Fluid Dynamic Characteristics of the Flow Over an Array of Large Roughness Elements

Flow visualization and measurements of velocity and turbulence intensity using laser Doppler velocimetry are used to investigate separation and reattachment processes in the flow over an array of protruding elements mounted on the bottom wall of a rectangular water channel. The concept of an array shear layer is introduced to demarcate the region of influence over which the resistance of the array retards the flow. Flow separation at the leading edge of the elements is documented. The confined or interacting nature of the flow in the cavities between elements is established as a function of element spacing. The reattachment length downstream of the element varies from 4 to 1.5 element heights, decreasing both with an increase in Reynolds number and a decrease in channel height.