Ahmed Body Challenge

1) Ahmed body and its importance.

Ans) Ahmed body is a simplified form of a vehicle which represents the basic geometry of a car and satisfy the aerodynamic properties. Although it has a very simple shape, Ahmed body allows us to capture characteristic features that are relevant to bodies in the automobile industry. This model is used to describe the turbulent flow-field around the car like geometry. Once the numerical model is validated, itis used to design new models of the car.

Researchers in aerodynamic sectors still work on this model by changing the angle of the slant portion at rear side of the body and analyse the obtained data to recreate or to design more efficient models.

2) Reason for the negative pressure in the wake region.

ANS) Firstly, The pressure in the front portion of the body is greater than rear portion of the body. As the rear end of the body posses an angle this slows the pressure and cause a reverse flow. This reverse flow in the wake region denotes negative pressure gradients.

3) The significance of the point of separation.

ANS) The point of separation is the place where the wall shear stress becomes zero and the flow rotates at the back of the body creating adherse or negative gradients in the wake region.

• ABOUT THE Y+: Y+ is a non-dimensional distance. It depicts the flow pattern through course and a fine mesh. Y+ is important in turbulent type flow to determine the proper size of the cell walls.

Ansys Fluent Setup:

Geometry:

Mesh:

RESULTS

1)VELOCITY AND PRESSURE CONTOURS:

VELOCITY:

PRESSURE:

2) DRAG COEFFICIENT FOR A REFINED BODY CASE:

• After running the simulation with two enclosures and decreasing the element size and as small as possible, my drag force is 0.33213489.

3) VECTOR PLOTS SHOWING THE WAKE REGION:

4) GRID INDEPENDENCY TEST:

MESH ELEMENT SIZE

LARGE ENCLOSURE =50

SMALL ENCLOSURE =25

DRAG FORCE

Cd: 0.33213922

LIFT FORCE

Cl: 0.39475012

MESH ELEMENT SIZE

LARGE ENCLOSURE =100

SMALL ENCLOSURE =50

DRAG FORCE

LIFT FORCE

MESH ELEMENT SIZE

LARGE ENCLOSURE =150

SMALL ENCLOSURE =100

DRAG FORCE

LIFT FORCE

My Files:

https://drive.google.com/drive/folders/1aOiZjFfiztO24IoP4EqK8cd9okHow042?usp=sharing