摘要
本文对空间发展Mac=0.61超声速湍流燃烧混合层流动开展了二维/三维大涡模拟(LES)研究,探讨了三维效应在超声速湍流燃烧流动的大涡模拟中的重要性。研究发现,相较于三维LES计算结果,二维LES大幅低估了超声速湍流燃烧混合层的增长率,湍动能的二维LES结果显著偏大而雷诺剪切应力显著偏小。因而,二维LES难以准确模拟超声速湍流燃烧混合层的增长率和湍流脉动特性。二维流动中漩涡拉伸、压缩机制失效,致使二维LES的漩涡结构与三维LES结果显著不同:二维LES计算所得流场呈现清晰的旋涡生成、发展、并对和破碎等演化现象,而三维LES的湍流结构呈不规则状。湍流与燃烧间存在强烈的耦合相互作用,由于二维LES难以准确模拟湍流特性,燃烧场进而在二维LES下呈现一系列特殊的、不同于真实燃烧流动情况的数值现象。漩涡运动带动燃料和氧化剂掺混,掺混界面为火焰前锋。由于漩涡结构不同,致使二维LES的火焰前锋面面积不同于三维LES结果,导致其难以获得准确的燃料效率,最终导致二维LES计算获得的统计平均火焰温度显著偏低。
A supersonic turbulent combustion mixing layer flow with convective Mach number of 0.61 is simulated by LES in the 2D/3D spaces,respectively.The 3D effects for LES of supersonic turbulent flows are analyzed consequently.Through the analyses of the results,it is found that the growth rate of the mixing layer obtained by 2D LES is underestimated substantially compared to results from the 3D LES.In addition,turbulent kinetic energy is higher while Reynolds shear stress is lower for the 2D LES.Therefore,the 2D LES is not adequate to depict the turbulent characteristics of supersonic turbulent combustion flows.In the 2D simulations,the vorticity stretching and compressing mechanism is invalid,which makes the structures of vorticity obtained by 2D LES are different remarkably compared to the 3D LES results.By analyzing the vortex results,the images of vorticity generation,development,pairing and breaking can be observed clearly for the 2D LES,while the structures of vorticity are irregular for the 3D LES.Generally,there are strong interaction between turbulence and combustion.Since the 2D LES is not adequate to depict the turbulent characteristics,the combustion related quantities of 2D LES appear a series of special and unphysical phenomenon.The mixing of fuel and oxidizer is driven by the movement of vorticity.Generally,there are strong reactions at the interfaces between fuel and oxidizer,which makes the interfaces the flame fronts.Because the structures of vorticity of 2D LES are quietly different from that of the 3D LES,the area of flame fronts of 2D LES also differ from the 3D LES results.Consequently,the 2D LES cannot obtain accurate combustion efficiency.Therefore,the present study finds that the mean flame temperature is underestimated remarkably by 2D LES.
作者
刘宏鹏
Liu Hongpeng(College of Aerospace Science and Engineering,National University of Defense Technology,Changsha 410073,China)
出处
《航空科学技术》
2022年第7期57-65,共9页
Aeronautical Science & Technology
基金
国家自然科学基金(12102469)。
关键词
二维和三维大涡模拟
超声速湍流燃烧
混合层流动
2D/3D large eddy simulation
supersonic turbulent combustion flows
mixing layer flows
