【作者】 叶靓；

【导师】 徐国华；

【作者基本信息】 南京航空航天大学 ， 飞行器设计， 2009， 博士

【摘要】 本文建立了一个适合于直升机旋翼流场和噪声计算的非结构自适应运动嵌套网格系统,发展了一套与该网格系统相对应的旋翼流场和噪声数值求解方法及程序。在此基础上,对直升机旋翼的流场和噪声特性进行了计算和分析,主要工作如下:作为背景和前提,首先论述了计算流体力学(CFD)方法在直升机流场和气动噪声等应用研究方面的发展概况,指出了开展旋翼流场和噪声研究的重要性以及计算网格对数值模拟的重要意义,提出了本文拟采用的研究方法和内容。在第二章,结合直升机流场的特征,综合分析了结构网格、非结构网格和直角网格(也可以认为是一种非结构网格)的特点,建立了一套新的适合于直升机流场计算的非结构自适应运动嵌套网格方法和相应贡献单元搜索策略,并分别给出了二维和三维情况下的自适应网格算例。在上一章建立的非结构网格基础上,发展了一套基于非结构网格的直升机悬停和前飞状态流场的数值模拟方法及程序。在求解N-S主控方程时空间方向上使用逆风单调守恒格式(MUSCL)与通量差分裂方法相结合来计算通量,并使用梯度重构的方法维持计算的精度;时间方向上采用双时间方法以计及旋翼流场的非定常特征,在伪时间方向上使用无矩阵存储的LU-SGS方法。应用发展的求解器,分别对旋翼的悬停和前飞情况下的桨叶表面压力、桨叶拉力和桨尖涡位置等进行了计算,验证了数值方法的有效性。第四章是直升机流场计算的应用研究。使用发展的网格系统和求解程序,深入讨论了旋翼在近地工作状态时的流场特性,计算了共轴式双旋翼在干扰状态下的气动力变化和涡轨迹位移,开展了直升机旋翼/机身组合流场的研究、分析了桨叶和机身空间相对位置变化及桨叶挥舞运动对流场特性的影响。在此基础上,得出了一些有意义的结论。在第五章,将所发展的基于非结构嵌套网格的流场计算方法和声场求解的Kirchhoff公式相结合,建立了一个适合于旋翼噪声数值计算的方法和求解程序,并给出了在非结构网格上建立各种不同积分面的方法。通过悬停和前飞状态的旋翼噪声算例计算,并与可得到的试验结果对比,验证了数值方法的可靠性。然后,以矩形桨尖作为参考依据,着重讨论了不同桨尖形式对旋翼高速噪声的影响。第六章是直升机旋翼噪声计算的应用研究。应用CFD/Kirchhoff方法对一种特殊的旋翼(尾桨)形式——剪刀式旋翼的噪声特性进行了分析,并对其气动力进行了相应的计算。在此基础上,研究了不同剪刀角、不同结构形式和工作状态组合情况下,剪刀式旋翼噪声的变化情况,得出了一些有实际意义的结果。更多还原

【Abstract】 In this paper, an unstructured adaptive overset grid technique and corresponding numerical method which is suitable for solving the flowfield and noise of helicopter rotors has been developed. Based on the developed technique and method, the flowfield and acoustic characteristics of the helicopter rotor were simulated and analysed. The major contributions of the author’s research work are as follows:As the background of the work, the development and application of the CFD method in the rotor flowfield simulation and rotor noise analysis were described firstly, and then the importance of the mentioned research and the significant influence of the grid quality on calculated results were pointed out. Also, the methods which would be used in this paper were briefly introduced.In Chapter 2, after analysing the characteristics of the structured grid, the unstructured grid and the Cartesian grid (can also be regarded as a kind of unstructured grid), a new unstructured adaptive overset grid method which suits for the helicopter flowfield calculation was developed, and a corresponding“donor searching”strategy was presented. As numerical examples, the 2-dimension and 3-dimension illustrations of the grid system were given, respectively.Based on the developed unstructured grid system, a new numerical method and solver were established to solve the flowfield of helicopter rotors in hover and forward flight. In the solution of the N-S equations, the flux was calculated by combining the upwind scheme (MUSCL) with the flux-difference splitting scheme, and the gradients of the primitive variables were achieved by reconstruction technique so as to maintain the precision of computations. Meanwhile, the dual-time stepping method was used for simulating the unsteady phenomenon in helicopter flowfield and the Matrix-free LU-SGS method was used in every pseudo-time step. By the solver, the pressure on blade surface, the blade lift and the tip-vortex trajectory were calculated and the capability of the presented method was demonstrated.Chapter 4 is the application of the method and solver developed in above chapters to the helicopter flowfield simulation. The flowfield characteristics of the rotor which works in ground effects, the aerodynamic force and vortex trajectory of the co-axial twin rotors were studied, the flowfield of the rotor/fuselage combination was also simulated and the influence of the blade flapping motion and the location change among the blades and fuselage on the flowfield were discussed. On the basis of the above simulations, some meaningful conclusions were drawn. In Chapter 5, a solver which is used for simulating the helicopter rotor acoustic characteristic was established by combining the Kirchhoff method and the developed N-S equation solving method on unstructured embedded grid, and the different generation approaches of the integrated surface which were used for sound pressure calculations were given. By this noise solver, the acoustic pressures of the rotor in hover and forward flight were predicted, and the comparisons between the calculation results and the available experimental data were made in order to validate the solver. Taking the rectangular blade tip as the baseline tip, the high-speed impulse (HSI) noise of the rotors with different new blade-tips were calculated and the effects of the new tips on the acoustic characteristics of a rotor were discussed emphatically.Chapter 6 is the application of the noise solver to the helicopter rotor noise computations. The presented method was used for analysing the noise characteristics of a special-configuration rotor or tail rotor, i.e., the scissor rotor. The aerodynamic force was also calculated for the scissor rotor. The effects of the different scissor angles, configurations and operation conditions on the noise of the scissor rotor, and some new results are obtained.更多还原