亚声速同轴射流波包敏感性研究(英文)
发布时间：2021-10-17 09:40
同轴射流广泛应用于航空航天领域,目前基于线性机制的理论模型对预测射流波包和噪声普遍存在局限性,非线性效应已成为研究热点。本文通过在线性抛物化稳定性方程（PSE）右端项中加入外部激励项,研究了亚声速同轴射流中非线性对波包演化的作用。当前工作主要聚焦于考察同轴射流中的波包特性,因为其存在两个剪切不稳定模态。基于同轴射流的基本流,采用求解线性PSE构建了线性波包,进一步通过求解伴随PSE方程得到了总体扰动能量对外部激励的敏感性。结果表明敏感性区域和流动较大响应区域均对应于内外临界层附近,且二者对外部激励均十分敏感,在下游区域可以看出,内外两个失稳模态之间存在一定程度的相互作用。最后,采用伴随优化的方法获得了关于外模态的最优激励,且施加最优激励之后波包得以更快速的增长。
【文章来源】：空气动力学学报. 2020,38(02)北大核心CSCD
【文章页数】：13 页
【部分图文】：
亚声速同轴射流基本流流向速度场
Firstly,the local stability analysis is carried out for different Strouhal numbers St=fDs/Upat z=z0near the nozzle exit where f=ω/2πrepresents the frequency.Two meshes with 280and 300 r-grid points are adopted to show the convergence of eigenvalues.Generally,the low-frequency and low-azimuthalwavenumber components of wavepackets are recognized to be associated with the major sound sources of turbulent jet noise,thus in the following the axisymmetric mode m=0is investigated.Gloor et al.[5]have reported a representative frequency of St=0.4in the sound pressure spectrum at low polar angle in their isothermal coaxial jet.Thus,we also take the axisymmetric mode m=0and St=0.4as an example.From the eigenvalue spectrum shown in Fig.2,two distinct unstable modes can be identified.The two different modes are corresponding to the hydrodynamic Kelvin-Helmholtz(K-H)modes of the two mixing layers,where the definition of‘inner mode’refers to the K-H mode at the primary mixing region,and the‘outer mode’refers to the K-H mode at the secondary mixing region.At St=0.4,the local growth rate of the outer mode is much higher than its counterpart of inner mode,indicating that the outer mode dominates the local instability near the nozzle exit,which is consistence with the conclusion of Kwan and Ko[12],Léon and Brazier[22].The imaginary part of the eigenvalues obtained by LST representing the local growth rate with respect to the Strouhal number is presented in Fig.2(d).It is seen that the peak frequency of growth rate is reduced when the velocity ratio decreases.For St=0.4and m=0,the growth rates in the two cases are relatively high,so this frequency component is appropriate for comparison between the two cases.2.2 Non-parallel analysis
Figure 4 compares the imaginary part of local streamwise wavenumberαiand the‘N-factor’,defined as imaginary part of-χin Eq.(11),representing the spatial growth rate between the two cases for outer modes.It shows that the rapid growth of instability wave mainly occurs before 3D～4Dto nozzle exit inside the potential core in both cases.Moreover,as the velocity ratio decreases,the peak of N-factor corresponding to the neutrally stable axial location moves upstream to the nozzle exit,due to a shorter length of the outer potential core in Case 2.The change of neutrally stable axial location will affect the spatial distribution of sensitivity and flow response.3 Sensitivity analysis and optimization
本文编号：3441545
【文章来源】：空气动力学学报. 2020,38(02)北大核心CSCD
【文章页数】：13 页
【部分图文】：
亚声速同轴射流基本流流向速度场
Firstly,the local stability analysis is carried out for different Strouhal numbers St=fDs/Upat z=z0near the nozzle exit where f=ω/2πrepresents the frequency.Two meshes with 280and 300 r-grid points are adopted to show the convergence of eigenvalues.Generally,the low-frequency and low-azimuthalwavenumber components of wavepackets are recognized to be associated with the major sound sources of turbulent jet noise,thus in the following the axisymmetric mode m=0is investigated.Gloor et al.[5]have reported a representative frequency of St=0.4in the sound pressure spectrum at low polar angle in their isothermal coaxial jet.Thus,we also take the axisymmetric mode m=0and St=0.4as an example.From the eigenvalue spectrum shown in Fig.2,two distinct unstable modes can be identified.The two different modes are corresponding to the hydrodynamic Kelvin-Helmholtz(K-H)modes of the two mixing layers,where the definition of‘inner mode’refers to the K-H mode at the primary mixing region,and the‘outer mode’refers to the K-H mode at the secondary mixing region.At St=0.4,the local growth rate of the outer mode is much higher than its counterpart of inner mode,indicating that the outer mode dominates the local instability near the nozzle exit,which is consistence with the conclusion of Kwan and Ko[12],Léon and Brazier[22].The imaginary part of the eigenvalues obtained by LST representing the local growth rate with respect to the Strouhal number is presented in Fig.2(d).It is seen that the peak frequency of growth rate is reduced when the velocity ratio decreases.For St=0.4and m=0,the growth rates in the two cases are relatively high,so this frequency component is appropriate for comparison between the two cases.2.2 Non-parallel analysis
Figure 4 compares the imaginary part of local streamwise wavenumberαiand the‘N-factor’,defined as imaginary part of-χin Eq.(11),representing the spatial growth rate between the two cases for outer modes.It shows that the rapid growth of instability wave mainly occurs before 3D～4Dto nozzle exit inside the potential core in both cases.Moreover,as the velocity ratio decreases,the peak of N-factor corresponding to the neutrally stable axial location moves upstream to the nozzle exit,due to a shorter length of the outer potential core in Case 2.The change of neutrally stable axial location will affect the spatial distribution of sensitivity and flow response.3 Sensitivity analysis and optimization
本文编号：3441545
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