共查询到19条相似文献,搜索用时 156 毫秒
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任意马赫数非定常流动数值模拟的统一算法 总被引:2,自引:0,他引:2
发展适用于从低速到高速任意马赫数非定常流动数值模拟的统一算法.通过引入一个伪时间导数项和一个新的预处理矩阵,得到双时间非定常预处理可压缩Navier-Stokes方程.方程的对流项采用三阶Roe通量近似差分格式离散,粘性项采用二阶中心差分格式离散.基于数值通量的线性化技术,实现伪时间步的隐式ADI-LU格式迭代,进而获得物理时间步的二阶推进精度.重点以低马赫数流动为例,求解了圆柱绕流和NACA0015翼型等速上仰动态失速问题.计算结果表明该统一算法能够较好地模拟低马赫数乃至任意马赫数非定常流动. 相似文献
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水下涡流场对声波的散射问题是声波在复杂流场中传播的基本问题,在水下目标探测和流场声成像领域具有重要意义.针对水下低频振荡涡流场声散射调制问题建立了理论分析模型与数值计算方法,探究了其声散射调制声场的产生机理与时空频特性.首先,基于运动介质的波动方程,通过引入势函数将波动方程分解为流声耦合项和非耦合项,并对流声耦合项进行频域分析处理,揭示了水下振荡涡流场的声散射调制机理;其次,采用间断伽辽金数值方法对水下低频振荡涡流场中声传播过程进行了数值模拟,分析了低马赫数条件下,不同入射声波频率、涡流场的振荡频率和涡核尺度对涡流场声散射调制声场时空频特性的影响规律,并结合理论分析模型对其特性进行了解释.研究表明:低马赫数下,振荡涡流场对声波的散射可产生包含涡流场振荡频率双边带调制谐波的散射调制声场,且随着入射声波频率、涡核尺度的增大,散射调制声场强度增强,总散射声场空间分布具有对称性和明显主瓣,且主瓣方位角趋近于入射波传播方向;在频率比远大于1条件下,涡流场振荡频率对散射调制声场强度影响较小. 相似文献
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在考虑了电子的反弹平均效应及高能电子的相对论效应下,通过数值求解电子的Fokker-Planck方程,研究了托卡马克等离子体中快波与电子回旋波电流驱动问题。采用九点差分法对方程进行离散,应用近似LU因子分解法对方程进行了数值求解。计算结果表明快波与电子回旋波联合电流驱动具有很强的协同效应,在两波联合电流驱动下,驱动电流大于单波电流驱动之和。 相似文献
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《Journal of sound and vibration》1998,210(3):391-401
The differential equations governing the transmission of one-dimensional sound waves in a non-uniform duct carrying a subsonic compressible mean flow have been the subject of a recent debate [1, 2]. Of the two formulations presented, one is considered to be non-acoustical and the other as neglecting the spatial variation of the speed of sound. The present paper shows that both formulations are acoustical and represent valid approximations to correct conditions for isentropic sound propagation in a subsonic low Mach number duct. Each formulation is associated with an “error wave”, which is essentially a hydrodynamic wave when the mean flow Mach number is small. Three-port modelling is required, however, to capture this wave when the Mach number of the mean flow is relatively large and a numerical matrizant approach is described which can be used for this purpose. 相似文献
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F. Grisch P. Bouchardy M. Péalat B. Chanetz T. Pot M. C. Coët 《Applied physics. B, Lasers and optics》1993,56(1):14-20
Rotational temperature and nitrogen number density are measured in the shock wave/boundary layer interaction region in the vicinity of a two-dimensional compression corner disposed in a low pressure, 55 K, Mach 10 hypersonic air flow. Spatially-resolved data are recorded using a nonlinear optical technique named dual-line coherent anti-Stokes Raman scattering (DLCARS). Averaged temperature and density profiles are compared with those predicted by a Navier-Stokes solver. Good agreement is found. 相似文献
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为考察气体第二粘性(体积粘性)对正激波内部流动的影响机制,数值求解含第二粘性的一维Navier-Stokes方程组.结果表明:第二粘性对激波内部的密度、热流和能量分布等物理量具有抹平效应,导致热流和熵流的峰值减小、激波厚度增加,体积粘性耗散的增加使得一部分机械能转化为内能;考虑第二粘性所计算的密度分布和激波厚度大为改善,与实验数据吻合较好;当马赫数为1.2≤Ma≤10,激波内部的Knudsen数满足0.12≤Kn≤0.4,对于马赫数Ma≤4.0的激波内部流动,考虑第二粘性的连续流Navier-Stokes方程组能够准确地模拟正激波结构. 相似文献
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高超音速进气道粘性流场的分块计算 总被引:1,自引:0,他引:1
本文采用一种隐式迎风型TVD格式求解二维Navier—Stokes方程,使用分块技术数值模拟了某超音速进气道在飞行马赫数2.291和2.557两种状态下的流动,给出了该进气道的内外流场结构、捕获面积比、表面压力分布、总压恢复系数等等。 相似文献
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An exact solution for one-dimensional acoustic fields in ducts in the presence of an axial mean temperature gradient and mean flow is presented in this paper. The analysis is valid for mean Mach numbers such that the square of the mean Mach number is much less than one. The one-dimensional wave equation for ducts with axial mean temperature gradient and mean flow is derived. By appropriate transformations, the wave equation is reduced to an analytically solvable hypergeometric differential equation for the case of a linear mean temperature profile. The developed solution is applied to investigate the dependence of sound propagation in a duct on factors such as temperature gradient and mean flow. The results obtained using the analytical solution compare very well with the numerical results. The developed solution is also compared with an existing analytical solution. 相似文献
