Intermittent Flow and Thermal Structures of Accelerating Transitional Boundary Layers: Part 1—Mean Quantities

Abstract

A conditional sampling technique was employed to separate the turbulent and nonturbulent parts of accelerated boundary layers undergoing laminar-turbulent transition on a uniformly heated flat plate. Tests were conducted with zero pressure gradient and two levels of streamwise acceleration parameter: K = 0.07 × 10−6 and 0.16 × 10−6 . The conditionally sampled distribution of the skin friction coefficients revealed that the values for Cf in the nonturbulent and turbulent portions deviated significantly from the respective laminar and turbulent correlations. These deviations increased as acceleration increased. Reconstructing the local average Cf values using the laminar and fully turbulent correlations consistently overestimated the unconditioned Cf values. Using the conditionally sampled data for reconstructing Cf values provided better results, but does not necessarily result in the same unconditioned Cf values. The mean velocity profiles from the turbulent portions had the appearance of a low-Reynolds-number turbulent boundary layer with a large wake region. In the late transition region, as acceleration increased, the wake region in the turbulent portion was suppressed relative to the unconditioned result. The integral parameters, δ*, θ, and shape factor, H, were conditionally sampled and analyzed.