Measurements and calculations of rough-wall heat transfer in the turbulent boundary layer

Abstract

Experimental Stanton number results from aerodynamically smooth, transitionally rough, and fully rough turbulent boundary layer flows are presented for four surfaces—three rough and one smooth. The rough surfaces are composed of 1.27 mm diameter hemispheres spaced in staggered arrays 2, 4, and 10 base diameters apart, respectively, on otherwise smooth walls. Stanton number data are reported for zero pressure gradient incompressible turbulent boundary layer air flows which give Re x up to 10000 000. These data are compared with previously published results on another, similar rough surface, and it is shown that some conclusions about heat transfer behavior based on data from that single rough surface do not extend to these new surface geometries. A refined roughness element energy transport model for use in the previously published discrete element prediction method is also presented. Calculations are compared with data from the four rough surfaces with well-defined roughness elements for both constant pressure and accelerated flow cases, and it is shown that the predictions are in excellent agreement with the data.