|February 22, 2016, 13:47||
FLow past cylinder. Mesh independency test
Join Date: Feb 2016
Posts: 3Rep Power: 2
I’m trying to do grid independence test of flow past cylinder using Ansys Fluent 17.0. I carried out calculation for several meshes (from 134 993 to 395 098), But i still don’t get coverage of results. The flow is 2D, so I think the numer of 395 098 elements is really high. And I should get coverage of results for mesh with less numer of elements. I know that I do sth wrong, but I don’t know what. Could you help me ? I’m beginner in CFD. I present the conditions of the test below.
Conditions of the test:
• Diameter of cylinder is 20mm; Domain size 900mmx300mm.
• Simulation type 2D
• Unsteady flow
• Turbulent model: k-omega SST
• Water as a fluid
• Reynolds numer: 19 904
• Boundary conditions:
o Inlet: Velocity inlet: 1m/s, turbulent intensivity 5%, Hydraulic Diameter 0,3m
o Outlet as outflow
o Top and bottom walls and cylinder : non slip walls
• Y+ =(0,2 -10)
• Time step: 0,0001s, Number of time steps: 100000
Below, I attached my results and image of my mesh
|February 24, 2016, 18:42||
Join Date: Mar 2014
Posts: 367Rep Power: 5
mesh independence testing is not the same as convergence of a simulation.
and mesh independence testing does not mean that the two meshes will have exact 0.0000001 and 0.0000001 cd or cl etc.
when you go from 1 million cells to 2 million and get a cd of 0.5 in the first and 0.7 in the second, then you can make a mesh with 3 million cells but if the cd goes to 0.72 now and for a 4 million cell mesh 0.74, you have to stick to the 2 million cell mesh, since the improvement you are getting is small compared to the double resources and computer power you are using.
Unless ofcourse you are in NASA and sending a space shuttle to pluto, then you can worry about the small difference.
|flow past cylinder, mesh independency|
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