Effect of acceleration on dynamic stall of airfoil in unsteady operating conditions

Abstract

In this paper the effect of accelerated flow over a moving airfoil is considered and based on the flow field around the airfoil the dynamic stall is evaluated. In contrast to ordinary pitching motion, the dynamic stall evaluation in this study is performed with a different motion pattern, in which the airfoil has a heaving motion in one direction. This motion pattern is also similar to rotation of an element of blade in horizontal axis wind turbines (HAWTs). In present investigation, the Reynolds number is changed during simulation time and variations of this parameter from initial to final values are shown by acceleration parameter. The operating Reynolds number is more than 10 6 , and a S809 airfoil is selected to move with accelerations of 1, 4 and 6 m/s 2 in normal direction to free stream. To resolve accelerated flow filed in the two-dimensional computational domain and to achieve results within a reasonable computation time, the unsteady Reynolds-Averaged Navier-Stokes (URANS) equations are employed. The governing equations are discretized based on the finite volume approach and semi-implicit method for pressure linked equations algorithm is used for pressure-velocity coupling. Furthermore, turbulence effect on flow field is accounted using shear stress transport (SST) k-ω model. It is shown that the accelerated flow can significantly influence on the aerodynamic loads and dynamic stall trend. This study may introduce a new concept regarding dynamic stall and aerodynamic loads when the rotational acceleration is involved in HAWTs. Copyright © 2014 John Wiley & Sons, Ltd. Initial time when the unsteady operating condition starts to occur (s) (2014) Published online in Wiley Online Library (wileyonlinelibrary.com).WIND ENERGY Wind Energ.

Comparative Study of Dynamic Stall under Pitch Oscillation and Oscillating Freestream on Wind Turbine Airfoil and Blade

“…An improvement over Karbasian, Esfahani, and Barati's CFD results [17] can be observed due to the consideration of the transition effect. The B-L model shows a reasonable representation of unsteady aerodynamics.…”

“…Similarly, it can be speculated that time-varying freestream velocity will bring about a different effect on perturbation velocity from that of the plunging motion. For the third pair, Karbasian et al [17] stated that OF can be referred to as PO. However, the equivalence relation between PO and OF still remains open from the point of view of Van der Wall and Leishman [16].…”

Vibration-induced aerodynamic loads on large horizontal axis wind turbine blades

“…Also, dynamic stall simulation of eroded airfoils showed that erosion of the airfoil could greatly affect the wind turbine performance. Karbasian et al [31] investigated the effect of acceleration on the dynamic stall of wind turbine airfoils. As in the case of rotation of an element of the blade in HAWTs, the dynamic stall evaluation was performed with a 'heaving' motion in one direction.…”

“…Using the 'dynamic mesh' technique in CFD, unsteady aerodynamic loads associated with pitching motion [26,[28][29][30] as well as translational motion [27,31] of the airfoil can be simulated. This suggests the feasibility of using CFD techniques to investigate the effects of the vibration-induced unsteady velocity components of the airfoil on the aerodynamic loads.…”

“…The SST k-ω model was chosen for turbulence closure, as it has been successfully applied by other researchers for dynamic stall simulation [29][30][31]38]. The airfoil surface was defined as a 'no-slip' wall.…”