Laminar flows confined between parallel surfaces, one of which is periodically "rough," are studied. The effect of surface roughness has been computed for both drag and pressure flows. A basis of comparison is defined so that the effect of roughness on the rate of flow parallel to the surfaces can be quantified. The external flow penetrates the roughness elements to a degree that depends upon the parameters that characterize the roughness. The presence of a pressure gradient exerts a strong influence on the degree of penetration of the roughness. Experiments on the terminal velocity of an axisymmetric grooved cylinder falling through a viscous liquid within a closed concentric tube are presented, and the results agree well with the computational studies.

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