Measurements of the Turbulent Transport of Heat and Momentum in Convexly Curved Boundary Layers: Effects of Curvature, Recovery and Free-Stream Turbulence

Abstract

The effects of streamwise convex curvature, recovery, and free-stream turbulence intensity on the turbulent transport of heat and momentum in a mature turbulent boundary layer are investigated. A special three-wire hot-wire probe developed for this purpose is described. Two cases with free-stream turbulence levels of 0.68 and 2.0 percent, taken in the same facility with moderate strength of curvature, δ/R = 0.03, are compared. Profiles of u′v′, t′, u′t′, and v′t′ are dramatically reduced within the curve, with asymptotic profiles being achieved quickly for the low TI case. Recovery occurs rapidly, with the profiles often overshooting flat-wall upstream values. Increased free-stream turbulence has the effect of increasing the profiles throughout the boundary layer on the flat developing wall. Profiles agreeing with the asymptotic profiles of the low TI case are observed by the end of the curve, however, illustrating the dominance of curvature over free-stream turbulence intensity. For the higher TI case, a reversal in the sign of u′v′ in the outer half of the boundary layer is observed, leading to negative values of the turbulent Prandtl number in this region. This indicates a breakdown in Reynolds analogy.