Effects of oscillating trailing-edge flap on the unsteady aerodynamics of an electrically controlled rotor under parallel blade vortex interaction

To investigate the aerodynamic characteristics of the blade flap segment of an electrically controlled rotor during pitching motion under parallel blade vortex interaction, an aerodynamic analysis model is developed based on the lattice Boltzmann method combined with large eddy simulation. Unsteady flow structures under vortex disturbance can be obtained through solving explicit and transient Lattice Boltzmann equations, followed by analysis of the resulting aerodynamic load response. The effects of different flap deflection amplitudes and phases are also evaluated. Upon impingement on the leading edge directly, the free vortex splits into two components above the upper and beneath the lower surfaces, each inducing corresponding disruptions. The upper-surface vortex component triggers boundary layer disturbances, which evolve into coherent vortex structures during convection downstream through overtaking and absorbing the boundary layer instabilities. Larger downward flap deflection appears to enhance the development of the induced vortex and further accelerate its propagating rate, eventually becoming more coherent and causing apparent load fluctuations during its separation from the trailing edge. Conversely, significant upward flap deflection simultaneously attenuates the development and convection rate of the induced vortex, leading to weaker and delayed vortex structure corresponding to a reduction in load oscillations. On the lower surface, the vortex component thickens the boundary layer, which subsequently becomes unstable. Increased downward flap deflection advances the onset of lower-surface boundary layer instability and promotes the formation of the vortex structure, while upward flap deflection effectively suppresses the boundary layer instability induced by the interaction of the vortex component with the lower surface.