The effect of expansion ramps on the acoustic behavior of a supersonic rectangular jet (AR = 2) is studied and compared to a plain rectangular jet. Unheated air jets are issued from converging–diverging nozzles which are operated at Mach number 1.8, Reynolds number (based on equivalent diameter) \(1.86 \times 10^{5}\), and at three different inlet total pressures corresponding to over, optimum and underexpansion levels. A plain rectangular nozzle is considered as the baseline model; two separate nozzles with expansion ramps cut at the diagonal ends on major and minor internal surfaces are considered for the investigation. These expansion ramps are intended to cause a Prandtl–Meyer expansion near the nozzle exit and together the diagonal arrangement of ramps induces vorticity to the jet in addition to the corner vortices emanating from the rectangular nozzle exit section. To understand the jet acoustic behavior and directivity of noise, far-field microphone measurements are performed in planes that are downstream, sideline, and upstream to the nozzle exit. The noise results obtained reveal a highly asymmetric nature in the sound field. Compared to the plain rectangular jet, the screech noise has been observed to be lesser in jet from the nozzle with ramps on the major sides. Acoustic benefit in terms of overall sound pressure levels has been exhibited by both ramped jets, especially for the overexpanded condition in all directions. For optimum expansion level, the plain rectangular jet radiated lesser noise levels in all directions. Of all cases studied, minor side ramps are observed to be the loudest at underexpansion conditions in upstream directions. With the obtained results, the major side ramps are observed to act as effective screech noise suppressors at all expansion levels. Both ramped jets have resulted in reduced overall noise levels (in comparison with the plain rectangular jet) at overexpansion level, with minor side ramps performing better.

研究了膨胀斜坡对超音速矩形射流 (AR = 2) 声学行为的影响，并与普通矩形射流进行了比较。未加热的空气射流从以 1.8 马赫数、雷诺数（基于等效直径）\(1.86 \times 10^{5}\)运行的收敛-发散喷嘴发出，并在三个不同的入口总压力对应于过度膨胀、最佳膨胀和欠膨胀水平。一个普通的矩形喷嘴被认为是基线模型；研究中考虑了两个独立的喷嘴，在主要和次要内表面的对角线末端切割了膨胀斜坡。这些膨胀斜坡旨在在喷嘴出口附近引起 Prandtl-Meyer 膨胀，并且斜坡的对角线排列除了从矩形喷嘴出口部分发出的角涡流外，还会引起射流的涡流。为了了解噪声的射流声学行为和方向性，在喷嘴出口下游、边线和上游的平面上进行远场麦克风测量。获得的噪声结果揭示了声场的高度不对称性。与普通的矩形射流相比，观察到在主侧面有斜坡的喷嘴的射流中发出的尖叫噪音更小。两种倾斜的射流都表现出在整体声压级方面的声学优势，特别是在所有方向的过度膨胀条件下。为了获得最佳的膨胀水平，平面矩形射流向各个方向辐射的噪音水平较低。在研究的所有案例中，观察到较小的侧坡道在上游方向的膨胀不足条件下声音最大。根据获得的结果，观察到主要侧斜坡在所有扩展级别都充当有效的尖叫噪声抑制器。两种倾斜的喷气机在过度膨胀水平上都降低了整体噪音水平（与普通矩形喷气机相比），较小的侧坡道性能更好。观察到从喷嘴喷出的尖啸噪音较小，主要侧面有斜坡。两种倾斜的射流都表现出在整体声压级方面的声学优势，特别是在所有方向的过度膨胀条件下。为了获得最佳的膨胀水平，平面矩形射流向各个方向辐射的噪音水平较低。在研究的所有案例中，观察到较小的侧坡道在上游方向的膨胀不足条件下声音最大。根据获得的结果，观察到主要侧斜坡在所有扩展级别都充当有效的尖叫噪声抑制器。两种倾斜的喷气机在过度膨胀水平上都降低了整体噪音水平（与普通矩形喷气机相比），较小的侧坡道性能更好。观察到从喷嘴喷出的尖啸噪音较小，主要侧面有斜坡。两种倾斜的射流都表现出在整体声压级方面的声学优势，特别是在所有方向的过度膨胀条件下。为了获得最佳的膨胀水平，平面矩形射流向各个方向辐射的噪音水平较低。在研究的所有案例中，观察到较小的侧坡道在上游方向的膨胀不足条件下声音最大。根据获得的结果，观察到主要侧斜坡在所有扩展级别都充当有效的尖叫噪声抑制器。两种倾斜的喷气机在过度膨胀水平上都降低了整体噪音水平（与普通矩形喷气机相比），较小的侧坡道性能更好。