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-   -   Equations in the MRFsimpleFOAM (http://www.cfd-online.com/Forums/openfoam-solving/58767-equations-mrfsimplefoam.html)

waynezw0618 June 5, 2008 01:24

Hi in the MRFsimpleFOAM,the
 
Hi

in the MRFsimpleFOAM,the basic equation seems in the Absolute Velocity Formulation,which have the relative velocity and abolute velocity both in the momentum eqution.that is why ?is there any
advantage in that way ?

hjasak June 5, 2008 02:15

Yes: you do not have to do exp
 
Yes: you do not have to do explicit coordinate transformation for the MRF interface, which makes the code MUSH simpler.

Enjoy,

Hrv

waynezw0618 June 29, 2008 03:12

Hi Hrv! thank you very much!b
 
Hi Hrv!
thank you very much!but i still cannot understand it very much for the question that,when you use absolut formulation,the "U" in the kepsilon model is relative velocity or absolute veloctiy?for example the production term in the k equation there is a Grad(U).what is this "U" is it relative velocity or abosolut velocity?

thanks

wayne

hjasak June 30, 2008 03:25

The "relative" or "absolute" v
 
The "relative" or "absolute" velocity is for the moving part of the multiple reference frames - in that region you have solid-body rotation + local flow velocity, giving you a choice of formulation.

Enjoy,

Hrv

waynezw0618 June 30, 2008 12:32

Hi Hrv! thanks!,but my equest
 
Hi Hrv!
thanks!,but my equestion is when in the rotation region,what velocity is used to calculate the "k","epsilon" and "omega" for KEpsilon or KOmega turbulence model.although the equation of k","epsilon" and "omega"have the same form in the both rotation and fixed frame,they have convection term and production term which is related to the velocity,for this velocity,i think there will be different from the rotation frame to the fixed one.or i think in the rotation frame the turbulence kinetic--k is convected with the "relative velociy" and produced by the gradient of "relative velociy" ,but for the station part that is "abosulte velocity". is that right?how about the MRFsimpleFoam? could you please tell me more


thanks
wayne

be_inspired May 7, 2015 04:43

Same doubt here.
I am using OF2.3.x and very strange results are obtained at first cell around blade. I am simulating a wind turbine.
Even if the first cell height has been calculated for a y+=100 taken into account that the blade is rotating.
pressure distribution is non-real and so epsilon field at that location. The simulation crashes quickly


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