Week 11- Broadband Noise modelling over Ahmed body

Ahmed body model

In the automobile industry, Ahmed Car Body is the standard wind tunnel model that can be used as a validating case, in CFD simulation. Ahmed Body is a generic car-type bluff body with a slant back that has different angles from 0 – 40 degree. Ahmed body is a generic car body (a simplified car model) i.e It is usually used as a benchmark test case for simulating the external aerodynamic flow characteristics over a car model. The flow of air around the Ahmed body captures the essential flow features around an automobile.

Ahmed body is a simplified car model created by Ahmed et in 1980’s to investigate the behaviour of newly developed turbulence models for complex geometry cases. It’s body is made up of a round front part, a moveable slant plane placed at back part of the body to study the coefficient of drag and separation phenomena at different angles, and a rectangular box, which connects the front part and the rear slant plane. As the wake separation flow behind the Ahmed body is the main contributor to the drag force, accurate prediction of the separation process and the wake flow are the key to the successful modelling of this case.

Ahmed body is a simplified model of a car body, but it demonstrates all the flow features involved in an actual case of a moving car.

Reasons for negative pressure in wake region

Before we discuss why there is a negative pressure region we need to understand the following terms:

1. Wake
2. Flow separation
3. Adverse pressure gradient

Setup:

Step-1 import geometry in space claim and make repairs if necessary

Step-2 open ansys mesh and follow the mesh settings

Step-3 body sizing settings

Step-4 inflation layer 1 setting

Step-5 inflation layer 2 setting

Step-6 Named selections

Step-7 Final mesh

Step-8 import mesh in ansys fluent

Step-9 general settings

Step-10 Viscous model

Step-11 Acoustics on

Step-12 Material selection

Step-13 Cell zones

Step-14 Boundaries

Step-15 inlet BC

Step-16 Slipping wall BC

Step-17 Lift report definitions

Step-18 Drag report definitions

Step-19 Solution methods

Step-20 Solution controls

Step-21 initialization

Step-22 run calculations

Results:

Residuals:

Cd and Cl plots:

Contour Plots:

Pressure Contour

Acoustic Power level (dB)

Lilley's total noise source

surface acoustic power level (dB)

Conclusion:

A simulation of Broadband Noise modelling over Ahmed body was conducted.