Simulating transitional and turbulent flow around airfoils at medium angles-of-attack

Abstract

Investigated topic of the presented research is transitional and turbulent flow around smallscale propeller blade airfoils that are characterized by small chords, low speeds and therefore, low Reynolds numbers. Here, an airfoil of medium relative thickness designed for nominal operating conditions of 0.3 MRe is considered. Prior studies by simpler computational models (including panel methods and 2D CFD simulations) have demonstrated that best lift-to-drag ratio (that is the desired working regime) ranging from 60 to 80 can be achieved at angles-of-attack 4-6°. Here, that observation is checked by more advanced turbulence models that incorporate the resolution of at least a portion of turbulence spectrum, in particular transition SST scale-adaptive simulation (SAS). Such complex turbulence models require 3D models and quite refined computational grids. Furthermore, the necessary computational effort is truly enormous due to small time-steps and slow convergence. The conducted computational process is presented and explained. Various obtained results, both quantitative and qualitative, are provided. In the end, it can be concluded that the choice of turbulence modeling (and/or resolving) greatly affects the final output, even at medium angles-of-attack where laminar, attached flow dominates. Distinctive flow phenomena still exist, and in order to be adequately simulated, a comprehensive modeling approach should be adopted.