Reynolds number effects on an adverse pressure gradient turbulent boundary layer

Many common engineering flows are characterized by high Reynolds numbers and complex geometries, including adverse pressure gradients. In these flows the turbulence is out of equilibrium with the mean flow the standard inner and outer layer velocity and length scales are no longer the only relevant scales in the flow and additional scales become necessary to characterize the flow.; The examination of an adverse pressure gradient boundary layer developing along a 4° ramp over a moderate range of Reynolds numbers, factor of 7, is achieved using a wind tunnel located inside a pressure vessel by varying the freestream velocity and the ambient pressure, and thus the air density. A custom made high resolution 2 component laser Doppler anemometer with a 40 mum by 80 mum measurement volume allows for measurement of the mean and turbulence over the range of Reynolds numbers examined.; Experimentally the mean velocity profiles are observed to be weak functions of Reynolds number, while the turbulence quantities are more affected by the changing Reynolds number. The mean velocity profiles are only moderately affected by the adverse pressure gradient, with no inflection point developing in the flow along the ramp. The turbulence quantities are observed to change greatly along the adverse pressure gradient ramp when scaled in traditional flat plate coordinates. The overall turbulence structure as indicated by the single-point structure parameters is not strongly affected by this adverse pressure gradient. Empirical scalings are proposed for the normal stresses, which collapse the flat plate stress profiles along with the adverse pressure gradient profiles for this range of Reynolds numbers. These scalings are mostly based on flat plate reference profile parameters, implying that the normal stresses are determined almost entirely by the upstream flow. The small angle that the flow must turn and the resulting pressure gradient only weakly affect the normal stresses. The streamwise normal stress collapses in the inner layer using local values implying that for the inner layer the pressure gradient does play a role in the stress profile unlike in the outer layer.