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Old   July 19, 2015, 12:07
Default Upwind Matrix
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Manuel Hagen
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Hello everyone,

i am trying to prepare for a task and i have got a few questions about the Theorie of cfd. I hope anyone can help me.

The first is about the Upwind process. I think is used in the central difference method. As an example i have 3x3 quadratic cells. The fluid is coming from left side down. Question could be: how does the Matrix look like? And does all cells been touched or impacted? The Matrix must have a equation like A*phi = S

but this is not all, how can i solve this Problem? i have 9 cells ....

The second question is about Reynolds Navier Stokes equation: There are 2 viscosites, the kinematic one and the viscosity for this equation. Its the whirl layer viscosity used in a k Epsilon model. What is the difference between them?
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Old   July 19, 2015, 14:56
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Filippo Maria Denaro
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first order upwind:

u>0 and v>0 the nodes involved are only (i-1,i),(i,j),(i,j-1).

For explicit schemes no formal matrix is necessary, each equation is decoupled from others.
For implicit schemes, the matrix of the system is of order NxN (N is the number of grid unknowns)
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Old   July 20, 2015, 03:06
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Manuel Hagen
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thank you for your reply. I made a small drawing for my example. Its a question i could get and now i am thinking of what i could write.
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