Assessment of subgrid scale mixing models used in LES at high pressures

Abstract

ABSTRACTMolecular mixing models for conditional scalar diffusion (CSD) in the filtered mass density function (FMDF) transport equation used in Large Eddy Simulations are evaluated against direct numerical simulation (DNS) of spatially evolving jets. A database of DNS of turbulent mixing slot jets of and is developed. The formulation includes compressible form of the governing equations, a generalized diffusion model, a real gas equation of state and realistic property models. Simulations are conducted at initial pressures between 1-100 atm and Reynolds numbers of 850, 1300. The CSD term in the FMDF transport equation is calculated from the DNS. An a priori analysis of Interaction by Exchange of Mean, Modified Curl and Mapping Closure models for CSD is conducted. At high pressures, significant deviations are observed between the CSD measured from the DNS and those predicted by the models. The source of the deviations is determined to be the mixing frequency used in the models. The significance of this term and its variation with change in pressure and diffusion models is studied. The primary objective of this work is to assess the applicability of the aforementioned models to flows at large pressures and determine the causes for deviation in prediction.