Direct Numerical Simulation, Analysis and Modelling of Mixing Processes in a Round Jet in Crossflow

Direct Numerical Simulations (DNS) for the flow with transport of passive scalars at different Schmidt numbers and chemical reactions at different Damköhler numbers has been carried out. As a result, a comprehensive database for studying mixing phenomena and chemical reactions in a jet in crossflow has been generated. Results obtained concerning instantaneous mixing structures and laminar to turbulent flow transition has been compared to companion experimental data showing a good agreement. The database obtained was used to perform various analyses of the mixing including a priori testing of mixing models (hypotheses) used in the Reynolds-averaged approach. By means of Lagrangian methods flow regions of intensive mixing have been identified. For the present configuration they have been found to be attributed to helical movement of fluid particles. Also regions, where the streamlines of the averaged flow diverge from each other downstream exhibit good local mixing. In the last part of the work bi-orthogonal wavelets are employed to construct novel, multiscale models for Large Eddy Simulations (LES). These are validated and tested with DNS of turbulent channel flow as well as with the present DNS database for the jet in crossflow. Unlike the Smagorinsky model, the new wavelet models have been found to produce no eddy-viscosity in the laminar inflow region of the round pipe from which the jet originates.