Performance Degradation of Wind Turbine Airfoils due to Dust Contamination: A Comparative Numerical Study

Abstract

Sand accumulation can pose significant problems to wind turbines operating in the dusty Saharan environments of the Middle East and North Africa. Despite its difficulty, sand particles can be to a great extent avoided using sealed power drive trains; however, surface contamination of the blades is certainly unavoidable. As a result, aerodynamic losses and even premature separation can be incurred. To mitigate such advert consequences and avoid significant power losses, the choice of properly designed airfoil sections with low contamination sensitivity is a must. Alternatively, mitigation techniques for premature separation may also be considered. In this paper the contamination sensitivity of a number of airfoil sections widely used in the wind turbine industry is compared. Additionally, the possibility of deploying a leading edge slat to mitigate the contamination-driven performance degradation of wind turbine airfoils is explored. A two dimensional CFD model of the particle laden flow over an airfoil section is developed by solving Navier-Stokes equations along with the SST k-ω turbulence model. Additionally, a particle deposition model has been deployed via FLUENT’s discrete phase modeling capability to simulate dust particles trajectories and hence predict their accumulation rate. The preliminary results obtained indicate that airfoil sections with low surface contamination sensitivity specifically designed for wind turbines perform better under dusty conditions. Furthermore installing a leading edge slat affects the aerodynamics of the particle laden flow and may therefore be used to mitigate the adverse effects of surface contamination that otherwise would require frequent cleaning which can be expensive.

Computational Study of NACA 0012 Airfoil in Air-Sand Particle Two-Phase Flow at Reynolds Number of Re=1.76×106

“…Computational study of the air flow and of the two-phase flow over NACA 0012 airfoil was conducted at Re=1.76×10 6 at various angles of attack.…”

“…The simulations were conducted at Re=1.76×10 6 , therefore the flow can be described as incompressible as well as turbulent, for various angles of attack ranging from -9 to 16 degrees, similarly as in previous study [10]. Since the flow is turbulent, the realizable k-ε turbulence model, that was suggested by Shih et al [12], was chosen for the simulations, because not only it is appropriate for aerodynamic applications but also it cooperates well with Discrete Phase Model (DPM).…”

“…Fig. 5 depicts the computational results of the lift coefficient for the NACA 0012 airfoil versus the angle of attack at Re=1.76×10 6 for air flow and two-phase flows consisted of 1% and 5% sand particles in the air compared with one-phase air flow reliable data. It is shown that the predicted lift coefficient curves increase linearly with the angle of attack and there is a good agreement with the XFOIL data for small angles of attack, while there is a difference between the computational results and the XFOIL data for angles of attack higher than 14 degrees, due to stall conditions.…”

“…Much research regarding the simulation of the particles flow over an airfoil has also been conducted by Diab et al [6]. They compared the contamination susceptibility of different airfoil types and they concluded that under dusty conditions, the airfoil types that perform better are these with low surface contamination sensitivity.…”

“…1% and 10%, using the realizable k-ε and SST k-ω turbulence models. Now, in this study, the aim is to investigate the aerodynamic behavior of a different airfoil type, NACA 0012 airfoil, in air phase flow and in air-sand particle two-phase flow consisted of 1% and 5% sand particles in air, using a commercial CFD code, at Re=1.76×10 6 , using the most appropriate turbulence model, which is the realizable k-ε, as it was found in previous study. The computational method as well as the calculations made in the previous study [10] were also used in the current study, that refers to a different airfoil operating under different conditions.…”