Experimental investigation of the wake dynamics for a NACA0012 airfoil with a cut-in serrated trailing-edge

An experimental investigation of the unsteady dynamics in the wake of a NACA0012 (National Advisory Committee for Aeronautics) airfoil with a narrow-angle cut-in serrated trailing-edge is presented. Time-resolved planar particle image velocimetry (PIV) has been performed in the wake region of the airfoil both with and without serrations at a Reynolds number of 78 000. The boundary layers on both sides of the airfoil surface are tripped and the angle of attack is held fixed at zero. Spectral analysis of the PIV results shows that the trailing-edge serrations are linked to increased velocity fluctuations in the wake region which are centered on a non-dimensional frequency range of fc/U∞≈3−5. Proper orthogonal decomposition (POD) is utilized to analyze the spatiotemporal characteristics of the most dominant structures in the wake. Three POD mode pairs identified in the serrated airfoil wake flow are described in detail in two different PIV measurement planes passing through the tip and root of the serrations. Overall, the serrations substantially increase the turbulent kinetic energy in the wake and concentrate this energy within the three identified mode pairs. Spectral analysis of the temporal coefficient signals pertaining to the three mode pairs shows energy concentrated within the frequency band of increased velocity fluctuations identified in the wake region. POD-based reconstruction unfolded a von Kármán-like vortex shedding from the truncated part of the airfoil with fc/U∞≈3.7, which is primarily v-fluctuation driven, convecting through the domain at close to 90% of the free stream velocity.