Numerical Investigation of Wind Turbine Airfoils under Clean and Dusty Air Conditions

About: The article was published on 2020-06-15 and is currently open access. It has received 4 citations till now. The article focuses on the topics: Turbine & Airfoil.

Figures

Fig. 11 Variation in lift coefficients of S809 airfoil under clean air condition using SA model, realizable k-ε model and comparison with experimental data

Fig. 10 Variation in lift coefficient of S809 airfoil with angle of attack at two Reynolds Numbers

Fig. 14 Change in lift coefficient of S809 airfoil under clean and dusty air conditions

Fig. 15 Change in drag coefficient of S809 airfoil under clean and dusty air conditions

Figure 6 and Fig. 7 show the pressure and velocity contours respectively around S809 airfoil at various angles of attack while Fig. 8 and Fig. 9 show the pressure and velocity contours respectively around S814 airfoil at various angles of attack. From the velocity contours, it can be seen that the larger camber near the trailing edge region at the lower surface of the S814 airfoil can create a very low velocity region that can induce separation as the angle of attack increases. Such a behavior of the velocity field affects the pressure field which reduces the lift and increase the drag [6].

Fig. 12 Variation in lift coefficients of S814 airfoil under clean air condition using SA model, realizable k-ε model and comparison with experimental data

Fig. 13 Comparison of computed lift coefficients of S809 and S814 airfoil under clean air condition using realizable k-ε model

Full text

Washington University in St. Louis Washington University in St. Louis
Washington University Open Scholarship Washington University Open Scholarship
Mechanical Engineering and Materials Science
Independent Study
Mechanical Engineering & Materials Science
10-28-2019
Numerical Investigation of Wind Turbine Airfoils under Clean and Numerical Investigation of Wind Turbine Airfoils under Clean and
Dusty Air Conditions Dusty Air Conditions
Siyuan Chen
Washington University in St. Louis
Ramesh K. Agarwal
Washington University in St. Louis
Follow this and additional works at: https://openscholarship.wustl.edu/mems500
Recommended Citation Recommended Citation
Chen, Siyuan and Agarwal, Ramesh K., "Numerical Investigation of Wind Turbine Airfoils under Clean and
Dusty Air Conditions" (2019).
Mechanical Engineering and Materials Science Independent Study
. 100.
https://openscholarship.wustl.edu/mems500/100
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1
Numerical Investigation of Wind Turbine Airfoils
under Clean and Dusty Air Conditions
Siyuan Chen
1
, Ramesh K. Agarwal
2
Washington University in St. Louis, St. Louis, MO 63130
This paper focuses on the simulation of the airflow around wind turbine airfoils
(S809 and S814) under both clean and dusty air conditions by using
Computational Fluid Dynamics (CFD). The physical geometries of the airfoils
and the meshing processes are completed in the ANSYS Mesh package ICEM.
The simulation is done by ANSYS FLUENT. For clean air condition, Spalart–
Allmaras (SA) model and realizable k-ε model are used. The results are
compared with the experimental data to test which model agrees better. For
dusty air condition, simulation of the two-phase flow is operated by realizable
k-ε model and discrete phase model (DPM) in different concentration of dust
particles (1% and 10% in volume). The results are compared with the data of
clean air to illustrate the effect of dust contamination on the lift and drag
characteristics of the airfoil.
Nomenclature
c
l
/C
L
=lift coefficient
c
d
/C
D
=drag coefficient
α=angle of attack/AOA
ρ
air
=density of air
ρ
p
=density of dust particles
μ=viscosity of air
Re=Reynolds number
Ma=Mach number
d
p
=diameter of dust particles
m󰇗
p
=mass flow rate of particles
Δt=time step
F
other
=other interaction forces
u󰇍

p
=velocity of particles
u󰇍

=velocity of airflow
1
Graduate Student, Computational Fluid Dynamics Laboratory, Dept. of Mechanical Engineering &
Materials Science.
2
William Palm Professor of Engineering, Dept. of Mechanical Engineering & Materials Science, Fellow
AIAA.

2
I. Introduction
Because of environmental concerns related to CO
2
emissions and global warming with use of fossil
fuels, there is currently great deal of interest in exploitation of renewable energy sources such as wind
energy among others. In the context of wind energy, great deal of research is being conducted on the
design of wind turbines and wind farms to extract maximum possible energy from the wind.
Optimization of aerodynamic performance of both Horizontal Axis Wind Turbines (HAWT) and
Vertical Axis Wind Turbines (VAWT) is being investigated. Several wind turbine airfoils/blades have
been analyzed and newer airfoils/blades are being analyzed in the literature. National Renewable
Energy Laboratory (NREL) in Colorado has led the effort in this research along with industry and
academia.
For HAWT, aerodynamic characteristics of S809 airfoil have been extensively studied in the
literature. S-series of airfoils are representative of many horizontal-axis wind-turbine (HAWT) airfoils;
S809 is a 21% thick low speed airfoil while S814 airfoil is 24% thick airfoil and there are other S-series
of airfoils of different thicknesses and cambers with different lift and drag characteristics. S809 and
S814 airfoils have been tested in a wind tunnel at the Delft University on Technology and at Ohio State
University and the results have been published [2,3], which are utilized in this paper for comparison
with the numerical results. However, there are very few publications that consider the influence of
dusty air condition on the aerodynamic performance of wind turbine airfoils. In 2017, Douvi, Margaris
and Davaris published a paper on the effect of dusty air effect on the aerodynamic performance of S809
airfoil [5].
The focus of this paper is on the evaluation of the aerodynamic performance of the S809 and S814
airfoils in clean air and dusty air by numerical simulation. Incompressible RANS equations are solved
with one-equation SA model and two-equation realizable k-ε model. The discrete phase, which consists
of dust particles in this case, is injected into the air flow and its effect is calculated using discrete phase
model (DPM) in FLUENT. By comparing the results of clean and dusty air conditions, conclusions
about the effects of dusty air condition on the aerodynamic performance of airfoils are drawn.
II. Numerical Method and Validation
A. Physical model and Mesh Process
The geometry models of airfoils are constructed using their coordinate’s data in Somers’s report [1].
The chord lengths of both airfoils are taken to be 1m. As shown in Figs. 2 and 4, the computational
domain consists of a semi-circle with radius 25m and a rectangle with 50m height and 25m width. The
airfoil is located at the center of the domain. Due to the turbulent boundary layer effects on the flow
field near the airfoil, mesh in this region is much denser than the mesh in the far field. ICEM is used for
mesh generation. Figure 5 demonstrates that the mesh is of high quality and is adequate for simulation.
The solutions are performed on a series of meshes and it is ensured that the solution is mesh
independent and the distance of first grid point from the airfoil surface y+ is less than 1.

