Large Eddy Simulation of Underexpanded Supersonic Impinged Jets
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摘要: 使用大涡模拟方法研究喷管总压与环境压力之比
${p_{{\rm{total}}}}/{p_0} = 4.03$ 、喷管高度与喷口直径之比$h/{D_j} = 2.08$ 的欠膨胀冲击射流，考察流场的特性与波系的结构。数值结果清晰地揭示了激波的位置与结构的周期性以及在冲击壁面与喷管唇部之间存在的反馈环。对脉动压力进行快速傅里叶变换的结果分析表明，反馈环与冲击单音具有相同的频率。通过对脉动速度进行本征正交分解，计算出各阶模态及其能量贡献率，详细讨论了湍流场中大尺度相干结构的产生、发展和演化现象。Abstract: Supersonic impinging jets are widely occurred in aeronautics, especially in vertically takeoff and landing of aircrafts. In this paper, large eddy simulation of a supersonic jet impinging on a large plate is presented. The nozzle-to-plate space is 2.08 times of nozzle exit diameter, and the nozzle-pressure ratio is equal to 4.03. Unit ring vortex forcing method for the inflow is used in LES to trigger the turbulence. Results indicate that the position and strength of shock wave are periodical. As the Mach disc oscillates in the axial direction, the underexpanded gas has more sufficient space for expansion, so it can reach a higher speed. In the wall jet zone, the large-scale annular vortical structures are continuous. Along the radial direction, the large-scale vortices break up and generate smaller vortices. Sound wave propagation to the upstream from the wall is observed. After reflection from the lip of the nozzle, it propagates to the downstream near the shear layer, thus a feedback loop is formed. It dominates the generation of monotone. Fast Fourier transform is applied to the pressure fluctuation. The results verify that the feedback loop has the same frequency as the tone. Proper orthogonal decomposition is employed to analyze the velocity fluctuation. The modes and their energy contribution rates are calculated. The jet boundary, Mach disc and the oblique shock wave, the recirculation area and the wall jet all have strong correlation. The generation and evolution of large scale turbulence structures in turbulent field are presented and analyzed. -
图 2 不同涡环扰动计算结果对比
Figure 2. Comparison of calculation results by different vortex ring perturbation
图 11 中心线脉动压力频率分布
Figure 11. Frequency distribution of pressure fluctuation on centerline
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