CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > FLUENT

Mesh Indepedence Test in Ahmed, Drag Coefficient still going down

Register Blogs Members List Search Today's Posts Mark Forums Read

LinkBack Thread Tools Search this Thread Display Modes
Old   December 6, 2017, 09:38
Default Mesh Indepedence Test in Ahmed, Drag Coefficient still going down
New Member
Join Date: Jul 2017
Posts: 7
Rep Power: 7
treviusss is on a distinguished road

I am trying to compute flow around Ahmed body in 2D and 3D in Fluent 18.1. I have done triangle mesh with inflation layer around body and refinement zone close to the body to capture all the vortices near wake and so on.

Drag coefficient is the factor that I want to monitor to see if the solution is independent of the mesh

For 2D case I've done several refinement of mesh and it went to level around Cd = 0.296 and flattened out so I considered this as proper mesh

For 3D case for every refinement I'm making it seems like Cd is still going down for example:
0,292 for 3 400 000 elements mesh
0,290 for 4 100 000 elements mesh
0,286 for 5 500 000 elements mesh
0,28 for 7 300 000 elements mesh
(I'm using symmetry plane in half of the Ahmed model to reduce mesh elements)
During it I'm trying to refine both mesh in refinement zone and outside it respectively but I can't do it more because my PC is running out of RAM

I assume I'm doing something wrong but I can't figure out what is it
For Fluent settings I'm using
-Steady state
- Realizable k-epsilon turbulence model with Non-Equilibirum Wall Function
-Inlet Velocity is 40m/s with 1% Turbulent Intensity and 10 Turbulent Viscosity Ratio
-Pressure Outlet is 5% Turbulent Intensity and 10 Turbulent Viscosity Ratio
- Solution Methods : Coupled, Least Squares Cell Based, Pressure Standard, First Order Upwind for Momentum, Turbulent Kinetic Energy and Dissipration Rate for around 50 first iterations then I'm changing it for Second Order Upwind
- Controls : 50 Flow Courant Number and 0,25 for Momentum and Pressure
- I'm initializing using values for k and epsilon from Velocity Inlet and 0 Velocity (according to page 13)
- All other settings should be default

If anyone knows how to do it properly or any kind of piece of advice I would be really grateful and sorry for this chaotic style of writing.
treviusss is offline   Reply With Quote


ahmed body, drag coefficient, grid independency, mesh independency

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Ahmed body -Drag coefficient not converging!! sam92 FLUENT 9 January 14, 2014 15:00
Ahmed body drag coefficient IvanST FLUENT 0 December 18, 2012 10:17
Incorrect Drag and Drag Coefficient for flow over a cylinder ozzythewise Main CFD Forum 8 June 13, 2012 07:24
[Gmsh] 2D Mesh Generation Tutorial for GMSH aeroslacker OpenFOAM Meshing & Mesh Conversion 12 January 19, 2012 04:52
Fluent validation test for calculate the drag of a car ostervi FLUENT 0 June 12, 2009 13:59

All times are GMT -4. The time now is 05:56.