Experimental Study on Turbulent Structures in Accelerating and Decelerating Open-Channel Flows

Abstract

It is very important to examine the effects of pressure gradient on the turbulent structures. In the present study, accurate FLDA measurements over wavy bed have been conducted in open-channel flows. The pressure gradient parameter p⁺ obtained in this study was compared with that of air duct flows. The friction velocity was accurately determined even in the pressure-gradient flows with ‘viscous-sublayer’ formula, i. e., U⁺=y⁺. On the other hand, the velocity profiles of inner region have deviated largely from the universal velocity profile, i. e., U⁺=1/k·ln y⁺As, which dose exist in zero-pressure gradient flows. The distributions of turbulence intensities and Reynolds stress near the wall gradually changed form universal distributions.