Ahmed Body Challenge
Ahmed Body Challenge
- Ahmed Body :
The Ahmed body was described originally by S. R. Ahmed in 1984. The Ahmed body represents a simplified, ground vehicle geometry of a bluff body type. Its shape is simple enough to allow for accurate flow simulation but retains some important practical features relevant to automobile bodies.
The experimental data from wind tunnel testing for Ahmed Body is easily available. Other numerical models can then be validated using that data.
Fig. Displays the general design of a Ahmed Body.
- Meshing :
- The geometry is readiy available for this challenge.
- We need to use enclosure option from space claim to create a rectangular region near the body.
- Create a base line mesh and edit further to get more accurate results.
- A layer of inflation is created near the surface of Ahmed Body.
- Also face sizing is used near base of Ahmed Body.
- Solver and Inlet Conditons :
Solver - K-Epsilon turbulence model
Material - Air
Velocity Inlet - 50 m/s
Temperature - 300K
Pressure Outlet - 0 (Gauge Pressure)
- Case I :
Element size - 100 mm
Body size - 50 mm
Nodes - 55241
Elements - 177861
Figure above shows the meshing for case 1.
Figure above shows the meshing zoomed in on inner enclosure for case 1.
Figure above shows the plot of residuals for case 1.
Figure above shows the velocity contour for case 1.
Figure above shows the pressure contour for case 1.
Figure above shows the velocity vectors for case 1.
Figure above shows the velocity vectors near the Ahmed Body for case 1.
- Case II :
Element size - 70 mm
Body size - 35 mm
Nodes - 120252
Elements - 417782
Figure above shows the meshing for case 2.
Figure above shows the meshing zoomed in near inner enclosure for case 2.
Figure above shows the plot of residuals for case 2.
Figure above shows the velocity contour for case 2.
Figure above shows the velocity contour for case 2.
Figure above shows the pressure contour for case 2.
Figure above shows the velocity vectors for case 2.
Figure above shows the velocity vectors near Ahmed Body for case 2.
- Case III :
Element size - 55 mm
Body size - 35 mm
Nodes - 170146
Elements - 485267
Figure above shows the meshing for case 3.
Figure above shows the meshing zoomed in near inner enclosure for case 3.
Figure above shows the plot of residuals for case 3.
Figure above shows the velocity contour for case 3.
Figure above shows the velocity contour for case 3.
Figure above shows the pressure contour for case 3.
Figure above shows the velocity vectors for case 3.
Figure above shows the velocity vectors near Ahmed Body for case 3.
- Clarification of Negative Pressure Region :
The pressure is actually postive but we have Gauge Pressure as zero therefore the Ansys displays the pressure as negative.
When air flows over the Ahmed Body the velocity increases and to compensate this pressure drop is obsereved. Also to overcome shear stress pressure might become negative.