随机分布介尺度油滴群的燃烧特性
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摘要
对液雾燃烧中随机分布油滴群的蒸发/燃烧特性进行了数值模拟研究,详细考虑了油滴尺寸、坐标分布、数密度等相关参数的随机性。采用一步总包反应机理对其进行大涡模拟,在不同的来流速度、环境温度下,剖析了不同数密度油滴群的阻力特性及蒸发率,并结合油滴群燃烧模态分析油滴间的相互作用规律。研究表明,油滴群燃烧模态同时包含单油滴三种油滴燃烧火焰模态;各油滴表面燃料蒸气的浓度分布呈现非对称性,反应核心区发生角度偏转;在强对流环境下,蒸发/燃烧油滴群的平均表面蒸发率与阻力系数的变化与蒸发/燃烧单油滴相似,油滴间的强烈相互作用加速了油滴群蒸发/燃烧的传热传质。
The evaporation/combustion characteristics of randomly distributed droplets in spray combustion were studied numerically,the randomness of the droplet size,coordinate distribution and number density was considered in detail.The large eddy simulation was carried out by the one step general package reaction mechanism,while the resistance characteristics and evaporation rate of droplets with different number density at different inflow rates and ambient temperatures were analyzed,and the interaction between droplets was analyzed in combination with the combustion modes.The results show that the combustion modes of the droplets include three flame modes(fully-enveloped flame,partially-enveloped flame and wake flame)of a single droplet at the same time.The concentration of ethanol vapor on the surface of each droplet presents asymmetrical distribution,and the core region of the reaction deflects at an angle.In the strongly convective environment,the variation of average surface evaporation rate and resistance coefficient of evaporation/combustion droplets is similar to that of a single evaporation/combustion droplet,the strong interaction between droplets could accelerates the heat and mass transfer of evaporation/combustion of droplets.
The evaporation/combustion characteristics of randomly distributed droplets in spray combustion were studied numerically,the randomness of the droplet size,coordinate distribution and number density was considered in detail.The large eddy simulation was carried out by the one step general package reaction mechanism,while the resistance characteristics and evaporation rate of droplets with different number density at different inflow rates and ambient temperatures were analyzed,and the interaction between droplets was analyzed in combination with the combustion modes.The results show that the combustion modes of the droplets include three flame modes(fully-enveloped flame,partially-enveloped flame and wake flame)of a single droplet at the same time.The concentration of ethanol vapor on the surface of each droplet presents asymmetrical distribution,and the core region of the reaction deflects at an angle.In the strongly convective environment,the variation of average surface evaporation rate and resistance coefficient of evaporation/combustion droplets is similar to that of a single evaporation/combustion droplet,the strong interaction between droplets could accelerates the heat and mass transfer of evaporation/combustion of droplets.
引文
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[19]周力行.燃烧理论和化学流体力学[M].北京:科学出版社,1986.
[2]KUO K K,ACHARYA R.Applications of turbulent and multiphase combustion[M].New Jersey:John Wiley&Sons Incorporation,2012.
[3]PETERS N.Multiscale combustion and turbulence[J].Proceedings of the Combustion Institute,2009,32(1):1-25.
[4]PARISI V,GIACONAZZI E,BRUNO C.Analysis of small scale turbulence-combustion interaction for LES modeling[R].AIAA 2005-1283,2005.
[5]SHINJO J,UMEMURA A.Droplet/turbulence interaction and early flame kernel development in an autoigniting realistic dense spray[J].Proceedings of the Combustion Institute,2013,34(2):1553-1560.
[6]KOURMATZIS A,PHAM P X,MASRIi A R.Characterization of atomization and combustion in moderately dense turbulent spray flames[J].Combustion&Flame,2015,162(4):978-996.
[7]SABELNIKOV V,FUREBY C.LES combustion modeling for high Re flames using a multi-phase analogy[J].Combustion&Flame,2013,160(1):83-96.
[8]CASTANET G,MAQUA C,ORAIN M,et al.Investigation of heat and mass transfer between the two phases of an evaporating droplet stream using laser-induced fluorescence techniques:comparison with modeling[J].International Journal of Heat&Mass Transfer,2007,50(17):3670-3683.
[9]CHIU H H.Advances and challenges in droplet and spray combustion:Ⅰtoward a unified theory of droplet aerothermochemistry[J].Progress in Energy&Combustion Science,2000,26(4):381-416.
[10]BILGER R W.A mixture fraction framework for the theory and modeling of droplets and sprays[J].Combustion&Flame,2011,158(2):191-202.
[11]CHEN W,GAO R,SUN J,et al.Modeling of an isolated liquid hydrogen droplet evaporation and combustion[J].Cryogenics,2018,96:151-158.
[12]ZHOU L X,LI K.Analytical and numerical studies on a single-droplet evaporation and combustion under forced convection[J].Acta Mechanica Sinica,2015,31(4):523-530.
[13]李科.液雾-空气两相湍流燃烧的多尺度模拟[D].北京:清华大学,2011.LI Ke.Multi-scale simulation of two-phase turbulent spray combustion[D].Beijing:Tsinghua University,2011.(in Chinese)
[14]周力行.两相燃烧的大模拟[J].中国科学(技术科学),2014,44(1):41-49.ZHOU Lixing.Large-eddy simulation of two-phase combustion[J].Scientia Sinica(Technologica),2014,44(1):41-49.(in Chinese)
[15]ZENG Z X,ZHOU L X,QI H Y.Large eddy simulation of particle wake effect and RANS simulation of turbulence modulation in gas-particle flows[J].Chinese Journal of Chemical Engineering,2007,15(1):12-16.
[16]ZHOU L X.Studies on evaporation and combustion of single droplet and spray combustion[D].Saint Petersburg,Russia:Saint Petersburg State Polytechnic University,1961.
[17]SANYAL A M D.Modeling of evaporation and combustion of droplets in a spray using the unit cell approach:a review[J].Heat Transfer Engineering,2012,33(4/5):375-386.
[18]SEGAWA D,YOSHIDA M,NAKAYA S,et al.Autoignition and early flame behavior of a spherical cluster of 49monodispersed droplets[J].Proceedings of the Combustion Institute,2007,31(2):2149-2156.
[19]周力行.燃烧理论和化学流体力学[M].北京:科学出版社,1986.