This paper studies the distribution and switching characteristics of three components in supersonic free jet noise through rectangular nozzles,including turbulence noise,screech and broadband shock-associated noise.The quasi-array experiments were conducted to analyze the jet noise through the rectangular nozzle with an aspect ratio of 4,and good agreements with theory were obtained in the comparison.The mode properties of jet-flow downstream noise signal were studied by changing the radial distances of the downstream measuring points and the angles of the line passing through the measuring points and the central point of nozzle exit with the jet axis (referring to as measuring point angle).Analysis indicates that turbulence noise is the main component of jet-flow downstream noise,the fundamental frequency is stable and irrelevant to angles changing,and the randomness of noise mode switching is relatively high.As radial distance increases,the dominant feature of the screech increases,the fundamental frequencies of turbulence noise change between 5 and 2.6 kHz,the high-frequency turbulent noise intensity decreases,and the fundamental frequency stabilizes gradually;as the measuring point angle increases,the dominant feature of screech increases with a longest pressure drop interval at the measuring point angle of 120°,wherein the dominant interval of the broadband shock-associated noise appears in the initial stage of the jet.According to the theory,the first-order fundamental frequency and the broadband shock-associated noise propagate to the upstream of the jet flow and present as a narrow beam.These conclusions will provide reference for sound protection and avoiding small-scale structural fatigue damage.%为了研究矩形喷嘴超音速自由射流噪声的湍流噪声、啸叫以及激波相关宽频噪声这3类成分的分布特性及其各成分的切换特性,通过准阵列实验方式对宽高比为4的矩形喷嘴射流噪声进行了分析研究,并与理论结果进行了对比验证.通过改变射流下游测点的径向距离和测点与射流轴线的夹角,研究了射流下游噪声信号的模式特性.通过分析得到,射流下游噪声主体是湍流噪声,其基频不受角度变化影响,并且噪声模式切换的随机性较高.研究发现:随着径向距离的增大,湍流噪声基频在5和2.6 kHz之间跳动,高频湍流噪声强度随之减弱,基频逐步稳定;随着射流上游测点角度的增大,啸叫的占优特性增强,在120°时啸叫的占优区间最长,而且在此位置的射流初始阶段出现了激波相关宽频噪声的占优区间,与理论结果进行对比,得出啸叫的第一阶主频和激波相关宽频噪声是向射流上游传播,并呈现一定的范围.此项研究可为工程中避免小尺度的结构疲劳破坏及对相关工作人员的声防护提供一定的参考依据.
展开▼
