fluctuation in force coefficients with dynamicTopoFvMesh

sepehr_s · May 1, 2018, 03:55

Hello
i want to simulate pitching and plunging airfoil with large amplitude in ground effect. because of large amplitude i use remeshing with dynamicTopoFvMesh.
first i simulate pitching and plunging airfoil out of ground effect. airfoil movement and remeshing is very good but when i active flow solver (pimpleDyMFoam), forces coeff (cl , cd) have fluctuations.

i solve this problem with dynamicFvMesh and compare result with kinsey and dumas, the results had very good agreement. then i simulate that problem with remeshing dynamicTopoFvMesh that results have fluctuation.
in both solver initial and boundary conditions are the same and flow solver is pimpleDyMFoam or icoDyMFoam with foam extend 3.1.
i examine different scheme, time step , ... but no effect on fluctuation.

what is the reason of this fluctuations?
how can i remove this fluctuation?
how can you help me please?
thanks.

wyldckat · May 1, 2018, 18:10

Quick answers/questions:

If you are running in parallel, try running a few iterations in serial mode instead. This is just so that you can put aside any influences that parallel decomposition may have on the flow field.
If you are using PIMPLE, then try setting the "nOuterCorrectors" parameter in "fvSolution.PIMPLE" to a value larger than 2 or 3 - see this page for more details: https://openfoamwiki.net/index.php/O...hm_in_OpenFOAM - hopefully this will help stabilize the flow field after each mesh motion.
Have you tried using Radial Basis Function (RBF) mesh deformation, instead of dynamicTopoFvMesh?

sepehr_s · May 2, 2018, 04:41

i ran the simulation in serial mode.
i set nOuterCorrectors up to 100 but after each remeshing of domain and remapping, the result show jumpping.
i didn't try RBF, because i must consider the ground effect and airfoils in tandem configurations.
thanks for rapid answer Bruno.

May 1, 2018, 03:55	fluctuation in force coefficients with dynamicTopoFvMesh	#1
sepehr_s New Member Join Date: Oct 2016 Posts: 9 Rep Power: 10	Hello i want to simulate pitching and plunging airfoil with large amplitude in ground effect. because of large amplitude i use remeshing with dynamicTopoFvMesh. first i simulate pitching and plunging airfoil out of ground effect. airfoil movement and remeshing is very good but when i active flow solver (pimpleDyMFoam), forces coeff (cl , cd) have fluctuations. i solve this problem with dynamicFvMesh and compare result with kinsey and dumas, the results had very good agreement. then i simulate that problem with remeshing dynamicTopoFvMesh that results have fluctuation. in both solver initial and boundary conditions are the same and flow solver is pimpleDyMFoam or icoDyMFoam with foam extend 3.1. i examine different scheme, time step , ... but no effect on fluctuation. what is the reason of this fluctuations? how can i remove this fluctuation? how can you help me please? thanks.

May 1, 2018, 18:10		#2
wyldckat Retired Super Moderator Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 10,981 Blog Entries: 45 Rep Power: 128	Quick answers/questions: If you are running in parallel, try running a few iterations in serial mode instead. This is just so that you can put aside any influences that parallel decomposition may have on the flow field. If you are using PIMPLE, then try setting the "nOuterCorrectors" parameter in "fvSolution.PIMPLE" to a value larger than 2 or 3 - see this page for more details: https://openfoamwiki.net/index.php/O...hm_in_OpenFOAM - hopefully this will help stabilize the flow field after each mesh motion. Have you tried using Radial Basis Function (RBF) mesh deformation, instead of dynamicTopoFvMesh? __________________ OpenFOAM: FAQ \| Getting started Forum: How to get help, to post code/output and forum guide Read this before sending me PM

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May 2, 2018, 04:41		#3
sepehr_s New Member Join Date: Oct 2016 Posts: 9 Rep Power: 10	i ran the simulation in serial mode. i set nOuterCorrectors up to 100 but after each remeshing of domain and remapping, the result show jumpping. i didn't try RBF, because i must consider the ground effect and airfoils in tandem configurations. thanks for rapid answer Bruno.