Week 7 - Mini project - Flow over an Airfoil
AIM -
To find the drag and lift coefficient for NACA 2412 Airfoil and compare the effects of different angles of attack.
Introduction -
Airfoil or aerofoil are used in various aerospace applications to produce the required lift and drag. The side profile of an airplane wing is an example of an airfoil. The angle of attack refers to the angle at which wind is incident to the airfoil. A positive angle of attack creates a larger amount of lift force and very low drag force; while a negative angle does the opposite. As the angle of attack increases, the lift force increases up to some angle. After this angle, the lift force starts decreasing. This decrease in lift is called stall.
To simulate the case of an airfoil, a virtual wind tunnel is made. This wind tunnel completely encloses the airfoil. The length of the wind tunnel should be 50 times to cord length and its height should be 30 times the chord length.
Formula Used -
Air with a calculated velocity is an inlet in the wind tunnel. The velocity of this air can be calculated using the formula Re = velocity*chord length / kinematic viscosity. The velocity inlet in this simulation is calculated taking Re = 200000, Velocity inlet = 28.414 m/s.
Case Setup -
Step 1 - A 2D geometry is created of the airfoil. This is done by plotting the .dir file points in coverge studio. The points are stiched and the airfoil is given some width (1m in my case) by mirroring these points. Using the two sets of points, triangles are created.
Step 2 - A wind tunnel of required dimensions is made. The inner triangles of the airfoil are deleted just the outer boundary (consisting of its side profile) is kept. All the normals are checked.
Step 3 - The boundaries of the wind tunnel are flagged. Inlet boundary is given 28.414 m/s velocity while front and back are given 2d boundary conditions. The airfoil boundary is given a no-slip wall BC.
Step 4 - The simulation parameters for transient solver are setup. The simulation run time is calculated using the formula flow through time = distance between inlet and outlet/initial velocity.
Step 5 - Velocity is input in regions and initialization.
Step 6 - A fixed embedding is applied to the airfoil boundary. (I've used a scale of 6 and 3 layers). Base grid size is also estimated by the no of cells being generated.
Step 7 - Boundary data is enabled in output files and simulation is ready to run.
RESULTS
Average drag force for angle of attack using k epsilon turbulence model
| Angle of attack | 1 Degree | 5 Degree | 10 Degree | 15 Degree |
| Average drag force | 8.49646193 | 13.08152281 | 41.58241004 | 129.3983102 |
Average drag force for angle of attack using k epsilon turbulence model
| Angle of attack | 15 degree | 10 degree | 5 degree | 1 degree |
| Average lift force | 452.2642385 | 448.0295576 | 290.6970276 | 120.7523213 |