Week 11- Broadband Noise modelling over Ahmed body

AIM:

• To simulate the flow over the Ahmed body.
• To understand the flow physics over the body at 31m/s.

THEORY:

Ahmed body is an aerodynamic shape invented in 1984 to reduce the drag of automotive vehicles. Later on, Ahmed's body becomes a test case to validate the solver using experimental results(Wind Tunnel results) compared with simulation results. This Ahmed body is one reason to have an aerodynamic shape in automotive vehicles. This shape reduces the large consumption fule and also increases the mileage of vehicles.

The above image describes the flow over Ahmed's body with smoke visualization in a wind tunnel.

PROCEDURE TO SET UP THE SIMULATION CASE:

GEOMETRY & MESH GENERATION:

• Import the geometry to mesh.
• Mesh Size = 75 mm
• Sizing - Body Sizing
• Mesh size of Ahmed body = 30 mm
• Inflation layer = 28 layers
• Growth rate = 1.2
• Mesh Type - First Layer Thickness
• First Layer Thickness size = 0.01 mm

TURBULENCE MODEL AND MATERIALS:

• Here realizable k-e, Enhanced wall function is used.
• The energy equation is turned to measure the temperature.
• In the acoustic model, Broadband Noise Sources is turned on to capture the sound noise produced from ahmed body.

• Air is used as a fluid material with constant parameters.

BOUNDARY CONDITIONS:

• Inlet as Velocity inlet with 31m/s and temperature as 300k.
• Outlet is considered as pressure outlet with temperature 300k.
• The bottom wall road is considered as a moving wall at the same velocity of 31m/s.

SOLUTION METHOD AND REPORT DEFINITIONS:

• Coupled scheme and second-order spatial discretization method are used.
• The Courant number is reduced to 10.

• The coefficient of drag and Coefficient of lift report definition is created.

INITIALIZATION AND RUN CALCULATION:

• Standard initialization is computed from the inlet.
• For calculation 1000 iterations are set.

RESULT:

STATIC PRESSURE CONTOUR:

TOTAL PRESSURE CONTOUR:

We can see that the wake is produced at the end of Ahmed's body, this leads to create a vortex and leads to increase drag which helps Ahmed's body to be on the ground.

VELOCITY CONTOUR:

ACOUSTIC POWER LEVEL CONTOUR:

CONCLUSION:

From this simulation, we came to that how to set up a case for the acoustic model to find out the sound source produced from ahmed's body.