- **OpenFOAM Running, Solving & CFD**
(*http://www.cfd-online.com/Forums/openfoam-solving/*)

- - **Some clarifications about twoPhaseEulerFoam**
(*http://www.cfd-online.com/Forums/openfoam-solving/59202-some-clarifications-about-twophaseeulerfoam.html*)

Hello to everybody,
I need Hello to everybody,
I need same clarifications about the granular kinetic theory used in twoPhaseEulerFoam. 1) what is the meaning of the properties in the file ppProperties? 2) To avoid unphysichal packaging (alpha to high) do I need to define packingLimiter as Yes? 3) What is the difference between alphaMax and alphaMinFraction in the file kineticTheoryProperties? And the difference between alphaMax in ppProperties and kineticProperties? 4) What is the meaning of HrenyaSinclairCoeffs? 5) Is the keyword equilibrium the switch to solve the PDE equation for granular temperature or to calculate it as function of alpha? 5) What are the guidelines (i.e. Reynolds number) to switch on turbulence models in granular flows (I'm a newby about this kind of flows)? Thank you for your attention! Michele |

Hello Michele,
1. The ppProHello Michele,
1. The ppProperties contains the values of the parameters used when you switch the particle-force "model" on, setting g0 to a positive value. This means that you have an additional term in the alpha equation and in the momentum equation to try to prevent overpacking. 2. Theoretically no. The packing limiter algorithm is a trick developed to avoid the packing limit in some particular models (Gibilaro's particle-bed model and its extensions), where there's no normal stress in the particulate phase to avoid overpacking. If you use the kinetic theory or the particle force model, you should not need the limiter. The current implementation of the two-fluid granular model in OF is not always stable if you switch the kinetic theory on however, because of the explicit management of the granular pressure. 3. alphaMax is the maximum value allowed for the dispersed phase. alphaMinFriction is the minimum value of the dispersed phase at which the particulate phase frictional stresses starts to act. alphaMax in kineticTheoryProperties is used if the kinetic theory is on, the other if the particle force model is on. 4. Check the paper from C. Hrenya and J. Sinclair. They're parameters used in their formulation of the two fluid model. 5. If equilibrium is set to true, an algebraic equation (local equilibrium) is solved instead a PDE for the granular temperature. 6. Sorry to answer with a question, but what kind of system are you trying to simulate? Usually turbulence models are not adopted in dense simulations (bubbling fluidised beds), while are used when the gas phase is faster and the system more dilute (risers). I hope this helps. With kind regards, Alberto |

Hello Alberto,
thank you foHello Alberto,
thank you for your detailed answer! I'm a newbie about multiphase flow! Can you give same references about the particle-force model, since I don't have understand very well its functions? Is it included in Mfix? "Effects of particle-phase turbulence in gas-solid flows" is the paper of C. Hernia and J. Sinclair that you are referring? About the object of my simulations: at the moment I'm training with multiphase flows performing same test cases, in particular fluid and spouted beds. In future the object of my attention is fixed bed gasification. Is the granular theory still valid for fixed bed, and OpenFoam support the packed options, like fluent and mfix? My last question: is the implementation of species transport and homogeneous and heterogeneous reaction in openfoam a complex task? best regards Michele |

Quote:
So this mean that if go is set to zero, the PPproperties file is not used and no particle-particle interaction are taking into account? regards, |

No, if the kinetic theory is used, g0 must be set to zero in ppProperties, and the particle pressure is accounted for elsewhere in the kinetic theory model.
Best, Alberto |

Sorry Alberto but I still don't get it.
I am simulating bubbles in water.. Due to the low vol. fraction, I don't want to account for bubble/bubble interaction How can I do so? How can I cancel any particle pressure calculation/kinetic theory model or granular temperature? I have tried to look in the solver but my c++ is very bad... Regards, |

Quote:
- g0 to zero in ppProperties - set kineticTheory to off in kineticTheoryProperties You can refer to the bubbleColumn tutorial for a case without the particle pressure and without kinetic theory models. Alternatively, you can use the bubbleFoam solver. Best, |

Thanks for the help dans the information you always provide Alberto.
I have used the settings you have juste mentioned. Miles P.S.: I can't use bubblefoam. I test the tutorial on my case and it did not work. That's why I decided to use twopahseeulerfoam. I am starting to get results. I do not have time to set up another solver. |

Quote:
Quote:
Best, Alberto |

dear alberto
i am simulating dust particles in room with air. in the twophaseEulerFoam how to simulate the dust particles.. and how to change the dust particle sizes thanking you in advance |

Quote:
If what you want to simulate is simply the normal environmental dust in the environment, its concentration is way too low for the equations in the hydrodynamic limit to be valid. You either can do rough approximations like considering the particles as a transported scalar, or you need more sophisticated models (High-order moment methods or Euler-Lagrange). Best, |

About Using only Frictional viscosityDear All,
I'm simulating gas-solid flows with high sold phase fraction. I don't want to use the kinetic theory and the particle-particle interaction force or specify a constant viscosity to the solids. I want the solid viscosity to be calculated from the frictional model, such as Schaeffer, How can this be implemented? I have set the the g0 term in ppProperties to 0 and also kept the kinetic theory off. Is this the right way. Thanking in aniticipation |

hey guys,
does anybody have good references for the twophaseeuler model? I am hoping to implement this solver, and would like to understand what the solver is doing and how the parameters are being used. Any help would be highly appreciated. (sorry if i am posting in wrong thread, just thought it seemed more appropriate than starting a new thread). Thanks -Rick |

Quote:
http://powerlab.fsb.hr/ped/kturbo/Op...chePhD2002.pdf A skeleton of this model you can find in OpenFOAMwiki, wrote by Alberto: http://openfoamwiki.net/index.php/BubbleFoam |

All times are GMT -4. The time now is 12:42. |