## Openfoam non orthogonal correctors

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Anonymous Login Signup for a new account. View Issue Details. Jump to Notes Jump to History. Issue History. Testcase is a box which is initially filled up to a certain height with a fluid, which flows out of the box due to gravitation.

Due to symmetry only a quarter is simulated. When using the constantAlphaContactAngle boundary condition with limit gradient a small fraction of alpha. This behaviour occurs with different mesh resolutions and viscosities. With increasing contact angle the behaviour declines but does not vanish.

One can get rid of this behaviour when limiting nHat in the gradient schemes, but this causes unrealistic interfaces shapes. I have made a few changes to speed-up the case, in particular not applying non-orthogonal correctors the mesh is orthogonalreducing the Courant number and the number of alpha sub-cycles, applying the velocity gradient limiter only to the velocity transport and a fet other minor improvements.

With this setup the alpha seems to be fine with either alpha or gradient limit in the constantAlphaContactAngle BC.

### Main UserGuideAddendum

I do not believe there is a bug in the code and you need some user support to optimize the case.Definition at line 51 of file pisoControl. Definition at line 40 of file pisoControl. Definition at line 50 of file pisoControl. Definition at line 30 of file pisoControlI.

Rsx type s stereo wiring diagram diagram base website wiringPublic Member Functions List of all members. Inheritance diagram for pisoControl:. Construct from mesh and the name of control sub-dictionary. TypeName "pisoControl". Return true if in the final inner PISO iteration. Foam pisoControl Generated by 1. Run-time type information. Public Member Functions inherited from pimpleControl. TypeName "pimpleControl". Maximum number of PISO correctors.

Current PISO corrector index. Pressure corrector loop control. Return true to store the intial residuals. Return true for final inner iteration. Return true to solve for flow. Return true to solve for turbulence. Public Member Functions inherited from solutionControl.

Fox 2 newsTypeName "solutionControl".February 9,Non-orthogonal correctors. Johan Magnusson. Okey, lets see how i should explain this. I have a mesh that is according to my previous knowledge ok regarding orthogonality but I still want to be sure that the solver dont make to large error on a different mesh, I need therefore an implementation of a non-orthogonal corrector.

The steps 4 and 5 can be repeated for a prescribed number of time to correct for non-orthogonality. I know also that there are other choices.

It confuses me since it seems to occur some kind of correction already! February 10, Gijsbert Wierink. Hi Johan, In fvSolutions you can actually define the number of non-orthogonal correctors, so it's probably separated from the schemes like that.

Originally Posted by gwierink. June 25, Join Date: Mar Originally Posted by magjohan. If i refer to my question i asked more whats the difference between the correction that occurs in the PISO loop compared to the one that seems to occur in the "laplacianSchemes". If there arent any difference, is the PISO loop even necessary? September 4, Tushar cfd. T Chourushi. September 7, Julian Langowski.October 16,nNonOrthogonalCorrectors.

Primoz Ternik. Hi, when simulating flow past cylinder one will most likely end up with the non-orthogonal mesh. How many "NonOrthogonalCorrectors" should be used? Non-orthogonality of my mesh after running checkMesh is: Max: October 17, Giovanni Ricci. Maybe someone more expert will correct me, but i believe there is no fixed rule Most of the time, I've noticed that 2 correctors are sufficient.

Sebastian Gatzka. I can confirm gricci's experience. I have played around with the number of non-orthogonal corrector loops and found that 2 are sufficient. If I used more than 2 corrector loops the computational time was severely increased without improving the solution. It's half dead!

## Non-orthogonal correctors

Originally Posted by sega. Alberto Passalacqua. I agree with 2 or 3. If you need more, it might be the case of reconsidering the mesh. October 18, Hrvoje Jasak. On this mesh you do not need non-orthogonal correctors at all.

**Laminar Pipe Flow with SimpleFoam in OpenFoam**

There's usually nothing to worry about until the max non-orthogonality angle is approx 70 deg. Originally Posted by hjasak. Not really "more accurate". Non-orthogonal correctorsare here to save you if your code is blowing up because the mesh is so non-orthogonal that the first solution is driving the velocity to be stupid.The equation solvers, tolerances and algorithms are controlled from the fvSolution dictionary in the system directory.

Below is an example set of entries from the fvSolution dictionary required for the icoFoam solver. However, there is a small set of standard subdictionaries that cover most of those used by the standard solvers.

It specifies each linear-solver that is used for each discretised equation; it is emphasised that the term linear- solver refers to the method of number-crunching to solve the set of linear equations, as opposed to application solver which describes the set of equations and algorithms to solve a particular problem. The syntax for each entry within solvers uses a keyword that is the word relating to the variable being solved in the particular equation.

For example, icoFoam solves equations for velocity and pressurehence the entries for U and p. The keyword is followed by a dictionary containing the type of solver and the parameters that the solver uses. The parameters, including tolerancerelTolpreconditioneretc. The solvers distinguish between symmetric matrices and asymmetric matrices.

The symmetry of the matrix depends on the structure of the equation being solved and, while the user may be able to determine this, it is not essential since OpenFOAM will produce an error message to advise the user if an inappropriate solver has been selected, e. The residual is ostensibly a measure of the error in the solution so that the smaller it is, the more accurate the solution. More precisely, the residual is evaluated by substituting the current solution into the equation and taking the magnitude of the difference between the left and right hand sides; it is also normalised in to make it independent of the scale of problem being analysed.

