Book Description

Details of the turbulence production process in turbulent boundary layers in the wall region have been clarified, especially the formation of the long streaky structure, and secondary hairpin vorticity. It appears that the outer region microscale coherent motion called a Typical eddy plays the dominant role in the process. Long time averaged statistics of the two point vorticity-vorticity correlations support the conditionally sampled data and interpretations. The typical eddy produces the long streaks along with the pockets, and one of the hairpins directly. Several other hairpins form from the evolution of the vorticity produced by the passage of the typical eddy over the wall. A model of the typical eddy/wall region interaction, i.e., a vortex ring/Stokes layer interaction, was investigated to see if it could reproduce all of the morphology. It was found that the model can produce all of the turbulent boundary layer features associated with production, including the long streaks. By using the model, we have gained new insights into the sensitivity of the production process. Relatively small differences in the convection velocity of the excitation eddies have been found to result in the difference between turbulent boundary layer production and spot production (which involves very strong lateral production). Our data suggest that there are many combinations of parameters that can result in critical conditions.