Turbulent boundary layer heat transfer experiments - A separate effects study on a convexly-curved wall
Surface heat transfer rates have been measured for several different flows on an isothermal, convexly curved surface. The freestream velocity, boundary layer thickness, acceleration parameter, and unheated starting length were varied systematically, and both turbulent and transitional boundary layers were studied. The effect of convex curvature on heat transfer rates is significant with Stanton numbers reduced 20-25% below flat wall values for the same enthalpy thickness Reynolds number. Heat transfer rates recovered slowly on a flat wall downstream of the curved wall, and after 60 cm, the Stanton numbers were still 15-20% below flat wall values. The behavior of the boundary layer suggests the existence of an asymptotic condition. Boundary layer thickness, freestream velocity, and boundary layer maturity affect the initial response to the introduction of curvature and the rate at which the asymptotic state is approached. Convex curvature appears to increase the boundary layer's sensitivity to acceleration; it also delays and retards transition. Near-laminar or early-transitional boundary layers recover from curvature rapidly, whereas late-transitional and mature boundary layers recover slowly.