Before solving an equation for a particular field, the initial residual is evaluated based on the current values of the field. After each solver iteration the residual is re-evaluated. The solver stops if either of the following conditions are reached: the residual falls below the solver tolerancetolerance ; the ratio of current to initial residuals falls below the solver relative tolerancerelTol ; the number of iterations exceeds a maximum number of iterationsmaxIter ; The solver tolerance should represent the level at which the residual is small enough that the solution can be deemed sufficiently accurate.

The solver relative tolerance limits the relative improvement from initial to final solution. In transient simulations, it is usual to set the solver relative tolerance to 0 to force the solution to converge to the solver tolerance in each time step.

## Non-orthogonal correctors

The tolerances, tolerance and relTol must be specified in the dictionaries for all solvers; maxIter is optional. Generally GaussSeidel is the most reliable option, but for bad matrices DIC can offer better convergence. In some cases, additional post-smoothing using GaussSeidel is further beneficial, i. The user must also specify the number of sweeps, by the nSweeps keyword, before the residual is recalculated, following the tolerance parameters. GAMG is faster than standard methods when the increase in speed by solving first on coarser meshes outweighs the additional costs of mesh refinement and mapping of field data.

The user is only required to specify an approximate mesh size at the most coarse level in terms of the number of cells nCoarsestCells. The agglomeration of cells is performed by the algorithm specified by the agglomerator keyword. Presently we recommend the faceAreaPair method. For all methods, agglomeration can be optionally cached by the cacheAgglomeration switch. The number of sweeps used by the smoother at different levels of mesh density are specified by the nPreSweepsnPostSweeps and nFinestSweeps keywords.

The nPreSweeps entry is used as the algorithm is coarsening the mesh, nPostSweeps is used as the algorithm is refining, and nFinestSweeps is used when the solution is at its finest level.

Synology domain name cannot be resolved quickconnectThe mergeLevels keyword controls the speed at which coarsening or refinement levels is performed. It is often best to do so only at one level at a time, i. Under-relaxation works by limiting the amount which a variable changes from one iteration to the next, either by modifying the solution matrix and source prior to solving for a field or by modifying the field directly. An under-relaxation factor specifies the amount of under-relaxation, ranging from none at all for and increasing in strength as.

The limiting case where represents a solution which does not change at all with successive iterations. An optimum choice of is one that is small enough to ensure stable computation but large enough to move the iterative process forward quickly; values of as high as 0.

There is no need to use any relaxation on pressure. This results typically in more robust solution and faster convergence. The user can specify the relaxation factor for a particular field by specifying first the word associated with the field, then the factor. The user can view the relaxation factors used in a tutorial example of simpleFoam for incompressible, laminar, steady-state flows.Notes to contributors: Please include the chapter number of the printed version to avoid confusion the Wiki might give different chapter numbers.

Contrary to what is stated in table 4. Non-orthogonal correctors are here to save you if your code is blowing up because the mesh is so non-orthogonal that the first solution is driving the velocity to be stupid.

If your velocity is OK, you just keep doing "normal" correctors, without special need for non-orthogonal ones. I use them on bad meshes, when the solver is giving me trouble. Usually, 1 is enough, and I never used more than 3. Section 5. By adding the following lines instead of the standard featureCos 0.

Where the separationVector is the vector between the two parts of the patch. If rotational patch is preferred, it can be specified by:.

Where the rotational axis and the rotational centre can be specified by the two vectors above. This gives you obj files of the patches and lines connecting each face. These can be visualized in paraview by conversion using objToVTK. In section 5. Looking at the source I would say that this problem is already fixed by the current versions of starToFoam but I can't test this theory because I have no StarCD. Body may only rotate around an axis fixed in global space.

Axial angular spring with moment values drawn from an interpolation table. Linear damping. By dropping FoamX and avoiding the additional work of creating a java-compatible interface for each featurethe developers could introduce very interesting and useful dictionary functionality fairly quickly:.

Toggle navigation.Definition at line 52 of file simpleControl. Definition at line 96 of file simpleControl. Read controls from fvSolution dictionary. Reimplemented from solutionControl. Definition at line 42 of file simpleControl. References solutionControl::read. Implements solutionControl. Definition at line 49 of file simpleControl.

### Main UserGuideAddendum

Definition at line of file simpleControl. Definition at line 62 of file simpleControl. Inheritance diagram for simpleControl:. Construct from mesh and the name of control sub-dictionary.

Here is the call graph for this function:. Return true if all convergence checks are satisfied. TypeName "simpleControl". Initialised flag. Foam simpleControl Generated by 1.

Run-time type information.

Public Member Functions inherited from solutionControl. TypeName "solutionControl".

Temple newsConstruct from mesh. Return the solution dictionary. Current corrector loop index. Current non-orthogonal corrector index. Maximum number of non-orthogonal correctors. Helper function to identify final non-orthogonal iteration. Flag to indicate to solve for momentum. Flag to indicate to solve using transonic algorithm. Flag to indicate to relax pressure using the. Flag to indicate that the flow system of equations should not.

Non-orthogonal corrector loop.

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