Aerodynamic Design and Analysis Of Horizontal Axis Wind Turbine (HAWT) Blades Using CFD

Aerodynamic Design and Analysis Of Horizontal Axis Wind Turbine (HAWT) Blades Using CFD

Mr. M. Eswaran1, Mr. A. Dyson Bruno2, Dr. P. Emmanuel Nicholas3

1Lecturer, 2,3Assistant Professor

1,2,3 PSNA College of Engineering and Technology, Dindigul

Abstract In the recent years wind power is broadly considered and utilizecd as one of the most promising renewable energy sources. In the recent research study, aerodynamic analysis of horizontal axis turbine is accomplished by using CFD. Blades which are mostly feasible for commercial grade wind turbines embody a straight span-wise profile along with airfoil shaped cross sections. Wind tunnel test is implemented in order to test aerodynamic efficiency wind turbine blade. In this paper, the researchers choice is NACA 4421 airfoil for analysis. CFD Analysis of HAWT Blade is executed at various blade angles with the aid of ANSYS CFX and also by correlating that result with experimental results. HAWT efficiency remarkably rely upon the blade profile and its orientation. The researchers are able to identify the optimum angle at which HAWT provides constant output.

Keywords: HAWT, CFD, NACA4421

INTRODUCTION

Wind turbine technology is one of the effective means to implement this renewable resource in order to produce environmentally friendly electrical energy. As it is an intricate system it depends upon the iunification of multiple engineering disciplines, which comprises of structures, aerodynamics, controls and electrical engineering. The main objective of the wind turbines is to capture maximum energy from the wind energy. Best design parameters has to be selected for each and every constituent of the wind turbine. It leads to increase in efficiency and life cycle. The two stages of a wind turbine blade design process are aerodynamic design and structural design.

1. Objective

   Maximum aerodynamic efficiency at specific wind speed. To optimize blade geometry to give the maximum power for a given wind speed The objectives of the research are to establish two Dimensional and three Dimensional CFD models of wind turbine blade and rotor, so as

   • To analyse the aerodynamic performance of different aero foils.

   • To predict wind turbine power output at different wind speeds.

1. Airfoil Nomenclature

   Chord length It is calculated as the length from the LE to the TE of a wing cross section which is similar to the vertical axis of symmetry.

   Mean camber line It is a line which is halfway between the upper and lower surfaces.

   Leading edge (LE)- It is the front most point on the mean camber line.

   Trailing edge (TE) It is the most rearward point on mean camber line.

   Camber It is the maximum distance between the mean camber line and the chord line which is measured perpendicular to the chord line – 0 camber or un cambered means the aerofoil is symmetric above and below the chord line.

   Thickness It refers the distance between upper surface and lower surface which is measured perpendicular to the mean camber line.

   Fig.1. Airfoil Nomenclature

2. NACA 4 DIGIT AIRFOIL SPECIFICATION

This NACA airfoil series is controlled by 4 digits e.g. NACA 4421, which designate the camber, location of the greatest camber and thickness. If an airfoil number is

NACA MPXX

e.g.

NACA 4421

then M will be regarded as the maximum camber which is divided by 100. In the example, M=4 hence the camber is

0.04 or 4% of the chord. Likewise, P is the position of the maximum camber that is divided by 10. In the model, P=4 consequently the maximum camber is at 0.4 or 40% of the chord. Mean while XX is noted as the thickness divided by

100. In the illustration, XX=21 thus the thickness is 0.21 or 21% of the chord.

2. DESIGNING OF HAWT

1. Determine the rotor diameter from power equation. Power generated due to wind speed is given by following equation.

   Power in the Wind P = Cp ½ R2 V3

   Cp — Coefficient of performance (0.4 for a modern three bladed wind turbine)

   — Expected Mechanical (or) Electrical efficiency (0.9 would be a suitable value)

