This paper presents results of turbulence measurements in boundary layers over surfaces of mild longitudinal curvature. The study indicates that convex wall curvature decreases both the length and velocity scales of turbulent motions, whereas concave curvature has the opposite effect. White being qualitatively similar to those brought about by stronger wall curvature, mild curvature effects are found to be much larger than what one expects from a linear interpolation between the effects of zero and strong curvature. It is also observed that curvature has a relatively larger effect on the Reynolds shear stress than on the turbulent kinetic energy. The present study, however, indicates that it is still possible to use some of the phenomenological models of turbulence (e.g., the mixing length model, the Prandtl-Kolmogorov model), provided an appropriate curvature model is available for describing the effect of curvature on the relevant length scale in the boundary layer. The present data are used to test the validity and limitations of such a curvature model (based on an analogy between streamline curvature and buoyancy) currently in use.

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