建立了一套基于非结构网格技术和动量源模型的直升机旋翼CFD方法，用来模拟贴地飞行时直升机旋翼非定常气动特性。其中，控制方程采用三维Navier-Stokes（N-S）方程，空间方向上采用Jameson格式，时间方向上采用五步Runge-Kutta迭代法，选用Spalart-Allmaras湍流模型。旋翼对流场的作用采用动量源项模拟，为更真实地模拟地面效应的作用，采用了“移动地面”的物面边界来代替常规的“固定地面”边界，并对旋翼附近及旋翼与地面之间的网格进行加密处理，以提高地面涡的捕捉精度。考虑实际飞行环境下旋翼的运动和操纵，在流场计算时考虑旋翼配平特性。其中，配平方程的旋翼气动力通过CFD方法和动量-叶素组合理论模型的耦合计算给出，为了提高配平方法的鲁棒性和效率，提出并建立了基于遗传算法/拟牛顿法的高效混合迭代算法。运用所建立的方法，首先，选用有试验结果可供对比的算例计算了地面效应作用下的旋翼拉力增益、诱导速度以及功率变化，验证了计算方法的有效性，解决了涡流理论方法较难模拟的“小速度前飞旋翼需用功率突增”问题。然后，着重研究了UH-60A直升机旋翼在不同离地高度、不同前进比贴地飞行时，旋翼需用功率、诱导速度、地面涡及旋翼操纵的变化规律。计算结果表明：地面涡出现在较小的前进比范围内，随前进比的增大，地面涡在纵向平面将顺来流方向移动，在轴向方位靠近地面方向移动，直至最后不断减弱消失。
A CFD (computational fluid dynamics) method based on the unstructured grid technique and momentum source method is developed aiming at simulating the unsteady aerodynamic characteristics of a rotor in ground effect (IGE). In this method, the three-dimensional Navier-Stokes equations have been taken as governing equations, the discretization of convective fluxes and the time marching are completed by Jameson scheme and the five-step Runge-Kutta iteration method respectively, and one equation Spalart-Allmaras turbulence model has been em-ployed. The rotor is modeled as a distribution of momentum source, to simulate the ground effect more realistically, the boundary of "moving ground" is used instead of the conventional "stationary ground", and the grids near the rotor plane and between the rotor and the ground are refined to capture the ground vortex more accurate. Consider-ing the motion and control of the rotor under the actual flight environment, the rotor trim is taken into account in the simulation of the rotor flowfield. The aerodynamic forces of trim equations are given by coupling of CFD method and momentum-blade element theory model. In order to improve the robustness and efficiency of the trim method, the genetic algorithm/Quasi Newton hybrid iterative algorithm is proposed and established. Firstly, the method is used to calculate the rotor thrust increment, rotor power required and induced velocity in ground effect. The calcu-lated results are compared with the experimental results aiming at verifying the validity of the method, the problem of ramp increment of rotor power required at a low speed flight have been solved which is difficult for wake analy-sis methods. Then, the flowfields of UH-60A helicopter rotor in different flight heights, different advance ratios have been calculated, the difference of the rotor power required, induced velocity, ground vortex and rotor control are investigated. The calculated results show that the ground vortex appears at small advance ratio, with increase of the advance ratio, it moves along inflow direction in the longitudinal plane and moves close to the ground in axial direc-tion, it becomes weaken continuously and finally disappears.
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