Week 7 - Minor Project
AIM:
To create a domain for flow analysis and Setup simulation for subsonic and supersonic regimes at
○5, 10, 15 angle of attack
THEORY:
Lift theory:
Air flowing around the airfoil is attached to the airfoil. The point at which the air first hits the airfoil is called the stagnation point as the velocity of air comes to rest and pressure is buildup. the flow separates at the leading edge of the airfoil and attached flow happens. The flow of fluid attaches to the surface near to it and follows the surface and this is called the Coanda effect. The fluid with high velocity has low pressure and vice versa this law is called Bernoulli's principle. The airfoil shape is in such a way that the lower part is concave and the upper part is convex, when the airfoil is kept in airflow the air above will have higher velocity than the air flowing below, this is because the convex shape decreases pressure and concave shape increases pressure( towards the trailing edge). The particles of the fluid above and below the airfoil will never meet as the velocity of the particle above is always greater than the particles below. The airflow is directed downward at the trailing edge soo according to Newton's third law of motion or mass conservation principle the downward motion of air creates upward force lift. This can be also explained as there will be higher pressure below and lower pressure above the airfoil this creates net upward force lift according to Bernoulli's principle.
Drag Theory:
Drag is the backward force on the airfoil. Drag consists of two types Surface drag and pressure drag. Pressure drag occurs when there is negative pressure at the trailing edge which opposes the forward motion. pressure drag increases when flow separation occurs earlier. Surface drag is related to the surface of the body according to no-slip condition the velocity of the fluid layer attached to the surface has zero velocity and increases gradually away from the body until it becomes free stream velocity. This gradient of the velocity of fluid around the surface of the body is called the boundary layer. This created deceleration forces on the body. Drag force is
Stalling: A stall is a condition in aerodynamics and aviation such that if the angle of attack is increased beyond a certain point, then lift begins to decrease. The angle at which this occurs is called the critical angle of attack. This angle is highly dependent upon the airfoil section or profile of the wing, its platform, its aspect ratio, and other factors, but is typically in the range of 8 to 20 degrees relative to the incoming wind for most subsonic airfoils. Stalling is caused by flow separation, the flow separation starts at the tip of the trailing edge and as the angle of attack increases grows towards the leading edge, and at the critical angle of attack, the flow separation is high enough to create a stalling effect.
NACA 0012: NACA 0012 is a symmetric airfoil that will not create any lift for zero angles of attack. NACA stands for National Advisory Committee for aeronautics. In NACA 0012 the first two digits tell about the camber in the airfoil, the first digit expresses the camber in the percentage of the chord,(chord length is the length of the airfoil) the second digit gives the location of the maximum camber point in tenths of a chord, and the last two digits give the thickness in the percentage of the chord.
In the following challenge, NACA 0012 airfoil is used.
PROCEDURE:
Geometry:
- We will import the NACA 0012 airfoil in Space claim
- We can find the airfoil shape in the workspace
- Now we will create a domain over the airfoil
- From the trailing edge we can find the last point from there we will create a rectangular domain with height of 20m and width 10m
- A bounding box of C-shaped is created with the diameter 10m using three point circle
- Then the surface is created from edges and by using boolean operator the airfoil surface is removed as we need to study the fluid that is around the airfoil.
Meshing:
- Then the design is saved and meshing is opened and proper edge sizing is given and face meshing is done.
- Naming for the Inlet, wall and outlet is given. The top and bottom of the enclosure can be named as far-field or can be named as inlet along with the arc. The airfoil is named as walls
SETUP:
General:
- Steady-state, absolute velocity, Pressure based, Planner
Boundaries:
- Inlet- Velocity specifications method: Components
- Outlet- 0 gauge pressure
Turbulence models:
- k-omega SST model
Post-processing:
- Velocity contour
- Pressure Contour
- Coefficient of drag and lift
Calculation:
- End time step: 700
- Time step size: 1
RESULTS:
ANGLE OF ATTACK= 5
COMPRESSIBLE:
Velocity contour:
Pressure contour:
Lift coefficient:
Drag coefficient:
INCOMPRESSIBLE:
Velocity contour:
Pressure contour:
Lift coefficient:
Drag coefficient:
ANGLE OF ATTACK = 10
COMPRESSIBLE:
Velocity contour:
Pressure contour:
Lift coefficient:
Drag coefficient:
INCOMPRESSIBLE:
Velocity contour:
Pressure contour:
Lift coefficient:
Drag coefficient:
ANGLE OF ATTACK = 15
COMPRESSIBLE:
Velocity contour:
Pressure contour:
Lift coefficient:
Drag coefficient:
INCOMPRESSIBLE:
Velocity contour:
Pressure contour:
Lift coefficient:
Drag coefficient:
COMPRESSIBLE FLOW :
- For the small angle of attack, the velocity on the top of an airfoil is more.
- Stagnation point occurs at a point where the airflow first meets the airfoil, this point travels toward below the airfoil as the angle of attack increases.
- The velocity of the flow increases with the increase in the angle of attack.
- Velocity is inversely proportional to the pressure as the pressure increases velocity decreases and vice versa.
- the point at which there is high pressure the velocity is less. The point where the velocity becomes zero where the air first meets the airfoil is called stagnation point and the pressure is called stagnation pressure.
- the lift coefficient increases with the increase in the angle of attack and increase till the critical angle of attack where the max lift is attained. After the critical angle of attack the lift coefficient drops. This is called stalling. The max lift is attained around an angle of attack 15 deg.
- The drag coefficient increases with the angle of attack as the flow separation increases.
INCOMPRESSIBLE FLOW :
- The flow velocity and pressure will not vary much with the increase in the angle of attack, but this is significant. This is because the inlet velocity is low.
- The lift coefficient increases with the increase in the angle of attack and increase till the critical angle of attack where the max lift is attained. After the critical angle of attack the lift coefficient drops. This is called stalling. The max lift is attained around an angle of attack 15 deg. The lift obtained from the compressible flow when the velocity is 273 is more compared to the incompressible flow.
- The drag is increased with the angle of attack as the flow separation means the increase in the turbulence region.
CONCLUSION:
- We have created a domain for flow analysis and Setup simulation for subsonic and supersonic regimes at 5, 10, 15 angle of attack
- We have also discussed about the lift ,drag,velocity ,pressure variation in different angle of attack