旋翼非定常气动特性CFD模拟的通用运动嵌套网格方法

针对直升机旋翼非定常气动特性CFD模拟中的网格生成难题,提出了一套高效、通用的运动嵌套网格生成方法.首先,基于Poisson方程求解和翻折法生成旋翼桨叶的正交贴体网格.其次,针对旋翼桨叶的扭转分布及变距、挥舞等复杂运动,建立了一套通用的洞单元识别的扰动衍射法;为保证洞包络面的封闭性,完善了挖洞过程中网格加密策略;在洞边界确立基础上,提出了一种高效、鲁棒的最小距离法贡献单元搜索的改进方法.在此基础上,建立了基于RANS(Reynolds-averaged Navier-Stokes)方程的旋翼非定常流场CFD模拟方法.最后,采用所建立的方法分别对悬停和前飞状态下的C-T(Caradonna-Tung)旋翼和7A(Helishape 7A)旋翼的气动特性、桨尖涡的位置进行了计算,计算结果与试验值误差小于5%,验证了该运动嵌套网格生成方法在旋翼非定常气动特性CFD模拟中的有效性.

A universal moving-embedded grid method for CFD simulation of unsteady aerodynamic characteristics of rotor

Targeting the problem on grid generation for the CFD simulation of the unsteady aerodynamic characteristics of helicopter rotor, a highly-efficient and universal moving-embedded grid generation method was proposed. Firstly, the orthogonal and body-fitted grid around rotor blade were generated by using Poisson equations and folding approach. Then, considering the twist distribution and the complex pitching, flagging motion of rotor blade, a method for the identification of hole cells named disturbance diffraction method was established. In order to ensure the closeness of hole envelope surface, the grid refinement strategy in the hole-cutting procedure was improved. Meanwhile, based upon the determination of the hole boundary, an modified minimum distance scheme of donor element method with high efficiency and robustness was developed for searching the donor cells. On these basis, the CFD simulation method for unsteady flowfield of rotor was conducted by solving the RANS (Reynolds-averaged Navier-Stokes) equations. Finally, the aerodynamic characteristics and location of the blade tip vortex for C-T(Caradonna-Tung) and 7A (Helishape 7A) rotors were simulated by the presented method in hovering and forward flight respectively. The errors of numerical results are less than 5% according to the experiment data, and the effectiveness of CFD simulation on the unsteady aerodynamic characteristics of different rotors is demonstrated.