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Laminar inflow into a turbulent domain
Posted Apr 4, 2013, 12:26 a.m. EDT 5 Replies
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In the distant past (pre-3.5) I was able to solve Poisson's equation on a disk to get the laminar profile and then couple that to the inlet boundary. I cannot figure out how to do that in 4.3a.
Any help would be appreciated.
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Steven Conrad, MD PhD
LSU Health
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I would say as in 3.5: you add a 2nd model, in the first mod1 you solve your 2D case, in the mod2 the 3D case and you get either a model coupling projection operator to map the two surfaces from mod1 to mod2, or you play with the equations to transfer the pertinent _u_,p vector/scalar fields from one to the next.
On the other hand, I usually set up a parabolic velocity profile and manage to work with that, less precise but even quicker to define
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Good luck
Ivar
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It seems the second approach is easier. I created an analytical function that defines a 2D parabolic profile, but cannot see how to apply it as a boundary condition on a particular boundary. I thought I could use the variables s1 and s2 as function parameters to 'fit' the function to the 2D inlet boundary as a velocity, but I it returns that s1/s2 could not be evaluated.
Any ideas or suggestions?
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Steven Conrad, MD PhD
LSU Health
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"s" works fine for 2D, but in 3D there is always some ambiguities.
So what I usually do is to place a cylindrical coordinate system (Model Definitions Coordinates) and define the formula directly as an equation depending on the sys2.r variable
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Good luck
Ivar
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To specify the velocity profile on the boundary, I would recommend following Ivar’s advice and specify the velocity profile as a function of the x,y,z coordinates rather than s1 and 2. In the attached model, I modified the backstep model from the model library and input a parabolic velocity profile.
The expression for such a profile is u=U_Max*(1-r^2/R^2) . Integrating this on the inlet surface, you get that U_Max= 2*U_Mean. Therefore, I used the following expression for the inlet velocity:
2*v_mean*(1-r^2/R^2)
The radius r is defined in the variable table as a function of y and z. Please let me know if you have more questions.
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I will implement this approach. Is is reasonable that this boundary condition should be available in the turbulent flow interface as it is in the laminar flow? If so, I can submit as a feature request.
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Steven Conrad, MD PhD
LSU Health