AN EXPERIMENTAL AND CFD ANALYSIS OF AIRFOILS USED IN … · 2020. 8. 16. · The rotor mission in a...

ISSN: 2455-2631 © June 2018 IJSDR | Volume 3, Issue 6

IJSDR1806047 International Journal of Scientific Development and Research (IJSDR) www.ijsdr.org 285

AN EXPERIMENTAL AND CFD ANALYSIS OF

AIRFOILS USED IN LOW SPEED WIND TURBINE

WITH DESIGN MODIFICATION

Vikas Kumar Sen1, Prof Pragyan Jain2, Prof S.V.H. Nagendra3

1Research Scholar, 2,3Assistant Professor

Department of Mechanical Engineering, GGITS, Jabalpur (M.P.)

ABSTRACT: Constraints on aerodynamic noise are also becoming increasingly important. The fundamental design

problem, common to all these disciplines, is to design a wing shape that provides the desired lift for given operating

conditions, while at the same time fulfilling the design constraints. However, design optimization normally requires a large

number of analyses of objectives and constraints. Consequently, a careful selection of computational methods, both for the

fluid flow analysis and the optimization process, is essential for a fast and efficient design process.

This papers provides an approach for determining the aerodynamics performance of different airfoils with some

modifications. The two airfoils NACA 0012 and S2027 has been considered for the study. By cutting the end point to convert

into flat surface, NACA 0012 airfoil has been modified in this work.

The CFD analysis has been carried out along with experimental validations. Eddy viscosity Pressure, Lift, Drag, Different

Velocities and Lift to Drag Ratio are the basic variables for the study.

Among all these parameters discussed above, the pressure drag constitutes the major portion of drag force

experienced by an airfoil. The most common method used to reduce this drag and optimization of other parameters is by

streamlining the airfoil design or it can be further reduced by some simple design modifications. Thus, the objective of this

research is to

“Optimize the Aerodynamic parameters by proper modifications in airfoil design via simulation as well as Experimental

analysis path.”

Keywords; Aerofoil; Aerodynamic performance; coefficient of lift; coefficient of drag; lift to drag ratio;

I-Introduction

1.1 General The atmosphere exerts pressure at all times. This type of pressure which exerts a force on all bodies, is called static pressure and

acts equally in all directions. When air is in motion, however, it possesses an additional energy (kinetic energy) due to the fact that

it is moving, and the faster it moves the more kinetic energy it has. In the event that moving air is presently conveyed to lean against

some protest, the kinetic energy is transformed into weight energy. This pressure on the surface of the body which causes the

moving air to stop is called dynamic pressure.

The dynamic pressure is given by

𝐷𝑦𝑛𝑎𝑚𝑖𝑐 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = 1

2𝜌𝑣2 ……… (1.1)

Figure 1.1 Effect of air on an object in static and dynamic condition. (Fundamentals of Aerodynamics, John D)

Lift is a direct phenomenon caused by pressure difference between upper and lower surface. However, drag is generally caused by

two reasons as follows,

A. Due to pressure difference at leading and trailing edge-Pressure drag B. Due to viscous resistance offered by the surface of airfoil- Viscous or friction drag.

1.2 Aerodynamic Characteristics of Wind Turbine Airfoils The efficiency of a wind turbine is mainly determined by the blade, and the aerodynamic performance of the airfoil directly

influences the aerodynamic performance of the wind turbine blade. Compared with traditional aviation airfoils, wind turbine airfoils

have different operating conditions and performance requirements.

Geometric Parameters of Airfoils

The geometric shape and parameters of a wind turbine airfoil shows in Figure 1.2. The following are the basic parameters:

Mean line: the connection of the inscribed circle center around the airfoil.

Leading edge: the forward point of the mean line for the airfoil.

Leading edge radius: the radius of inscribed circle for the airfoil leading edge.

Trailing edge: the last point of the mean line for the airfoil.

http://www.ijsdr.org/



Trailing edge angle: the angle between the upper surface and lower surface of the trailing edge.

Trailing edge thickness: the thickness for the airfoil trailing edge.

Chord: the connection between the leading edge and the trailing edge.

Thickness: the diameter of the inscribed circle for an airfoil.

