Numerical investigation on the aerodynamic performance of airfoil with local flexible structure

Abstract

Recently, the use of flexible structure in aerospace vehicles and micro-air vehicles are increased due to its ability to adapt to severe flow conditions; however; fully flexible structure has the risk to get damage in the case of long chord or high Reynolds number. In this work, a CFD analysis is carried out to study the influence of local flexible structure on the lift performance of airfoil. Single mode vibrations of local flexible structure on the upper surface of the airfoil are investigated with various frequencies and amplitudes. Finite Volume Method is used to discretize the incompressible Navier-Stokes equations and partial fluid structure interaction is examined under the dynamic mesh technique. The flow configurations consist of flow over NACA0012 at Re=1000 and at a low angle of attack. Numerical simulations are conducted for different vibration frequencies and the corresponding flow field characteristics are investigated. Vibrations with a range of amplitudes are then carried out under the same flow conditions and their results are compared with the conventional rigid airfoil. Vibration frequency close to the natural vortex shedding frequency results in the frequency lock-in or synchronization phenomenon. At the frequency lock-in condition and at some moderate vibration amplitude, the amplitude of lift coefficient oscillations is increased. These vibrations on the upper surface of the airfoil resulted in increasing the average lift coefficient, which is further increased with increasing the vibration amplitude. Moreover, the displacement of local flexible structure is completely in phase with the vortex shedding. The length of local flexible structure is also varied between 0.1c and 0.2c and results show that the length of 0.1c has better performance at higher vibration amplitudes. Pressure distributions and vortices around the local flexible airfoil are evaluated. In addition; power spectra based on the lift coefficient are also examined to capture energy in the flow field.