Large Eddy Simulation in the Scalar Field

Focusing on Large Eddy Simulation (LES) in the scalar field, this work has threefoldachievement:The development, validation and application of a new anisotropy subgrid scale (SGS)model that is designed to better describe the behavior of SGS scalar flux transportIn the frame of LES, a new developed anisotropy model is proposed and implemented.Unlike the isotropic SGS scalar flux models, the new model involves the anisotropicdiffusivity and takes into account the scalar gradients in different directions of flows. Thismodel is validated in different engineering related configurations of various complexities,which include a mixing layer problem, a jet in cross flow and jet in channel flowconfiguration. Thereby mixing processes involving low Schmidt number and high Schmidtnumber effects have been carefully examined. It is shown that the proposed model achievesa good agreement with the experimental data and significantly outperforms isotropic formmodels.The characterization and quantification of turbulent mixing processes, in terms of scalarstructures and degree of mixing along with implementation of passive and activemodification techniquesTo provide a methodic analysis of turbulent mixing processes, a representation of mixing isinvolved, which includes its physical nature, scales and resolution study. With thisunderstanding, the so-called “Mixing parameters” are introduced. The ability of theseparameters to retrieve the mixing mechanism is clearly established within different mixingprocesses. A mixedness parameter (MIX) can represent the probability of mixed fluids in thecomputational domain. The following two are the spatial mixing deficiency (SMD) and thetemporal mixing deficiency (TMD) parameters for characterizing the macromixing andmicromixing.The attempt towards an optimization of mixingA numerical mixing optimization procedure is demonstrated using LES. The motivation isthat LES has the approved ability to obtain detailed, accurate and comprehensive data ofmixing quantities, which meets the requirement of mixing optimization design. Although theprincipal focus is a specific impingement mixing mixer problem, the methodologydeveloped is equally applicable to virtually any aspect of technology and engineering, wheremixing processes are important.