【作者】 冯定华；

【导师】 李桦；

【作者基本信息】 国防科学技术大学 ， 力学， 2010， 博士

【摘要】 超声速/高超声速条件下的复杂流动一直是流体力学理论研究和工程应用中的重点和难点问题,涉及激波、流动转捩、高雷诺数流、非定常流、湍流旋涡分离流等流动现象。本文针对超声速/高超声速流动中出现的这些复杂流动现象,以及由这些复杂流动引起的包括气动光学效应等在内的复杂物理现象,开展了精细数值模拟和实验研究。针对超声速/高超声速复杂流动精细求解中存在的精度和效率问题,提出了基于Menter SST两方程湍流模型的LES/RANS混合数值模拟方法,建立了相应算法模型,并对其进行了可压缩效应修正,编制了程序。为提高程序计算效率,采用了大规模并行计算技术,搭建了基于PC集群的并行计算平台,并实现了程序的并行化。基于Lax激波管、运动激波/密度波干扰、强激波双马赫反射和激波/涡干扰等问题考察了LES/RANS混合数值模拟方法的格式精度,确定采用5阶WENO空间格式、3阶TVD Runge-Kutta时间格式作为LES/RANS数值模拟的基本格式,研究了超声速/高超声速的激波/边界层干扰复杂流动现象。研究结果表明,该方法满足精细求解超声速/高超声速复杂流场要求。通过实验和数值模拟对高超声速来流情况下进气道开启过程的起动特性进行了研究,重点分析了进气道内流激波/边界层干扰对起动特性的影响,得到了非常有价值的结果。实验中,自主设计了高超声速直联式风洞模拟自由来流马赫数5.3,通过测量进气道上壁面压力分布,研究了进气道开启过程的起动特性;在实验基础上,利用本文建立的数值方法,对进气道开启过程中的典型状态进行了数值模拟,分析了进气道开启过程中的复杂激波/边界层干扰现象,讨论了进气道起动特性受到边界层分离影响的规律。针对超声速/高超声速复杂流场引起的气动光学效应,阐明了光学传输与流场属性的内在联系,给出了高速飞行器“近场”如湍流边界层、剪切层以及激波等引起的光学传输效应的表征形式与计算方法,分析了求解气动光学时对流场计算精度的判定准则,并做了讨论和推广。基于超声速/高超声速流场网格和流场数据,提出了步长自适应光线追迹的思想和方法,该方法根据当地折射率梯度和网格几何尺寸自动调节追迹步长,较好地解决了光场中存在大折射率梯度(对应流场中大密度梯度)时光线追迹的精度和效率问题。综合运用LES/RANS数值方法、大规模并行计算技术,数值模拟了Settles凹腔超声速三维流动,得到了剪切层区和再附区的速度型分布和质量流脉动,与实验结果符合较好。在计算所得流场的基础上,采用步长自适应光线追迹方法,研究了凹腔剪切层区域引起的光学传输效应,结果表明凹腔流场剪切层将导致严重的波面畸变,明显降低光强Strehl比。同时还计算了长深比L/D=5开式凹腔的三维非定常流动,对凹腔的自激振荡特性和非定常流动引起的气动噪声进行了研究,分析了凹腔自激振荡模式,相关结果与文献结果符合较好。更多还原

【Abstract】 As a key problem in fluid dynamics research and technology application, the complex supersonic/hypersonic flow involves shock waves, flow transition, high Reynolds number flow, unsteady flow, and turbulent vortex separation. Caused by the supersonic/hypersonic flow, there exist complex physical phenomena such as aero-optical effects. In this dissertation these flow phenomena and physical phenomena were studied based on detailed numerical simulation and experimental method.The LES/RANS hybrid algorithm was proposed, considering the compressibility effects, to solve the problem of fine simulation of supersonic/hypersonic flow. In order to enhance the simulation efficiency a large-scale parallel simulation strategy was carried out, a PC cluster based parallel computing platform was set up, and a parallel program was achieved.Some classic examples, such as Lax shock wave tube problem, moving shock/density wave interference, double Mach reflection and shock/vortex interference, were carried out for investigating numerical methods. And supersonic/hypersonic shock/boundary layer interaction problem was in-depth validated and studied. At last, the 5th order WENO space scheme and 3rd order TVD Runge-Kutta temporal scheme are used in LES/RANS hybrid method to solve the problem of supersonic/hypersonic fine flow simulation. The results showed that the method meets the requirements of sophisticated simulation of supersonic/hypersonic flow.Experimental research and numerical simulation were used to study hypersonic inlet’s flow structure and starting characteristics in the process of inlet lip opening, and got some very valuable results. During experiment, a directly connected wind tunnel was independently designed to simulate a free stream Mach at 5.3, based on which the dynamic process of inlet opening was studied; by measuring the wall pressure distribution on the inlet, the inlet flow characteristics during the process of inlet opening were studied. Based on experiment, the numerical simulation method was used to simulate some typical states in the process of inlet opening. The complex shock/boundary layer interaction phenomenon was analyzed, and the starting characteristics of the inlet with boundary layer separation were also discussed.Focus on the aero-optical effect derive from high speed flow field, the intrinsic link between optical transmission and flow field property was analyzed; the forms of expression and simulation method were built to analyze the optical transmission effect caused by "near field", such as turbulent boundary layer, shear layer and shock wave; then a criterion of solution is proposed and discussed particularly.The ray tracing method used in the study of aero-optical effects was developed. The method was based on grids and flow field data, using Runge-Kutta ray tracing method as the basic way. Based on flow field grid and data, a self-adaptive ray tracing algorithm was proposed, where the tracing step distance is self-adaptive according to local refraction index gradient and grid geometry scale. It can well solve the light field in the presence of large refractive index gradient (corresponding to large density gradient).Using large scale parallel computing, Settles cavity’s supersonic three-dimensional flow was simulated. The velocity distribution and pulse mass flow rate of shear layer and re-attached region has been calculated, and results tallied with experimental data. Based on the calculated flow field, the optical transmission effects caused by cavity shear layer were researched. The results showed that, cavity flow leaded to severe wave front distortion and significantly reduced light intensity Strehl ratio. Another typical open cavity with the length-depth ratio L/D=5 was also studied. Its three-dimensional unsteady flow and self-oscillation characteristics were researched, as well as aerodynamic noise, self-oscillation mode. The results tallied with the data from relevant publications.更多还原