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为改善超燃冲压发动机液体燃料的雾化和混合效果,提出一种液体横向脉冲喷入超声速气流的喷注方式,并进行数值计算以探究射流脉动对一次破碎的影响.使用两相流大涡模拟(LES)算法计算超声速气流中液体的雾化,使用CLSVOF方法追踪气液界面,可压缩流动求解器求解气相,不可压缩求解器求解液相.结果表明:脉冲射流的表面破碎和液柱破碎都得到了增强,射流破碎长度显著缩短,在所研究的脉冲频率方案下,脉冲引起的不稳定性会替代Rayleigh-Taylor不稳定性,主导射流一次破碎;由于射流速度的脉动,脉冲射流的穿透深度相比于稳态射流可以提高20%,尾迹区宽度可以扩大25%,展现了更好的雾化和混合效果. 相似文献
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基于射流不稳定性理论系统研究了一个圆柱形可压缩气流喷入有限厚度的幂律流体的时间模式不稳定性.在对幂律流体本构方程线性近似的基础上,推导了表征轴对称模式幂律流体气流雾化射流不稳定性的色散方程.通过数值计算,分析了液相雷诺数、韦伯数、气/液密度比和速度比、气流马赫数以及幂律指数对于剪切变稀流体与剪切变稠流体两种情形气流雾化射流的不稳定性影响.结果表明:无论是剪切变稀情形还是剪切变稠情形,液体的黏性力总是抑制其不稳定性,减小幂律指数均可促进幂律流体气流雾化射流的不稳定性.随着气流速度的不断增大,由气/液相互运动导致的剪切波逐渐主导幂律流体气流雾化射流的不稳定性与破碎过程.当液相的参数保持不变,增大气流密度、气流速度以及气流可压缩性均可有效地促进幂律流体气流射流的破碎.空气动力是促进幂律流体射流破碎的有效措施.同时,对于一个小韦伯数,表面张力促进气体射流不稳定性;而随着韦伯数增大到临界值后,表面张力将会逐渐抑制其不稳定性. 相似文献
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基于Gerris网格自适应技术和高精度流体体积(VOF)函数方法,建立了受迫扰动的直喷雾化数值模型,分析了不同扰动频率和扰动幅度下高速柴油直喷雾化破碎过程及其喷雾场结构特征,获得了全场液滴的空间粒径分布.在理论和试验数据验证数值计算模型的基础上对受迫扰动直喷雾化特性和喷雾场结构进行了数值分析.结果表明:射流的频率响应影响可分为3个状态,当St0.3或St0.6时,射流的频率响应较弱,但雾化索特平均直径(SMD)及其分布集中程度比0.3St0.6时更好.此外,射流来流扰动幅度也会显著影响雾化效果.随着扰动幅度的增加,液柱破碎长度会急剧减小并最终趋于恒定,同时,雾化SMD及其分布集中程度也会得到明显改善. 相似文献
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柴油机喷油嘴内的残余气泡在一定程度上影响燃油的初期雾化效果,从而影响柴油机排放特性.采用高速可控闪光摄影技术拍摄了喷油器透明喷嘴孔内流动及近场喷雾,结果表明:在针阀开启之前,喷油嘴内部存在残余气泡;在喷射初期阶段,柴油喷雾结构呈现两种形态:传统的"蘑菇"形态和前端带有细长液丝的"蘑菇"形态,第一种形态出现概率远大于第二种.基于可压缩流体体积函数(VOF)多相流模型,采用大涡模拟方法,研究残余气泡对初期喷射阶段射流破碎的影响,结果表明:残余气泡的初始位置对初期射流雾化形态有显著影响;当残余气泡处于喷孔前端时射流前端会形成初始尖端,尖端周围涡环运动使其拉伸形成细长液丝,从而形成第二种射流形态. 相似文献
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喷雾的应用领域非常广泛,在汽车、航空航天、军事装备等动力装置的燃烧室中,液体雾化能够明显增大液体与气体接触的表面积,使随之发生的燃烧、传质传热过程大为加强。因此,雾化机理的研究对于实际喷雾和燃烧系统的设计和改进是十分重要的。喷射射流的一级碎裂是当今国际流体与燃烧学界研究的热点和难点,对其进行不稳定性研究异常繁复,每进展一步都是难能可贵的,至今尚未完善。本文将系统研究液体喷射的多级表面波、气液交界面的瑞利波和泰勒波、表面波的时间、空间和时空模式、扰动的维数、线性和非线性不稳定性理论等喷雾理论中的深层次问题。 相似文献
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设计搭建了喷油器试验平台,采用数码相机和高放大倍数、高分辩率的长距离显微镜成像技术,对燃油近场区域射流破碎进行可视化试验.并以试验工况下的流动为研究对象,基于开源计算流体动力学(CFD)软件OpenFOAM对针阀启闭过程近场射流破碎进行了数值模拟.结果表明:喷油初期,针阀开启后燃油撞击喷孔内初始气泡造成近场初始射流不同破碎形态,初始气泡大小以及位置导致近场初始射流头部不同结构形态;射流表面形成不稳定的表面波以及表面波的增长导致了近场区射流初始破碎、射流与环境气体的交互作用,加速射流破碎以及液丝、液滴的形成,在射流表面液丝和液滴剥离处存在较强的微尺度湍流,该区域具有较高的湍动能和亚网格涡黏系数;喷油末期,随着针阀关闭射流逐渐收缩,最终形成较粗液丝状,并呈非轴对称摆动. 相似文献
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可压缩气体中的三维黏性液体射流雾化机理 总被引:3,自引:0,他引:3
建立了可压缩气体中的三维黏性液体射流雾化数学模型,在射流雾化过程中起控制作用的参数主要有气液速度、气液密度、气液界面表面张力、液体黏性、喷嘴直径及音速.采用线性空间稳定性分析方法详细分析了这些参数在高速射流雾化过程中不稳定性的作用.结果是:增加液体射流速度、气体密度及喷嘴直径;减少液体密度、液体黏性及表面张力,可使射流不稳定性增强.此外,当气流与液体射流反向时增加气体流速也可以使流动不稳定性增强,但当气流与液体射流同向时结果相反.气体可压缩性的增加使流动变得不稳定,但它的影响是很小的. 相似文献
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This paper analyzes the behavior of coating particle as Well as the gas flow both of inside and outside the High-Velocity Oxy-Fuel (HVOF) thermal spraying gun by using quasi-one-dimensional analysis and numerical simulation. The HVOF gun in the present analysis is an axisymmetric convergent-divergent nozzle with the design Mach number of 2.0 followed by a straight passage called barrel. In the present analysis it is assumed that the influence of the particles injected in the gas flow is neglected, and the interaction between the particles is also neglected. The gas flow in the gun is assumed to be quasi-one-dimensional adiabatic flow. The velocity, temperature and density of gas in the jet discharged from the barrel exit are predicted by solving Navier-Stokes equations numerically. The particle equation of motion is numerically integrated using three-step Runge-Kutta method. The drag coefficient of the particle is calculated by linear interpolation of the experimental data obtained in the past. Particle 相似文献
