MECHANISM OF RESISTANCE TO FLOW OVER ARTIFICIAL ROUGHNESS ELEMENTS

Abstract

This thesis presents the results of an experimental investi gation concerning the mechanism of resistance to flow over two-dimensional sharp-edged roughness elements of negligible thickness. The studios viere carried out in a tilting flume with water and also in two wind tunnels, one of them being an open r"'rcult tunnel & other of the closed-circuit type. Experi ments were carried out to cover the following aspects of the problem :- a) Effect of contraction of the stream on the drag coefficient o^ sharp-edged plates. b) Effect of submergence of a normal plate in a turbulent boundary on the drag coefficient of "^he plate. c) Porm resistance of an element kept in series on a plane boundary and the total resistance of the plane boundary. d) Effect of introduction of a small roughness element in the wake of a large oni_ on the resistance characteristics of both the elements. In addition to the aspects mentioned above, information has also been obtained on the nature of velocity distribution in the flow over artificial roughness elements and on the location of datum as related to the relative spacing of the roughness elements . Also the applicability of the method suggested by Morris to the type of roughness elements used in this study has been examined. The conclusions derived on the basis of the analysis of. data concerning the various aspects mentioned above afford a better insight into the problem of resistance of artificial roughness elements.