Numerical Simulation Study On The Unsteady Aerodynamic Force Of Variable-sweep Morphing Aircraft

In nature insects and birds can change their shapes during flight to accommodate the changingenvironment, which gives us the inspiration to put forward the concept of morphing aircrafts.Nowadays, with the development of fluid mechanics, materials and structural mechanics and controltechnologies, this idea has become feasible gradually. Compared to the traditional aircraft, morphingaircrafts can change their shapes according to the changes of mission requirements and externalenvironment to achieve the best aerodynamic performance. As an example, in the Morphing AircraftStructure project carried out by Defense Advanced Research Projects Agency, the Lockheed MartinCompany proposed the folding-wing UAV concept, which can fold its wings according to the flightenvironment and tasks, thereby changing the UAV’s sweep and wing area significantly during flight toobtain a better flight efficiency. From the above description, one can conclude that aircraft morphingis a continuous process, where may exist complex unsteady aerodynamic force. If the unsteadyaerodynamic force is not figured out in this process, it will be difficult to design the control system ofthe morphing aircraft. Therefore, the purpose of this thesis is to establish an unsteady numericalsimulation method for variable sweep morphing aircrafts and calculate the unsteady aerodynamicforce during the wing morphing to provide data and recommendations for the control system design.The commercial fluid dynamics software FLUENT is used in this research, using its secondarydevelopment function, a user-defined function describing the wing movement is written andembedded into the software to do the unsteady calculation. Firstly, two standard examples, a steadyand an unsteady one is chosen to do the calculation and the results have shown that the method usedin this thesis is feasible and highly accurate. Then the steady aerodynamic force of flexible and rigidsweep way were solved separately, results show that the aerodynamic characteristics of flexible sweepway is better than the rigid sweep way, so the flexible sweep way is chosen to do the unsteadyaerodynamic calculation. Thereafter, the unsteady aerodynamic calculation is done with respect to thelinear-speed variable-sweep and the cosine-speed variable-sweep in three different cycles, showingthat the difference between steady and unsteady aerodynamic force is no more than7%and theunsteady aerodynamic force is caused by wing additional-velocity, which has nothing to do with flowfield hysteresis. Finally, some recommendations are proposed for the control system design, and pointout the direction of future research.This project is supported by National Natural Science Foundation of China (Grant No.11372133),Program for ChangJiang Scholars and Innovative Research Team in University (PCSIRT)(NO.IRT0968) and funded by the Priority Academic Program Development of Jiangsu HigherEducation Institutions.