Abstract Owing to their simple structure and high performance, swirl injectors have been used as propellant injectors for rocket engines in various countries, starting from Russia. However, when a swirl injector is used in combustion, flow instability becomes important because of its relation to combustion instability. Because the external flow of a swirl injector is a thin liquid sheet, wave-forming self-excited instability could occur. In this study, the effect of self-excited instability on the flow characteristics of a swirl injector was investigated. Moreover, through the use of a mechanical pulsator, the effect of self-excited instability frequency on the dynamic characteristics of the swirl injector was examined. As a result, self-excited instability was determined to cause the periodic breakup of the spray sheet. In addition, large droplets generated immediately after breakup are confirmed to be periodically concentrated with a specific frequency equal to the self-excited instability frequency. With external pulsation, breakup length was observed to be shortened with pulsation and had minimum value when pulsation of frequency equal to the self-excited instability frequency was applied. Droplet characteristics with pulsation were also investigated, and external pulsation was determined to cause mean droplet diameter (D10) and Sauter mean diameter (SMD) to be smaller. When SMDs at pulsations of different frequencies were compared, the SMD at pulsation with self-excited instability frequency was observed to be larger because this frequency causes droplet distribution to be more non-uniform. Through this study, self-excited instability was confirmed to be able to change the static and dynamic characteristics of a swirl injector. This result can serve as a reminder of the importance of the self-excited instability of a sheet in the design of a swirl injector.

中文翻译：

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自激不稳定性对单液旋流喷射器流动特性的影响

摘要 旋流喷射器由于结构简单、性能优良，从俄罗斯开始，已被各国用作火箭发动机的推进剂喷射器。然而，当在燃烧中使用涡流喷射器时，流动不稳定性变得很重要，因为它与燃烧不稳定性有关。由于涡流喷射器的外部流动是薄薄的液体层，因此可能会发生波形自激不稳定。在这项研究中，研究了自激不稳定性对旋流喷射器流动特性的影响。此外，通过使用机械波轮，研究了自激不稳定频率对旋流喷射器动态特性的影响。结果，自激不稳定性被确定为导致喷片周期性破裂。此外，破碎后立即产生的大液滴被证实以等于自激不稳定频率的特定频率周期性地集中。对于外部脉动，观察到断裂长度随着脉动而缩短，并且在施加等于自激不稳定频率的脉动频率时具有最小值。还研究了具有脉动的液滴特性，并确定外部脉动导致平均液滴直径 (D10) 和 Sauter 平均直径 (SMD) 更小。当比较不同频率脉动下的 SMD 时，观察到具有自激不稳定频率的脉动时的 SMD 更大，因为该频率导致液滴分布更不均匀。通过这项研究，自激不稳定性被证实能够改变涡流喷射器的静态和动态特性。这个结果可以提醒人们在涡流喷射器的设计中片材的自激不稳定性的重要性。