Analysis of shed vortices in the wake of an airfoil profile relevant to low-speed axial flow rotors

This paper presents a concerted Computational Fluid Dynamics (CFD) and analytical investigation of the profile vortex shedding (PVS) phenomenon for an asymmetric RAF-6E airfoil, being representative of low-speed axial flow rotors. The study focuses on vortex dynamics in the blade wake within the operational range of α = 0.0°–2.7° and R e c = 0.6×10 5 –1.0×10 5 . CFD simulations were validated against experimental data and literature correlations. Utilizing the CFD data, coherent vortex structures were identified using the Lagrangian-Averaged Vorticity Deviation (LAVD) method. The transversal locations of the LAVD-identified vortex centers (VCs) of the PVS vortex multitude have been assigned to characteristic points of the wake mean velocity profile. The analysis shows that, while viscous effects play a local role, convective processes and turbulent mixing dominate the near-wake dynamics: turbulent shear stresses were found to be approximately three orders of magnitude greater than viscous stresses. The CFD-based observations of vortex topology in the wake are in accordance with the trends predicted using the free shear layer equation (FSLE) developed by the authors, being an analytical minimal model for characterizing the PVS-dominated blade wake. A generalized universal Strouhal number ( S t ∗ )—playing a key role in predicting the PVS frequency—has been proposed on the basis of systematic processing of experimental data in the literature. The results provide an aid to comprehension of vortex dynamics in PVS-dominated airfoil wakes. Such comprehension offers a potential for contribution to future elaboration of guidelines aiming at reducing noise and vibration of low-speed axial flow rotors.