Camber: the maximum vertical distance between the mean line and the chord line

Figure 1.2 Geometric Parameters of Airfoil

II- Literature Review

2.1 Previous Research based on Airfoils

The development of wind turbine airfoils started with the application of low-speed aviation airfoils, such as glider airfoils, FX-77

airfoil and NASA LS airfoil, etc. In order to adapt to the requirements of wind turbine operating conditions, companies abroad

started to develop wind turbine airfoils from the mid-1980s and by now have developed several series of airfoils, such as American

NREL-S series, Danish Riso series, Dutch DU series and Swedish FFA-W series.

J. L. Tangier; 1987, carried out the work which was directed at developing thin and thick airfoil families, for rotors with diameters

of 10 to 30 m that enhance annual energy output at low to medium wind speeds and provide more consistent operating characteristics

with lower fatigue loads at high wind speeds. Performance is enhanced through the use of laminar flow, while more consistent rotor

operating characteristics at high wind speeds are achieved by tailoring the airfoil such that the maximum lift coefficient C is largely

independent of roughness effects lmax Using the Eppler airfoil design code, two thin and one thick airfoil family were designed;

each family had a root, outboard, and tip airfoil.

J.W. Larsen; 2007 presented a modal for aerodynamic lift of wind turbine profiles under dynamic stall. The model combines

memory delay effects under attached flow with reduced lift due to flow separation under dynamic stall conditions. The model is

based on a backbone curve in the form of the static lift as a function of the angle of attack. The static lift is described by two

parameters, the lift at fully attached flow and the degree of attachment. A relationship between these parameters and the static lift

is available from a thin plate approximation.

2.3 Previous Research based on Aerodynamic Shape of Wind Turbine Blades

The wind energy is an indirect form of the solar energy, since they are the temperature differences and the pressure-induced in the

atmosphere by absorbing solar radiation, which set in motion the winds. The rotor mission in a wind turbine is transforming this

kinetic energy of wind to mechanic energy

In the research study, aerodynamic analysis of the upwind three-bladed horizontal axis turbine is carried out by Mojtaba Tahani et

al ; 2014 using blade element momentum theory (BEM), and a genetic algorithm (GA) is applied as an optimization method. Output

power generation is considered as an objective function, which is one of the most common choices of objective function. The

optimization variables also involve chord and twist distribution variations and the placement of the airfoil sections along the blade

length.

S. Rajakumar and D. Ravindranan 2012 exhibited an approach for the assurance of streamlined execution attributes of even pivot

wind turbines. The ideal spot of a windmill blade is analyzed based on basic blade-component hypothesis. For a given breeze speed

and blade rakish speed, it is demonstrated that the most extreme power effectiveness is accomplished when the blade is contorted

by a program that relies on the variety of the sectional lift and drag coefficients with approach.

III- Research Methodology

3.1 General

The nonlinear behavior makes it difficult to analysis and access the changes in response of airfoils to the flow analytically based on

equations and calculations. Thus it is required to use numerical simulation methods as well as experimental analysis for find out the

behavior.

The analysis has been carried out using two approaches i.e. CFD and experimental analysis. The validation of experimental results

has been first carried out for two different airfoil and thereafter a design modification has been made with the help of CFD analysis.

The three airfoil has been considered for the study i.e. NACA 0012, S2017 and modified NACA 0012.

3.2 Experimental Analysis

3.2.1 Airfoil model

The experimental analysis has been carried out using wooden airfoil experimental model with airflow control.

3.2.2 Experimental Setup

A wind tunnel has been constructed for having cross sectional area for air flow about as shown in Figure 3.1 available at

turbulence laboratory of Department of Mechanical Engineering, Gyan Ganga Institute of Technology and Sciences. For wind flow

at different speed a fan applied in the wind tunnel end.

The three airfoil has been considered for the study i.e. NACA 0012, S2017 and modified NACA 0012. Experimental model is

shown in figure 3.1.




Figure 3.1 Wind Tunnel Set up (GGITS Laboratory)

Test conditions and procedures

The experimental analysis has been carried out at atmospheric condition i.e. room temperature about 25°C and atmospheric pressure.

The results has been obtained at different wind velocities. Specific density of both air and water corresponding to room temperature

was assumed to be 1.145 kg/m3 and 994 kg/m3 respectively.

Figure 3.2 Experimental Setup ( Gyan Ganga College Laboratory)

Figure 3.3 Airfoil placement in air stream in experimental analysis

Figure 3.4 Lift and Drag measurement set up.

