跨声速压气机转子非定常流场的DMD模态分析
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摘要
采用动力模态分解(DMD)方法对跨声速轴流式压气机转子叶尖区域的复杂流场进行分析。通过DMD分解技术捕获转子叶尖流场的动力学信息和对应的流动结构,选取小质量流量工况下的非定常计算结果为基础数据,得到该工况下99%叶高平面上流线方向速度、径向速度的DMD模态云图以及特征频率,评估了DMD方法分析跨声速压气机叶尖非定常流动特征的能力。结果表明:DMD方法能捕捉到转子叶尖非定常流场的特征频率,第二阶DMD模态的频率与转子叶尖区域小质量流量工况下的振荡频率相等,其他较高的几阶模态频率正好是振荡频率的倍频;提取的前四阶DMD模态中,第一阶模态与均匀流场较为相似;流场振荡主要由低阶模态引起,高阶模态只是流场信息的补充;在一个波动周期内,叶尖区域流场存在正负速度的交替变化过程。
A dynamic mode decomposition(DMD)analysis was performed to investigate the unsteady flow field in the tip region of a transonic axial compressor rotor.Based on the spatial and temporal information as well as the spatial coherent structure in the tip region captured with DMD technology,and taking the results calculated for the unsteady flow field under low mass flow condition as the basic data,the DMD cloud map and characteristic frequency of streamwise velocity and radial velocity at 99% span were acquired,and subsequently the capability of DMD method was evaluated in analyzing the unsteady flow in the tip region of axial compressor rotor blade.Results show that DMD can obtain the frequency of the unsteady flow field in the tip region of blade,and the frequency of the second DMD mode is equal to the blade tip frequency under low mass flow condition;the frequency of other higher order modes is just multiples of the operating frequency.Among the first four DMD modes,the first mode is similar to homogenous flow field.The flow field oscillation is mainly caused under low-frequency mode;higher order modes are only supplementary information of field details.Within a period of oscillation,the unsteady flow field experiences alterative changes from positive velocity to negotive velocity in the tip region of blade.
A dynamic mode decomposition(DMD)analysis was performed to investigate the unsteady flow field in the tip region of a transonic axial compressor rotor.Based on the spatial and temporal information as well as the spatial coherent structure in the tip region captured with DMD technology,and taking the results calculated for the unsteady flow field under low mass flow condition as the basic data,the DMD cloud map and characteristic frequency of streamwise velocity and radial velocity at 99% span were acquired,and subsequently the capability of DMD method was evaluated in analyzing the unsteady flow in the tip region of axial compressor rotor blade.Results show that DMD can obtain the frequency of the unsteady flow field in the tip region of blade,and the frequency of the second DMD mode is equal to the blade tip frequency under low mass flow condition;the frequency of other higher order modes is just multiples of the operating frequency.Among the first four DMD modes,the first mode is similar to homogenous flow field.The flow field oscillation is mainly caused under low-frequency mode;higher order modes are only supplementary information of field details.Within a period of oscillation,the unsteady flow field experiences alterative changes from positive velocity to negotive velocity in the tip region of blade.
引文
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[2]刘波,茅晓晨,张鹏,等.叶尖间隙效应对跨声速压气机性能影响的研究[J].推进技术,2016,37(8):1402-1410.LIU Bo,MAO Xiaochen,ZHANG Peng,et al.Research on influence of tip clearance effects on transonic compressor performance[J].Journal of Propulsion Technology,2016,37(8):1402-1410.
[3]张晨凯,胡骏,王志强,等.轴流压气机转子叶尖间隙流动结构的数值研究[J].航空学报,2014,35(5):1236-1245.ZHANG Chenkai,HU Jun,WANG Zhiqiang,et al.Numerical study on tip clearance flow structure of an axial flow compressor rotor[J].Acta Aeronautica et Astronautica Sinica,2014,35(5):1236-1245.
[4] WU Yanhui,LI Qingpeng,TIAN Jiangtao,et al.Investigation of pre-stall behavior in an axial compressor rotor—part I:unsteadiness of tip clearance flow[J].Journal of Turbomachinery,2012,134(5):051027.
[5] SCHMID P J.Dynamic mode decomposition of numerical and experimental data[J].Journal of Fluid Mechanics,2010,656:5-28.
[6] LIU Yingzheng,ZHANG Qingshan.Dynamic mode decomposition of separated flow over a finite blunt plate:time-resolved particle image velocimetry measurements[J]. Experiments in Fluids,2015,56(7):148.
[7]潘翀,陈皇,王晋军.复杂流场的动力学模态分解[C]//第八届全国实验流体力学学术会议论文集.广州:中国力学学会,2010.
[8] ROWLEY C W,MEZIC I,BAGHERI S,et al.Spectral analysis of nonlinear flows[J].Journal of Fluid Mechanics,2009,641:115-127.
[9] SEENA A,SUNG H J.Dynamic mode decomposition of turbulent cavity flows for self-sustained oscillations[J].International Journal of Heat and Fluid Flow,2011,32(6):1098-1110.
[10] DUNNE R,MCKEON B J.Dynamic stall on a pitching and surging airfoil[J].Experiments in Fluids,2015,56(8):157.
[11]丁杰,胡晨星,刘鹏寅,等.无叶扩压器中非定常流动的DMD模态分析[J].动力工程学报,2017,37(6):447-453.DING Jie,HU Chenxing,LIU Pengyin,et al.Dynamic mode decomposition of the unsteady flow in a vaneless diffuser[J].Journal of Chinese Society of Power Engineering,2017,37(6):447-453.
[12] REID L,MOORE R D.Design and overall performance of four highly-loaded,high speed inlet stages for an advanced,high-pressure-ratio core compressor[R].Washington D C,USA:NASA,1978.