基于直接力控制的阵风响应及阵风减缓研究

考察某无人机模型的阵风气动响应特性和基于直接力操纵的阵风减缓效果.在求解非定常Euler方程时引入“网格速度”方法模拟阵风边界条件,通过动态嵌套网格技术实现舵面运动.首先对NACA0006翼型迎角阶跃型阵风的气动力响应进行了验证计算,计算结果与理论结果、文献计算结果吻合良好.在此基础上对某无人机模型在迎角阶跃型、One-minus-cosine型阵风作用下的气动力响应过程进行了数值模拟,并分析评估了不同舵面运动方式对飞机气动性能的影响.最终研究比较了不同舵面运动方式下阵风气动响应的减缓效果.结果表明:通过合理设计舵面运动,可以有效达到抑制阵风引起的非定常气动干扰的目的.

Research of the gust response and gust alleviation based on direct force control

The paper presents a methodology for calculating the unsteady aerodynamic forces characteristics and gust response of the unmanned air vehicle(UAV) model using computational fluid dynamics(CFD) tools,and the efficiency of gust alleviation based on direct force control are also studied.Based on unsteady Euler equations,dynamic responses in vertical gust flow perturbation are investigated.The grid velocity method,which is used to model unsteady flow via grid movement,is introduced to simulate the gust influence.This approach avoids numerical instabilities and decouples the step change in the angle of attack from a pitch rate.And the dynamic chimera grid method is used to simulate the rudder movement of the gust alleviation effect.Numerical results for the NACA0006 airfoil are validated by comparison with analytical results for two-dimensional indicial responses.The initial and final lift values of the indicial responses closely match the exact analytical values as given by piston theory and quasi steady thin airfoil theory respectively.The solutions at small times match quite closely the exact solution which is known only for small times given by linear theory.The application of the same method to the UAV model reveals important characteristics of the three-dimensional vertical discrete gust response for the One-minus-cosine gust profile and gusts cause step changes in the angle of attack,and important characteristics of the gust response and resulting flow features are explained.Furthermore,the flow perturbations under dynamic rudder motion are investigated using moving chimera grid technique.Our study shows that with certain designed motions,the flapping rudder can effectively alleviate the freestream gust fluctuation and ensure a stable flight.However,no single parameter can determine whether the flapping rudder can reduce the gust effect.Finally,unsteady aerodynamic loads are computed for the wing of model with the designed rudder motion,the significance of the gust propagation effects is shown.It is found that the direct calculation of the gust response using CFD gives quite accurate results and provides a rich database.In general,this paper shows that the well-designed rudder movement can effectively alleviate the freestream gust fluctuation and ensure high flight qualities.