6. Conclusions
Synthetic jet control technology for a flying wing UAV under cruising conditions is studied in this paper. The study mainly fo-cuses on improvement of aircraft longitudinal pitching moment characteristics and further analyzes the effects of typical flow con-trol parameters on the control efficiency. The results show that:
(1)At medium angles of attack, synthetic jet disturbances from the leading edge of the model can increase the moment per-formance through improvement of the flow separation, and the control effect in the nonlinear area of pitching moment is more significant.
(2)Periodic disturbance produced by the synthetic jet enhances the momentum transport inside and outside of the boundary layer by improving boundary layer mixing of the disturbance flow. This provides the disturbance flow with enough energy to overcome the adverse pressure gradient and viscosity loss, enabling the flow separation to be eased and even leading to reattachment of separated flow.
(3)The excitation effect of flow arranged at the leading edge of the model is obvious. Under certain conditions, the larger the jet momentum coefficient is, the more significant the distur-bance produced by the main flow field, and the aerodynamic characteristics of the flow field and the jet momentum coeffi-cient show a linear growth trend. The optimal dimensionless jet frequency occurs at around unity, where the flow control effect based on vortex interference reaches an optimal level. The selection of an appropriate jet frequency can not only in-crease the slope reversal angle of pitching moment, but can also achieve an increase or decrease of moment coefficient, thus achieving the goal of controlling the pitching moment of the model.
Conflict of interest statement
The authors confirm that there are no conflicts of interest asso-ciated with this publication and there has been no financial sup-port for this work that could have influenced its outcome.
Acknowledgements
The work described in this paper was supported by the National Natural Science Foundation of China (11302178), Aeronautical Sci-ence Foundation of China (2013ZA53002).