Drag and Heat-Transfer Characteristics of Small Longitudinally Ribbed Surfaces

THE drag and heat-transfer characteristics of longitudinally ribbed surfaces have been examined for the case of a turbulent boundary layer. The purpose of the longitudinal fins is to confine the turbulent bursts to regions of small transverse extent, thus altering the local turbulence production. Rectangular, triangular, and razor blade rib geometries were examined. There was some indication that small drag reductions (< 4%) were obtained with two of the triangular grooved models, but further testing, consisting of detailed pitot and hot-wire surveys, is required for validation. The heat-transfer results indicated that several of the triangular grooved surfaces had heat-transfer increases 10% greater than the corresponding drag increases. These surfaces are unique in that heat-transfer augmentation results previously reported in the literature for airflows over external surfaces have always shown greater increases in drag than heat transfer.