脉冲放电等离子体控制火箭发动机高频燃烧不稳定性机理

Mechanism of high frequency combustion instability control by pulsed discharge plasma in rocket engine

为研究等离子体对火箭发动机高频燃烧不稳定性的影响,提出了一种基于脉冲激励准直流放电等离子体的控制方案,采用数值仿真方法研究了脉冲放电等离子体对燃烧室流场平均参数及动态特征的影响规律。结果表明:脉冲激励下燃烧室平均温度和压力都较定常激励下有所降低,对整个燃烧室的影响可以忽略。与定常激励相似,等离子体可以在一段时间内抑制高频压力振荡,而且在特定控制参数下其对不稳定燃烧的抑制效果优于定常激励方式;从功率谱密度分析可知脉冲激励下燃烧室压力振荡特征频率由燃烧室固有声学频率和脉冲激励频率两者共同决定,提高激励频率则特征频率幅值有所降低。脉冲激励方式与定常激励一样不改变燃烧室压力-释热耦合特征,但是通过降低释热率能够改变压力振荡幅值,进而实现对高频不稳定燃烧的抑制。在所研究工况中,激励频率为50 kHz、占空比为20%的脉冲控制参数下等离子体的抑制效果最佳。

To explore the effect of plasma on high frequency combustion instability of rocket engine,a control scheme of pulsed quasi-direct current discharge plasmas was provided.The effects of pulsed discharge plasmas on average parameters and dynamic characteristics of combustor flow field were all numerically studied.Results showed that compared with the steady actuating way, the average temperature and pressure both decreased under the pulsed actuating way, yet the effect of plasma on the whole combustor can be ignored.Similar to that of steady actuating way,the plasma could depress the high frequency pressure oscillation within a certain time.However,the depression effect of pulsed discharge plasma was better than steady actuating way when suitable actuating parameters were adopted.According to the power spectral density plots, the characteristic dominant frequencies of combustor pressure oscillation were mainly determined by both the combustor intrinsic acoustic frequencies and the actuating frequencies for the pulsed actuating way.The power spectral density amplitude of dominant frequency decreased as the actuating frequency increased.The coupling charateristics of combustor pressure and heat release was not altered by the plasma.However,through decreasing the heat release rate,the pressure oscillating amplitude can be reduced,indicating that the pulsed discharge plasma can be used for depressing high frequency combustion instability.A pulsed actuating scheme with an actuating frequency of50 kHz and a duty cycle of 20% can achieve the best control effect among the studied conditions.