气相化学反应与声学振荡的耦合机理数值研究

Numerical Research on Mechanism of Coupling between Gas-Phase Chemical Reaction and Acoustic Oscillation

关键词:  热声耦合  化学动力学  任意拉格朗日欧拉算法  冷流声学相似场  数值仿真

Key words:  Thermo acoustic coupling  Chemical kinetics  Arbitrary Lagrange Euler algorithm  Cold field of acoustic similarity  Numerical simulation

摘要:

通过数值仿真方法针对液体火箭发动机内的气相化学动力学与振荡声场的热声耦合机理进行了研究。采用任意拉格朗日算法解耦流动与化学源项间的刚性。采用的多步总包反应机理考虑了底层的准稳态组分脉动。通过入口流量边界的流量脉动向燃烧室中引入纵向声波，并建立了冷流声学相似场模型以分析热声耦合效应的强度。研究发现:在线性小振幅声场中，气相化学动力学控制的释热系统与声学振荡无明显耦合激励；在非线性有限幅值声场中，燃烧室压力与释热波动出现“突跃”并表现为陡峭前沿波，气相化学动力学控制的释热系统与声学振荡发生耦合激励，反应流较其冷流声学相似场的压力振荡振幅增强约300%。最后分析了耦合激励发生的可能原因，提出了气相化学动力学体系的“释热分岔”假说。

Abstract:

The mechanism of the coupling between gas-phase chemical kinetics and acoustic fields in liquid rocket engines was studied through numerical methods. The arbitrary Lagrange Euler algorithm was applied to decouple the stiffness between flow and chemical source term. The chosen multistep global reaction mechanism could consider the pulse of the underlying quasi-steady-state components. Longitudinal acoustic waves were introduced into the chamber through mass-flow boundary disturbance. To analyze the magnitude of the thermo acoustic coupling effect，cold field of acoustic similarity model was established. The simulation results show that there was not obvious encouraging coupling between thermo system controlled by chemical kinetics and acoustic oscillation in acoustic fields of little amplitude. However，in the nonlinear acoustic fields of finite amplitude，encouraging thermo-acoustic coupling was gained with pressure and heat-release oscillation acting as ‘abrupt change’ and ‘steep rise’. Amplitude of pressure oscillation in reaction flow was 300% stronger than that in its cold field of acoustic similarity. At last，the possible reason for the excitation was analyzed and the presumption of heat release bifurcation in gas-phase chemical kinetic systems was presented.