Week 3 - External flow simulation over an Ahmed body.

AIM- To analysis the wake drags and other parameters on the Ahmed body at the different velocity flow over the body.

Introduction – Transport vehicles will move from one place to another at different speeds.As air or any medium flow over the body will have external forces will applied to the body. Due to this analysis flow over body will give the results to select the material for the bodies at the different locations of body parts . Every material has the its own limits like strengths, ductility ,break point ,yield point etc.The safety of passengers & environmental can be analyses. fuel consumption can be reduced for vehicles.

Examples : car, Rockets, ships, aeroplanes , bullet trains, fast moving vehicles.

Ahmed body is a experimental model which gives the closer result for the car models for basic design of cars. To know the external forces at different velocity for structural withstands & material selection for design .

The wake is the region of disturbed flow after the body is appeared . the wake region will produce the vacuum due to the low pressure . Air flow separation & net pressure generate after the body is the region for negative pressure.

Flow separation will occur at the point where air leaves the flow from the surface of the object.

Solving & Modelling approach:

Import the Ahmed body model to the space claim .check the units weather in mm or mts .if any change convert it from the file menu option. Prepare the encloser to the Ahmed body with the dimension of lengths ,widths, heights around the body at 2 axis. Before the that uncheck the unsymmetric in the right side in details. repeat the process for the local encloser body for refine mesh. Check for the tropology is shared. Generate the 3 axis plane for the geometry .click on the xy plane and check the section plane.

Split the body by using the split body tool .then apply the interface tool for the geometry . subpressed the ahmed body

Ahmed body model in space clam

Two different enclousers for ahmed body

3 layers for geometry

Split tool used geometry

Interface

Topology shared

Meshing

Model & labelling

Meshing -100mm , multi zones , body sizing-50mm ,face sizing-50mm , inflation to the car boundary

Setup & Results.

Physical model & settings

Residuals plots

CL plots-0.20614878

CD plots -0.32479191

Contours

Velocity

Pressure

vector plot

case-2

Meshing -150mm , multi zones , body sizing-80mm ,face sizing

-50mm , inflation to the car boundary

Setup & Results

Residuals plots

CL plots- 0.241

CD plots – 0.389

Contours

Velocity

Pressure

vector plot

CONCLUSION -

As per my results for the mesh course and fine mesh have large different at the car wall . wake region behind the ahmed body is slight different for for 2 cases. The result will vary depend on the parameter of velocity ,Aera ,mesh of the body. finner the mesh better the results.