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R Waxler 《The Journal of the Acoustical Society of America》2001,109(6):2739-2750
The second-order time-averaged acoustics of a viscous, thermally conducting gas between closely spaced parallel plates is studied. The acoustic disturbance is studied by expanding the equations of fluid dynamics and heat transfer to second order in Mach number. The undisturbed state is allowed to have a nonzero temperature gradient. A set of coupled equations for the time-averaged pressure gradient, velocity, and temperature are obtained and solved. Particular attention is paid to the relation between the time-averaged mass flux and pressure gradient. An explicit expression is obtained relating the time-averaged pressure drop across a thermoacoustic stack to the time-averaged mass flux through the stack. 相似文献
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A kinetic equation with a relaxation time model for wave-particle collisions is considered. Similarly to the BGK-model of
gas dynamics, it involves a projection onto the set of equilibrium distributions, nonlinearly dependent on the moments of
the distribution function. Under a diffusive and low Mach number scaling the macroscopic limit is a generalization of the
incompressible Navier-Stokes equations, where the momentum equations are coupled to a diffusive equation for an energy distribution
function. By a moment approximation, this system can be related to a low Mach number model of fluid mechanics, which already
appeared in the literature. Finally, for a linearized version corresponding to Stokes flow an existence result for initial
value problems is proved. 相似文献
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Guillaume Beardsell Guillaume Blanquart 《Proceedings of the Combustion Institute》2021,38(2):1923-1931
Thermo-acoustic instabilities remain problematic in the design of propulsion systems such as gas turbine engines, rocket motors, and ramjets. They arise from the constructive interaction of heat release rate and acoustic pressure oscillations, and can result in increased noise and mechanical fatigue. In the present work, we are concerned with the flame response to the thermodynamic fluctuations that accompany an incident acoustic wave. The objective is to investigate the flame dynamics under engine-relevant conditions using high-fidelity numerical simulations and detailed chemical kinetics. The focus is placed on the combustion of hydrogen and n-heptane, as they are both of practical interest and behave very differently when subjected to acoustic waves. We extract the phase and gain of the unsteady heat release response, which are directly related to the Rayleigh criterion and thus the stability of the system. We highlight the differences between results obtained using the fully compressible Navier-Stokes equations and the low Mach number approximation. The two simulation frameworks agree very well for acoustic wavelengths much larger than the flame thickness. However, they differ significantly at high frequencies. The gain erroneously reaches a plateau under the low Mach number approximation, while it decays to zero using the fully compressible framework. This difference is attributed to the spatial variations in the acoustic pressure, which are not captured by the low Mach number approximation. 相似文献