PIV Study of Shallow Open Channel Flow Over d- and k-Type Transverse Ribs

Abstract

A particle image velocimetry was used to study shallow open channel turbulent flow over d-type and k-type transverse ribs of square, circular, and semi-circular cross sections. The ratio of boundary layer thickness to depth of flow varied from 50% to 90%. The mean velocities and turbulent quantities were evaluated at the top plane of the ribs to characterize interaction between the cavities and overlying boundary layer. It was found that the overlying boundary layer interacts more strongly with k-type cavities than observed for d-type cavities. The profiles of the mean velocities and turbulent statistics were then spatially averaged over a pitch, and these profiles were used to study the effects of rib type and cross section on the flow field. The mean velocity gradients were found to be non-negligible across the boundary layer, and the implications of this observation for momentum transport, eddy viscosity, and mixing length distributions are discussed. The results show that the skin friction coefficient, Reynolds stresses and mixing length distributions are independent of rib cross section for d-type. For the k-type ribs, significant variations in skin friction coefficient values, mean flow, and turbulence fields are observed between square ribs and circular/semi-circular ribs.

Structure of wake of a sharp-edged bluff body in a shallow channel flow

“…2(b) shows the streamwise turbulent intensity of the approaching flow. The present result is compared with the open channel data of Roussinova et al (2008) and Tachie and Arden (2007). Overall, the agreement is within a satisfactory range, except for the fact that the present data underestimates the turbulent fluctuation close to the bed.…”

Use of PIV to highlight possible errors in hot-wire Reynolds stress data over a 2D rough wall

“…Similar high values of ‹u 2 › 1/2 /U 0 and ‹v 2 › 1/2 /U 0 were also observed in previous studies in open channel with similar rough walls (e.g. Tachie and Adane 2007;Roussinova 2009). The high level of the Reynolds stresses is a combination of relative turbulence high intensity in the water open channel, the water depth and the presence of free surface.…”

Influence of PIV interrogation area on turbulent statistics up to 4th order moments in smooth and rough wall turbulent flows

“…For the rib roughness, on the other hand, the roughness sublayer extended up to 2.9d, which is well outside the edge of the boundary layer. A similarly extreme roughness sublayer extent was reported for shallow open channel turbulent flow over k-type ribs of circular, semi-circular and square cross-sections (Tachie and Adane [41]). …”