剪切稀化非牛顿射流撞击液膜破碎直接数值模拟
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摘要
液态射流撞击是液体火箭推进系统中广泛采用的一种燃料雾化方法,其破碎特征直接影响燃料最终的掺混及燃烧效率。采用直接数值模拟(DNS)工具,研究了低雷诺数(Rel=41)和中等韦伯数(Wel=163)条件下剪切稀化非牛顿射流撞击液膜破碎的问题,着重分析了对角液膜的三维结构、破碎特征和非牛顿特性等。研究结果表明:在所研究的射流参数下,该非牛顿撞击液膜破碎属于Open Rim类别,破碎过程具有三维特性并伴随液丝与边缘的融合、液丝向液滴的转变等时域流动特征。液体的总表面积随时间不断增长,但单位表面积随液膜破碎的发生而下降,液膜扩张半角随时间逐渐增加并趋于恒定值43°,而后部液膜的长度几乎不随时间发生变化。此外,撞击液膜表现出明显的剪切稀化特性,液体内部最低黏性系数仅为零剪切黏性系数的1/5。
Impinging liquid jets have been widely used in liquid rocket propulsion systems as a fuel atomization method.The breakup mechanism of impinging liquid jets directly affects the mixing and combustion efficiency of the fuel.In the present work,a Direct Numerical Simulation(DNS)tool is applied to study the sheet breakup formed by two impinging jets with nonNewtonian shear thinning properties under low Reynolds number(Rel=41)and moderate Weber number(Wel=163),including in particular the three-dimensional structure,breakup mechanism,and non-Newtonian feature of the diagonal liquid sheet.The results indicate that the breakup regime of the impinging sheet under current conditions belongs to the Open Rim type.Collison of ligament with rim as well as transition from ligament to droplet can be observed during the sheet breakup.The total liquid surface area increases with time,whereas the specific surface area decreases with the occurrence of sheet breakup.The half-expansion angle of the liquid sheet increases with time and eventually tends to be a constant 43°,but the length of the back sheet shows no tendency of change with time.Additionally,a strong shear thinning feature can be found within the liquid sheet,with the lowest viscosity of the liquid sheet being only 1/5 of that at zero shear rate.
Impinging liquid jets have been widely used in liquid rocket propulsion systems as a fuel atomization method.The breakup mechanism of impinging liquid jets directly affects the mixing and combustion efficiency of the fuel.In the present work,a Direct Numerical Simulation(DNS)tool is applied to study the sheet breakup formed by two impinging jets with nonNewtonian shear thinning properties under low Reynolds number(Rel=41)and moderate Weber number(Wel=163),including in particular the three-dimensional structure,breakup mechanism,and non-Newtonian feature of the diagonal liquid sheet.The results indicate that the breakup regime of the impinging sheet under current conditions belongs to the Open Rim type.Collison of ligament with rim as well as transition from ligament to droplet can be observed during the sheet breakup.The total liquid surface area increases with time,whereas the specific surface area decreases with the occurrence of sheet breakup.The half-expansion angle of the liquid sheet increases with time and eventually tends to be a constant 43°,but the length of the back sheet shows no tendency of change with time.Additionally,a strong shear thinning feature can be found within the liquid sheet,with the lowest viscosity of the liquid sheet being only 1/5 of that at zero shear rate.
引文
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[25]QIAN J,LAW C K.Regimes of coalescence and separation in droplet collision[J].Journal of Fluid Mechanis,1997,331(1):59-80.
[2]KAMPEN J,MADLENER K,CIEZKI H K.Characteristic flow and spray properties of gelled fuels with regard to the impinging jet injector type:AIAA-2006-4573[R].Reston,VA:AIAA,2006.
[3]MADLENER K,CIEZKI H K,KAMPEN J,et al.Characterization of various properties of gel fuels with regard to propulsion application:AIAA-2008-4870[R].Reston,VA:AIAA,2008.
[4]RAMASUBRAMANIAN C,NOTARO V,LEE J G.Characterization of near-field spray of nongelled-and gelled-impinging doublets at high pressure[J].Journal of Propulsion and Power,2015,31(6):1642-1652.
[5]FAKHRI S,LEE J G,YETTER R A.Atomization and spray characteristics of gelled-propellant simulants formed by two impinging jets:AIAA-2009-5241[R].Reston,VA:AIAA,2009.
[6]YANG L J,FU Q F,QU Y Y,et al.Breakup of a power-law liquid sheet formed by an impinging jet injector[J].International Journal of Multiphase Flow,2012,39:37-44.
