5505

5165

كارشناسي ارشد

تبديل انرژي

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مكانيك

1389

[ده]،91ص.: مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

محسن دوازده امامي

محمود اشرفي زاده

11/8/89

محمدرضا سليم پور، احمد صداقت

مهندسي مكانيك

ID5165

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

Modeling of Mixture Fraction Variance in Turbulent Diffusion Flames Ali Bayat a bayat@me iut ac ir June 27 2010 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree MS c Language FarsiSupervisor Mohsen Davazdah Emami mohsen@cc iut ac irAbstractCalculation of Temperature and Species mass fractions is one of the most importantconcerns in solving combusting flows In laminar diffusion flames in order to calculate theexact values of Temperature and Species mass fractions it is usual to define a parameternamed mixture fraction which indicate the ration of fuel mass to total fuel and oxidizer Inturbulent diffusion flames in addition to the mean mixture fraction the mixture fractionvariance also plays an important role in predicting the Temperature and Species massfractions Therefore finding appropriate models and equations to simulate these twoparameters would be really helpful In turbulent diffusion flames important parameterssuch as velocity temperature and species mass fractions act like random parameters Studyof these parameters requires appropriate averaging methods such as the Favre averagingmethod In the turbulent regime temperature and species mass fractions are functions ofmean mixture fraction and its variance The transport equation of mixture fraction varianceincludes terms representing the production and the dissipation of mixture fraction variance The dissipation term in this equation needs modeling There are two different ways toconsider the effects of scalar dissipation rate The first one is to develop a transportequation for this parameter In order to write such equation many of scientists have tried tofind the best coefficients for the equation This method is very complicated because thereare many terms in this equation Therefore it is better to find another way to solve theproblem In the field of modelling there are two categories of sub models The first onewhich is called the Equal Scales model is based on the hypothesis that time and lengthscales of scalar are equal to time and length scales of fluid flow field This model is one ofthe most applicable models and for years it has been used to calculate the scalar dissipationrate The constant coefficient in this model has been considered 2 The second one is theNon Equal Scales model In this model these scales are not necessarily equal In this modelthe scalar dissipation rate depends on the values of fuel jet velocity and its diameter In thepresent study these two models with different coefficients have been used to calculate themixture fraction variance in three diffusion flames and the best coefficients for each flamehave been presented Besides for the first time a new model is proposed which is derivedfrom the transport equation of mixture fraction dissipation rate In this model it is assumedthat the diffusion and convection terms in the transport equation of the scalar dissipation cancel out each other therefore the method is very similar to the algebraic Reynolds stress

محسن دوازده امامي

محمود اشرفي زاده

محمدرضا سليم پور، احمد صداقت