EFFECTS OF ADVERSE PRESSURE GRADIENTS ON TURBULENT STRUCTURES IN OPEN CHANNEL FLOWS

Abstract

Experimental studies were conducted on turbulent structures in open channel flows with adverse pressure gradients. A laser Doppler anemometer (LDA) was used to obtain velocity data, and we succeeded in acquiring velocity profiles in the viscous-sublayer. Accordingly, the friction velocity was precisely calculated with the ‘viscous-sublayer’ law. Although the friction velocity is important to analyze turbulence characteristics, most studies have not employed this method due to restrictinns of measurement techniqucs and anemometers. Using this accurate friction velocity, this study examined the opinions that other researches have presented about open channel flows with adverse pressure gradients. It was found that von Karman constant is universal as pressure-gradient parameter changes. On the other hand, the integral constant in the log-law becomes smaller than that of uniform flow. The results also showed that the log-wake law correctly represents velocity profiles in the equilibrium region.