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大展弦比柔性机翼结构重量轻、气动效率高,广泛应用于高空长航时无人机(UAVs)。飞行过程中,这类机翼在气动力作用下发生大变形,线性结构模型不再适用,需要建立考虑几何大变形的结构模型。采用牛顿力学方法推导了考虑结构几何非线性的机翼结构动力学模型,该方法推导过程简洁、物理意义明确,可以与Hodges基于哈密顿原理的推导方法相互补充,相互验证。为了能够更准确地求解大展弦比柔性机翼的非定常气动力,建立了能够考虑机翼三维效应且适用于机翼空间大变形的非定常气动力模型。基于建立的非线性结构模型和非定常气动力模型,采用松耦合方法建立了非线性气动弹性模型,并通过算例验证了气弹模型的准确性。研究结果表明,大展弦比柔性机翼颤振速度对来流迎角和机翼的展长均较为敏感;当来流速度大于颤振速度时,由于几何非线性,机翼振动并未发散而是形成稳定的极限环振荡(LCO);随着来流速度进一步增加,机翼再次穿过临界稳定点,由不稳定系统变为稳定系统,直到随着速度的增加系统再次达到临界稳定状态。
Large aspect ratio flexible wing structure, light weight, high aerodynamic efficiency, is widely used in high-altitude long-haul UAVs. During the flight, the large deformation of such wing occurs under aerodynamic force, and the linear structural model is no longer applicable. Therefore, it is necessary to establish a structural model that takes into account the large geometric deformation. Newton mechanics method is used to derive the aerodynamic model of the wing structure considering geometric nonlinearity of the structure. The derivation of the proposed method is concise, the physical meaning is clear, and it can complement and verify with Hodges’ Hamiltonian-based derivation method. In order to solve the unsteady aerodynamics of flexible wing with large aspect ratio more accurately, an unsteady aerodynamic model which can consider the three-dimensional effect of wing and is suitable for large deformation of wing space is established. Based on the established nonlinear structural model and unsteady aerodynamic model, a nonlinear aerodynamic model is established by the loosely coupled method. The accuracy of the aeroelastic model is verified by an example. The results show that the flutter velocity of the large aspect ratio flexible wing is more sensitive to the flow angle of attack and the wing span. When the velocity of the flutter exceeds the flutter velocity, the wing vibration does not diverge due to the geometric nonlinearity But forms a stable limit cycle oscillation (LCO). As the incoming velocity increases further, the wing once again crosses the critical stability point and becomes a stable system from an unstable system until it reaches a critical steady state again as the speed increases .