Figure 3.5 Load Cell Arrangement




3.3 CFD Analysis

The CFD simulation has been carried out in following steps:

3.3.1 Model Geometry

The geometry consider for the study is in 2-Dimension in which dimension in X and Y axis is considered as per the model

constructed for experimental setup while Z axis is neglected. For geometry generation of NACA 0012 the NACA 4 digit geometry

profile has been considered. The first digit specifies the maximum camber (m) in percentage of the chord (airfoil length), the second

indicates the position of the maximum camber (p) in tenths of chord, what's more, the last two numbers give the most extreme

thickness (t) of the airfoil in level of chrod

For NACA 0012 profile, the airfoil has a maximum thickness of 12% with a camber of 0% located 0% back from the airfoil leading

edge. The coordinates has been calculated using the following relationship. [ Jin Chen, Quan Wang]

𝑦𝑡 = 5𝑡 [ 0.2969√𝑥

𝑐− 0.126 (

𝑥

𝑐) − 0.3516 (

𝑥

𝑐)

2

+ 0.2843 (𝑥

𝑐)

3

0.1015 (𝑥

𝑐)

4

] (3.1)

In the formulae the x coordinates from 0 to c i.e. chord length, the t value represents the maximum thickness and 𝑦𝑡 is the variation in y axis i.e. half thickness corresponding to the chord length variation.

The mean camber line coordinates has been calculated by using following relationship

𝑦𝑐 = 𝑚

𝑝2 (2𝑝𝑥 − 𝑝2) 𝑤ℎ𝑒𝑛 𝑥 𝑣𝑎𝑟𝑖𝑒𝑠 𝑓𝑟𝑜𝑚 0 𝑡𝑜 𝑝 ……….. (3.2)

𝑦𝑐 = 𝑚

(1−𝑝)2 ((1 − 2𝑝) + 2𝑝𝑥 − 𝑝2) 𝑤ℎ𝑒𝑛 𝑥 𝑣𝑎𝑟𝑖𝑒𝑠 𝑓𝑟𝑜𝑚 𝑝 𝑡𝑜 𝑚 .. (3.3)

Here, the 𝑦𝑐 is the variation in y axis i.e. half thickness corresponding to the length of foil, t represents the maximum air foil thickness and p represents the maximum camber in- respect of 10th of chord.

The final coordinates for both above and below surfaces can be given by

For Above surface

𝑥𝑎 = 𝑥𝑐 − 𝑦𝑡 𝑆𝑖𝑛 𝛼 ……….. (3.4) 𝑦𝑎 = 𝑦𝑐 − 𝑦𝑡 𝐶𝑜𝑠 𝛼 ……….. (3.5) For Below surface

𝑥𝑏 = 𝑥𝑐 + 𝑦𝑡 𝑆𝑖𝑛 𝛼 ……….. (3.6) 𝑦𝑏 = 𝑦𝑐 − 𝑦𝑡 𝐶𝑜𝑠 𝛼 ……….. (3.7) Here the angle α varies according to

tan 𝛼 = 2𝑚

𝑝(𝑝 − 𝑥) 𝑓𝑜𝑟 0 ≤ 𝑥 ≤ 𝑝 …….. (3.8)

And

tan 𝛼 = 2𝑚

(1−𝑝)2(𝑝 − 𝑥) 𝑓𝑜𝑟 𝑝 ≤ 𝑥 ≤ 1 ….. (3.9)

Figure 3.6 NACA 0012 airfoil curve

Figure 3.7 S2027 airfoil curve

3.3.2 Discretization

Mesh generation or discretization is the next step for CFD analysis. The mesh generated during the analysis has been shown in

figure 3.8. A C-type computational grid is used with boundaries. The airfoil is located at center of domain. The computational

domain consist two parts semicircular and rectangular domain. The semicircular domain considered while considering the symmetry

of air foil for proper discretization. A situation comprising of 2 rectangle and 1 semicircle encompasses the National advisory

committee of aeronautics airfoil

The cross area procured to be fine at district close to the airfoil and with prominent imperativeness, and coarser more remote far

away from the airfoil. For this particular airfoil an organized quadratic lattice work was utilized The total nodes and element

generated are 12269 and 122403 respectively for NACA 0012 airfoil, 127221 nodes and 126690 elements for S2027 airfoil and

about 125315 nodes and 124766 elements generated in modified airfoil.