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Numerical Simulation of the Supersonic Flows in the Second Throat Ejector —Diffuser Systems 总被引:1,自引:0,他引:1
INTRODUCTIONThe ejector system is a device which employs ahigh-velocity primary motive fluid to enirain and accelerate a slower moving secondary fluid. The resulting kinetic energy of the mixture is subsequently usedfor self-compression to a higher pressure, thus performing the function of a compressor. The ejectorsystem has lOng been applied to jet pumps, vacuumpumps, high-altitude simulators, V/STOLs, etc[lrv4],because of the major advantages of its structural simplicity and reliabili… 相似文献
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Heuy-Dong kim 《热科学学报(英文版)》1999,(2)
INTRODUCTIONUnloosetheconvenhonalfluidmachineryinwhichusuallyhavesomerotatingormovingparts,theejectorisadevicewhichemploysahigh-velocityprimalmotivefluidtoentrainandaccelerateasecondalsuctionfluidwhichmovesslower.Theresulhngkinehcenergyofthefutureissubsequentlyusedforself-compressiontOahigherPressure,thusPerformingthefunchonofacompressor.TheejectorsystemhaslongbeenappliedtOjetpumps,vacuumPumps,high-altitUdesimulators,V/STOLs,etc['-'l;becauseofthemajoradvantagesofitsstrUcturalsimplicit… 相似文献
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FlowPatternsandThermalDraginSupersonicDuctFlowwithHeating¥Zeng-YuanGuo;Zhi-HongLiu(DepartmentofEngineeringMechanics,TsinghuaU... 相似文献
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Navier—Stokes Computations of the Supersonic Ejector—Diffuser System with a Second Throat 总被引:3,自引:0,他引:3
The supersonic ejector-diffuser system with a second throat was simulated using CFD.An explicit finite volume scheme was applied to solve two-dimensional Navier-Stokes equations with standard κ-εturbulence model.The vacuum performance of the supersonic ejector-diffuser system was investigated by changing the ejector throat area ration and the operating pressure ratio.Two convergent-divergent nozzles with design Mach number of 2.11 and 3.41 were selected to give the supersonic operation of the ejector-diffuser system.The presence of a second throat strongly affected the shock wave structure inside the mixing tube as well as the spreading of the under-expanded jet discharging from the primary nozzle.There were optimum values of the operating pressure ratio and ejector throat area ratio for the vacuum performance of the system to maximize. 相似文献