3
(a) S809 airfoil
(b) S814 airfoil
Fig.1 Physical models of airfoils
1m
1m

4
Fig.2 Computational domain and mesh around S809 airfoil
（a）Zoomed-in-view of mesh near S809 airfoil
airfoil
outlet
inlet

Frequently asked questions

Q1. What is the effect of dust particles on the aerodynamic performance of the wind turbine?

2. Injection of dust particles can generate negative effects on the aerodynamic performance of the wind turbine airfoil; the drag coefficient increases and the lift coefficient decreases resulting in a lower lift to drag ratio. 

Q2. What is the way to simulate dusty air?

For dusty air simulation, realizable k-ε model is chosen and the discrete phase model (DPM) in FLUENT is employed to inject the dust particles into the flow field. 

Q3. Why is the mesh in the far field much denser than the mesh in the airf?

Due to the turbulent boundary layer effects on the flow field near the airfoil, mesh in this region is much denser than the mesh in the far field. 

Q4. What is the effect of dust on the aerodynamic performance of wind turbines?

4. The wind turbines will not only have erosion and degradation of blades in dusty environment but also poor power generation in countries where sand dust is very common in the environment e.g. countries in the Middle East. 

Q5. What is the effect of dust contamination on the airfoil?

The discrete phase, which consists of dust particles in this case, is injected into the air flow and its effect is calculated using discrete phase model (DPM) in FLUENT. 

Q6. What is the common method for calculating multiphase flows?

C. Discrete phase model (DPM)Currently there are two numerical methods for calculation of multiphase flows: the Euler-Lagrange approach and the Euler-Euler approach. 

Q7. What is the name of the professor?

2William Palm Professor of Engineering, Dept. of Mechanical Engineering & Materials Science, Fellow AIAA.I. IntroductionBecause of environmental concerns related to CO2 emissions and global warming with use of fossil fuels, there is currently great deal of interest in exploitation of renewable energy sources such as wind energy among others. 

Q8. How are the results of dusty air condition calculated?

By using realizable k-ε model and discrete phase model, results of dusty air condition are calculated and compared with results of clean air condition. 

Q9. What is the effect of dust particles on aerodynamic performance of wind turbines?

3. Based on the comparison between results of 1% and 10% concentration of particles by volume in dusty air, it is found that larger concentration of dust particles has more detrimental effects on aerodynamic performance as expected and therefore on the power output of the wind turbine. 

Q10. What is the relative Reynolds number of the flow?

Re is the relative Reynolds number, which is defined asRe ≡ ⃑ ⃑(4)Since the flow is regarded as incompressible and the temperature effects are very small, the energy equation is not considered. 

Q11. What is the effect of stall on the cl- curve?

As α increases, linearly dependence no longer exists and the computed results are significantly different from the experimental data due to the effect of stall [8]. 

Q12. What is the Mach Number of the airfoil?

According to theformula,𝑅𝑒 = 𝜌 ∙ 𝑉 ∙ 𝑑𝜇with the density of air ρair=1.176674 kg/m3 and the viscosity of air μ=1.7894×10-5kg/m∙s, the velocity at the inlet is 22.8m/s and the Mach Number is 0.066.B. 

Q13. What is the difference between the Reynolds Number and the free stream velocity?

Results for S809 airfoil at different Reynolds Number under clean air conditionSince Re and free stream velocity V are linearly dependent with ρ, d and μ being unchanged, differentRe means different free stream velocity faced by the airfoil. 

Q14. How is the change in momentum of a sand particle calculated?

The change in momentum of a sand particle through each control volume can be calculated by the following equation:F = 18𝜇𝐶 𝑅𝑒24𝜌 𝑑 𝑢 − 𝑢 + 

Q15. What is the computational domain of the airfoil?

As shown in Figs. 2 and 4, the computational domain consists of a semi-circle with radius 25m and a rectangle with 50m height and 25m width. 

Q16. What is the lift coefficient of the airfoil?

Figure 10 shows that the lift coefficient increases slightly when the Reynolds number increases from 1×106 to 1.5×106, which leads to change in lift to drag ratio.