Artificially thickened turbulent boundary layers for studying heat transfer and skin friction on rough surfaces

A technique has been developed to produce artificially thickened boundary layers on a uniformly rough surface which have two-dimensional, equilibrium properties representative of normal behavior at the level of spectra of the longitudinal velocity fluctuations. Skin surface friction coefficients and Stanton numbers are obtained for rough surface boundary layers much thicker than those previously studied. The results provide additional understanding of turbulent shear flow and a basis for testing engineering calculation schemes and design procedures for situations where thick, rough-wall boundary layers are present. The Stanton numbers and skin friction coefficients are shown to be representative of natural behavior because three higher levels of information, as well as the turbulent transport of momentum and heat, are the same as would have existed in naturally developed layers of the same thickness.