Abstract The blade air loads of the Airborne Wind Turbine (AWT) may be significantly influenced by the unsteady flow-field at high altitude. Under these susceptible situations, the rotor needs in-depth considerations with respect to transient aspects. The present study focuses on the unsteady aerodynamic performance of stand-alone rotor under the influence of wind shear, yawed, and tilted configurations. The Computational Fluid Dynamics (CFD) transient simulations based on the sliding mesh approach are carried out for analyzing the unsteady behavior of the rotor by lifting the rotor assembly at an airborne altitude from the ground. All simulations are conducted at optimal operating conditions of wind speed and tip speed ratio. In-house Unsteady Blade Element Momentum (UBEM) code using the wind shear, dynamic stall, dynamic wake, and yaw /tilt model are applied to acquire an empirical assessment in terms of rotor torque, thrust, and power coefficient. Finally, the CFD simulated results are compared against the performance curves generated by the UBEM model and acceptable agreement is found within 4.1% deviation at peak operational conditions. The results further reveal that the time-varying aerodynamic loads on the rotor blade gradually achieve steady behavior after three rotation periods. Meanwhile, unique similarities are found in yawed and tilted inflow cases and a 10.7% loss in power coefficient is observed due to rotor yawed inflows. Additionally, in the absence of tower shadows, the strong flow interactions around the rotor blade impose a positive impact on power output. Despite the complexity of unsteady flow phenomena, this present study would be helpful to design a more proficient airborne rotor under the varying load conditions.

中文翻译：

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高空变载荷条件下机载风力机非定常气动性能分析

摘要 机载风力涡轮机（Airborne Wind Turbine，AWT）的叶片空气载荷可能受高空非定常流场的显着影响。在这些易受影响的情况下，转子需要深入考虑瞬态方面。本研究的重点是在风切变、偏航和倾斜配置的影响下独立转子的非定常气动性能。执行基于滑动网格方法的计算流体动力学 (CFD) 瞬态模拟，通过将转子组件从地面提升到空中高度来分析转子的不稳定行为。所有模拟都是在风速和叶尖速比的最佳运行条件下进行的。使用风切变、动态失速、动态尾流、和偏航/倾斜模型用于获得转子扭矩、推力和功率系数方面的经验评估。最后，将 CFD 模拟结果与 UBEM 模型生成的性能曲线进行比较，在峰值运行条件下发现可接受的偏差在 4.1% 以内。结果进一步表明，转子叶片上随时间变化的气动载荷在三个旋转周期后逐渐达到稳定行为。同时，在偏航和倾斜入流情况下发现了独特的相似性，并且由于转子偏航入流观察到功率系数损失 10.7%。此外，在没有塔影的情况下，转子叶片周围的强流动相互作用会对功率输出产生积极影响。尽管不稳定流动现象很复杂，