“2-lead”多直升机升力系统的气动干扰和性能变化

Aerodynamic Interference and Performance Changes in“2-lead”Multi-lift System with Helicopters

参与协同吊挂的直升机属于近距离编队飞行,旋翼尾流之间存在严重的气动干扰,从而带来复杂的气动力学耦合问题。因此在研究性能优化、先进编队控制之前,有必要研究协同吊挂系统的气动干扰及其带来的性能变化。本文以4架纵列式直升机组成的“2-lead”队形的协同吊挂系统为研究对象,采用黏性涡粒子/面元法研究直升机协同吊挂系统稳定飞行状态下的性能和流场。其中,系统的稳定飞行状态通过分层配平法得到,涡/面法通过风洞试验数据验证。在此基础上,研究了不同飞行速度及不同直升机相对位置下的系统气动干扰和性能变化。计算结果表明:前飞时,研究对象中前后布置的直升机间存在严重的气动干扰。其中,前进比为0.1时,队列中后方纵列式直升机的前旋翼存在20%的推力损失和15%的功耗增加。当队列中直升机间的纵向距离大于3.5倍旋翼直径D、侧向距离大于0.75倍旋翼直径D,或垂向距离大于0.5倍旋翼直径D时,气动干扰均会大大降低。

As the helicopters in a multi-lift system fly in a close formation,there is severe aerodynamic interference between the wake of the rotors,bringing complex aeromechanics coupling.So it is necessary to investigate interference and resulting performance changes before studying performance optimization and advanced formation control.A baseline configuration of four tandem helicopters carrying a load cooperatively in a“2-lead”formation is performed to explore the interference and performance.A vortex-panel approach based on the viscous vortex particle method is employed to investigate the performances and flow fields in a steady-flight state.The steady-flight state is obtained by a hierarchical trimming method,and the vortex-panel approach is validated by wind tunnel experiments.On this basis,aerodynamic interferences and performances at different flight speeds and variant relative positions are investigated.Computational results indicate that for the baseline configuration,there exists serious interference between helicopters in the front-and-rear arrangement,especially at forward flight.At the advance ratio of 0.1,there exists a 20%thrust loss and a 15%power increase for the front rotor of the tandem helicopter behind the formation.The aerodynamic interference will be reduced significantly if the distance between the front and the rear helicopter meets any of the three conditions below:more than 3.5D(D represents the rotor diameter)in the longitudinal direction,more than 0.75D in the lateral direction,or more than 0.5D in the vertical direction.