Report on PDF Models for Turbulence Chemistry Interaction

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Authors
  1. Etele, J.
Corporate Authors
Defence Research and Development Canada, Valcartier Research Centre, Quebec QC (CAN);Aldanox Group Inc. - Manotick, ON (CAN)
Abstract
Many numerical solvers aimed at the solution of high speed chemically reacting flows employ methods that solve directly for both the change in thermal and mass diffusivity due to turbulence through the solution of a turbulent Prandtl and turbulent Schmidt number directly. In many cases, the solution of the turbulent Schmidt number requires a method of modelling the effects of species massfraction fluctuations on the source terms representing the chemical reactions occurring. One approach that has seen reasonable success is the use of Probability Density Functions (PDFs) to evaluate the time averaged values of fluctuating massfraction terms appearing in the governing equations. Both assumed forms for these PDFs as well as PDFs where their evolution itself is part of the solution procedure have been implemented. The assumed forms have generally been regarded as being the best combination of accuracy and computational efficiency. Indeed, the use of a multivariate β PDF for the species massfraction fluctuations reduces to an algebraic expression avoiding the need to numerically integrate the PDF (as is required when using a Gaussian PDF). This report details the implementation of assumed, jointly un-correlated PDFs for both temperature and species massfraction fluctuations. It shows that provided one is already using a variable Prandtl and/or variable Schmidt number numerical solver, no additional conservation equations are required (the use of a temperature PDF requires the
Keywords
CFD (Computational Fluid Dynamics;modelling;variable Schmidt;PDF (Probability Density Function);multivariate beta;chemical reaction
Report Number
DRDC-RDDC-2014-C238 — Contract Report
Date of publication
01 Mar 2014
Number of Pages
38
DSTKIM No
CA039484
CANDIS No
800534
Format(s):
Electronic Document(PDF)

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