Hydrodynamic characteristics in separation bubbles of airfoil under acoustic vortex interaction
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摘要: 基于LBM-LES方法对中等雷诺数下NACA0012翼型气动噪声进行了直接模拟，得到了声涡相互作用下气动噪声声场和流场，分析了剪切层内流体动力学特征。结果表明：翼型壁面附近剪切层内，扰动从分离前 T-S不稳定分离后向K-H不稳定转变，K-H不稳定对扰动的增长起重要作用；分离泡内湍流强度显著增长直至转捩成湍流，但流动再附后，湍流强度有所降低；750 Hz的大尺度旋涡结构是在分离泡内形成并发展成稳定结构，而2次和3次谐波频率对应的旋涡结构形成于流动转捩后，在分离泡外发展成稳定结构，说明远场2次及3次谐波纯音噪声和750 Hz主纯音噪声生成机理不同。Abstract: Based on the LBM-LES method, aeroacoustic of the NACA0012 airfoil at medium Reynolds numbers was directly simulated. The flow field and aeroacoustic field under acoustic vortex interaction were obtained, and the hydrodynamic characteristics in the shear layer were analyzed. The results show that in the shear layer near the airfoil surface, the T-S wave turns into the K-H instability after the flow separation, and the K-H instability plays an important role in the growth of the disturbance. Turbulence intensity in the separation bubble increases significantly until transition to turbulence, but the turbulence intensity decreases again after the flow reattachment. The large-scale vortex structure of 750 Hz is formed and developed into a stable structure inside the separation bubble, while the vortex structures corresponding to the 2nd and 3rd harmonics are formed after the transition, and developed into stable structures outside the separation bubble. It suggests that the generation mechanism of the 2nd and 3rd harmonic tonal noise is different from that of the 750 Hz fundamental one.
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Key words:
- hydrodynamic /
- separation bubble /
- acoustic vortex interaction /
- tonal noise
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图 1 NACA0012翼型格子分布网格
Figure 1. Grid distribution of the NACA0012 airfoil enlarged view
图 2 翼型吸力面时均压强系数分布和点（1C，0.5C）处声压级频谱图
Figure 2. Mean pressure coefficient distribution on the suction side of the airfoil and SPL spectrum at the point (1C, 0.5C)
图 3 边界层内压强及远场声压PSD图
Figure 3. PSD diagram of pressure in the boundary layer and sound pressure in the far field
图 5 时均压强系数和时均湍流强度分布
Figure 5. Distributions of the time averaged pressure coefficient and turbulence intensity
图 6 翼型边界层内750 Hz压强声压级分布
Figure 6. Distribution of pressure SPL at 750 Hz in the airfoil boundary layer
图 7 翼型吸力面离散纯音压强脉动均方根分布
Figure 7. RMS distribution of the discrete tonal pressure fluctuation on the suction side of the airfoil
图 8 分离前边界层流向速度脉动均方根
Figure 8. RMS of the streamwise velocity fluctuation in the boundary layer before separation
图 9 分离后边界层内脉动分布
Figure 9. fluctuation distribution in the boundary layer after separation
图 10 流动分离前后流向速度脉动分布
Figure 10. Streamwise velocity fluctuation distributions before and after the flow separation
图 11 0.6C边界层内速度及脉动均方根分布
Figure 11. Distributions of the velocity and fluctuation RMS in the boundary layer at 0.6C
图 12 不同时间分离泡内涡量的分布（等值线为Q值）和0.65C 表面压力系数
Figure 12. Vorticity distribution in the separation bubbles at different time instances (contour lines are for Q values) and pressure coefficient
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