高韦伯数下煤油液滴的破碎机理研究
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摘要
为了探究高韦伯数下气流速度及液滴初始直径对液滴破碎以及Rayleigh-Taylor不稳定波的影响,进行了煤油单液滴在气流中破碎的实验,采用高速摄影技术记录了液滴的破碎过程,应用包含粘性和表面张力的Rayleigh-Taylor不稳定性理论分析了液滴的破碎过程,对Rayleigh-Taylor不稳定波波长与液滴破碎时间进行了理论计算,并与实验结果做了对比研究。结果表明:当We为321左右时,煤油液滴开始呈现灾型破碎模式;气流速度、液滴初始直径对液滴表面的最大增长率Rayleigh-Taylor不稳定波的波长、增长率和临界波长均有影响;RayleighTaylor不稳定性理论在预测最不稳定波长时,结论与实验结果的误差不超过6%;取经验参数M为8.9时,液滴破碎时间理论与实验误差最小。
In order to study the influence of the airstream velocity and droplet initial diameter on the secondary atomization process and the Rayleigh-Taylor wave,the experiment of recording the breakup process of a kerosene droplet at high Weber numbers was conducted,where the photographs were taken by a high speed camera.The analysis based on the Rayleigh-Taylor instability theory which includes viscosity and surface tension was done.The calculation was conducted in order to predict the wavelength of the most unstable Rayleigh-Taylor wave and breakup time,and the results were compared with the experimental data.The results indicate that the catastrophic breakup takes place when the Weber number is greater than 321.The airstream velocity and droplet initial diameter have great influence on the wavelength of the Rayleigh-Taylor wave with the maximum growth rate,the growth rate and the critical wavelength.The Rayleigh-Taylor instability theory which contains the viscosity and surface tension fits the experimental data well when being used to predict the wavelength of the most unstable Rayleigh-Taylor wave,the error less than 6%.Setting the value of M to be 8.9can minimize the breakup time error.
In order to study the influence of the airstream velocity and droplet initial diameter on the secondary atomization process and the Rayleigh-Taylor wave,the experiment of recording the breakup process of a kerosene droplet at high Weber numbers was conducted,where the photographs were taken by a high speed camera.The analysis based on the Rayleigh-Taylor instability theory which includes viscosity and surface tension was done.The calculation was conducted in order to predict the wavelength of the most unstable Rayleigh-Taylor wave and breakup time,and the results were compared with the experimental data.The results indicate that the catastrophic breakup takes place when the Weber number is greater than 321.The airstream velocity and droplet initial diameter have great influence on the wavelength of the Rayleigh-Taylor wave with the maximum growth rate,the growth rate and the critical wavelength.The Rayleigh-Taylor instability theory which contains the viscosity and surface tension fits the experimental data well when being used to predict the wavelength of the most unstable Rayleigh-Taylor wave,the error less than 6%.Setting the value of M to be 8.9can minimize the breakup time error.
引文
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[2]曹建明.喷雾学[M].北京:机械工业出版,2005:10-11.Cao J M.Atomization[M].Beijing:Publishing House of Mechanical Industry,2005:10-11.
[3]Hsiang L P,Faeth G M.Drop deformation and breakup due to shock wave and steady disturbances[J].International Journal of Multiphase Flow,1995,21(4):545-560.
[4]刘静.超声速气流中横向燃油喷雾的数值模拟和实验研究[D].北京:北京航空航天大学,2010.Liu J.Numerical and experimental investigation of fuel spray in supersonic cross flow[D].Beijing:Beihang University,2010.
[5]Guildenbecher D R,López-Rivera C,Sojka P E.Secondary atomization[J].Experiments in Fluids,2009,46(3):371-402.
[6]Liu A B,Reitz R D.Mechanisms of air-assisted liquid atomization[J].Atomization&Sprays,1993,3(1):55-75.
[7]Hwang S S,Liu Z,Reitz R D,et al.Breakup mechanisms and drag coefficients of high-speed vaporizing liquid drops[J].Atomization&Sprays,1996,6(3):353-376.
[8]Joseph D D,Beavers G S,Funada T.Rayleigh-Taylor instability of viscoelastic drops at high Weber numbers[J].Journal of Fluid Mechanics,1999,453(6):109-132.
[9]Joseph D D,Belanger J,Beavers G S.Breakup of a liquid drop suddenly exposed to a high-speed airstream[J].International Journal of Multiphase Flow,1999,25(6-7):1263-1303.
[10]Theofanous T G,Li G J,Dinh T N.Aerobreakup in rarefied supersonic gas flows[J].Journal of Fluids Engineering,2004,126(4):516-527.
[11]蒋德军,赵辉,刘海峰,等.黏性流体的二次雾化特性[J].石油学报:石油加工,2011,27(4):575-582.Jiang D J,Zhao H,Liu H F,et al.Experimental characteristics of viscous fluid secondary breakup[J].Acta Petrolei Sinica(Petroleum Processing Section),2011,27(4):572-582.
[12]赵辉.同轴气流式雾化机理研究[D].上海:华东理工大学,2012.Zhao H.Studying on the mechanism of coaxial air-blast atomization[D].Shanghai:East China University of Science and Technology,2012.
[13]Shraiber A A,Podvysotsky A M,Dubrovsky V V.Deformation and breakup of drops by aerodynamic forces[J].Atomization&Sprays,1996,6(6):667-692.
[14]Taylor G I.The shape and acceleration of a drop in a high speed air stream[J].The Scientific Papers of GI Taylor,1963,3:457-464.
[15]Chandrasekhar S.Hydrodynamic and hydromagnetic stability[D].London:Oxford University Press,1961.
[16]Orourke P J,Amsden A A.The TAB method for numerical calculation of spray droplet breakup[C].International Fuels and Lubricants Meeting and Exposition,Toronto,Ontario,1987:1.
[17]Lopez R C.Secondary breakup of inelastic non-Newtonian liquid drops[D].Indiana:Purdue University,2010.