Shock-induced energy transfers in dense gases
Shock-induced energy transfers in dense gases
复制标题
稠密气体中冲击引起的能量转移
DOI：
10.1088/1742-6596/821/1/012019
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Alferez N
中科院分区：
文献类型：
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作者：
Alferez N
稠密气体的特征在于分子具有大量的活性自由度（通过cv/R比量化）。在这种气体中，等熵线具有非常接近等温线的独特性质（在cv/R趋于无穷大的极限下，两者变得相同）。在液体-蒸气临界点附近，这使得等熵线非常浅，并且可能是凹的（在压力-比容图中）。虽然在设计膨胀机时需要采用浅等熵线（即，在几乎没有压降的情况下，可以实现较大的比容积增加），但这种极端的压缩性效应能否以深刻的方式改变湍流？本文讨论了两个特别有趣的方面：（i）激波折射性质（即激波重新分配入射扰动能量的方式），（ii）均匀湍流中的涡度拟能产生。对激波构形进行了线性干扰分析（LIA），将引入的扰动分解为可压缩欧拉方程的线性模态。相对于每个本征模式的传输系数解析求解和结果进行了比较完全非线性可压缩直接数值模拟再现弱扰动的孤立的二维压缩激波。线性分析被认为是能够预测的冲击引起的能量的重新分配的传入的扰动之间的不同的本征模式。非理想气体效应的观察分析和数值，特别是一个不寻常的选择性响应的一些特定的选择来马赫数。一个二维各向同性的湍流配置，然后数值研究的情况下，无粘可压缩稠密气体流接近液-汽临界点。强非理想气体涡激波的形成对涡度拟能产生的影响。在这两种情况下，接近液-汽临界点的非凸等熵线对激波和湍流重新分配湍流动能的影响是非常大的，而这在理想气体中是根本无法观察到的。这将有望激发湍流建模者（以及他们的最终用户？）的热情。
Dense gases are characterised by molecules featuring large numbers of active degrees of freedom (quantified by the c v/R ratio). The isentropes in such gases have the distinct property of following rather closely the isotherms (the two become identical in the limit of c v/R going to infinity). Near the liquid-vapour critical point, this makes the isentropes very shallow and possibly concave (in the pressure-specific volume diagram). Whilst shallow isentropes are desirable when designing expanders (ie a large specific-volume increase may be achieved for virtually no pressure drop), could such extreme compressibility effects modify turbulence in a profound manner? This paper discusses two particularly interesting aspects:(i) shock-refraction properties (ie the way a shock can redistribute the energy of incoming perturbations),(ii) enstrophy production in homogeneous turbulence. A linear interaction analysis (LIA) is conducted on the shock configuration for which the incoming perturbation is decomposed into linear modes of the compressible Euler equations. The transmission coefficients relative to each eigen modes are solved analytically and results are compared against fully non-linear compressible direct numerical simulation reproducing the weak perturbation of an isolated two-dimensional compression shock wave. The linear analysis is found to be capable of predicting the shock-induced redistribution of the energy of the incoming perturbation between the different eigen modes. Non-ideal gas effects are observed both analytically and numerically with especially an unusual selective response for some particular choice of incoming Mach number. A two-dimensional isotropic turbulence configuration is then numerically investigated for the case of an inviscid compressible dense-gas flow close to the liquid-vapour critical point. Strong non-ideal-gas effects on enstrophy production are observed with the formation of eddy shocklets. In both cases non-convex isentropes close to the liquid-vapour critical point are extremely influential in letting both the shock and the turbulence redistribute any supply of turbulence kinetic energy in ways which are simply not observable in ideal gases. This will hopefully spark enthusiasm amongst turbulence modellers (and their end users?).