Flow over an airfoil
Flow over a Airfoil
Aim :
To simulate the air flow over the airfoil of the NACA0017 model by using the flow simulation tool in solidworks software.
Objective :
- To simulate the flow over the Airfoil from the NACA0017 model data.
- To obtain the Drag force and the Lift force For the various angles of the airfoil model.
Introduction :
An airfoil is the cross-sectional shape of a wing, blade ( of a propeller, rotor or turbine), or sail (as seen in cross-section). An airfoil-shaped body moving through a fluid produces an areodynamic force. The component of this force perpendicular to the direction of motion is called lift. The component of this force perpendicular to the direction of motion is called lift. The component parallel to the direction of motion is called drag. Subsonic flight airfoils have a characteristic shape with a rounded leading edge, followed by a sharp trailing edge, often with a symmetric curvature of upper and lower surfaces. Foils of similar function designed with water as the working fluid are called hydrofoils.
The lift on an airfoil is primarily the result of its angle of attack. when oriented at a suitable angle, the airfoil deflects the on comming air (for fixed-wing aircraft, a downward force), resulting in a force on the airfoil in the direction opposite to the deflection. This force is known as aerodynamic force and can be resolved into two components its called lift and drag force. Most foil shapes require a positive angle of attack to generate lift, but cambered airfoils can generate lift at zero angle of attack.
Lift forces :
A fluid flowing around the surface of an object applies a force against it. It makes no difference whether the fluid is flowing past a stationary body or the body is moving through a stationary volume of fluid. Lift is the component of this force that is perpendicular to the oncomming flow direction. Lift is always accompanied by a drag force, which is the component of the surface force parallel to the flow direction. An airfoil is a streamlined shape that is capable of generating significantly more lift than drag. A flat plate can generate lift, but not as much as a streamlined airfoil, and with some what higher drag.
Therefore the lift equation is given by,
where, L is the lifting force, Rho is the density of air , V is the relative velocity of the airflow , S is the area of the airfoil as viewed from an overhead perpective, and Cl is the lift co-efficient.
Drag Forces :
As with lift, the Drag of an airfoil depends on the density of the air, the velocity of the airflow, the viscosity and compressibility of the air, the surface area of the airfoil, the shape of the airfoil, and the angle of attack. The complexities associated with drag and the airfoil's shape, angle of attack, the air's viscosity and air's compressibility are simplified in the drag equation by use of the drag co-efficient. The drag coefficient is generally found through testing in a wind tunnel, where the drag can be measured and the drag coefficient is calculated by rearranging the drag equation,
In the drag equation, D is the drag force, Rho is the density of the air, V is the velocity of the air, A is a reference area, and Cd is the drag coefficient.
Geometric modelling :
At first the coordinates of airfoil is imported into solidworks through insert curve options and in a suitable plane its converted into an entity for further sketching. The tail section of the airfoil is not closed so a line is drawn between the two point of tail to make it a closed sketch. For simulation for different angle of attacks, it can be rotated about a reference point by providing angle of rotation. Then it extruded to a certain width.
For 0 Deg angle of attack :
For 2 Deg angle of attack :
For 4 Deg angle of attack :
For 6 Deg angle of attack :
For 8 Deg angle of attack :
For 10 Deg angle of attack :
Flow Simulation Setup :
- After modelling, flow simulation was setup and following input conditions are given
- Analysis type : External and Time- Dependent with simulation time of 5 seconds and time step of 1 second.
- Type of fluid : Air
- Type of flow : Laminar & Turbulent
- Wall Condition : Adiabatic wall with 0 micro-meter roughness.
- Initial Condition : Pressure : 101325 Pa , Temperature : 293.2K, velocity X-direction - 600 m/s
- Global goals and surface of airfoil for a much refinement around it.
Simulation Result :
At 0 Deg Angle :
Velocity Contour :
Pressure Contour :
Drag force and Lift force :
At 2 Deg Angle :
Velocity Contour :
Pressure Contour :
Drag force and Lift force :
At 4 Deg Angle :
Velocity Contour :
Pressure Contour :
Drag force and Lift force :
At 6 Deg Angle :
Velocity Contour :
Pressure Contour :
Drag force and Lift force :
At 8 Deg Angle :
Velocity Contour :
Pressure Contour :
Drag force and Lift force :
At 10 Deg Angle :
Velocity Contour :
Pressure Contour :
Drag force and Lift force :
Conclusion :
As angle of attack increases from, the drag forces and lift forces increases simultaneously and stalling conditions is not achived yet. In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded.
The velocity must be higher on the top side than the lower side. This will mean higher pressure at the bottom and lower pressure at the top thereby generating lift. As the angle of attack increases the velocity profile above the airfoil increases as compared to lower face of airfoil. And pressure increases in lower face when compared to the above face of the airfoil.