基于非定常面元/黏性涡粒子混合法的旋翼/平尾非定常气动干扰

旋翼/平尾非定常气动干扰是导致直升机纵向“抬头（Pitch-up）”现象的主要原因。为在直升机设计阶段准确分析旋翼/平尾非定常气动干扰以及由此引起的低速纵向操纵特性变化，通过涡量等效原则和Neumann物面边界条件建立了适用于旋翼/平尾气动干扰分析的非定常面元/黏性涡粒子混合法。该方法耦合了考虑尾迹时变效应的非定常面元法、黏性涡粒子法及涡量镜面法，以准确模拟旋翼和平尾的非定常气动载荷、旋翼尾迹的非定常特性以及旋翼尾迹对平尾的气动干扰效应。首先通过计算NASA ROBIN（Rotor Body Interaction）旋翼尾迹几何和诱导速度分布，并与实验测量值、时间精确自由尾迹及CFD计算结果对比验证方法的准确性。相比于时间精确自由尾迹，本文方法计算精度更高。随后分析了旋翼/平尾非定常气动干扰对平尾向下气动载荷和气动导数的影响，并分析了平尾构型对旋翼/平尾非定常气动干扰的影响规律。分析表明：旋翼尾迹与平尾干扰导致低速状态的平尾载荷突增，气动导数反号；低平尾气动载荷突增较大，高平尾较小，但高速气动导数反号；前置平尾载荷突增量减小，但对应速度范围较宽；右旋直升机右平尾载荷突增量较小，但气动导数特性基本不变。

Rotor/Empennage Unsteady Aerodynamic Interaction with Unsteady Panel/Viscous Vortex Particle Hybrid Method

The unsteady aerodynamic interaction of the rotor and empennage of a helicopter is the main cause of the "Pitch-up" phenomenon in helicopter flight dynamics. To accurately predict the rotor/empennage unsteady aerodynamic interaction and the variation of transverse handling characteristics caused by it under low-speed flight in the helicopter design phase, an unsteady panel/viscous vortex particle hybrid method is established through the equivalence of vorticity and Neumann boundary conditions. The unsteady aerodynamic loads of a rotor blade and empennage are described by the unsteady panel method while the rotor time-varying effect and the viscous and stretch effect of the rotor wake are represented by the viscous vortex particle method, and the interaction of the rotor wake and empennage is implemented through a vorticity mirror method. The rotor wake and induced velocity distribution of NASA ROBIN (Rotor Body Interaction) are predicted and compared with experiment, time-accurate free-wake and CFD results. It demonstrates that the present method is more accurate than the free-wake method. The effect of rotor wake/empennage unsteady aerodynamic interaction on empennage airloads is then analyzed, and the influence of empennage type on rotor wake/empennage aerodynamic interaction is also studied. It is shown that rotor wake/empennage aerodynamic interaction leads to an abrupt increase of empennage airloads and the reversal of aerodynamic derivatives in low-speed flight. The increase of low-set empennage's airload is relatively large, while that of high-set empennage is small, and the reversal of aerodynamic derivatives for high-set empennage occurs in high speed. Although the increasing of forward-set empennage airload is small, the range of speed is wide. Increase of the right-set empennage airload for right-handed rotor is small, but the derivative is similar to that of the left-set empennage.