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Fluid-Thermodynamic Mode Decomposition of a Supersonic Jet

机译：超声速射流的流体热力学模式分解

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The flowfield of a Mach 1.3 cold jet obtained through Large-eddy Simulation is decomposed into its acoustic, hydrodynamic and thermal components using Doaks's momentum potential theory. The hydrodynamic mode closely follows the shear layer roll-up and core turbulence. Both acoustic and thermal modes reveal themselves as having wavepacket form in the core region. The acoustic mode reproduces the universal spectra observed in the sideline and downstream directions. The filtering properties of the jet along the shallow-angle direction are examined using scalograms. Although broadband in the core, the hydrodynamic mode has peak energy around St = 0.08 in the nearfield. On the other hand, the acoustic mode has a narrowband nature around St = 0.2, with distinct intermittent events in the nearfield. The acoustic coherent axial wavepacket has a principal frequency of about St = 0.4 and exhibits jittering phenomena, yielding the nearfield radiation pattern. An analysis of the total fluctuating enthalpy (TFE) transport equation highlights the role of individual modes in the generation and transport of acoustic energy to the nearfield of the jet. While the solenoidal fluctuations contribute the most to sideline radiation, the downstream transport of acoustic energy occurs primarily through the irrotational field. For this cold jet, the hydrodynamic mode is found to be the primary source of radiated energy due to its interaction with the fluctuating Coriolis acceleration. The entropic fluctuations lead to dissipation of the Total Fluctuating Enthalpy.
机译：通过Doaks动量势理论将通过大涡流模拟获得的Mach 1.3冷射流的流场分解成其声学，流体动力和热学成分。流体动力模式紧随剪切层的卷起和岩心湍流。声模和热模都表明自己在核心区域具有波包形式。声学模式再现了在边线和下游方向观察到的通用光谱。使用比例尺检查沿浅角方向的射流过滤特性。尽管核心处是宽带，但水动力模式在近场中的峰值能量约为St = 0.08。另一方面，声学模式在St = 0.2附近具有窄带性质，在近场具有明显的间歇性事件。声相干轴向波包的主频率约为St = 0.4，并表现出抖动现象，从而产生近场辐射图。对总波动焓（TFE）输运方程的分析突出了各个模式在声能的产生和向射流近场的输运中的作用。尽管螺线管波动对边线辐射的贡献最大，但声能的下游传输主要通过非旋转场发生。对于这种冷射流，由于流体动力学模式与波动的科里奥利加速度相互作用，因此发现流体动力学模式是辐射能的主要来源。熵的波动导致总波动焓的消散。

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