Control of the Radiation of Screech Tone by Cavity Tone Generated in the Supersonic Jets

近年来，下一代超音速客机正在研制中。这架飞机将使用超音速喷气式飞机作为推力。然而，众所周知，被称为尖叫声的非常强的声波会被辐射出来。这种尖叫声是由喷流周围下行对流的相干涡旋结构和环境中向上传播的声波组成的反馈回路产生的。超音速喷气式飞机发出的如此强烈的噪声辐射会造成机场附近严重的噪声污染以及飞机的疲劳失效。因此，这项实验研究是为了阐明超音速射流辐射降噪的可能性。在过去的一年里，我们研究了带腔的矩形喷管喷流所辐射的腔音和尖叫声的声学特性。在这一年里，…排放的超音速喷流辐射的音调特性并对带空腔的圆形喷管进行了研究。实验结果表明：(1)有效地降低了频率高于腔音频率的尖叫声。(2)有腔喷嘴射出的尖音声压级(SPL)比无腔喷嘴自由射流射出的尖音声压级(SPL)最多低约30dB.空腔声的声压级最多比无空腔喷嘴自由喷出的尖叫声低约20dB.(3)当腔体长度为喷嘴直径的1.2倍时，出现11.5 kHz和14.0 kHz两个共振频率之一。在压比大于3.5的范围内出现11.5 kHz的腔音频率时，该频率随压比的降低而突变为14.0 kHz。没有观察到相反的过程。在压比小于3.5的范围内产生空腔音时，发现压比降低时，最先出现空腔音的频率不变。较少

In recent years, a supersonic passenger airplane of next generation is developping. The supersonic jets will be used as the thrust of this airplane. However, it is well known that very strong sound waves called screech tone is radiated. This screech tone is generated by the feedback loop consisting of downstream-convecting coherent vortical structures around the jet and upstream-propagating sound waves in the ambient. The radiation of such very intense noise from the supersonic jets will cause the serious noise pollution near the airports as well as the fatigue failure of the airplanes. Therefore, this experimental study was performed to clarify the possibilty of the noise reduction radiated from supersonic jets. The acoustical characteristics of the cavity tone and the screech tone radiated by the jet issuing from a rectangular nozzle with cavity were investigated in the last year. In this year, the acoustical characteristics of the tones radiated by the supersonic jet discharged from … More the circular nozzle with cavity were investigated. From the experimental results, the following things were found : (1) The screech tone whose frequency is higher than that of cavity tone is effectively reduced. (2) The sound pressure level (SPL) of the screech tone radiated from the jets exhausting from the nozzle with cavity becomes lower than that of the screech tone radiated from the free jet discharging from the nozzle without cavity by about 30dB at most. The SPL of the cavity tone is lower than that of the screech tone radiated from the free jet issuing from the nozzle without cavity by about 20dB at most. (3) When the length of the cavity is 1.2 times the nozzle diameter, one of two resonance frequencies, 11.5kHz and 14.0kHz, is appeared. When the frequency of the cavity tone of 11.5kHz is appeared in the pressure ratio range higher than 3.5, the frequency is changed into 14.0kHz abruptly during decreasing of the pressure ratio. The reverse process is not observed. When the cavity tone is produced in the pressure ratio range lower than 3.5, it is observed that the frequency of the cavity tone firstly appeared is not changed during decreasing of the pressure ratio. Less