Week 3 - External flow simulation over an Ahmed body.

Aim: To study the External flow simulation over an Ahmed body using ANSYS fluent.

Ahmed body significance: The Ahmed body is a simplified car-shaped made-up of a parallelepiped with rounded edges at the front and a slanted face at the rear. The slant at the rear side of the vehicle causes the separation of flow and also a significant factor for drag forces of Ahmed body.

Wake region: It is due to the boundry layer separation, vaccum region is genearated & in that region there is presence of negative pressure.

The direction of flow the pressure increases which causes decreases in velocity and creates condition for separation to occur.

Procedure:

Create 2 setups to perform grid dependency test,

Step 1: Create the wind tunnel setup in space claim around the ahmed body.

Step 2:Mesh the ahmed body and wind tunnel by creating a seperate enclosure around the ahmed body.

Step 3:Assign the inlet boundary conditions and create the contours of velocity magnitude of 25m/s.

Step 4: Create a plane in the middle and create the velocity and pressure plot.

Step 5:Create the vector lines on the tunnel setup.

Result:

As the mesh becomes finer the results are accurate.

Y+wall function is very imporant to get the correct result of coefficient drag.

Coefficent of drag is around 0.33 for 25m/s.