Imposing periodic conditions and initialize

tsero · November 4, 2011, 06:53

I am running a 3D mesh of a conical pipe created in Gambit in Fluent and use periodic conditions at the inlet and the outlet, as i am trying to solve steady state and the problem is periodic by nauture. I specify the Mass Flow (it is 8kg/s) and i also have gravity contribution (I make sure to specify the opperating density at 0).

Though i achieve convergance at 1e-5 when i export the results into Techplot for Velocity magnitude I get results of Velocity scaling from 450 to 1800. That cannot be true because if we divide the mass flow (8L/s) with the surface at the inlet we obdain Velocity at the inlet of around 1m/s.

What exactly should I initialize at the initialization window?and from what zone?
My boundaries are Periodic, Symmetry and Walls.

swetkyz · November 5, 2011, 09:47

I like starting with a hybrid initialization and then performing an fmg initialization after that. The fmg is only available in the TUI, but it solves the flow more realistically than just setting the same pressure and velocity over the entire flow domain, which is what may happen using a standard initialization.

To get fmg, simply type the following in the TUI: "solve", "init", "fmg-init". It may also help you to set fmg to verbose so you can watch the progress (convince yourself that you didn't break it).

-Zachariah

tsero · November 6, 2011, 06:29

any idea of how I can export the non periodic pressure plot, in order to obdain the pressure drop along the pipe?

swetkyz · November 7, 2011, 08:57

tsero,

I would do it is by first creating a line in the pipe, then using an x-y plot to see the pressure drop (assuming your pipe is straight). To do this, use Surface>Line/Rake... to create the line, then do an XY plot of pressure along the vector of the line you just made. The "Plot Direction" must be specified to align with the line, and the line must be selected under surfaces.

November 4, 2011, 06:53	Imposing periodic conditions and initialize	#1
tsero New Member Join Date: Sep 2011 Posts: 8 Rep Power: 14	I am running a 3D mesh of a conical pipe created in Gambit in Fluent and use periodic conditions at the inlet and the outlet, as i am trying to solve steady state and the problem is periodic by nauture. I specify the Mass Flow (it is 8kg/s) and i also have gravity contribution (I make sure to specify the opperating density at 0). Though i achieve convergance at 1e-5 when i export the results into Techplot for Velocity magnitude I get results of Velocity scaling from 450 to 1800. That cannot be true because if we divide the mass flow (8L/s) with the surface at the inlet we obdain Velocity at the inlet of around 1m/s. What exactly should I initialize at the initialization window?and from what zone? My boundaries are Periodic, Symmetry and Walls.

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November 5, 2011, 09:47		#2
swetkyz Member Zachariah Swetky Join Date: Aug 2011 Posts: 36 Rep Power: 14	I like starting with a hybrid initialization and then performing an fmg initialization after that. The fmg is only available in the TUI, but it solves the flow more realistically than just setting the same pressure and velocity over the entire flow domain, which is what may happen using a standard initialization. To get fmg, simply type the following in the TUI: "solve", "init", "fmg-init". It may also help you to set fmg to verbose so you can watch the progress (convince yourself that you didn't break it). -Zachariah

November 6, 2011, 06:29		#3
tsero New Member Join Date: Sep 2011 Posts: 8 Rep Power: 14	any idea of how I can export the non periodic pressure plot, in order to obdain the pressure drop along the pipe?

November 7, 2011, 08:57		#4
swetkyz Member Zachariah Swetky Join Date: Aug 2011 Posts: 36 Rep Power: 14	tsero, I would do it is by first creating a line in the pipe, then using an x-y plot to see the pressure drop (assuming your pipe is straight). To do this, use Surface>Line/Rake... to create the line, then do an XY plot of pressure along the vector of the line you just made. The "Plot Direction" must be specified to align with the line, and the line must be selected under surfaces.