Analysis and calculation of acoustic frequency of swirl injector in hot⁃fire testing
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摘要:
针对采用离心喷嘴的氢氧预燃室,基于高频脉动压力的热试验数据,对比了试验频率的变化趋势和与之相关的主要测试参数的变化规律,初步推测影响热试验频率的根本因素是离心喷嘴内部液膜的声速和燃烧室压力。发展形成了基于声学理论计算喷嘴频率的半经验公式,使用喷前压力和修正了的液氧温度查询声速计算的喷嘴频率。半经验公式的计算结果与试验实测频率吻合很好,分析认为类似管路声学频率计算的半经验公式同样适用于离心喷嘴。声学频率决定了离心喷嘴液膜主导表面波波长的初始值,主导表面波流动所受气体阻力随压力及液膜速度升高而增大使其波长减小,液膜一次破碎的频率升高,可能是热试验频率与燃烧室压力正相关的影响机制。
Abstract:The high frequency pressure oscillation data of a hydrogen⁃oxygen preburner with swirl injectors in hot⁃fire testing were analyzed.The change trend of the frequency and associated testing parameters were compared.It was found that,the testing frequency of hot⁃fire testing may be influenced inherently by the sound speed of liquid film within the injector and the pressure of the combustion chamber.A semi⁃empirical formula based on acoustic theory was developed for swirl injector.The acoustic frequency calculated by using the data of pre⁃injection pressure and modified liquid oxygen temperature for sound speed agreed well with the measured data.It was believed that the semi⁃empirical formula similar to the acoustic frequency calculation of pipeline can be applied to swirl injector.The acoustic frequency determined the initial value of the dominant surface wave length of the liquid film in the swirl injector.The gas resistance of the dominant surface wave flow increased with the increasing pressure and liquid film velocity,which reduced the wavelength and increased the frequency of the first breaking of the liquid film,may be the influence mechanism of the positive correlation between the hot⁃fire testing frequency and the combustion chamber pressure.
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表 1 离心喷嘴几何尺寸
Table 1. Geometrical parameters of the swirl injector
参数 数值 氧喷嘴长度L0/mm 59.8 切向孔中心与出口距离L1/mm 56.8 切向孔直径dt/mm 1.5 切向孔中心长度Lt/mm 3.02 氧喷嘴缩进比Lr/d 0.85 表 2 热试验测点
Table 2. Measuring point parameters of hot⁃fire testing
参数 采样频率/kHz 气蚀管前压力pwio 1 气蚀管前温度Twio 1 氧头腔压力pio 1 氧头腔高频速变压力pio,d 50 氧头腔温度Tio 1 燃烧室压力pc 1 燃烧室高频速变压力pc,d 50 燃烧室温度Tc 1 -
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