二维叶栅通道直接数值模拟涡系分析

Vortex System Analysis of Two-dimensional Cascade Based on Direct Numerical Simulations

该文基于有限体积法对NACA0065叶栅内二维不可压缩流动进行直接数值模拟,得到不同雷诺数下叶栅通道内的瞬时涡系结构和时均物理量分布,进而表明了涡系结构对叶片气动系数的影响。在低雷诺数情况下,尾迹旋涡的周期性脱落频率导致升阻系数的周期性变化。利用傅立叶变换,气动系数谱中的主频与涡脱落频率精准对应,进一步分析表明次频是由脱落周期内相邻区域的不同涡核低压区交替出现而导致。在高雷诺数下,气动力系数频谱中出现了更多的高频谐波。此外,该文利用Liutex理论中的R-S分解和涡量输运方程解释了NACA0065叶片表面剪切层产生旋涡的机理,并研究了强剪切区和弱剪切区处的涡核特性。该研究结果可使工程界对NACA0065叶栅中的相应旋涡结构及其相互作用有了更深入的物理理解。

The two-dimensional incompressible flows in the NACA0065 cascades are simulated based on direct numerical simulations(DNS)with the finite volume scheme.The transient vortex-system structures and time-averaged physical quantities are obtained at the different Reynolds numbers.Based on the DNS results,the influence of aerodynamic coefficient on the blade is clarified.For the low Reynolds number cases,the periodic shedding frequency of wake vortices leads to the periodic fluctuations of lift and drag coefficients.Applying the fast Fourier transform(FFT),the dominant frequency precisely coincides with the vortex shedding frequency,and the sub-harmonics are generated by the alternative appearances of different low-pressure zones induced by the vortex cores in the adjacent region for an entire shedding period.For the higher Reynolds number cases,more sub-harmonics with the higher frequencies can be observed in the aerodynamic coefficient spectra.In addition,the R-S decomposition of the Liutex and vorticity transport equations are used to explain the mechanism of vortexes generated in the shear layer on the NACA0065 blade surface,and the vortex characteristics in both the strong and weak shear regions are studied.The present research provides profound physical understandings of the corresponding vortex structures and their interactions in the NACA0065 cascades.