Figure 3.8 Domain consideration

Figure 3.9 Airfoil domain Meshing

Figure 3.10 Mesh generation around NACA 0012 airfoil.

Figure 3.11(a) Mesh generation around NACA 0012 modified airfoil.

Figure 3.11(b) Mesh generation around NACA 0012 modified airfoil (Tip)

Figure 3.12 Mesh generation around S 2027 airfoil

3.3.3 Boundary and Initial Condition

Over the inflow part of the outer boundary of the grid, the velocity is fixed, while constant pressure gradient is assumed over the outflow part. In order to create a flow field to be used as initial condition, a steady flow around the airfoil is simulated.

The Fluent Work bench using Double Precision panel window has been used for the simulation The computer simulation procedure continuous till the corresponding coefficient of lift (CL) or coefficient of drag (Cd) appeared to

show stable out suitably

The Spalart- All as model is considered for the simulation which defines a single-equation model that resolves a transport equation of the designed modelled for the unavoidable kinematic viscosity that forms turbulence eddies.

Density based steady state solver is used during the simulation.

IV- Result Analysis




4.1 General

The Experimental and FEA has been carried out for three different airfoils. Results are described for all the three different airfoils.

4.2 CFD Results for NACA 0012

In this section the CFD results have been discussed

4.2.1 CFD Results for NACA 0012 Airfoil at 6.6 m/s Air Velocity

Figure 4.1 and 4.2 shows the distribution of eddy viscosity and Pressure for NACA 0012 airfoil at 6.6 m/s air velocity

respectively.

Figure 4.1 Distribution of Eddy Viscosity for NACA 0012 Airfoil at 6.6 m/s Air Velocity

Figure 4.2 Distribution of Pressure for NACA 0012 Airfoil at 6.6 m/s Air Velocity





respectively.





respectively.







Figure 4.7 and 4.8 shows the distribution of eddy viscosity and Pressure for NACA 0012 airfoil at 4.6 m/s air velocity respectively.

4.2.5 CFD Results for NACA 0012 Airfoil at 4 m/s Air Velocity





respectively.








4.3 CFD Results for S2027 airfoil

4.3.1 CFD Results for S2027 Airfoil at 6.6 m/s Air Velocity

Figure 4.21 Distribution of Eddy Viscosity for S2027 Airfoil at 6.6 m/s Air Velocity

Figure 4.22 Distribution of Pressure for S2027 Airfoil at 6.6 m/s Air Velocity













4.3.5 CFD Results for S2027 Airfoil at 4 m/s Air Velocity











4.4 CFD results for NACA 0012 Modified Airfoil

4.4.1 CFD Results for NACA 0012 MODIFIED Airfoil at 6.6 m/s Air Velocity

Figure 4.41 Distribution of Eddy Viscosity for NACA 0012 Modified Airfoil at 6.6 m/s Air Velocity

Figure 4.42 Distribution of Pressure for NACA 0012 Modified Airfoil at 6.6 m/s Air Velocity

4.4.2 CFD Results for NACA 0012 Modified Airfoil at 6.0 m/s Air Velocity












4.4.5 CFD Results for NACA 0012 MODIFIED Airfoil at 4 m/s Air Velocity
















Figure 4.57 and 4.58 shows the distribution of eddy viscosity and Pressure for NACA 0012 Modified airfoil at 1.3 m/s air velocity

respectively.









4.5 Discussion and Comparison

4.5.1 Eddy Viscosity

Figure 4.61 Comparison for Eddy Viscosity in all the three airfoils

4.5.2 Pressure

Figure 4.62 Comparison for Pressure in all the three airfoils

4.5.3 Lift and Drag

Figure 4.63 Comparison of Lift on the basis of CFD and Experimental result for all the three airfoils

Figure 4.64 Comparison of Drag on the basis of CFD and Experimental result for all the three airfoils

Figure 4.77 Lift to Drag Ratio for all the three airfoils




V-Conclusion

For the study basically two airfoils have been considered i.e. NACA 0012 and S2027. NACA 0012 air foil has been modified by

some geometrical changes i.e. cut at the toe. The comparison is made on the basis of CFD and Experimental analysis.

Eddy Viscosity, Pressure, Lift, Drag, Different air Velocities and Lift to Drag Ratio are the basic variables consider for the study.

