ 5 known as d-type roughness. 3 Similarly, Barman et al 27 used chain of hemispherical ribs with p/k = 2, 4, and 8 as the bottom roughness.…”

Turbulence anisotropy with higher-order moments in flow through passive grid under rigid boundary influence

“…In Table 1, the uncertainty associated with the estimation of turbulence parameters for the undisturbed flow conditions are presented at the elevation z = 0.04 h from the bottom boundary using method similar to the literature. 32–35 For all the turbulent quantities (mean velocities and Reynolds shear stresses) for a given set of experiments, the standard deviation is converted to a 95% confidence level uncertainty which is known as measurement uncertainty ( u m ). The measurement uncertainty ( u m ) is equal ±2σ. If, the average of all the experimental measurements are x avg , then the measured quantities ( x m ) are expressed as xavg±um in the standard engineering notation.…”