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#1 |
Member
Ardalan
Join Date: Feb 2010
Location: Baku
Posts: 50
Rep Power: 16 ![]() |
Hello to everyone
I've written a code to simulate laminar backward facing step flow. The main features of the method I have developed are as follows: - incompressible flow - finite volume - Simple algorithm on Staggered grids - 1st order Upwinding for convection terms - central differencing for diffusion terms - Iterative solution to obtain steady solution (no time marching) - using line TDMA for the solution of algebraic equations of x-y momentum and pressure correction at lower Reynolds numbers the code works satisfactorily but at higher Reynolds numbers (e.g. 600, 800) the L2 norm of mass unbalance decreases 1 or 2 order of magnitudes, then it oscillates but doesn't decrease further. I have checked the Residuals, the cells where the mass unbalance doesn't decrease, are located near the end of lower wake. I have tested the code for simulating cavity driven flow, it works fine. Does anybody have any suggestion? What shall I do? Does the flow have unsteady nature at high Reynolds numbers? |
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#2 |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,830
Rep Power: 73 ![]() ![]() ![]() |
yes, after Re=700- 800 the flow is transitional and it has no sense the 2D laminar solution. You can search for a paper of Armaly et al. on JFM
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#3 | |
Senior Member
Join Date: Aug 2011
Posts: 272
Rep Power: 16 ![]() |
Quote:
For Re=600, 800 the flow is not anymore steady and is definitely unsteady. So it is normal that your code can not find a steady solution of a flow which is unsteady. So implement unsteady version of your solver accounting for time derivative. refine the grid because you increase the Reynolds and re-run it,it should be fine. |
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#4 |
Member
Ardalan
Join Date: Feb 2010
Location: Baku
Posts: 50
Rep Power: 16 ![]() |
Thanks a lot
I have another question regarding the flow over a backward step: How can I calculate the reattachment region length? |
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#5 |
Super Moderator
Alex
Join Date: Jun 2012
Location: Germany
Posts: 3,426
Rep Power: 49 ![]() ![]() |
The reattatchment point is usually defined by the position where the wall shear stress (its streamwise component) changes sign.
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