Computational study of unsteady turbulent flows around oscillating and ramping aerofoils

Abstract

SUMMARYThe aim of this work is to computationally investigate subsonic and transonic turbulent ows around oscillating and ramping aerofoils under dynamic-stall conditions. The investigation is based on a highresolution Godunov-type method and several turbulence closures. The Navier-Stokes and turbulence transport equations are solved in a strongly coupled fashion via an implicit-unfactored scheme. We present results from several computations of ows around oscillating and ramping aerofoils at various conditions in order to (i) assess the accuracy of di erent turbulence models and (ii) contribute towards a better understanding of dynamic-stall ows. The results show that the employed non-linear eddyviscosity model generally improves the accuracy of the computations compared to linear models, but at low incidence angles the Spalart-Allmaras one-equation model was found to provide adequate results. Further, the computations reveal strong similarities between laminar and high-Reynolds number dynamicstall ows as well as between ramping and oscillating aerofoil cases. Investigation of the Mach number e ects on dynamic-stall reveals a delay of the stall angle within a range of Mach numbers. Investigation of the reduced frequency e ects suggests the existence of an (almost) linear variation between pitch rate and stall angle, with higher slope at lower pitch rates. The pitch rate a ects both the onset of dynamic-stall as well as the evolution of the associated vortical structures.

Direct numerical simulation of the flow around an aerofoil in ramp-up motion

“…A complete review on the numerical simulations of dynamic stall [14][15][16][17][18][19][20] can be found in the work of Ekaterinaris and Platzer. 21 One of the major outcomes of this survey is a list of research topics that required further advancements for achieving reliable predictions.…”

The Role of Wind Tunnel Experiments inCFDValidation

“…Many experiments and CFD calculations have been performed on the flow around airfoils forced to oscillate in different kinds of motions (Barakos and Drikakis, 2003;Maresca, Favier and Rebont, 1979;Piziali, 1994;Pascazio et al, 1996;Favier et al, 1988), including ramping, translation, pitching, plunging, and combined motion in either pitching-plunging or translation-pitching. However, very few experiments have been dedicated to the characterization of the flow close to the moving wall and within the boundary layer region.…”

Dynamic Stall Prediction of a Pitching Airfoil using an Adjusted Two-Equation URANS Turbulence Model

“…At the beginning, the compressibility effect was neglected due to limitation of the computational time (Fung and Carr 1991). This problem was brought up again to the surface in the late of '90s by considering the compressibility and turbulence model influences (Ekaterinaris 1995;Ekaterinaris et al 1995;Barakos and Drikakis 2003). However, due to the lack of robust CFD methods, most CFD works were done only focusing on the validation of the CFD codes rather than the physical phenomena of the flow.…”

“…Past studies on turbulent flow have shown that the accuracy of numerical predictions is signicantly affected by the accuracy of the employed turbulence model (Barakos and Drikakis 2003). The zeroequation turbulence model was shown to inaccurately predict separated flow by Baldwin and Lo-max (Baldwin and Lomax 1978).…”

“…The linear eddy-viscosity models have several advantages in the prediction for turbulent flows. They provide satisfactory results for attached, fully developed turbulent boundary layers with weak pressure gradients and are also relatively easy to implement into CFD codes (Barakos and Drikakis 2003). Among them, two-equation eddy viscosity turbulence models were the most commonly used in practice.…”