Week 3 - External flow simulation over an Ahmed body.
AIM: To perform a grid independence test on the ahmed body and to compare the results.
Introduction:
The Ahmed Body is a general-purpose bluff body model designed to use computational fluid dynamics to analyse the external flow and its properties across car bodywork.The Ahmed body accurately models a passenger car and aids in capturing all pertinent flow physics required for car body design.In 1984, S.R. Ahmed developed the Ahmed Body for the first time in his research paper, "Some Salient Features of the Time-Averaged Ground Vehicle Wake".It has since grown to be a significant benchmark for aerodynamics simulation software.The turbulent flow field surrounding an automobile is likewise described by this model, using similar geometry.The numerical model is used to create a new car model after it has been validated.
The figure shown above is the geometric model of Ahmed Body having standard dimensions
Airflow modelling over the Ahmed body:
Two aspects comprise the modelling of the air flow across the Ahmed Body, which are explained below:
PART I: In this section, the numerical simulation is continued while the air flow is simulated by creating an enclosure over the Ahmed Body.
PART II: However, in this instance, an additional enclosure has been added as a refining zone to better capture the flow surrounding the Ahmed Body than in the preceding instance.
Part 1:
Geometry:
Spaceclaim has altered the geometry, and the body is surrounded by an enclosure to catch the flow in the necessary dimensions.
MESHING:
- Mesh Element size: 400 mm
- Number of Elements: 84000
SETUP:
- Pressure based solver has been used to solve the problem, as only the inlet velocity is 25 m/s.
- Steady states were employed.
Viscous Model: Turbulence - k- omega SST
Material : Fluid - Air
Results:
1.1 Pressure contour
1.2 Velocity Contour:
1.3 Vector Plot result at both the lines:
Series 1 at /LINE:Line 1
[Data]
Y [ m ],Velocity u [ m s^-1 ]
0.00000000e+00, 2.03445454e+01
1.41029999e-01, 2.22021255e+01
2.82059997e-01, 2.36258888e+01
4.23089981e-01, 2.49612675e+01
5.64119995e-01, 2.53141556e+01
7.05150008e-01, 2.54061623e+01
8.46180022e-01, 2.54345608e+01
9.87210035e-01, 2.54677200e+01
1.12823999e+00, 2.54839821e+01
1.26926994e+00, 2.54994125e+01
Series 2 at /LINE:Line 2
[Data]
Y [ m ],Velocity u [ m s^-1 ]
0.00000000e+00, 2.31829567e+01
1.41029999e-01, 2.34581337e+01
2.82059997e-01, 2.38860188e+01
4.23089981e-01, 2.44764862e+01
5.64119995e-01, 2.51058941e+01
7.05150008e-01, 2.52911453e+01
8.46180022e-01, 2.53191299e+01
9.87210035e-01, 2.53355675e+01
1.12823999e+00, 2.53391342e+01
1.26926994e+00, 2.53396397e+01
- The aforementioned graphs demonstrate that the wake regions and the pressure-reduction zones are not very noticeable.Therefore, we must add an additional enclosure that may be thought of as the region of refinement and provide inflated layers around the Ahmed Body in order to properly capture the flow and produce a body-fitted mesh.We may thus compare the various outcomes by changing the meshing in this location.It is possible to lower the computational expense of providing a considerably more refined grid around the vast enclosure by narrowing the mesh size refinement to only the enclosure close to the Ahmed Body.
Part 2:
Geometry:
The geometry of the refined model is shown above.
Meshing:
The meshing has been done by applying multizone meshing method to the outer enclosure
- Type of meshing element : Outer enclosure - Hexa dominant mesh and Inner enclosure - Tetrahedral
- Meshing profile showing the inflation layers for a body sizing for inner enclosure element size 20 mm.
- Meshing profile with the hexa dominant meshes in the outer enclosure.
SETUP:
- Pressure based solver
- Steady-state simulation
Model :Turbulence Model - k - epsilon Realizable with scalable wall functions.
Material : Fluid - Air
Boundary Condition : inlet - velocity inlet (25 m/s)
{UNABLE TO SOLVE POST THIS}