共轴刚性双旋翼非定常气动干扰载荷分析

共轴刚性双旋翼系统提高直升机最大前飞速度，但旋翼振动载荷明显增大。为研究高速共轴刚性双旋翼系统振动载荷特性，须首先分析共轴刚性双旋翼气动干扰下的非定常气动载荷。基于非定常面元法建立满足桨叶前缘和后缘边界条件的旋翼反流区气动模型以体现高速共轴刚性双旋翼后行边反流区影响，且增加共轴刚性双旋翼桨尖涡-桨叶气动干扰模型以体现共轴刚性双旋翼非定常气动干扰影响，并结合基于黏性涡粒子法的共轴刚性双旋翼尾迹模型，构建高速共轴刚性双旋翼气动干扰下的气动载荷分析方法。通过计算前飞状态下的X2共轴刚性双旋翼特征剖面非定常气动载荷时间历程，并与PRASADUM以及基于NASA OVERFLOW和CREATE AV Helios的CFD/CSD计算结果对比，验证本文共轴刚性双旋翼非定常气动载荷分析方法的有效性。相比于PRASADUM，本文分析更好地体现上、下旋翼在前行边和后行边非定常气动载荷的变化特性，并与CFD/CSD计算结果更吻合。分析X2上、下旋翼气动干扰对共轴刚性双旋翼桨叶非定常气动载荷的影响，以及单旋翼与共轴刚性双旋翼非定常气动载荷差异。分析表明，低速状态下的共轴刚性双旋翼非定常气动载荷受双旋翼桨尖涡干扰显著，而高速前飞状态受双旋翼桨叶干扰明显，且表现出桨叶片数整数倍的辐射状干扰特征。

Analysis of rigid coaxial rotor unsteady interactional aerodynamic loads

The maximum forward speed for helicopter increases by adopting rigid coaxial rotor system, while the vibration load in rotor system obviously increases.In order to analyze the vibration characteristics of high-speed rigid coaxial rotor system, it is necessary to investigate unsteady aerodynamic loads of rigid coaxial rotor with aerodynamic interaction.Therefore, a rotor reverse flow aerodynamic model is established based on an unsteady panel method through satisfying boundary conditions of blade leading-edge and trailing-edge to re-flect the influence of the reverse flow on the retreating side of the high-speed coaxial rotor.Moreover, a rigid coaxial rotor tip-vortex-blade aerodynamic model is added to describe the influence of aerodynamic interaction between the coaxial rotors.Coupling those models with the wake model of coaxial rotor based on a viscous vor-tex particle method, an unsteady aerodynamic analysis method under aerodynamic interaction of high-speed rigid coaxial rotor is established.The aerodynamic load at characteristic span of X2 rigid coaxial rotor is simu-lated during forward flight, and compared with the results of PRASADUM and CFD/CSD based on NASA OVERFLOW and CREATE AV Helios to validate the effectiveness of the present unsteady aerodynamic analy-sis method.Compared to PRASADUM, the present method better describes the variation characteristics of un-steady airloads of the upper and lower rotors on the advancing and retreading sides, and the results agree better with the computational results of CFD/CSD.Finally, the influence of aerodynamic interaction between the X2 upper and lower rotors on the unsteady aerodynamic loads is analyzed, and the difference of unsteady aerody-namic load between the single rotor and coaxial rotor is also investigated.It is shown that the unsteady aerody-namic load of rigid coaxial rotor is affected obviously by the tip vortex of coaxial rotor at low speed, while it is influenced by coaxial rotor blade at high speed.The characteristic of aerodynamic load of coaxial rotor is radial distribution with number of blades at high speed.