VELOCITY DISTRIBUTION OVER EXTREME ROUGH SURFACE

Abstract

Recently it has been found that the velocity distribu-tion near a rough boundary deviates from the rough boundary equations obtained by Prandtl and Karman. Very little reliable data are available to study this variation of velocity near rough boundary in detail. To explain this deviation attempts have been made to establish mathematical basis for it with the help of semi-empirical hypothesis. Two such mathematical models are tested with the help of data collected in an open channel whose bed was coated with uniform sand grains of 4.36 mm and 7.75 mm sizes. According to the first model the deviation can be,.explained.on the basis of an additional mixing length which is a function of relative roughness. Alternatively according to second model the experimental velocity distribution can be expressed in terms of two log4rithmic laws giving a break in the velocity profile at a certain value of y/k.