Measurements of velocity and turbulence intensity profiles and skin friction coefficient are presented for turbulent flat-plate boundary layer flow over a test surface with a rough-to-smooth step change in surface roughness. The first 0.9 m length of the test surface is roughened with 1.27 mm diameter hemispheres spaced 2 base diameters apart in a uniform staggered array, and the remaining 1.5 m length is smooth. The profiles are compared with previous data for all-rough cases under closely matched conditions in the same facility. The skin friction data are compared with previous data for both all-rough and all-smooth cases.

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