共轴双旋翼悬停地面效应气动特性分析

Aerodynamic Characteristics Analysis for Hovering Coaxial Rotors in Ground Effect

基于时间步进算法建立了适用于共轴双旋翼气动特性分析的旋翼自由尾迹模型,并采用面元法对水平和倾斜地面效应影响下共轴双旋翼系统气动特性进行了研究。在建模的过程中,采用Weissinger-L一阶升力面模型模拟了桨叶的三维效应,并充分考虑了旋翼/旋翼和旋翼/地面之间的气动干扰。通过与尾迹几何和诱导速度试验数据的对比,验证了计算模型的可行性。在此基础上,对共轴双旋翼在地面效应影响下的旋翼尾迹几何形状、流场诱导速度矢量分布和上下两旋翼桨叶的拉力系数分布进行了计算及分析。结果表明,悬停状态下,共轴双旋翼上下旋翼间存在强烈的气动干扰,且地面的影响使旋翼尾迹涡线径向扩展且向上卷起,对共轴双旋翼下旋翼拉力产生明显的影响。

A free-wake model is developed to analyze the aerodynamic characteristics of coaxial rotors system based on the time-marching method, and the aerodynamic characteristics of coaxial rotors operating in ground effect in hover are studied by using the surface panel method. Weissinger-L lifting surface model, whieh is included in the free-wake model is used to simulate the blade three-dimensional effect considering the aerodynamic interference between the rotor/rotor and rotor/ ground. The algorithm is verified by comparing the simulational results with test data of wake geometry and induced velocity values. Then, the wake geometry of coaxial rotors, the induced velocity distribution and aerodynamic load distribution of coaxial rotors in ground effect are calculated and analyzed. The results show that the strong aerodynamic interference exists between the upper and lower rotors in hover, and the phenome- na, which are the rotor wake geometry expand rapidly in radial direction and roll up in ground effect, influence the thrust of the lower rotor obviously.