[7]夏振炎,李珍妮,李建军,等,撞击式射流破碎特性的实验研究[J].天津大学学报,2016,49(7):770-776.XIA Z Y,LI Z N,LI J J,et al.An experimental study on breakup characteristics of impinging jets[J].Journal of Tianjin University,2016,49(7):770-776(in Chinese).
[8]杨伟东,张蒙正.凝胶推进剂流变及雾化特性研究与进展[J].火箭推进,2005,31(5):37-42.YANG W D,ZHANG M Z.Research and development of rheological and atomization characteristics of gelled propellants[J].Journal of Rocket Propulsion,2005,31(5):37-42(in Chinese).
[9]邓寒玉,封锋,武晓松,等.基于扩展TAB模型的凝胶液滴二次雾化特性研究[J].推进技术,2015,36(11):1734-1740.DENG H Y,FENG F,WU X S,et al.Characteristics of second atomization for gelled droplet based on extended TAB model[J].Journal of Propulsion Technology,2015,36(11):1734-1740(in Chinese).
[10]XIAO H,SHI Y,XU Z,et al.Atomization characteristics of gelled hypergolic propellant simulants[J].International Journal of Precision Engineering and Manufacturing,2015,16(4):743-747.
[11]MA D J,CHEN X D,KHARE P,et al.Atomization patterns and breakup characteristics of liquid sheets formed by two impinging jets:AIAA-2011-0097[R].Reston,VA:AIAA,2011.
[12]ZHU C X,ERTL M,WEIGAND B.Numerical investigation on the primary breakup of an inelastic non-Newtonian liquid jet with inflow turbulence[J].Physics of Fluids,2013,25(8):083102.
[13]刘虎,强洪夫,韩亚伟,等.幂律型凝胶推进剂射流撞击雾化SPH模拟[J].推进技术,2015,36(9):1416-1425.LIU H,QIANG H F,HAN Y W,et al.SPH simulation of atomization characteristics of power-law gelled propellant formed by two impinging jets[J].Journal of Propulsion Technology,2015,36(9):1416-1425(in Chinese).
[14]刘虎,强洪夫,王广.凝胶推进剂射流撞击雾化研究进展[J].含能材料,2015,23(7):697-708.LIU H,QIANG H F,WANG G.Review on jet impinging atomization of gelled propellant[J].Chinese Journal of Energetic Materials,2015,23(7):697-708(in Chinese).
[15]HIRT C W,NICHOLS B D.Volume of fluid(VOF)method for the dynamics of free boundaries[J].Journal of Computational Physics,1981,39(1):201-225.
[16]RIDER W J,KOTHE D B.Reconstructing volume tracking[J].Journal of Computational Physics,1998,141(2):112-152.
[17]SCHLOTTKE J,WEIGAND B.Direct numerical simulation of evaporating droplets[J].Journal of Computational Physics,2008,227(10):5215-5237.
[18]GOMMA H,KUMAR S,HUBER C,et al.Numerical comparison of 3Djet breakup using a compression scheme and an interface reconstruction based VOF-code[C]∥24th ILASS-Europe,2011.
[19]MOTZIGEMBA M,ROTH N,BOTHE D,et al.The effect of non-Newtonian flow behavior on binary droplet collisions:VOF-simulation and experimental analysis[C]∥18th ILASS-Europe,2002.
[20]FOCKE C,BOTHE D.Computational analysis of binary collisions of shear thinning droplets[J].Journal of NonNewtonian Fluid Mechanics,2011,166(14-15):799-810.
[21]SCHRDER J,LEDERER M L,GAUKEL V,et al.Effect of atomizer geometry and rheological properties on effervescent atomization of aqueous polyvinylphrrolidone solution[C]∥24th ILASS-Europe,2011.
[22]朱呈祥,尤延铖.横向气流中非牛顿液体射流直接数值模拟[J].航空学报,2016,37(9):2659-2668.ZHU C X,YOU Y C.Direct numerical simulation of a non-Newtonian liquid jet in crossflow[J].Acta Aeronautica et Astronautica Sinica,2016,37(9):2659-2668(in Chinese).
[23]朱呈祥,陈荣钱,尤延铖.低韦伯数非牛顿射流撞击破碎直接数值模拟[J].航空学报,2017,38(8):120764.ZHU C X,CHEN R Q,YOU Y C.Direct numerical simulation of impinging jet breakup with non-Newtonian properties at low Weber number[J].Acta Aeronautica et Astronautica Sinica,2017,38(8):120764(in Chinese).
[24]BATCHELOR G K.The theory of homogeneous turbulence[M].Cambridge:Cambridge University Press,1953:133-168.
[25]QIAN J,LAW C K.Regimes of coalescence and separation in droplet collision[J].Journal of Fluid Mechanis,1997,331(1):59-80.