Simulation of Flow over an Airfoil

AIM

To simulate the Flow over an Airfoil

OBJECTIVES

• To run a simulation for flow over a NACA0017 airfoil over various angle of attack.
• To compare the Lift and Drag Forces for the different angle of attack.

INTRODUCTION

Computational Fluid Dynamics or CFD is a technique that deals with the solution of fluid flow fields through numerical analysis. SOLIDWORKS Flow Simulation is a CFD software designed for the everyday SOLIDWORKS user and analyst. It provides dynamic feedback on the fluid flow and Thermal performance of their products. With Parametric optimization capabilities, users can automate the design and analysis process to discover the best iteration of their design within the familiar SOLIDWORKS environment.

The Aerospace industry is increasingly relying on advanced numerical flow simulation tools for analyzing all the components of aircraft. The main part which helps in producing lift is wings. So, the shape of the aerofoil should be designed in such a manner so that maximum lift can be achieved.

An Airfoil is a body of such a shape that when it is placed in an airstream, it produces an aerodynamic force. This can be seen in the cross-section of wings, propeller blades, windmill blades, compressor, and turbine blades in a jet engine.

THEORY

NACA Airfoil: The NACA airfoils are airfoil shapes for aircraft wings developed by the National Advisory Committee for Aeronautics (NACA). The shape of the NACA airfoils is described using a series of digits following the word "NACA”.

Angle of attack: Angle of attack is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is moving.

Effects of angle of attack: With the increase in angle of attack, lift force also increases proportionately up to a critical point called as critical angle of attack. At the critical angle of attack upper flow is more separated and the airfoil produces maximum coefficient of lift.

The study of airfoil behaviour to varying angle of attacks is made in order to determine the best possible dimension for practical condition. In most aeroplanes this is about 16 to 18 degrees. During a cruise, the requirement is to maintain the angle of attack such that drag experienced is minimum so as to use minimum thrust and to improve fuel consumption, this could occur at an angle of 3 to 5 degrees.

The dimensions(minimum) of the computational domain for an external flow should be decided as follows:

CASE SETUP

1. The airfoil data for NACA0017 is downloaded.
2. The curve is created using the option ‘Curve through XYZ points’.
3. Then the sketch is made on the Front Plane using ‘Convert Entities’ and the end points are joined by a line.
4. Then using the ‘Circular Pattern’ option and unchecking the ‘Equal spacing checkbox, another profile of airfoil was made at 10 degrees.Then the original sketch is set as ‘Construction Geometry’
5. Then this sketch is extruded by 0.2 m.
6. Then using the ‘Wizard’ option in‘Flow Simulation’, features and required conditions are set
7. The Analysis type is set to External and Fluid is chosen as Air. Taking the animation time of 1 sec with a step count of 0.1 sec, the velocity along X-axis is set as 600 m/s.
8. Then the dimensions of computational domain so created is varied as required with respect to the chord length of airfoil(1 m).
9. The inflow length was taken as 10m and the outflow was taken as 15m and the total height of computational domain was taken as 10m
10. The Global Mesh level is chosen to be 3.A Local mesh is also inserted on the surface of airfoil for better results.
11. Cut Plots are made for displaying the Velocity and Pressure variations.
12. The Surface Goals are defined as the Force along x and Y-directions(i.e. the Drag and Lift Forces)
13. After this a Parametric study is made. The Input parameter is selected as the Angle of Attack and its value is varied as 0,2,4,6,8,10 using ‘Range with Numbers’ option.
14. The Cut plot and the Surface Goals are defined as Output Parameters.
15. Then the Parametric Study is Run and the Results obtained.

Isometric View of the Airfoil

RESULTS

Angle of attack: 0 degree:

Cut Plot for Velocity

Cut Plot for Pressure

Angle of attack: 2 degree:

Cut Plot for Velocity

Cut Plot for Pressure

Angle of attack: 4 degree:

Cut Plot for Velocity

Cut Plot for Pressure

Angle of attack: 6 degree:

Cut Plot for Velocity

Cut Plot for Pressure

Angle of attack: 8 degree:

Cut Plot for Velocity

Cut Plot for Pressure

Angle of attack: 10 degree:

Cut Plot for Velocity

Cut Plot for Pressure

Comparison of Drag and Lift for different angle of attack:

• Drag and Lift Forces for different Angle of Attack

• Comparing Drag Force and Angle of Attack

• Comparing Lift Force and Angle of Attack

• Comparing Drag Force and Lift Force

OBSERVATIONS

• It was observed from the contours of velocity that maximum velocity increases with increase in Angle of Attack.
• Both the Drag and Lift Forces increases with increase in Angle of Attack.But the rate of increase for Lift Force is Higher(i.e. Lift Force increases rapidly and Drag Force increases slowly with increase in Angle of Attack)

CONCLUSION

Therefore, the Simulation for Flow over the NACA0017 Airfoil is successfully completed and the variation with Angle of Attack is studied.