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

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 106, and a S809 airfoil is selected to move with accelerations of 1, 4 and 6 m/s2 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.

[1]  T. Theodorsen.  General Theory of Aerodynamic Instability and the Mechanism of Flutter , 1934 .

[2]  Jochen Kriegseis,et al.  Rapid flow separation for transient inflow conditions versus accelerating bodies: An investigation into their equivalency , 2013 .

[3]  M. J. Hoffman,et al.  Effects of grit roughness and pitch oscillations on the S809 airfoil , 1995 .

[4]  Morten Hartvig Hansen,et al.  Aeroelastic instability problems for wind turbines , 2007 .

[5]  David A. Johnson,et al.  Numerical modeling of an S809 airfoil under dynamic stall, erosion and high reduced frequencies , 2012 .

[6]  Shengyi Wang,et al.  Numerical investigations on dynamic stall of low Reynolds number flow around oscillating airfoils , 2010 .

[7]  S. Pope.  Turbulent Flows: FUNDAMENTALS , 2000 .

[8]  Zhiwei Shi,et al.  EXPERIMENTAL INVESTIGATION ON A PITCHING MOTION DELTA WING IN UNSTEADY FREE STREAM , 2009 .

[9]  M. Akbari,et al.  Simulation of dynamic stall for a NACA 0012 airfoil using a vortex method , 2003 .

[10]  P. Moin,et al.  Turbulence statistics in fully developed channel flow at low Reynolds number , 1987, Journal of Fluid Mechanics.

[11]  Frank N. Coton,et al.  A Modified Dynamic Stall Model for Low Mach Numbers , 2008 .

[12]  Javad Abolfazli Esfahani,et al.  Effect of caudal on hydrodynamic performance of flapping foil in fish-like swimming , 2013 .

[13]  J. Gordon Leishman,et al.  Dynamic stall modelling of the S809 aerofoil and comparison with experiments , 2006 .

[14]  Zhiwei Shi,et al.  Effects of Unsteady Freestream on Aerodynamic Characteristics of a Pitching Delta Wing , 2008 .

[15]  S Wang,et al.  Notice of RetractionNumerical investigations on dynamic stall associated with low Reynolds number flows over airfoils , 2010, 2010 2nd International Conference on Computer Engineering and Technology.

[16]  Zhi Tao,et al.  Turbulence modeling of deep dynamic stall at relatively low Reynolds number , 2012 .

[17]  Kobra Gharali,et al.  Dynamic stall simulation of a pitching airfoil under unsteady freestream velocity , 2013 .

[18]  D. M. Somers,et al.  Design and experimental results for the S809 airfoil , 1997 .

[19]  N. Jenkins,et al.  Wind Energy Handbook: Burton/Wind Energy Handbook , 2011 .

[20]  M. Koochesfahani.  Vortical patterns in the wake of an oscillating airfoil , 1987 .

[21]  Hekmat Alighanbari,et al.  An investigation into the effects of unsteady parameters on the aerodynamics of a low Reynolds number pitching airfoil , 2010 .

[22]  Maureen Hand,et al.  HAWT dynamic stall response asymmetries under yawed flow conditions , 2000 .

[23]  Goodarz Ahmadi,et al.  Numerical analysis of flow field around NREL Phase II wind turbine by a hybrid CFD/BEM method , 2013 .

[24]  Ken Badcock,et al.  Investigation of Three-Dimensional Dynamic Stall Using Computational Fluid Dynamics , 2005 .

[25]  Frank N. Coton,et al.  On the S809 airfoil's unsteady aerodynamic characteristics , 2009 .

[26]  P. K. Chaviaropoulos,et al.  Investigating Three-Dimensional and Rotational Effects on Wind Turbine Blades by Means of a Quasi-3D Navier-Stokes Solver , 2000 .

[27]  Hester Bijl,et al.  Comparing different dynamic stall models , 2013 .

[28]  F. Menter.  Two-equation eddy-viscosity turbulence models for engineering applications , 1994 .