The following observations has been made:

It is found that the eddy viscosity maximizes in between 2 to 3 m/s airflow velocity for all the three airfoils and thereafter it lowers. The minimum Eddy viscosity depicts in NACA 0012 modified air foil, which can be due to the reduction in turbulence due to

modification in shape of the airfoil.

It is found that all the three foil exerts almost same maximum pressure but maximum in case of S2027 and minimum in case of modified NACA 0012 airfoil.

It can be seen that Lift is maximum in S 2027 airfoil and it is decreasing in order of NACA 0012 modified and NACA 0012 airfoil. The minimum drag is shown by NACA 0012 and it is increasing in order of S2027 and NACA 0012 modified airfoil respectively. It can be seen that NACA 0012 shows minimum lift to drag ratio and with the modification the Lift to Drag ratio improves. The

modified NACA airfoil shows higher Lift to Drag ratio in between 2 m/s to 4.6 m/s air velocity and at higher velocity it reduces.

While in the case of S 2027 airfoil at higher velocity high L/D ratio can be achieved.

References

[1] A.J. Vitale, A.P. Rossi; 2008, “Computational method for the design of wind turbine blades”, Internat Ional Journal of Hydrogen Energy 33 (2008) 3466– 3470

[2] Baxevanou CA, Chaviaropoulos PK, Voutsinas SG, et al. “Evaluation study of a Navier–Stokes CFD aero-elastic model of wind turbine airfoils in classical flutter. Journal of Wind Engineering and Industrial Aerodynamics”. 2008 ;( 96):1425–1443.

[3] Erick Y. Gómez U., Jorge A. López Z., Alan Jimenez R.,Victor López G., J. Jesus Villalon L., 2013,“Design and manufacturing of wind turbine Blades of low capacity using CAD/CAM Techniques and composite materials”, 2013 ISES Solar World Congress

[4] Eelco Hoogedoorn, Gustaaf B. Jacobs, Asfaw Beyene; 2008, “Aero-elastic behavior of a flexible blade for wind turbine application: A 2D computational study.” Energy. 2010 ;( 35):778–785.

[5] J.W. Larsena, S.R.K. Nielsena, S. Krenk, 2007, “Dynamic stall model for wind turbine airfoils”, Journal of Fluids and Structures 23 (2007) 959–982

[6] J-Y Li, R Li,Y Gao, and J Huang, 2009, “Aerodynamic optimization of wind turbine airfoils using response surface techniques”, DOI: 10.1243/09576509JPE888

[7] Jong-Won Lee, Jun-Seong Lee, Jae-Hung Han, Hyung-Ki Shin, 2012, “Aero-elastic analysis of wind turbine blades based on modified strip theory”, J. Wind Eng. Ind. Aerodyn. 110 (2012) 62–69

[8] Jin Chen, Quan Wang (Eds.), “Wind Turbine Airfoils and Blades”, GREEN Alternative Energy Resources [9] Liping Dai, Qiang Zhou, Yuwen Zhang, Shigang Yao, Shun Kang, Xiaodong Wang; 2017, “Analysis of wind turbine blades aero-

elastic performance under yaw conditions”, Journal of Wind Engineering & Industrial Aerodynamics 171 (2017) 273–287

[10] Lin Wang, Xiongwei Liu, Athanasios Kolios, 2016, “State of the art in the aero-elasticity of wind turbine blades: Aero-elastic modelling”, Renewable and Sustainable Energy Reviews 64 (2016) 195–210

[11] Liu X, Wang L, Pang X. “Optimized linearization of chord and twist angle profiles for fixed-pitch fixed-speed wind turbine blades”. Renewable Energy. 2013 ;( 57):111–119.

[12] Mojtaba Tahani, Tahmine Sokhansefat, Kiana Rahmani, Pouria Ahmadi; 2014, “Aerodynamic optimal design of wind turbine blades using genetic algorithm”, energyequipsys/ Vol 2/No2/AUG 2014

[13] Rajakumar S, Ravindran D. “Iterative approach for optimizing coefficient of power, coefficient of lift and drag of wind turbine rotor”. Renewable Energy. 2012; (38):83–93.

AN EXPERIMENTAL AND CFD ANALYSIS OF AIRFOILS USED IN … · 2020. 8. 16. · The rotor mission in a...

Documents

Transcript of AN EXPERIMENTAL AND CFD ANALYSIS OF AIRFOILS USED IN … · 2020. 8. 16. · The rotor mission in a...