Nonlinear flow control mechanism of two flexible flaps with fluid-structure interaction

The flow control at low Reynolds numbers is one of the most promising technologies in the field of aerodynamics, and it is also an important source of the innovation for novel aircraft. In this study, a new way of nonlinear flow control by interaction between two flexible flaps is proposed, and their flow control mechanism is studied employing the self-constructed immersed boundary-lattice Boltzmann-finite element method (IB-LB-FEM). The effects of the difference in material properties and flap length between the two flexible flaps on the nonlinear flow control of the airfoil are discussed. It is suggested that the relationship between the deformation of the two flexible flaps and the evolution of the vortex under the fluid-structure interaction (FSI). It is shown that the upstream flexible flap plays a key role in the flow control of the two flexible flaps. The FSI effect of the upstream flexible flap will change the unsteady flow behind it and affect the deformation of the downstream flexible flap. Two flexible flaps with different material properties and different lengths will change their own FSI characteristics by the induced vortex, effectively suppressing the flow separation on the airfoil’s upper surface. The interaction of two flexible flaps plays an extremely important role in improving the autonomy and adjustability of flow control. The numerical results will provide a theoretical basis and technical guidance for the development and application of a new flap passive control technology.