Mora Pablo, Baier Florian, Kailasanath K, Gutmark Ephraim J
Department of Aerospace Engineering & Engineering Mechanics, University of Cincinnati, 745 Baldwin Hall ML 0700, Cincinnati, Ohio 45221, USA.
Naval Research Laboratory, Washington, DC 20375, USA.
J Acoust Soc Am. 2016 Dec;140(6):4130. doi: 10.1121/1.4967158.
A jet exhausting over a plate at different distances away from the nozzle was investigated to simulate jets exhausting over airframe surfaces and the jet-ground interaction during take-off and landing operations. A supersonic rectangular nozzle of 2:1 aspect ratio and 1.5 design Mach number was tested with and without the plate. Far-field acoustics from the cold and heated jets at over-expanded, design, and under-expanded conditions were measured at the reflected, sideline, and shielded azimuthal directions. When the plate starts at the nozzle exit, the "scrubbing" and "scattering" noise from the surface-jet interaction was observed at the low-end frequencies of the reflected and shielded measurements and increased as the plate approached the jet. In the sideline, the plate attached to the nozzle exit diminished the broadband shock-associated noise while the shadowgraph results showed a connection to weakening of the shock-cell structures. In the cold jet, screech was mitigated with the plate attached at the nozzle exit. When the plate was moved away from the nozzle, screech tones were intensified at the under-expanded condition. Crackle levels were significantly intensified in the sideline within a range of plate positions. Noise levels in the shielded region were considerably lower due to the shielding effect.
对在距喷嘴不同距离的平板上排出的射流进行了研究，以模拟在机身表面排出的射流以及起飞和着陆操作期间的射流与地面相互作用。测试了长宽比为2:1、设计马赫数为1.5的超音速矩形喷嘴，测试时有无平板。在反射、边线和屏蔽方位方向上测量了过膨胀、设计和欠膨胀条件下冷射流和热射流的远场声学特性。当平板从喷嘴出口处开始时，在反射和屏蔽测量的低频端观察到了来自表面射流相互作用的“擦洗”和“散射”噪声，并且随着平板靠近射流而增加。在边线方向，连接到喷嘴出口的平板降低了与宽带激波相关的噪声，而纹影图结果显示与激波胞结构的减弱有关。在冷射流中，连接在喷嘴出口处的平板减轻了啸声。当平板从喷嘴移开时，在欠膨胀条件下啸声音调增强。在一定范围的平板位置内，边线方向的噼啪声水平显著增强。由于屏蔽效应，屏蔽区域内的噪声水平要低得多。
