Effect of Single Roughness Elements on the Heat Transfer From a 1:3 Elliptical Cylinder

Abstract

Abstract The effect of single roughness elements on the heat transfer from the surface of a 1:3 elliptical cylinder to an air stream has been investigated by placing single spanwise nylon filaments on the surface of the cylinder. The results are compared with those for the smooth surface of the same cylinder which have already been presented and, as before, these results are given in terms of the pressure coefficient, recovery factor, and local heat-transfer coefficient. On-stream air speeds ranged from 184 to 423 fps giving Reynolds numbers, based on the 6-in. chord of the cylinder, from 531,000 to 1,200,000. The roughness element produced an effect in all cases and in the majority there was an apparent transition to turbulent flow either at or downstream of the element. In those cases in which the roughness element was not too large compared to the thickness of the laminar boundary layer, the heat-transfer coefficients after the point of transition were in good accord with those predicted from the Colburn equation. The point of transition itself was in approximate agreement with values found by other experimenters.