Combined effects of concave curvature and high free-stream turbulence intensity of boundary layer heat and momentum transport

Experiments are conducted in the turbulent boundary layer over a concave wall under high free-stream turbulence conditions (TI to approximately 8%). This study simulates some of the features of the flow of the pressure side of a gas turbine blade. The combined effects of concave curvature and elevated TI, both present in that flow, have received very little attention and computation of such flows is inadequate. In the present study, the boundary layer grows naturally under high-TI conditions remaining turbulent from essentially the leading edge of the concave wall. Results show that turbulence intensities in the outer region of the boundary layer increase profoundly above values found in the flat-plate boundary layer residing in a low free-stream disturbance level (0.6%) environment. Boundary layer turbulence is enhanced by penetration of the high-momentum, large-scale eddies from outside the boundary layer. Stationary, Gortler-like vortices, observed under low-TI conditions do not form and skin friction coefficients increase about 2% above maximum (spanwise) values of the low-TI case. Stanton numbers show very little increase on the upstream part of the concave wall but rise about 5% above low-TI values, downstream. This is considered to be a result of the influence of large-scale eddies in the high-TI flow. Measurements in the core of the flow show that cross transport of momentum which raises the stagnation pressure near the concave wall is active both within and outside the concave boundary layer, creating more shallow gradients of velocity. Such cross transport is discussed.