# [GAMBIT] Setting a boundary layer as a function of pressure or specific volume

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February 4, 2011, 12:20
Setting a boundary layer as a function of pressure or specific volume
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Kit Wrightson
Join Date: Feb 2011
Posts: 3
Rep Power: 6
Hi there, I'm a beginner to CFD, with only a few months of experience, I've analysed compressible flow through a chocked convergent/divergent nozzle, that's about it. The geometry software I use is gambit 2.2 and Fluent 6.3 for CFD.

I'm trying to model a buffering system used in a Photo-voltaic pumping system. Power is supplied to a centrifugal pump from the PV cells. This buffering system is intended to ease flow fluctuations caused by the centrifugal motor and the PV cells.

In essence here, referring to attachment, (sorry its a rough schematic)

I am trying to model the accumulating chamber to reach a certain pressure or specific volume and when that critical value is achieved; valve 1 changes from closed to open and flow continues vertically.

Initially when Valve 1 and valve 2 are closed flow is induced along a pipe by a centrifugal pump. The fluid enters the Accumulating chambre (this is similar to a capacitor if you were thinking of an electrical analogy). The purpose of the chambre is to increase specific volume (this is achieve by having the chamber full of rubber balls, which compress when flow enters and increases specific volume or by modelling it as a cyclinder with a piston on top.)

When the accumulating chambre reaches a certain pressure or specific volume, I want valve 1 to change from closed to an open state. So that flow can continue vertically to a storage tank.

Will I need to write a user define function on a boundary wall? (where the accumulating chamber is for this instance) I'm unsure how to go about modelling this. Some colleagues have mentioned a dynamic mesh, is this correct? is this easier to achieve in Gambit or Fluent?

I'm assuming that the fluid is water, incompressible, adiabatic, isentropic, fluid flow is instaneously, the valves operate perfectly/instaneously, 2D and piping walls are frictionless. Flow is steady.

thanks for taking the time to read this. I hope it clear and easy to understand and I look forward to hearing your input.
Attached Images
 pumpingsystemdiagram.jpg (39.8 KB, 10 views)

 February 7, 2011, 02:50 #2 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 2,964 Rep Power: 30 Defining events could be a solution, but I am not sure you can switch an interior face into wall. But maybe you can change a fluid zone into solid zone, or something like that. I cannot check since I am not using Fluent anymore Else, yes, you could handle your problem with moving mesh or sliding mesh to open/close your valve. (resp. moving up /down a "door") ------------- || ---------- >>>>>>>>>> ||>>>>>>>> ------------- ||----------- "moving door" __________________ In memory of my friend Hervé: CFD engineer & freerider

 February 15, 2011, 15:23 #3 New Member   Kit Wrightson Join Date: Feb 2011 Posts: 3 Rep Power: 6 Thank you max, would you recommend the best method of solving this problem or setting up this problem is better implimented in fluent instead of the geomety meshing program gambit? regards

 February 16, 2011, 02:48 #4 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 2,964 Rep Power: 30 If you already have a surface (available for picking) you could use for closing your valve, then you can try to define an event (and switch from interior to wall). But as I sait I am not sure you can do that. Else you need to go back to gambit and setting a kind of sliding mesh __________________ In memory of my friend Hervé: CFD engineer & freerider

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