Week 3 - External flow simulation over an Ahmed body.
1.1 Aim: Flow simulation on Ahmed body.
1.2 Introduction:
Ahmed body: It is a car body which is used to check the effect of air flow over the surface. From this body, various parameters and properties are taking in the consideration such as turbulence effect occurs, lift coefficient, drag coefficient, wake region formation, velocity distribution over the region.
This Ahmed body is created by S.R. Ahmed in 1984 and it is benchmark for all aerodynamic analysis.
1.3 Theory:
Wake region: When car moves with high velocity, flow separation happens at this velocity. The pressure decreases in this region. The boundary layer formation on surface of Ahmed body separates as it reaches the rear end of the edge and hence separate flow experience high shear force and due to which wake region are formed.
Significance of point of separation
The rear slant angle should be in the range of 12.5 to 30 degree respectively. As the angle of slant increases, wake region formation is also increase. The separation point of flow affects the wake region formation as well as drag experienced by the body.
2.1 Modelling approach: This model is used to simulate the flow characteristics for turbulent flow condition. Here k indicates kinetic energy and e indicates turbulent kinetic energy. This model is very accurate for free flow fluids.
The main purpose of this type of model is to anticipate the time averaged velocity, pressure changes and temperature field. The turbulent kinetic energy is used to measure the intensity of turbulence.
3.1 Geometry
This geometry is in step file format. For the simplicity of operation, it is cuts into two portions.
4.1 Conclusion
Turbulence effect on the wall Y+ over the car wall is found to be
- Area-weighted average = 21.0981
- Wall shear stress = 1.851
- For slant angle 20
|
Mesh 1 |
Mesh 2 |
Mesh 3 |
|
|
Coefficient of drag |
0.324 |
0.348 |
0.304 |
|
Coefficient of lift |
0.220 |
0.207 |
0.252 |
|
Velocity |
44.39 |
36.43 |
43.94 |
|
Pressure |
381.2 |
371.4 |
406.3 |
- For slant angle 30
|
Mesh 1 |
|
|
Coefficient of drag |
547.07 |
|
Coefficient of lift |
603.52 |
|
Velocity |
47.45 |
|
Pressure |
411 |
https://drive.google.com/file/d/10UDLbYlP_8EzwUw03XcVD9uqJLUNVKLF/view?usp=share_link