湍流燃燒模擬ppt課件-在線瀏覽
2025-06-18 08:37本頁(yè)面
【正文】 e species. ? Accounts for dissociation effects. ? Accounts for coupling between turbulence and chemistry. ? Does not require the solution of a large number of species transport equations ? Robust and economical ? Disadvantages: ? System must be near chemical equilibrium locally. ? Cannot be used for pressible or nonturbulent flows. ? Not applicable to premixed systems. Partially Premixed Combustion Model(部分預(yù)混燃燒模型 ) ? 該模型針對(duì)預(yù)混和非預(yù)混燃燒都存在的湍流反應(yīng)流動(dòng)。 The Laminar Flamelet Model ? Temperature, density and species (for adiabatic) specified by two parameters, the mixture fraction and scalar dissipation rate ? Recall that for the mixture fraction PDF model (adiabatic), thermochemical state is function of f only ? c can be related to the local rate of strain ? Extension of the mixture fraction PDF model to moderate chemical nonequilibrium ? Turbulent flame modeled as an ensemble of stretched laminar, opposed flow diffusion flames 2)/( xf ???c),( c?? fii ?將湍流火焰看成嵌入湍流流場(chǎng)內(nèi)的局部具有一維結(jié)構(gòu)的薄層流火焰。 Laminar Flamelet Model (2) ? Statistical distribution of flamelet ensemble is specified by the PDF P(f,c), which is modeled as Pf (f) Pc (c), with a Beta function for Pf (f) and a Diracdelta distribution for Pc (c) ? Only available for adiabatic systems in V5 ? Import strained flame calculations ? prePDF or Sandia’s OPPDIF code ? Single or multiple flamelets ? Single: user specified strain, a ? Multiple: strained flamelet library, 0 a aextinction ? a=0 equilibrium ? a= aextinction is the maximum strain rate before flame extinguishes ? Possible to model local extinction pockets (. lifted flames) ??? ?? 10 0)()(),( dfdPfPf fii ccc?? c模型的應(yīng)用 ? 層流小火焰模型在湍流預(yù)混燃燒和湍流擴(kuò)散燃燒中表達(dá)形式有很大不同； ? 在湍流擴(kuò)散燃燒中，輸運(yùn)方程中無化學(xué)反應(yīng)源項(xiàng)，可以唯一地確定燃燒狀態(tài)的守恒標(biāo)量是混合分?jǐn)?shù)，攝動(dòng)參量是標(biāo)量的耗散率； ? 在湍流預(yù)混燃燒的層流小火焰模型中，輸運(yùn)方程中無源項(xiàng)的可以唯一確定燃燒狀態(tài)的守恒標(biāo)量是描述火焰面位置的標(biāo)量，攝動(dòng)變量為使層流火焰面皺褶的變形率。 不論是在湍流擴(kuò)散燃燒中 ,還是在湍流預(yù)混燃燒中 , Premixed Combustion Model（預(yù)混燃燒模型） ? 主要針對(duì)純預(yù)混湍流燃燒問題，在這些問題中，反應(yīng)物和生成物由火焰峰面隔開，該模型通過求解各種反應(yīng)過程參數(shù)來預(yù)測(cè)火焰峰面的位置 。 The Zimont Model for Premixed Combustion ? Thermochemistry described by a single progress variable, ? Mean reaction rate, ? Turbulent flame speed, Ut, derived for lean premixed bustion and accounts for ? Equivalence ratio of the premixed fuel ? Flame front wrinkling and thickening by turbulence ? Flame front quenching by turbulent stretching ? Differential molecular diffusion ? For adiabatic bustion, ? The enthalpy equation must be solved for nonadiabatic bustion ? ? ? ??? ? ?? ? ?? ? ? ??t c x u c x Sc cx R ciiitt ic??????? ??????? ? ? ?0 1R U cc unburnt t? ????? p adpp p YYc /adu n b u r n t TcTcT ??? )1(第三部分 Fluent軟件中的湍流燃燒模擬 Applications ? Wide range of homogeneous and heterogeneous reacting flows ? Furnaces ? Boilers ? Process heaters ? Gas turbines ? Rocket engines ? Predictions of: ? Flow field and mixing characteristics ? Temperature field ? Species concentrations ? Particulates and pollutants Temperature in a gas furnace CO2 mass fraction Stream function Aspects of Combustion Modeling Dispersed Phase Models Droplet/particle dynamics Heterogeneous reaction Devolatiliz
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