利用尖头瓣片实现椭圆超声速射流形态操控
Elliptic supersonic jet morphology manipulation using sharp-tipped lobes
AI总结：
本研究通过实验证明，在椭圆超声速射流喷嘴短轴两端加装尖头瓣片，可抑制射流扑动、降低噪声，并使近场混合速率提升约一倍，势核长度缩短40%。
摘要：
椭圆喷嘴几何形状对于增强超声速射流的混合具有吸引力。然而，射流动力学（如扑动）会产生高强度音调噪声。我们通过使用两个尖头瓣片对超声速椭圆射流形态进行实验操控。瓣片放置在椭圆喷嘴短轴的两端。椭圆喷嘴和瓣片喷嘴的设计马赫数和纵横比分别为2.0和1.65。超声速射流在几乎完全膨胀的条件下排入环境。进行了时间分辨纹影成像、纵向和横截面平面激光米散射成像、平面粒子图像测速以及近场麦克风测量，以评估两种喷嘴的流体行为。对纹影和米散射图像进行了动态模态分解（DMD）和本征正交分解（POD）分析。通过图像处理程序从米散射图像中提取混合特性。扑动椭圆射流由两个主导DMD模态组成，而瓣片喷嘴仅有一个主导模态，且扑动被抑制。麦克风测量显示相关噪声降低。瓣片喷嘴中的射流柱分叉，使得与周围流体的接触表面积更大，并且在喷嘴出口近场具有更高的混合速率。双瓣片喷嘴的射流宽度增长率在近场约为椭圆射流的两倍，且势核长度减少了40%。粒子图像测速（PIV）等值线证实了这些结果。
英文摘要：
Elliptic nozzle geometry is attractive for mixing enhancement of supersonic jets. However, jet dynamics, such as flapping, gives rise to high-intensity tonal sound. We experimentally manipulate the supersonic elliptic jet morphology by using two sharp-tipped lobes. The lobes are placed on either end of the minor axis in an elliptic nozzle. The design Mach number and the aspect ratio of the elliptic nozzle and the lobed nozzle are 2.0 and 1.65. The supersonic jet is exhausted into ambient at almost perfectly expanded conditions. Time-resolved schlieren imaging, longitudinal and cross-sectional planar laser Mie-scattering imaging, planar Particle Image Velocimetry, and near-field microphone measurements are performed to assess the fluidic behavior of the two nozzles. Dynamic Mode and Proper Orthogonal Decomposition (DMD and POD) analysis are carried out on the schlieren and the Mie-scattering images. Mixing characteristics are extracted from the Mie-scattering images through the image processing routines. The flapping elliptic jet consists of two dominant DMD modes, while the lobed nozzle has only one dominant mode, and the flapping is suppressed. Microphone measurements show the associated noise reduction. The jet column bifurcates in the lobed nozzle enabling a larger surface contact area with the ambient fluid and higher mixing rates in the near-field of the nozzle exit. The jet width growth rate of the two-lobed nozzle is about twice as that of the elliptic jet in the near-field, and there is a 40\% reduction in the potential core length. Particle Image Velocimetry (PIV) contours substantiate the results.
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