Flow over a rough surface

Abstract

NOTE: text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. An experimental investigation was conducted on the flow over a rough surface. The roughness consisted of sets of square cavities ranging in size from 1/8 to 1 in. The flow over this series of roughness was observed for a range of [...] values from 11 to 260. The quantity [...] may be regarded as a Reynolds number for the roughness and it is the essential parameter governing the flow over the roughness elements. It is defined as [...] where [...] is the cavity depth, [...] is the shear velocity, and [...] the kinematic viscosity of the fluid. The desired approaching flow was obtained in an open surface water channel at free stream velocities of from 0.1 to 0.75 ft/sec. The velocity profile showed the characteristics of a turbulent boundary layer. The velocity measurements necessary to determine the profile were obtained by means of a hot film anemometer. Visualization of the flow in the cavities lead to the classification of five characteristic flow types or modes. The observations could be described consistently in terms of these modes and as a function of [...]. At values of [...] below 100 different mode forms appeared periodically and large disturbances of the fluid within the cavity were noted. This type of flow had not been observed previously. At values of [...] beyond about 200 a rather stable vortex formed in the cavities, as had been reported by previous experimenters. Some possible effects of the flow behavior on heat transfer are discussed. Photographic materials on pp. 106-150 are essential and will not clearly reproduce on Xerox copies. Photographic copies should be ordered.