Investigation of Turbulent Boundary Layers Subjected to Internally or ExternallyImposed Time-Dependent Transverse Shear

摘要

Both experimental and modeling efforts are aimed at understanding the non-equilibrium effects introduced by a 2-D turbulent boundary layer suddenly subjected to transverse wall shear. A new turbulence model has been developed which can be used to predict the Reynolds stress development in 3-D shear flows. This theta-l model allows for a misalignment to occur between the stress and strain as observed in 3-D turbulent boundary layers. The misalignment is determined by accounting for the flow history through solving a transport equation (first derived by Bradshaw, 1971) for theta. Excellent agreement is observed for both mean profiles and Reynolds stress when compared with the experiments of Driver and Johnston (1990). For the experiments, a 36' long 18 diameter cylinder surface is used. One section of the model is designed to rotate about its axis; thereby, introducing non-equilibrium effects into the developing 2-D boundary layer. Stereoscopic PIV is being used to acquire all three components of the velocity in both the x-y and x-z planes. Comparison of the detailed experimental results with subsequent modifications of the modeling should result in improved non-equilibrium turbulence prediction capabilities.