شبيه سازي عددي احتراق مغشوش در مشعل كانال به روش مدل فليملت آرام پايا و گذرا

چكيده انگليسي :

425 Numerical Simulation of Turbulent Combustion in Duct Burner Using Steady and Unsteady Laminar Flamelet Model Fardad Ghanati F ghanati@me iut ac ir Date of Submission 2015 07 26 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor Mohsen Davazdah Emami Mohsen@cc iut ac irAbstractIn recent years reducing environmental pollution caused by combustion in transportation and industrialburners systems has been a major concern Predicting accurate values of the temperature and products in acombustion field is essential for specifying the pollutants concentrations Therefore modeling and simulatingturbulent combustion flows have been the focus of many researches In order to simulate turbulent reactingflows an appropriate combustion model is required Due to separating chemical reactions calculations fromthe solution of turbulent flow field flamelet model provides the possibility to consider chemical kinetic withany level of complexity Therefore different chemical mechanisms can be analyzed through this model Thepurpose of this research is to study the application of steady and unsteady flamelet model in simulating severalcases such as bluff body pilot and duct burner turbulent diffusion flames The most important feature of thisresearch is a precise prediction of pollutants such as NO and CO by using unsteady flamelet model as themost appropriate model represented in this field Developing Eulerian particle unsteady model from oneparticle to several particles is another aim of this research For this purpose a database entitled flameletlibrary has been primarily created for steady state combustion from which temperature and mass fractionquantities of chemical components can be extracted This flamelet library has been obtained through solvingsteady flamelet equations for non premixed flames in mixture fraction space The effects of turbulent flowon these quantities have been considered by the means of probability density functions The influences oftime have been considered in a post processing way using Eulerian particle flamelet model In this model forcreating unsteady flamelet library a parameter known as surface averaged conditional scalar dissipation rateis required which has been obtained by considering a virtual unreal index particle in order for findingunsteady flamelets The probability of finding flamelet or unsteady flamelets can be determined by solvingEulerian transfer equation which includes unsteady diffusion and convection terms The results indicate thatthe predictions of temperature field and mass fraction of main components using steady flamelet model retainan acceptable concordance with empirical results However the simulation with steady flamelet modeloverestimates the mass fraction of NO and CO components and using unsteady solution provides betterresults for them Furthermore using several unsteady flamelet in pilot flame leads into a noticeabledevelopment in the results Contrary to CO NO expresses sensitivity toward chemical mechanism Considering Lewis number 1 for flamelet equations is an acceptable assumption regarding the turbulent flow and would provide better results compared to differential diffusion effect KeywordsPollutant Turbulent combustion Flamelet model probability density function NO and

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شبيه سازي عددي احتراق مغشوش در مشعل كانال به روش مدل فليملت آرام پايا و گذرا

آلاينده , توابع چگالي احتمال , گونه هاي NO و CO