Unsteady Flow Separation and High Performance of Airfoil with Local Flexible Structure at Low Reynolds Number

Abstract

The unsteady flow separation of airfoil with a local flexible structure (LFS) is studied numerically in Lagrangian frames in detail, in order to investigate the nature of its high aerodynamic performance. For such aeroelastic system, the characteristic-based split (CBS) scheme combined with arbitrary Lagrangian-Eulerian (ALE) framework is developed firstly for the numerical analysis of unsteady flow, and Galerkin method is used to approach the flexible structure. The local flexible skin of airfoil, which can lead to self-induced oscillations, is considered as unsteady perturbation to the flow. Then, the ensuing high aerodynamic performances and complex unsteady flow separation at low Reynolds number are studied by Lagrangian coherent structures (LCSs). The results show that the LFS has a significant influence on the unsteady flow separation, which is the key point for the lift enhancement. Specifically, the oscillations of the LFS can induce the generations of moving separation and vortex, which can enhance the kinetic energy transport from main flow to the boundary layer. The results could give a deep understand of the dynamics in unsteady flow separation and flow control for the flow over airfoil.

Mode Competition in a Plunging Foil with an Active Flap: A Multi-Scale Modal Analysis Approach

“…This can be identified from the clear resonance peaks in the power spectrum and periodic orbit in the phase portrait. A similar lock-in phenomenon has been reported in several recent studies of airfoils with morphing surfaces [52][53][54].…”

Effects of local oscillation of airfoil surface on lift enhancement at low Reynolds number

“…In this study, the flow conditions are chosen the same as those in previous work (Kang et al, 2012Lei et al, 2014) for flow past NACA0012 airfoil with locally flexible structure at Re ¼5000, α¼61. The effects of frequency, equilibrium and amplitude of the oscillation on lift enhancement and flow evolutions are discussed in the subsequent sections.…”

“…The flexible structure is located at the leading edge of the airfoil, and the perturbation raised by the aeroelastic coupling of LFWS can propagate downstream and change the flow pattern to improve aerodynamic performance of airfoil at low Reynolds number Lei et al, 2014). The results in the works have highlighted the positive impact of LFWS on aerodynamic performance of the airfoil.…”

“…Choose the primary frequency and amplitude of flexible structure with elastic modulus E ¼ 5 Â 10 4 in the previous study Lei et al, 2014) as reference oscillating frequency, f ref ¼ 1:3570 and the reference amplitude is A mref ¼ 0:00222. The corresponding mode shape is chosen as reference equilibrium of the oscillation w ref ¼ A 0ref n sin πx=l À Á , where A 0ref ¼ 0:00365.…”

“…The oscillation part is located at the leading edge of the upper surface, x A ½0; 0:1, in light of the study of an airfoil with a dynamically deformed leading-edge (DDLE) shape (Sahin et al, 2003) and comments of Greenblatt's review on periodic excitation's location (Greenblatt and Wygnanski, 2000). According to the previous work Lei et al, 2014), the vibration of the structure with simply supported boundary conditions can be expanded as the sum of mean deflection and a set of Fourier functions. During the coupling, the amplitude of the first mode is much larger than the other ones shown in Fig.…”