An Experimental Investigation Of Heat Transfer In Three Dimensional And Separating Turbulent Boundary Layers PDF Download

The turbulence structure of convective beat transfer was studied experimentally in complex three-dimensional and separating turbulent boundary layers. Three test cases whose fluid dynamics have been well documented were examined. In case 1, time- and spatially-resolved surface heat transfer was measured in the nose region of a wing-body junction formed by a wing and a flat plate. Both the wing and the endwall were heated and held at a constant uniform temperature 20 C above ambient temperature. Heat flux rates were increased up to a factor of 3 over the heat flux rates in the approach boundary layer. The rms of the heat flux fluctuations were as high as 25% of the mean heat flux in the vortex-dominated nose region. Away from the wing, upstream of the time-averaged vortex center, augmentation in the heat flux is due to increased turbulent mixing caused by large-scale unsteadiness of the vortex. Adjacent to the wing the augmentation in heat flux is due to a change in the mean velocity field. In case 2, simultaneous surface heat flux and temperature profiles were measured at 8 locations in the spatially-developing pressure-driven three-dimensional turbulent boundary layer upstream of a wing-body junction. Mean heat transfer was decreased 10% by three-dimensionality. The turbulent Prandtl number in the near-wall region of logarithmic temperature variation was approximately 0.9 at all measurement locations in the three-dimensional boundary layer. Profiles of the skewness factor of temperature fluctuations and conditionally-averaged temperature signals during a sweep/ejection event suggest that the strength of ejections of hot fluid from the near-wall region are decreased by three-dimensionality.