August 9, 2018 at 7:06 pmdray19Subscriber
I am looking at the fluid dynamics in a square microchannel for 0.1<=Re<=1000. This involves determining the hydrodynamic entrance length and the friction factor for both the developing and developed regions.
I have conducted a mesh independent study for several Re>100 and validated the results with previous researchers experimental and analytical work
When I did the mesh independent study (7 meshes) for Re=0.1,1,10, inlet pressure increases by 2% (~0.01, 0.1, 1 Pa respectively) with each mesh refinement. The other parameters (velocity, entrance length) seem to constant expect entrance length changed in last few meshes. I increased the number of elements in each direction by 25% to give approximately 2x the number of elements.
Should I keep increasing the mesh? Am I missing something else? I have read (forums) that fluent should be able to handle creep flow but maybe it can't.
Any help is greatly appreciated.
Attached are the results for Re=0.1 mesh study
Microchannel: 100um x 100um x 210um
Model Domain: 50um x 50um x 210um (symmetry applied)
CFD: Ansys Fluent 19.1
Solver - Pressure-Based, Steady State
Model – Laminar
Residual – 10E-6: Continuity, Velocity in X,Y,Z Direction
Gradient: Least Squares Cell Based
Pressure: Second Order
Momentum: Second Order Upwind
August 9, 2018 at 8:36 pmRaef.KobeissiSubscriber
how did the pressure inlet increase by 2% ? This is a boundary condition and should remain constant regardless of the mesh, can you send a picture that shows this increase.
August 9, 2018 at 9:26 pmKarthik RAdministrator
Could you please elaborate your meshing strategy near the wall? How is your boundary layer mesh? How does it change with each successive refinement?
August 9, 2018 at 9:39 pmdray19Subscriber
I am using a Velocity-Inlet and Pressure-Outlet boundary conditions. If I apply a Pressure-Inlet B.C, the velocity profile is fully developed at the inlet and I can't determine entrance length or developing friction factor.
August 9, 2018 at 9:54 pmdray19Subscriber
I set the number of elements for each direction (ex: 15 in x, 15 in y, 65 in z-axial direction) and apply a bias factor to have smaller elements at the walls and in the developing flow regime. For refining, I increased the number of elements in each direction by 25%
August 9, 2018 at 10:08 pmKarthik RAdministrator
Please take a look at this discussion on the student community. This might help you understand mesh independence better.
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