AHMED BODY SIMULATION

Ans 1 : Ahmed body is a simple generic, bluff body i.e.(its a simple model of a car) that is used for simulating the flow around the car body .

Although its very simple in shape its used for capturing the characterstic features of the flow around the body. Its used for validating the numerical ( also turbulent ) models that can be tested around the car.

Ans 2 : For the refinement of the mesh we built an enclosure around the ahmed body the first enclouser which is also the large enclosure is there for understanding the basic nature of flow. The small eclouser around the ahmed body is used for the refinement of the flow around the ahmed body. The dimensions of the enclousers ate as follows.In the (LENGTH.DOCS)

For the refined enclousure we have

Finally for the globally shared topoplogy we have

For creating the mesh :

*Case 1:

Element size: 50 mm

Number of elements: 257615

The mesh which has to be prepared with the outer enclosure is the multizone mesh with the element size of (50)mm. Further we will be decreasing the elements size for the better refinement of the mesh.

After creating the mesh we have to make the named selections namely [ wall symmetry , car wall, inlet , outlet.]

We then make the enclosure around the ahmed body refine by several methods among which making the refine holes is one as shown

Next we make the inflation layeer around the ahmed body for the better refineent by the metod of total layer thickness . With the maximum height of (12.5)mm

*Setting up the physics

Steady state

density based solver

k epsilon model of turbulence

Inlet velocity (50) m/s

* Residuals

*Velocity magnitude contours

*Results

*Velocity magnitudes

The velocity at the stagnation point and in the wake region can be seen as (0)

*Presuure magnitudes:

The pressure seems to be the highest at the stagnation point that means its following the energy equation.

*Vector Represntation of the velocity magnitude:

*Case 2:

Element size: 40 mm

number of elements:420865

*Mesh:

*Residuals:

*Velocity contours

*Results:

*Velocity magnitude

The wake region seems well formed at the back end of the car.

*Pressure magnitude:

*Vector represntation:

*Case 3:

Element size: 45 mm

Number of elements: 325494

*Mesh:

*residuals

*vector contour:

*Results:

*velocity magnitude:

*pressure magnitude:

* velocity vectors:

CONCLUSION :

The refinement of the mesh results in the more refined vector magnitudes of velocity as seen. Case 2 is the most refined mesh case 3 on the other hand shows error while refinig it more. Better and accurate results can be predictited by using the refined meshes and the simulation tends to be more accurate to the physical phenomenon. More refined mesh can be recommneded for the analysis for accuracy.

Ans 3 ;

In the front end of the car maximum pressure can be seen and the velocity as its the stagnation point is 0.The pressure becomes 0 in the wake region and as the takes place over the body which means its correctly following the energy equation, as the velocity increases the pressure decreases the terms are connected to the friction coefficient. In the wake region as due to the body effects the velocity seems to be changing.

Also at the backside(wake region) due to the reciculating flows the negative regions are formed which results in negative pressure.