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ternik August 10, 2009 12:02

Hi Foamers!
 
although that I am quite "fresh" in OpenFoam, I found out that it is pretty powerful and it is gaining on popularity. But on the other hand I am missing the capability to use (prescribe) the combination of "zero gradient" and "mass flow rate" boundary conditions at inlets (or at outlets)! So, do you know someone that has already (or is willing and able) wrote down small piece of program for this? Unfortunately my knowledge in C++ is extremely low...

Of course one can overcome this by modeling long enough "inlet section"(but this can be quite "computer memory" consuming, especially for higher values of Re number) or by prescribing fully developed values for velocity, etc. (but this is known only for Newtonian as well as some basic non-Newtonian fluid models and not for Carreau-Yasuda or some other "industrially" interesting non-Newtonian models)!

ternik August 12, 2009 07:01

Mass Flow Rate And Zero Gradient
 
Quote:

Originally Posted by ternik (Post 225856)
although that I am quite "fresh" in OpenFoam, I found out that it is pretty powerful and it is gaining on popularity. But on the other hand I am missing the capability to use (prescribe) the combination of "zero gradient" and "mass flow rate" boundary conditions at inlets (or at outlets)! So, do you know someone that has already (or is willing and able) wrote down small piece of program for this? Unfortunately my knowledge in C++ is extremely low...

Of course one can overcome this by modeling long enough "inlet section"(but this can be quite "computer memory" consuming, especially for higher values of Re number) or by prescribing fully developed values for velocity, etc. (but this is known only for Newtonian as well as some basic non-Newtonian fluid models and not for Carreau-Yasuda or some other "industrially" interesting non-Newtonian models)!

In order to "push a bit" my previous post, I will explain "why and what":
  • there are numerous numerical examples (either for validation purposes or calculating something new) that requires fully developed flow conditions at inlets for particular flow field; e.g. velocity, pressure, now with OpefFoam.1.5-dev even for viscoelastic shear stresses
  • currently, there are following possibilities for this
    • defining theoretical profiles for particular flow field, but this is (most likely) limited to Newtonian and some "simple" non-Newtonian (Power law) fluids
    • taking the advantage of pressureInletVelocity boundary conditions (defining pressure at inlet and outlet), but this (pressure drop) on the other hand is not always known!
    • defining the average velocity at inlet and then model "long-enough" section to obtain fully developed conditions, which I find extremely "computer memory & time" consuming
So, it is my strong opinion, that modelling of fully developed inflow conditions with a combination of mass flow rate and zero gradients for particular flow variable would not be only of great interest (for both, steady and transient flow) but would also reduce unnecessary "computer memory & time" consumption!

Unfortunately, I am rather fresh to OpenFoam and C++ and therefore I kindly ask "is there anybody out there" that is willing to hear "my cry for help":).

Enjoy the day,
Primoz.

maysmech October 26, 2010 11:35

Hi,


I have problem to define mass flow rate B.C too. Any suggestion will be appreciated.


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