FLUME STUDIES ON RESISTANCE OF TWO - DIMENSIONAL STRIP ROUGHNESSES

Abstract

This thesis presents the results of an experimental Investigation on the mechanism of resistance to flow over artificial roughness elements. The studies were carried out on two»dimensional sharp-edged strips of negligible thickness placed on the bed of an open channel. The various aspect$ of the problem covered by the experiments included the resistance characteristics of a single roughness element as well as those of series of roughness elements placed on a smooth boundary« In case of el events in series, using ti dimensional, strips having relative spacings of 60 and 801, the total resistance of the boundary$ as well as the akin friction of the plan* unary were measured; the latter was measured using a Preston tube. Experiments were sls* performed to verify the hypothesis of Rangaraju and Garde that for roughness elements In series on a plane boundary, upto a relative Spacing of 40, the negative friction in the standing eddy cancels with the positive friction further downstream and thus the net skin friction is zero. For this purpose experiments were made using t w dimenaio na1 st rip placed on a boundary to which gravel particles were glued. As a result of the present investigation it1was proved that the above hypothesis is true upto a relative spacing of 40. In addition, information has also been presented about the form resistance of the strips and the skin friction of the plane boundary at relative spacings exceeding 40. Analysis of data on the drag of a single element has indicated, a unique relation between the drag coefficient and the relative depth;,of flow