推力室中压力剧烈振荡区域的燃烧特性分析

Analysis of Combustion Characteristics in the Region with Violent Pressure Oscillations in Thruster Chamber

在不施加任何扰动的情况下,对液氧/煤油双组元液体火箭发动机模型燃烧室进行三维非稳态数值模拟,获得了其中的压力自激振荡现象。基于定义的能够辨识定容和定压燃烧特征的第三邓克尔数分析了压力剧烈振荡区域的燃烧特性。结果表明,在压力剧烈振荡区域内,第三邓克尔数取值很大,即发生了准定容燃烧或介于定容和定压之间的燃烧过程。可见尽管液体火箭发动机燃烧室整体表现为定压燃烧特性,但在头部附近区域出现了局部具有非定压特性的燃烧过程,其产生的压力膨胀波来不及迅速传播而使当地的压力迅速升高,形成了定容弹效应,从而导致了燃烧不稳定性的发生。该压力峰的传播及其与室壁相互作用在燃烧室中产生声学不稳定性,与研究燃烧不稳定性的定容弹试验机理相同。

Numerical simulation of the three-dimensional unsteady two-phase reacting flows in the thrust chamber of LOX/ RP-1 liquid rocket engine was conducted. Self-triggered pressure oscillations were obtained without any artificial excitations. The combustion characteristic in the region with violent pressure oscillation was analysed through the third Damk^ihler number defined to classify a combustion process as constant-volume combustion, constant-pressure combustion and combustion with partial expansion and pressure increase. It is shown that the third Damkfihler number is large in the region where violent pres- sure oscillation exists, which means there is constant-volume combustion or combustion with partial expansion and pressure in- crease. Although the overall combustion characteristic of the thrust chamber is constant-pressure combustion, constant-volume combustion may occur locally in the head region of the combustion chamber. The expansion wave generated by exothermic chemical reaction of the constant-volume combustion does not have time to propagate and will lead to pressure peaks. The com- bustion instabilities may be triggered when such pressure peaks propagate and interact with chamber walls. It is the same as the mechanism of the bomb test used to investigate the combustion instability, which indicates that the results obtained is rea- sonable.