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共轴双旋翼直升机在近地悬停时存在复杂的旋翼/旋翼/地面干扰效应.为分析近地悬停时共轴双旋翼流场及拉力变化,发展一种共轴双旋翼悬停地面效应计算方法.首先,分别采用升力面法和面元法模拟桨叶和地面对流场的作用,使用三阶精度时间步进格式进行桨叶尾迹计算,并在尾迹迭代过程中引入“等体积”法修正尾迹.然后,运用模型得到共轴双旋翼无地效的诱导速度分布和单旋翼地面效应下的拉力增益并与试验结果对比,验证方法的合理性.最后,基于算例,分析了共轴双旋翼在地面效应悬停状态下的特性,包括尾迹及流场特点、诱导速度与拉力分布、旋翼间干扰和拉力增益.结果表明:悬停地面效应下共轴双旋翼的尾迹发生卷起并径向扩展,其桨盘平面的诱导速度由上旋翼、下旋翼和地面共同引起;分析也表明了悬停地面效应下共轴双旋翼桨盘平面诱导速度及桨叶拉力分布更均匀,在相同功率下,共轴双旋翼的地面效应拉力增益大于同实度单旋翼的拉力增益.
Coaxial twin-rotor helicopters have complex rotor / rotor / ground disturbance effects when hovering in the near field. In order to analyze the variation of flow field and tension of coaxial dual rotor when hovering in near-field, a co-axial double-rotor hover ground effect First of all, the effect of blade and ground convection field is simulated by the method of lift-plane method and face-element method respectively, the third-order precision time stepping format is used to calculate the blade wake, and the wake iteration process is introduced into “ Volume ”method is used to correct the wake.After that, the model is used to obtain the induced velocity distribution of the co-rotating twin rotor without ground effect and the pull gain under the ground effect of the single rotor, and compared with the experimental results to verify the rationality of the method.Finally, The characteristics of co-rotating twin rotor under ground effect hovering are analyzed, including wake and flow field characteristics, induced velocity and tension distribution, rotor-to-rotor interference and drag gain.The results show that the wake of coaxial double rotor The roll induced by the upper rotor, the lower rotor and the ground caused the roll-up and radial expansion of the propeller plane. The analysis also showed that the plane-induced velocity of the co-rotor and the propeller Tension more evenly distributed, at the same power, ground effect coaxial dual rotors gain is greater than the tension force gain with a single rotor solidity.