Dynamic coupling of nonlinear motion and unsteady aerodynamic load of helicopter bluff-body slung load

直升机钝体吊挂物非线性运动与非定常气动载荷动态耦合研究

¹ Chinese Flight Test Establishment, Xi'an 710089, China
² National Key Laboratory of Science and Technology on Rotorcraft Aerodynamics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

Received: 12 February 2025

Abstract

To analyze the dynamic coupling mechanisms between the nonlinear motion of a helicopter's bluff-body slung load and its unsteady aerodynamic load, and to further improve the prediction accuracy of coupling effects during the helicopter' slung load operations, this paper establishes the numerical simulation method based on computational fluid dynamics (CFD), which is applicable to the bluff-body slung load. Then, the mathematical model of the sling constraining the motion of the slung load is developed, and its rigid-body dynamics model of the slung load is also established. By coupling the CFD model of the slung load with the six-degree-of-freedom rigid-body dynamics model, the dynamic coupling mechanisms between the nonlinear motion of the bluff-body slung load and its unsteady aerodynamic loads are analyzed. The paper clarifies the influence of the transition from narrow-side to broad-side orientations of the slung load on the aerodynamic motion coupling characteristics. The analysis results indicate that the transition, which is triggered by the continuous increase in yaw angle oscillation amplitude, is the primary cause of instability during high-speed flight. During the transition, the drag, the side force and the roll and pitch moments of the slung load rapidly exchange and redistribute. This leads to the rapid attenuation of longitudinal oscillation, while the lateral oscillation amplitude increases significantly. Simultaneously, the yaw angle enters into a stable "spinning" mode. When the speed increases from 40 km/h to 64 km/h, the instability time occurs 40% earlier, and the oscillation amplitude increases by 150%.

摘要

为了分析直升机钝体吊挂物的非线性运动与非定常气动载荷的动态耦合机理, 进一步提高直升机吊挂飞行耦合效应的预测精度, 提出了适用于钝体吊挂物的CFD数值模拟方法, 建立了约束吊挂物运动的吊索数学模型以及吊挂物刚体动力学模型, 通过耦合吊挂物CFD模型和吊挂物刚体六自由度动力学模型, 开展了钝体吊挂物非线性运动与非定常气动载荷动态耦合机理分析, 阐明了吊挂物NS-BS过渡(从窄面到宽面姿态转换)对吊挂物气动-运动耦合特性的影响。结果表明: 偏航角振荡幅值持续增加引起的NS-BS过渡是直升机吊挂高速飞行失稳的核心诱因。过渡时, 吊挂物的阻力与侧力、滚转力矩和俯仰力矩快速交换并重新分布, 导致纵向摆动振荡快速减弱, 但横向摆动幅值激增, 同时偏航角进入稳定"打转"模式。当速度从40 km/h提升至64 km/h时, 失稳时间提前40%, 振荡幅值增加150%。