   — Effect of air density R — Tip Radius

   V — Wind velocity

2. Choose Tip Speed Ratio (): For a)Electrical power Generation Pick 4<<10

3. Choose Number of Blades (B=3)

4. Select an Aero foil.

5. Attain and study thoroughly the lift and drag coefficient Curves (CL & Cd) by using CFD Software.

6. Determination of chord length: C=8 R cos / 3Br

   Here tan =r(1+a)/(1-a) r=r/v – Relative flow angle

   r – Local tip speed ratio a – Axial induction factor

   a Angular induction factor Blade rotational speed

7. Divide the blade into N elements and moreover 10 to 20 elements are typically used.

8. Relative flow angle

   = 900 (2/3)tan-1 (1/r)

   a= {1 + (4cos2 / CL sin )}-1 a=1-3a/4a-1 here local solidity =Bc/2r

9. Calculate the rotor performance and then modify the design procedure.

   Cp= a(1-a){1- tan }dr

   1. METHOD OF ANALYSIS

      The aerofoil NACA 4421 is chosen for blade modeling as shown in fig.3. NACA 4421 profiles are obtained from Ansys fluent. The blade is modeled for the specification given in Table1.

      NACA 4421 Profile
      Root chord length	1635mm
      Tip chord length	620 mm
      Length of blade	10640mm
      Hub diameter	318.5mm
      Hub length	1446 mm
      Hub to blade (neck)	1460 mm

      Table 1. Blade specification

      Fig 3 Wind Turbine Blade

   2. CFD ANALYSIS PROCEDURE

1. Cavity model of horizontal axis wind turbine blade is created.

   Fig 4. Cavity model of NACA 4421 airfoil

2. Save the above the cavity model in IGES file Format and import this IGES file Into ANSYS CFX.

3. Geometry in ANSYS CFX is generated.

4. Meshing geometry.

5. ANSYS CFX for Pre- processing.

6. Air domain is created.

   Domain Type	Fluid Domain
   Fluid	Air Ideal Gas
   Domain Motion	Stationary
   Heat Transfer Model	Total energy
   Turbulence Model	K-Model

   Table 2 Dimensions of Domain

7. Define inlet

8. Define outlet

9. Define solver control criteria.

   1. RESULT AND DISCUSSION

      Inlet velocity for the experiments and simulations is 16 m/sec and turbulence viscosity ratio is 10. In ANSYS CFX, turbulent flow solution was completely used. A simple solver had been employed and it was set Zero for operating the pressure. For the linear region, calculation must be done earnestly. [7, 8].The airfoil profile and boundary conditions are all created. In cavity domain one inlet, outlets other are symmetry boundary.

      Fig 5. Velocity plot -00 blade angle

      Fig 6 . Velocity plot -22.50 blade angle

      Fig 7. Velocity plot -300 blade angle

      Fig 8. Velocity plot -37.50 blade angle

      Fig .9. Velocity plot -450 blade angle

      Fig 10 . Velocity plot -600 blade angle

      Fig 11 . Velocity plot -50 blade angle

      Fig 12. Velocity plot -900 blade angle

      S.No	Blade angle	Velocity(m/s)	Density(kg/ m)	Power(W)
      1	0	15.5	1.225	1457710.87
      2	22.5	16	1.225	1603379.2
      3	37.5	16.05	1.225	1618457.90
      4	45	16.10	1.225	1633630.84
      5	60	16.17	1.225	1655031.85
      6	75	16.94	1.225	1902902.40
      7	90	17.8	1.225	2207680.92

      Table 3.Effect of power in various angle of blade

      Fig 13.Effect of power in various angle of blade

   2. CONCLUSION

The researchers, in this paper, identify a horizontal axis wind turbine blade with NACA 4421 which is designed and analyzed for different blade angle and wind speed. The CFD analysis is executed by using ANSYS CFX software. In the given figure, the velocity distribution at various blade angles is clearly shown. The upper surface on the airfoil experiences a higher velocity when compared to the lower surface which is easily observed through this.

1.8 References

• NACA airfoil series.pdf

• H. Abbott, A.E. von Doenhoff, L. Stivers, NACA Report No. 824 Summary of Airfoil Data, National Advisory Committee for Aeronautics.

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• Ansys cfx tutorial 12.pdf

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