Turbulent transport measurements in a heated boundary layer: Combined effects of free-stream turbulence and removal of concave curvature

Turbulence measurements for both momentum and heat transport are taken in a boundary layer over a flat, recovery wall downstream of a concave wall (R=0.97m). The boundary layer appears turbulent from the beginning of the concave wall and grows over the test wall with negligible streamwise acceleration. The strength of curvature at the bend exit, δ_99.5/R, is 0.04. The free-stream turbulence intensity is ∼8% at the beginning of the curve and is nearly uniform at ∼4.5% throughout the recovery wall. Comparisons are made with data taken in an earlier study, in the same test facility, but with a low free-stream turbulence intensity (-0.6%). Results show that on the recovery wall, elevated free-stream turbulence intensity enhances turbulent transport quantities such as -uv and vt in most of the outer part of the boundary layer, but near-wall values of vt remain unaffected. This is in contrast to near-wall vt values within the curve which decrease when free-stream turbulence is increased. At the bend exit, decreases of -uv and vt due to removal of curvature become more profound when free-stream turbulence intensity is elevated, compared to low-TI behavior. Measurements in the core of the flow indicate that the high levels of cross transport of momentum over the upstream concave wall cease when curvature is removed. Other results show that turbulent Prandtl numbers over the recovery wall are reduced to -0.9 when free-stream turbulence intensity is elevated, consistent with the rise in Stanton numbers over the recovery wall.