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- - **How to specify BCs to solve a Poiseuille flow**
(*https://www.cfd-online.com/Forums/openfoam-solving/59140-how-specify-bcs-solve-poiseuille-flow.html*)

Hello,
I was trying to solvHello,
I was trying to solve a parabolic flow in 2D square-like domain. * In blockMeshDict and boundary file I specified just "patch" for inlet and outlet, * In /0/U I set zeroGradient on in/out, (0 0 0) on walls + empty * In /0/p I set fixedValue on in/out, zeroGradient on walls + empty. But.... solution obviously diverge. Aren't those BCs sufficent to describe a problem? I think, I don't understand how to set BCs in OpenFOAM, for example - why should I use physicalType? Maybe you can advice something useful at least for that poiseuille flow? |

Oh, I see a parabolic velocityOh, I see a parabolic velocity distribution now and it feels so good! The problem was - I forgot to take into account a fact, that for icoFoam pressure must be divided by density. So I tried to solve for 1000 times greater pressure!
Maybe I'll see somewhere else why physicalType should be specified... |

I checked solution more carefuI checked solution more carefully and .. trouble doesn't stop - I have almost exactly 2x greater U values comparing with analytical!
So in SI: nu = 1e-4, geometry: dx=0.01, dy=0.1, dz=0.001, flow is in y direction, delta p = 0.016 (divided by ro) According to wikipedia, Umax = 0.01. But solution gives 0.02!! How come? |

Hi Karlis
The Poiseuille-flHi Karlis
The Poiseuille-flow I could find on wiki (please add link in the future), was for a circular pipe flow. Your setup is for a 2D case, i.e. Poiseuille flow between two flat plates. The ratio between u_max in these two cases is exactly a factor of 2. / Niels |

Thank you, Niels!
I was thinkThank you, Niels!
I was thinking in a quick way - take a plane of cylinder and calculate for it.. Actually different problem is solved in such way. |

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