Direct measurements of secondary currents at a river inflexion point
SECONDARY currents are defined as currents which occur in a plane normal to the local axis of primary flow. They may develop in pipes or open channels as a result of non-equal distribution of boundary shear stress or by skewing of cross-stream vorticity into a long stream direction1–3. Secondary currents distort the distributions of primary isovels and boundary shear stress from those found in simple flows and have important effects on sedimentary processes of erosion and deposition4,5. Direct measurements of secondary currents in river bends were reported recently6. Further data have been obtained for the reach around the inflexion point between bends (Fig. 1) and are reported here.
Unsteady Turbulence in Tidal Bores: Effects of Bed Roughness
A tidal bore is a wave propagating upstream as the tidal flow turns to rising. It forms during spring tide conditions when the flood tide is confined to a narrow funneled channel. To date, theoretical and numerical studies rely upon physical experiments to validate the developments, but the experimental data are limited mostly to visual observations and sometimes free-surface measurements. Herein turbulent velocity measurements were obtained in a large-size laboratory facility with a fine spatial and temporal resolution. The instantaneous velocity measurements showed rapid flow deceleration at all vertical elevations, and large fluctuations of all velocity components were recorded beneath the bore and secondary waves. A comparison between undular (nonbreaking) and breaking bores suggested some basic differences. In an undular bore, large velocity fluctuations were recorded beneath the first wave crest and the secondary waves showing a long-lasting effect after the bore passage. In a breaking bore, some la...
Boundary Shear Stresses in Curved Trapezoidal Channels
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Sanitary Engineering, 1961.