CFD Online Logo CFD Online URL
Home > Forums > General Forums > Main CFD Forum

Mesh independence, internal fluid-dynamic

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

LinkBack Thread Tools Search this Thread Display Modes
Old   January 29, 2019, 15:25
Default Mesh independence, internal fluid-dynamic
New Member
Join Date: Jan 2019
Posts: 2
Rep Power: 0
Francesco_93 is on a distinguished road
Hello everyone! I'm new to the forum and I hope this is the right section for my question. Basically I deal with a problem of internal fluid dynamics, in particular I have a hydraulic conduit with water working fluid, which ends with a valve. The study requires assessing the risk of cavitation within the valve. For the assigned data I have a turbulent flow with Re of 10 ^ 5. I have an input speed of 9.5 m / s and standard conditions. The outlet pressure is 118750 Pa. The length of the initial conduit section and the terminal part are free parameters to be imposed according to the boundary conditions.
The problem must be solved with a 2D axisymmetric approach and a structured block grid. I created the geometry in gambit and I created blocks in order to respect a low equisize skewness (about 0.35). At this point I chose to solve the problem with an enhanced wall treatment approach given the low number of reynolds. I have generated two grids and I have therefore considered a y + of 1.5 for the first grid and of 1 for the second, in order to have y + <5 on the whole domain. Basically I chose interval count and then in the inflate I have increased by multiplying the interval count by 1.5 and approaching the centroid on the wall (as already said y + = 1).
In order to have adjacent elements with a low volume variation it was necessary to use a double side refinement even in areas that are not wall-mounted and therefore where it was not needed.
By exporting the mesh to fluent I chose a pressure based solver, axismetric, steady, implicit, green gauss. I chose to work in terms of relative pressure (operating preassure = 118750, pgauge = 0).
As boundary conditions I chose velocity inlet and I assumed to have a fully developed bike as the valve is part of a conduit. I then made the hypothesis that upstream there is a sufficiently long and straight duct. So I assigned as parameters, of the k-epsilon model, the input hydraulic diameter and the turbulence intensity = 3.76 calculated on the basis of the reynolds.
As a backflow condition I put the viscosity ratio = 350 and a turbulence intensity = 1%.
Reference values ​​I take those of the inlet.
In the simple algorithm I chose a 2nd order upwind.
My problem is this: the problem goes to convergence and also respects the constraints of the two layer, but when I go to thicken and evaluate the mesh independence in the most important areas, I get values ​​of 150% of the RMSEP.
Also the trends of the two grids are different for some sizes. I thought it would need to further deepen the grid but my PC can not do it because you would get millions and millions of items.
So I thought the mistake was elsewhere. It is not a problem to thicken the grid but there is some other problem. Please help me. Thanks in advance.
Francesco_93 is offline   Reply With Quote


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
[ICEM] Nuclear fuel assembly, Mesh Check: "missing internal faces, uncovered faces" swparth ANSYS Meshing & Geometry 2 June 27, 2017 07:12
[ICEM] 3D Dynamic Mesh - Boundary layer mesh issues nathanricks ANSYS Meshing & Geometry 0 September 23, 2015 05:14
sliding mesh problem in CFX Saima CFX 45 September 22, 2015 10:53
[ANSYS Meshing] Combine solid mesh generated in workbench mesh and fluid mesh in fluent meshing ? RPjack ANSYS Meshing & Geometry 2 August 27, 2015 09:33
Overflow Error in Multiphase Modelling with Two Continuous Fluids ashtonJ CFX 6 August 11, 2014 14:32

All times are GMT -4. The time now is 04:46.