Coupling of twin rectangular supersonic jets
Coupling of twin rectangular supersonic jets
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双矩形超音速喷气机的耦合
DOI：
10.1017/s0022112097007441
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发表时间：
1997
影响因子：
3.7
通讯作者：
R. Taghavi
中科院分区：
文献类型：
--
作者：
G. Raman;R. Taghavi
飞机上的双喷气羽流可以耦合，产生足以引起结构疲劳的动态压力。对于具有中等展弦比（例如5）的紧密间隔射流，先前的工作已经确定了两种耦合模式（反对称和对称）在运动学上是允许的。然而，双射流耦合的动力学仍然没有被探索。本文试图对双射流耦合的定常和非定常方面进行更基本的评估。当我们记录和讨论发生锁相耦合的喷管间距和马赫数时，我们的注意力更多地集中在回答下列问题上：（a）是什么机制导致喷流以一种模式或另一种模式耦合？(b)为什么喷气机从一种模式切换到另一种模式？(c)这两种模式是相互排斥的，还是在过渡点重叠？我们的研究结果揭示了以下几点。(i)对于非常接近的并排配置中的双射流，基于相邻射流的源到喷嘴出口距离的相位反馈不能完全解释耦合模式。然而，“零”相位区域周围的射流的声学波前（从下游到达）的相位不发生变化似乎与对称模式的存在相关。当相邻射流的“零”区域不重叠时，发生反对称耦合，而当它们重叠时，射流对称耦合。我们提供了一个简单的相关性，使用参数（α），可以作为一个简单的测试，以确定耦合模式。(ii)从反对称到对称耦合模式的切换似乎是由于有效尖叫源从第三冲击到第四冲击的突然转变而发生的，这反过来又导致围绕射流的“零”相区域突然增长并重叠。(iii)这两种模式是相互排斥的。我们的研究结果提供了相当深入的了解双喷流耦合问题，并提供了设计双喷流配置，尽量减少对飞机部件的损坏的希望。
Twin jet plumes on aircraft can couple, producing dynamic pressures significant enough to cause structural fatigue. For closely spaced jets with a moderate aspect ratio (e.g. 5), previous work has established that two coupling modes (antisymmetric and symmetric) are kinematically permissible. However, the dynamics of twin-jet coupling have remained unexplored. In this paper a more fundamental assessment of the steady and unsteady aspects of twin-jet coupling is attempted. While we document and discuss the nozzle spacings and Mach numbers over which phase-locked coupling occurs, our concentration is much more on answering the following questions: (a) What mechanism causes the jets to couple in one mode or the other? (b) Why do the jets switch from one mode to another? (c) Are the two modes mutually exclusive or do they overlap at the transition point? Our results reveal, among many things, the following. (i) For very closely spaced twin jets in the side-by-side configuration phased feedback based on source to nozzle exit distance of adjacent jets does not fully explain the coupling modes. However, the ‘null’ phase regions surrounding the jets where the phase of an acoustic wavefront (arriving from downstream) does not vary appears to correlate well with the existence of the symmetric mode. When the ‘null’ regions of adjacent jets do not overlap antisymmetric coupling occurs and when they do overlap the jets couple symmetrically. We provide a simple correlation using a parameter (α) that can be used as a simple test to determine the mode of coupling. (ii) The switch from the antisymmetric to the symmetric mode of coupling appears to occur because of an abrupt shift in the effective screech source from the third to the fourth shock, which in turn causes the ‘null’ phase region surrounding the jets to grow abruptly and overlap. (iii) The two modes are mutually exclusive. Our results provide considerable insight into the twin-jet coupling problem and offer hope for designing twin-jet configurations that minimize damage to aircraft components.