Turbulence and Vorticity in a Laboratory Channel Bend at Equilibrium Clear-Water Scour with and without Stream Barbs

Abstract

Laboratory flume experiments were conducted to study the flow field and sediment dynamics in a mobile-bed channel bend with and without the presence of stream barbs (upstream-angled submerged groynes). This paper presents spatial distributions of the vorticity field and the turbulent Reynolds shear stresses, kinetic energy, and integral scales. The objectives of the present paper were to (1) advance understanding of the role that vorticity and turbulence play in the erosion process in channel bends with and without barbs, and (2) optimize barb design for reducing erosion along the outer bank regions of channel bends through consideration of flow-field turbulence and vorticity. Results indicate that (1) increased z-vorticity occurred in the outer bank scour zone for all runs with and without barbs; (2) for the runs without barbs and with moderately sized barbs, increased streamwise-cross-stream Reynolds stress (τuv) was found to coincide with locations of scour; and (3) for the run with large barbs, all three Reynolds shear stresses increased, but τvw was most consistently associated with scour locations. In general, local scour near the barbs was associated with increased z-vorticity, tke, and nonprincipal Reynolds stresses (τuv and τvw). Furthermore, it was observed that the outer bank region (particularly between adjacent barbs) may be susceptible to increased erosion if stream barbs, due to their size and layout, generate excessive turbulence and secondary velocities.