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February 18, 2015, 05:43 
Boundary condition slip

#1 
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Hello,
i've got a question about the boundary condition "slip". In the UserGuide OpenFOAM defines slip boundary condition: "zeroGradient if φ is a scalar; if φ is a vector, normal component is fixedValue zero, tangential components are zeroGradient" But I don't understand the definition "tangential components are zeroGradient" for velocity. My problem is a test rig to visualize water flow around a zylinder. I've uploaded a picture. I need the boundary condition for the free surface. I tested "zeroGradient" and "slip", because I won't simulate a multiphase flow. What's the better choice? I don't know the exact definition for the slip boundary condition. Can somebody help me? 

February 18, 2015, 13:26 

#2  
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Thiago Parente Lima
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Hi,
Quote:
In your experiment, apparently, only the flow around the cylinder is of your interest. Therefore, the experiment should be designed in a way that the upper and bottom boudaries do not affect the flow around the cylinder. If it is true, a symmetry plane in your simmulation would be a good choice. But I have a question, this is a test rig for a HeleShaw flow visualization? Last edited by thiagopl; February 18, 2015 at 13:34. Reason: Question added in the end 

February 18, 2015, 14:09 

#3  
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Quote:
I have aalready been thinking to use a symmetry plane for the top of the test rig. But I'm also interested in the effect of the boundary conditions  in especially the boundary condition at the top of the test rig. So which boundary condition should I use, to show the effect of the boundary conditions to the flow around the cylinder? 

February 18, 2015, 14:21 

#4 
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Thiago Parente Lima
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PLanger90,
I suggest you to read the Breaking of a dam tutorial at the User Guide. The tutorial shows the treatment for the same boundary condition as yours, a surface free to the atmosphere.
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Fields of interest: Heat transfer; Convection heat transfer; Conjugate heat transfer. 

February 18, 2015, 15:00 

#5  
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Quote:
i've already read the "Breaking of a dam" tutorial. In my simulation I used the solver simpleFoam. For the pressure I used this boundary condition: { type totalPressure; p0 uniform 0; U U; gamma 1; value uniform 0; } And for the velocity: { type pressureInletOutletVelocity; value uniform (0 0 0); } I uploaded a picture with the stream lines. Obviously, this is wrong. But what's the mistake? The second picture shows the solution with the "slip" boundary condition at the top of the test rig. When I use symmetryPlane, the solution is equal. Thank's a lot for your help. 

February 18, 2015, 15:10 

#6  
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Quote:


February 19, 2015, 07:15 

#7 
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Thiago Parente Lima
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You could write all your boundary conditions here (using [ CODE] [ / CODE] ), so it would be easier to find a problem. Before, check your fvSolutions or fvSchemes (sometimes we copy/paste some tutorials and forget to check them).
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Fields of interest: Heat transfer; Convection heat transfer; Conjugate heat transfer. 

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