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This paper describes an experimental work to investigate the effect of a reflector on supersonic jet noise radiated from a convergent-divergent nozzle with a design Mach number 2.0. In the present study, a metal reflector and reflectors made of three different sound-absorbing materials (grass wool and polyurethane foam) were employed, and the reflector size was varied. Acoustic measurement is carried out to obtain the acoustic characteristics such as frequency, amplitude of screech tone and overall sound pressure level (OASPL). A high-quality schlieren optical system is used to visualize the detailed structure of supersonic jet. The results obtained show that the acoustic characteristics of supersonic jet noise are strongly dependent upon the jet pressure ratio and the reflector size. It is also found that the reflector with sound-absorbing material reduces the screech tone amplitude by about 5-13dB and the overall sound pressure levels by about 2-5dB, compared with those of the metal reflector. 相似文献
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IntroductionMixing of fuel with oxidizer and their combustionare encountered in many engineering applicationsincluding hypersonic propulsion system in space vehicles.Particularly, the fuel injection scheme in hypersonicvehicles incorporating Scramet (Supersonic CombustionRamjet) engines, requires special attention for efficientmixing and stable combustion. Though a considerablenumber of researches has been cwhed out on ndxing andcombustion of fuel with oxidizer in Scramet program,still it fa… 相似文献
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The results of experimental research of multi-injector combustors in the regime of the attached pipe are presented. As a source
of high-enthalpy working gas (air), hot shot wind tunnel IT-302M of ITAM, the Siberian Branch of the Russian Academy of Sciences
was used. Tests have been carried out at Mach numbers 3, 4 and 5, in a range of change of total temperature from 2000K up
to 3000K and static pressure from 0.08MPa up to 0.23MPa. Injector section has been manufactured in two versions with a various
relative height of wedge-shaped injectors with parallel fuel injection. Influence of conditions on the entrance of the combustion
chamber on ignition and a stable combustion of hydrogen was investigated. Intensive combustion of hydrogen has been received
only at Mach numbers 3 and 4. Advantage of injector section with the greater relative height of injectors is revealed. The
mechanism of fuel ignition in the combustion chamber of the given configuration was investigated: two-step ignition process
including “kindling” and intensive combustion over all channel volume. 相似文献
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Effect of Nonequilibrium Homogenous Condensation on Flow Fields in a Supersonic Nozzle 总被引:1,自引:0,他引:1
INTRODUCTIONManystudies[1-131onthecondensationshockwaveoccurringinthecaseoftheraPidexPansionofmoistairorsteaminasupersonicnozzlehavebeenper-formed,andthecharacteristicsofcondensationshock'wavehavenearlybeenclarilied.Acondensationshockwavealsooccursinthebladepassageinasteamturbinel14,15]andsuchacondensationshockwavinteractswiththeboundarylayeronthesurfaceoftheblade.Thus,thefiowinthebladepassageofthesteamturbinewiththecondensationshockwavehasnotyetbeenclariliedl16'17].InthepreseDtstudythee… 相似文献
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