Multiphase CFD in Enclosed Space (no inlets/outlets)

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Discussion Overview

The discussion revolves around modeling a multiphase flow scenario involving a rotating cylinder inside a sealed pipe filled partially with water. The focus is on the challenges of applying appropriate boundary conditions in a computational fluid dynamics (CFD) context, specifically using CFX, without any inlets or outlets.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant describes the problem as a multiphase flow with a rotating cylinder in a sealed pipe, seeking advice on boundary conditions in CFX.
  • Another participant questions the specific goals of the simulation, asking whether it involves heat transfer or fluid velocity, and suggests that CFX may not be the best tool for the problem.
  • A clarification is provided that the multiphase flow refers to non-mixing water and air, with the spinning cylinder affecting water distribution, and emphasizes the need for a simplified model to run.
  • Literature on similar problems is mentioned, noting that existing studies typically involve simpler scenarios with clear inlet and outlet conditions.
  • One participant proposes the idea of assuming a very small flow through the system to treat it as effectively closed, questioning whether this assumption could be valid for the Ansys model.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of CFX for the problem and the necessity of defining boundary conditions, indicating that there is no consensus on the best approach to take.

Contextual Notes

Participants highlight the complexity of the problem due to the absence of inlets and outlets, which may affect the choice of boundary conditions and the overall modeling approach.

minger
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Hi guys, I have a co-worker here who is stuck on a problem, and I cannot give him much help either. He is trying to model a multiphase flow with no inlets or outlets. The problem is essentially a rotating cylinder inside of a pipe that is sealed on both sides. Assume that the pipe is half filled with water.

That's it. We are trying to do this in CFX, but having difficulty determining what, if any, boundary conditions can be applied. The Ansys people are of very little help, it any. Any suggestions?
 
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What exactly are you trying to solve for? Heat transfer? Fluid velocity? When you say multi-phase flow, are you literally trying to keep track of two fluid vapor phases? Do you really have to solve this problem using CFD?

It's possible CFX is not the proper solution for your problem. There will most certainly be much more than boundary conditions that have to be nailed to to get the problem solved; perhaps you should find a professional consultant?
 
By multiphase, I actually mean non-mixing water/air (sorry about the confusing). The cylinder inside is spinning and throwing water on the top of the chamber. The problem that we are trying to solve is related to heat transfer, but for the time being, just getting a simplified model to run would be nice.

I have found literature related to this problem, but the spinning cylinder is always in a simple channel flow with easy inlet and outlet boundary conditions. I have just never run into a case where there are no inlets or outlets. I'm not sure how to approach the boundary conditions.
 
Does the Ansys model require your system to be open? I don't have much of any experience with CFD but if this is the case could you possibly just assume a very small amount of flow through the system? So small that as far as accuracy is concerned, the system can be considered closed?
 

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