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

Abstract

The necessity in the analysis of dynamic stall becomes increasingly important due to its impact on many streamlined structures such as helicopter and wind turbine rotor blades. The present paper provides Computational Fluid Dynamics (CFD) predictions of a pitching NACA 0012 airfoil at reduced frequency of 0.1 and at small Reynolds number value of 1.35e5. The simulations were carried out by adjusting the k − ε URANS turbulence model in order to damp the turbulence production in the near wall region. The damping factor was introduced as a function of wall distance in the buffer zone region. Parametric studies on the involving variables were conducted and the effect on the prediction capability was shown. The results were compared with available experimental data and CFD simulations using some selected two-equation turbulence models. An improvement of the lift coefficient prediction was shown even though the results still roughly mimic the experimental data. The flow development under the dynamic stall onset was investigated with regards to the effect of the leading and trailing edge vortices. Furthermore, the characteristics of the flow at several chords length downstream the airfoil were evaluated.

Unsteady Navier-Stokes studies on loads, wake, and dynamic stall characteristics of a two-bladed vertical axis wind turbine

“…The model has been widely used for industrial and academic purposes and is well known to be able to deliver good predictions for flows involving a strong adverse pressure gradient and separation. This has been also shown by previous works, for examples as in [3,18,19,25,10,21,24]. Three variants of time step sizes will be investigated, namely ∆t = T /360, T /720 and T /1440 which are equivalent to 1 • , 0.5 • and 0.25 • blade rotation per physical time step, respectively.…”

“…The origin is quite obvious as the clockwise vortical structure start to detach from the blade surface, depicted in Figure 6d. It has been documented by many authors that deep dynamic stall happens when the breakdown of the travelling vortex takes place [2,3,25,28,29]. The clockwise vortex breakdown (blue color) is caused by the flow insertion effect by the counter-clockwise vortex (red color) near the leading edge.…”

Active separation control on a very thick wind turbine airfoil - A URANS and DDES perspective

“…Both models use the same turbulence closure for the wall bounded flow namely the Shear-Stress-Transport (SST) k-ω as the model is able to predict flows with a strong APG. The same model was used in preceding works either as pure URANS [2,[11][12][13][14][15] or as DDES [14][15][16] with good accuracy.…”

Numerical simulations of a large offshore wind turbine exposed to turbulent inflow conditions

“…The FLOWer code has been extended at the Institute of Aerodynamics and Gas Dynamics (IAG) during the last years for wind turbine applications. Turbulence closure of the unsteady Reynolds Averaged Navier–Stokes (URANS) equations in this study is provided by the eddy viscosity two-equation shear stress transport (SST) k − ω model according to Menter (1994) since the model is able to give good predictions for flows experiencing an adverse pressure gradient (Bangga et al, 2017a, 2017d, 2017e, 2018; Bangga and Sasongko, 2017). Figure 2 presents the mesh used for the 3D CFD computations.…”