Turbulent Transport Characteristics in a Low-speed Boundary Layer Subjected to Adverse Pressure

Thermal anemometry measurements were performed to evaluate the heat and momentum transport characteristics of wall turbulence over a slightly heated, smooth flat plate with a stepchange in wall temperature. Single-wire, X-probe and triple-wire sensors were employed to measure mean and fluctuating velocity and temperature as well as Reynolds stress and heat flux productions. “Equilibrium” boundary layers were considered for mild (β ≈ 0.8, Reθ ≈ 3500) and moderate (β ≈ 1.8, Reθ ≈ 3800) adverse-pressure-gradient (APG) conditions for a wall-to-freestream temperature difference ∆T of approximately 12C. The base case for zero-pressuregradient (ZPG) conditions (β ≈ 0, Reθ ≈ 2700) was also investigated. The origins of the momentum and thermal boundary layers did not coincide, resulting in a layer development ∆/∆-T of approximately 0.8, 1.2 and 1.5 for ZPG, mild and moderate APG, respectively. Findings suggest that the mean flow field and the fluctuating streamwise and normal flow fields responded proportionally to the magnitude of the adverse-pressure gradient present. The failure of the lawof-the-wall for velocity for the APG conditions considered was not severe. And the equilibrium condition of the flow was maintained through a balance of adverse pressure and turbulent stress production. The Reynolds analogy was confirmed for ZPG conditions while, in adverse pressure, the turbulent stress production scaled with the streamwise heat flux. The heat flux production was found to be self-similar for the pressure gradient cases investigated.