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Piece-wise compressible flow in pipe system

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Old   March 2, 2017, 11:50
Unhappy Piece-wise compressible flow in pipe system
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Justin B.
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Hi,

My problem is this: I have a reasonably complex oxidizer feed system I have inherited that was poorly designed for the desired mass flow. My goal is to simulate the system with a known initial pressure and atmospheric outlet, however due to being a grad student I am using a cell-limited version of Fluent so it is necessary I solve the system in a piece-wise fashion. In reading on how to accomplish this I see that the Outflow condition in Fluent isn't valid for compressible flows (in addition to pressure inlet boundary conditions). I do not know the outlet conditions for each section before hand so the pressure outlet condition isn't necessarily applicable either. Is there a boundary condition setup available that will allow me to solve this system?


PS: The flow in the system is likely choked at some point early in the system and also goes through numerous rapid constrictions and expansions so it may not be feasible to "guess" at outlet boundary conditions to try and match the flow I have seen experimentally.
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Old   March 2, 2017, 16:00
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Lucky Tran
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Quote:
Originally Posted by jabier14 View Post
PS: The flow in the system is likely choked at some point early in the system and also goes through numerous rapid constrictions and expansions so it may not be feasible to "guess" at outlet boundary conditions to try and match the flow I have seen experimentally.
Unfortunately that's exactly what you need to do. Either you solve the entire coupled system or you break it up into parts (segregate them) and solve the segregated system using predictor-corrector approach or something equivalent.
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