针对直升机旋翼CFD仿真的复杂性,提出了改进的适合于格心格式求解器的非结构嵌套网格算法。采用自适应网格技术在旋翼流场仿真的整个过程中进行网格的自适应加密和疏化操作,以更好地捕捉桨尖涡等流动细节。对于频繁的自适应过程中产生...针对直升机旋翼CFD仿真的复杂性,提出了改进的适合于格心格式求解器的非结构嵌套网格算法。采用自适应网格技术在旋翼流场仿真的整个过程中进行网格的自适应加密和疏化操作,以更好地捕捉桨尖涡等流动细节。对于频繁的自适应过程中产生的大量重复点和无用点,采用了高效的交替数字树算法(Alternating digital tree,ADT)和标记-删除-移动算法(Mark,delete,move,MDM)进行删除,节约了不必要的存储。针对格心格式的求解器,采用了基于梯度的网格间插值方式,简化了网格间数值传递的复杂性,同时不降低求解器的精度。对Caradonna&Tung旋翼悬停算例和HLISHAPE 7A旋翼悬停算例进行了模拟验证,计算值与实验值吻合,表明本文建立的方法具有良好的鲁棒性和有效性。最后,与未采用自适应时求解器对桨尖涡的捕捉效果进行了对比,结果表明本文所采用的方法可以明显地提高求解器对桨尖涡的捕捉。展开更多
An investigation is conducted on optimizing the control allocation for trimmed flight on the compound helicopter.The compound helicopter features a single main rotor,a vectored thrust ducted propeller(VTDP)and lifting...An investigation is conducted on optimizing the control allocation for trimmed flight on the compound helicopter.The compound helicopter features a single main rotor,a vectored thrust ducted propeller(VTDP)and lifting wings.Due to the redundant controls for thrust,elevator deflection,and differential and symmetric flap deflection,there is a wide range of trim solutions in forward flight for compound helicopter.A method is developed to calculate optimal trim solutions.Firstly,aerodynamics models for deferent subsystems of the compound helicopter are conducted,which consider the mutual interaction of each part.Secondly,a flight dynamics model is developed based on which the method of trim optimization is performed.Finally,the method is demonstrated using a compound helicopter UH 60L/VTDP.The trim optimization of flight conditions from hover to 370 km/h is conducted using the optimization method.The controls,fuselage attitudes as well as the allocation of lift and thrust along with the flight speed are obtained.展开更多
This paper focuses on the prediction of the safe autorotation landing operations of a helicopter following engine failure.The autorotation landing procedure is formulated as a nonlinear optimal control problem based o...This paper focuses on the prediction of the safe autorotation landing operations of a helicopter following engine failure.The autorotation landing procedure is formulated as a nonlinear optimal control problem based on an augmented six-degree-of-freedom rigid-body flight dynamic model.First,the cost function and constraints are properly selected.The direct transcription approach is then employed to solve the optimal control problem.For a UH-60 helicopter,the optimal solutions with the rigid-body model are compared with those obtained using a two-dimensional point-mass model.It is found that the optimal solutions using the two different models show reasonably good agreement,and furthermore the optimal solutions using the rigid-body model involve the time histories of angular rates and attitudes,lateral velocity and position,as well as pitch controls.Finally the optimal control formulations with different cost functions are proposed for taking account of 1-s time delay and minimum touchdown speed.The calculated control strategies and trajectories are realistic.展开更多
文摘针对直升机旋翼CFD仿真的复杂性,提出了改进的适合于格心格式求解器的非结构嵌套网格算法。采用自适应网格技术在旋翼流场仿真的整个过程中进行网格的自适应加密和疏化操作,以更好地捕捉桨尖涡等流动细节。对于频繁的自适应过程中产生的大量重复点和无用点,采用了高效的交替数字树算法(Alternating digital tree,ADT)和标记-删除-移动算法(Mark,delete,move,MDM)进行删除,节约了不必要的存储。针对格心格式的求解器,采用了基于梯度的网格间插值方式,简化了网格间数值传递的复杂性,同时不降低求解器的精度。对Caradonna&Tung旋翼悬停算例和HLISHAPE 7A旋翼悬停算例进行了模拟验证,计算值与实验值吻合,表明本文建立的方法具有良好的鲁棒性和有效性。最后,与未采用自适应时求解器对桨尖涡的捕捉效果进行了对比,结果表明本文所采用的方法可以明显地提高求解器对桨尖涡的捕捉。
基金supported by the National Natural Science Foundation of China(No.51505216)
文摘An investigation is conducted on optimizing the control allocation for trimmed flight on the compound helicopter.The compound helicopter features a single main rotor,a vectored thrust ducted propeller(VTDP)and lifting wings.Due to the redundant controls for thrust,elevator deflection,and differential and symmetric flap deflection,there is a wide range of trim solutions in forward flight for compound helicopter.A method is developed to calculate optimal trim solutions.Firstly,aerodynamics models for deferent subsystems of the compound helicopter are conducted,which consider the mutual interaction of each part.Secondly,a flight dynamics model is developed based on which the method of trim optimization is performed.Finally,the method is demonstrated using a compound helicopter UH 60L/VTDP.The trim optimization of flight conditions from hover to 370 km/h is conducted using the optimization method.The controls,fuselage attitudes as well as the allocation of lift and thrust along with the flight speed are obtained.
文摘This paper focuses on the prediction of the safe autorotation landing operations of a helicopter following engine failure.The autorotation landing procedure is formulated as a nonlinear optimal control problem based on an augmented six-degree-of-freedom rigid-body flight dynamic model.First,the cost function and constraints are properly selected.The direct transcription approach is then employed to solve the optimal control problem.For a UH-60 helicopter,the optimal solutions with the rigid-body model are compared with those obtained using a two-dimensional point-mass model.It is found that the optimal solutions using the two different models show reasonably good agreement,and furthermore the optimal solutions using the rigid-body model involve the time histories of angular rates and attitudes,lateral velocity and position,as well as pitch controls.Finally the optimal control formulations with different cost functions are proposed for taking account of 1-s time delay and minimum touchdown speed.The calculated control strategies and trajectories are realistic.
