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An experimental and numerical investigation of under-expanded turbulent jets

机译：扩流湍流射流的实验和数值研究

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The work described here concentrates on under-expanded, axisymmetric turbulent jets issuing into quiescent conditions. Under-expanded turbulent jets are applicable to most aircraft propulsion applications that use convergent nozzles. Experimental studies used laser doppler velocimetry (LDV) and pitot probe measurements along the jet centreline. These measurements were made for two nozzle pressure ratios (2.5 and 4.0) and at various streamwise positions up to 10 nozzle diameters downstream of the nozzle exit plane. A computational fluid dynamics (CFD) model was developed using the Fluent code and utilised the RNG κ-ε two-equation turbulence model. A mesh resolution of approximately one hundredth of nozzle exit diameter was found to be sufficient to establish a mesh independent solution. Comparison of the jet centreline axial velocity (LDV data) and pressure ratio (pitot probe data) showed good agreement with the CFD model. The correct number of shock cells had been predicted and the shock strenglh agreed well between the experiments and numerical model. The CFD model was, however, found to over-predict the shock cell length resulting in a longer supersonic core. There was some evidence, based on analysis of the LDV measuremenls that indicates the presence of swirl and jet unsteadiness, which could contribute to a shortening of the shock cell length. These effects were not modelled in the CFD. Correlation between the LDV and pitot probe measurements was generally good, however, there was some evidence lhal probe interference may have caused the premature decay of the jet. Overall, this work has indicated the good agreement between a CFD simulation using the RNG K-e lurbulence model and experimental data when applied to the prediction of the flowfield generated by under-expanded turbulenl jets. The suitability of the LDV technique to jet flows with velocities up to 500ms~(-1) has also been demonstrated.
机译：此处描述的工作集中于扩张到静止状态的膨胀不足的轴对称湍流射流。膨胀不足的湍流射流适用于大多数使用会聚喷嘴的飞机推进应用。实验研究沿射流中心线使用了激光多普勒测速（LDV）和皮托管探头测量。这些测量是针对两个喷嘴压力比（2.5和4.0）以及在各种流向位置进行的，直到喷嘴出口平面下游的喷嘴直径最大为10。使用Fluent代码开发了计算流体动力学（CFD）模型，并利用了RNGκ-ε二方程湍流模型。发现约百分之一的喷嘴出口直径的网格分辨率足以建立独立于网格的解决方案。射流中心线轴向速度（LDV数据）和压力比（皮托管探头数据）的比较表明与CFD模型吻合良好。可以预测正确数量的冲击波单元，并且冲击强度在实验和数值模型之间吻合得很好。但是，发现CFD模型会过度预测激波单元的长度，从而导致超音速磁芯更长。根据对LDV测量方法的分析，有一些证据表明存在涡旋和射流不稳定，这可能有助于缩短激波单元的长度。这些影响未在CFD中建模。 LDV和皮托管探头测量之间的相关性通常很好，但是，有一些证据表明lhal探头的干扰可能导致了喷头的过早衰减。总的来说，这项工作表明，当将RNG K-e湍流模型用于CFD模拟和实验数据时，可以很好地达成共识。还证明了LDV技术可喷射速度高达500ms〜（-1）的流。

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