Ahmed body and its importance

Objectives:

• To define the Ahmed body and its importance.
• To Simulate flow over the Ahmed body.
• To perform the grid dependency test and post process the results

1. Ahmed Body and Its Importance:- Ahmed body is a simplified car body and was first created by S.R Ahmed.This shape provides a model to study geometrical effects on the wakes of ground vehicles. This is the kind of baseline geometry for automobile bodies. The flow of air around Ahemd body captures the essential flow features around an automobile and it describes how to calculate the turbulent flow field around a simple car-loke geometry using the turbulent, flow, K-epsilon interface. People working in vehicle aerodyanamics use Ahemdbody to validate their numerical model because the experimental data for Ahemd body. Once the numerical model is validated, its is used to design new models of the car and also used for faster calculation and for comparision of analytical results.

Geometry of Ahem-body

2.

case 1Number of nodes = 26501Number of elements = 79276Mesh diagram:Residual Graph:Velocity Contour:Pressure Contour:
The above contour are represnts the less refined mesh and can be used as baseline mesh to check whether everything is working or not. This baseline mesh helps to get a basic idea of the whole process.

2. Case 2

Number of nodes = 60579

Number of elements =198493

Mesh:

Residual Graph:-

Velocity Contour:-

Pressure Contour:-

The flow is converged at 633rd itreation. The velocity and pressure contours are less smooth compared to case 3 but they are smoother than the case 1.

3. Case 3

Number of nodes = 152097

Number of elements = 673683

Mesh:

Residual Graph:-

Velocity Contour:-

Pressure contour:-

The mesh and contours are much better than the other two cases. These kind of refinments in mesh provides much better and accurate results.

Grid dependency test:-

• There are notable changes in the three cases, mesh is more refined from case 1 to 3 to check the grid dependecy
• A smoother mesh provides a more accurate results, from all 3 cases we can conclude that the flow is more defined at lower elemets size
• The finer the mesh gets, the easier it gets in visualizing the contours.

3. Why the presuure goes negative

• pressure goes negative to maintain the flow when there is an increase in the velocity of flow
• It can be the result of flow separation at the curved surface interferance of the body.
• Separtion bubbles are produces due to flow separation which results in negative pressure values.
• The pressure also becomes negative due to flow recirculation and to counter balance the effect of shear stress.