Momentum Transport in Turbulent Boundary Layers With Multiple Pressure Gradients

摘要

An experimental study was performed to examine the effects of multiple extrarates of strain imposed on a turbulent boundary layer. This study is motivated by the necessity to develop predictive models of momentum and heat transport to facilitate design of turbomachinery, especially in the leading edge region of inlet guide vanes. The strain rates considered in the simplified experimental configuration resulted from wall curvature and axial pressure gradient. The effects of these strains on the transport of turbulence were studied for various combinations of strong and moderate curvature coupled with favorable and adverse pressure gradients. Extensive laser Doppler velocimetry measurements were made in a low-speed water channel, with an ability to resolve the near-wall region. Mean velocities, Reynolds stresses and production terms were computed from the measurements. Time-resolved velocity records were used to infer turbulent burst period and ejection duration using the uv2 quadrant technique, with grouping. The results revealed that the strain rates interacted nonlinearly and that the rate of application was at least as important as the magnitude of the applied strains. The friction velocity provided appropriate scaling for Reynolds stresses in the inner layer, but outside of the logarithmic layer large changes caused by the extra strains were not compensated by this scale. An analytical framework based on the orientation of the principle axes of the strain rate and Reynolds stress tensors was evaluated.