Study on Themo-Fluiddynamic Coupling involved in Supercritical Droplet Combusion and Vaporization/Combustion Characteristics Prediction

超临界液滴燃烧热流耦合研究及汽化/燃烧特性预测

基本信息

批准号：
07650234
负责人：
UMEMURA Akira
金额：
$ 1.22万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1997
项目状态：
已结题

项目摘要

The effects of thrmo-fluidynamic coupling phenomena which take place near the critical mixing surface of liquid fuel have been examined for droplet vaporization and liquid fuel jet flow.(1) Our previous study on supercritical droplet vaporization has been extended to reveal new features which intrinsically appear in such a gasification regime that the droplet experiences a transition to continuous phase change, showing that (a) The gasification lifetime becomes very short and comparable to the temperature relaxation time of the droplet. (b) The heating of droplet is indespensable for the transition. (c) The fuel diffusivity is greatly increased by the loss of phase equilibrium constraint. (d) A moving droplet without surface deforms to enlarge its surface area, thus enhancing vaporization and mixing rates. (e) Sprays confined in a chamber may experience an acoustically resonant vaporization mode.(2) The atomization, vaporization and mixing characteristics of a liquid fuel issued into an inert gas whose pressure and temperature exceed the critical values of the fuel have been examined by means of linear stability analysis and TVD simulation. Main findings are ; (a) The reduction of surface tension at elevated pressures requires the formation of thinner liquid fragments, for which Rayleigh instability effectively works to atomize liquid. (b) The inviscid analysis conducted for the linear stability of shear flow in vicinity of the jet surface shows that the maximum growth rate rapidly increases to a saturated value due to density variation and vanishing surface tension as the critical mixing condition is approached. (c) Since the sound speed takes a small value near critical conditions, the effect of compressibility (supercompressibility) must be taken into account for the numerical simulation of supercritical fluid flow- a new flow regime in which both Reynolds number and Mach number may take large values.

已经检查了液体燃料临界混合表面附近发生的热流动力学耦合现象对液滴汽化和液体燃料射流的影响。（1）我们之前对超临界液滴汽化的研究已得到扩展，揭示了本质上的新特征出现在这样的气化状态中，液滴经历了向连续相变的转变，表明(a)气化寿命变得非常短并且与液滴的温度弛豫时间相当。 (b) 液滴的加热对于转变是必不可少的。（c）由于相平衡约束的丧失，燃料扩散率大大增加。 (d)没有表面的移动液滴变形以扩大其表面积，从而提高汽化和混合速率。 (e) 限制在室内的喷雾可能会经历声共振汽化模式。 (2) 液体燃料进入压力和温度超过燃料临界值的惰性气体时的雾化、汽化和混合特性已通过线性稳定性分析和TVD模拟手段。主要发现是； (a) 在升高的压力下降低表面张力需要形成更薄的液体碎片，为此瑞利不稳定性有效地使液体雾化。 (b) 对射流表面附近剪切流的线性稳定性进行的无粘性分析表明，随着接近临界混合条件，由于密度变化和表面张力消失，最大增长率迅速增加到饱和值。 (c) 由于声速在临界条件附近取很小的值，超临界流体流动的数值模拟必须考虑压缩性（超压缩性）的影响——一种雷诺数和马赫数都可以取的新流态大值。