共查询到16条相似文献,搜索用时 562 毫秒
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利用线性不稳定性理论研究了旋转气体介质对黏性环膜液体射流破碎的影响。研究结果表明,无论是轴对称模式还是非轴对称模式,由液体环膜内部气体介质旋转所产生的离心力是液体射流的失稳因素,有助于液体射流的破碎。另外,由液体环膜外部气体介质旋转所产生的离心力是液体射流的促稳因素,不利于液体射流的破碎。当相同强度的旋转同时存在于内部和外部气体介质中时,对于轴对称模式,内部气体介质的影响显著,而对于非轴对称模式,则外部气体介质的影响更为明显。通常情况下,非轴对称模式的扰动增长率强于轴对称模式的扰动增长率,因此会在环膜液体射流的破碎中占据主导地位。 相似文献
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环膜液体射流的破碎机理研究对于GDI汽油机的雾化过程具有重要的意义。利用线性不稳定性理论研究了旋转气体运动对低阶和高阶模式黏性环膜液体射流破碎的影响。对于色散方程的数值计算结果表明,无论是对称模式还是非对称模式,低阶模式的扰动增长率通常较之高阶模式要大得多,但较之低阶模式扰动,高阶模式对气体旋转运动更为敏感。研究结果同时表明,对于非对称模式,无论是低阶模式还是高阶模式的扰动,气体旋转运动都是液体破碎的失稳因素;对于对称模式,气体旋转运动是低阶模式扰动的促稳因素,然而却是高阶模式扰动的强烈的失稳因素。 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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利用线性热不稳定性理论,对黏性液体射入高温气体介质模型所对应的色散方程进行了数值求解。利用所得到的计算结果,研究了加热条件下轴对称模式扰动液体射流破碎机理,探讨了表征各种影响射流破碎作用力的无量纲Weber数(We)、密度比(Q)、Marangoni数(Ma)和Ohnesorge数(Z)对液体射流破碎最大扰动增长率及占优波数的影响。研究结果表明,液体和气体介质之间的温度梯度对液体射流稳定性有着非常显著的影响,表明热毛细力对于液体射流的破碎有促进作用,这种作用对处于Taylor模式下的液体射流尤为显著,并且这种热力作用可使液体射流从一种模式进入另一种模式,并可以大大改变射流的破碎尺序。 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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本文分析粘性液体射流的线性稳定性问题,本文首次根据理论预测所确定的物理条件观察到了射流在各种非轴对称模式支配下的破碎情况,实验采用的是高速公路分幅激光全息技术,实验结果表明,液体射流结构遵守稳定性理论所预测的规律,实验还发现,液体射流的实际破碎尺寸要大于线性稳定必伯预测结果。 相似文献
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A spatial linear instability analysis is conducted on an annular viscous liquid jet injected into compressible gases and a three-dimensional model of the jet is developed. The model takes into account differences between the velocities, densities of the gases inside and outside of the liquid jet. Theoretical analysis reveals that there exist 9 dimensionless parameters controlling the instability of the liquid jet. Numerical computations reveal some basic characteristics in the breakup and atomization process of the liquid jet as well as influences of these relevant parameters. Major observations and findings of this study are as follows. The Mach number plays a destabilizing role and the inner Mach number has a greater effect on the jet instability than the outer Mach number. The Reynolds number always tends to promote the instabilities of the liquid jet, but its influence is very limited. The Weber number and the gas-to-liquid density ratio also have unstable effects and can improve the atomization of liquid jets. Furthermore, the effects of the Weber number and gas-to-liquid density ratio on the maximum growth rates of axisymmetric and non-axisymmetric disturbances and corresponding dominant wave numbers are manifested in a linear way, while that of the Mach number is non-linear. The effect of Reynolds on the maximum growth rates is non-linear, but the dominant wavenumber is almost not affected by the Reynolds number. 相似文献
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A spatial linear instability analysis is conducted on an annular viscous liquid jet injected into compressible gases and a
three-dimensional model of the jet is developed. The model takes into account differences between the velocities, densities
of the gases inside and outside of the liquid jet. Theoretical analysis reveals that there exist 9 dimensionless parameters
controlling the instability of the liquid jet. Numerical computations reveal some basic characteristics in the breakup and
atomization process of the liquid jet as well as influences of these relevant parameters. Major observations and findings
of this study are as follows. The Mach number plays a destabilizing role and the inner Mach number has a greater effect on
the jet instability than the outer Mach number. The Reynolds number always tends to promote the instabilities of the liquid
jet, but its influence is very limited. The Weber number and the gas-to-liquid density ratio also have unstable effects and
can improve the atomization of liquid jets. Furthermore, the effects of the Weber number and gas-to-liquid density ratio on
the maximum growth rates of axisymmetric and non-axisymmetric disturbances and corresponding dominant wave numbers are manifested
in a linear way, while that of the Mach number is non-linear. The effect of Reynolds on the maximum growth rates is non-linear,
but the dominant wavenumber is almost not affected by the Reynolds number. 相似文献
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In this paper, the integral method is used to derive a complete set of results and expressions for selected physical turbulent properties of a non-buoyant jet or momentum-dominated buoyant jet regime of small-scale hydrogen leakage. Several quantities of interest, including the cross-stream velocity, Reynolds stress, velocity-concentration correlation (radial flux), dominant turbulent kinetic energy production term, turbulent eddy viscosity and turbulent eddy diffusivity are obtained. In addition, the turbulent Schmidt number is estimated and the normalized jet-feed material density and the normalized momentum flux density are correlated. Throughout this paper, experimental results from Schefer et al. [Schefer RW, Houf WG, Williams TC. Investigation of small-scale unintended releases of hydrogen: momentum-dominated regime. Int J Hydrogen Energy 2008;33(21):6373–84] and other works for the momentum-dominated jet resulting from small-scale hydrogen leakage are used in the integral method. For a non-buoyant jet or momentum-dominated regime of a buoyant jet, both the centerline velocity and centerline concentration are proportional with z−1. The effects of buoyancy-generated momentum are assumed to be small, and the Reynolds number is sufficient for fully developed turbulent flow. The hydrogen–air momentum-dominated regime or non-buoyant jet is compared with the air–air jet as an example of non-buoyant jets. Good agreement was found between the current results and experimental results from the literature. In addition, the turbulent Schmidt number was shown to depend solely on the ratio of the momentum spread rate to the material spread rate. 相似文献