Dynamic mode decomposition analysis of flow characteristics of an airfoil with leading edge protuberances

Abstract

A numerical investigation of the flow mechanisms and fluctuating aerodynamic performances of an airfoil with leading-edge protuberances is presented within post-stall regime at a Reynolds number of 1.2×105. In detail, a large eddy simulation (LES) has been conducted and then validated through quantitative comparisons with experimental and numerical results. Furthermore, dynamic mode decomposition (DMD) analysis has been carried out. Superior to the proper orthogonal decomposition (POD) method, DMD could extract mode with single-frequency characteristics. Therefore, the physical backgrounds of corresponding modes could be identified, and the flow control mechanisms could be uncovered, together with the influence on spanwise coherent structures. From the analysis at a streamwise section near laminar separation bubbles (LSBs), it has been found that the improved aerodynamic characteristics at peaks stem from the strong streamwise vortices induced by leading-edge protuberances, which lead to momentum transfer process from troughs to neighboring peaks. Meanwhile, DMD modes corresponding to the shear layers of LSBs have also been found, and the frequency characteristics are quantitatively depicted. On the other hand, from the analysis at selected lateral slices, the first DMD mode of smooth airfoil case is obviously related with Karman vortex shedding process according to the spatial distribution and frequency characteristics. Although wavy leading-edge causes the breakdown of spanwise coherent structures and the degradation of flow energy, Karman vortex shedding pattern could also be identified at particular troughs in modified airfoil case.