Flow Reversed from what is expected

fatirishman53 · December 9, 2012, 16:43

Hello,

I am running a simulation of a firebox and I have it configured as follows:

Inlet: pressure-inlet with 0 gauge pressure, initial velocity 0 m/s, and temperature of 300 K.

Outlet: pressure-outlet with 0 gauge pressure, initial velocity 0 m/s, and temperature of 400 K. (400 K is just an estimate to try to get flow moving in the correct direction)

Heat Source: wood at constant temperature of 922 K

Walls: steel at 300 K, adiabatic

Analysis method: Pseudo-Transient

What I am trying to do is allow FLUENT to begin heating air within the interior, making it more buoyant and flowing out of the outlet stack until a steady state condition is reached. However, for some reason it is flowing in from the outlet and out through the inlet. I've tried reducing flow area at the inlet and increasing flow area at the outlet, among trying other computation techniques. However, I haven't found out why the flow is reversed from what I know to be true in reality. If anyone could help me, I would certainly appreciate it!

By the way, the mesh is composed of > 400000 elements. Unfortunately, with the student version of the sofware, I cannot increase this much more.

thousand · December 10, 2012, 07:04

hi
i think your inlet boundary condition isnt valid u should use velocity inlet with v=0

idil · December 11, 2012, 06:38

I'm struggling from the same issue, I have a micro reactor with velocity inlet= 5m/s pressure outlet =0 gauge p. nothing wrong with mesh. what should I do to fix it?

RodriguezFatz · December 11, 2012, 07:37

Can you post a picture, that shows all boundaries and boundary conditions?

fatirishman53 · December 21, 2012, 23:46

I found a solution to my issue. After doing some research using the help files, I found that using 0 gauge pressure B.C.'s is not preferable. So what I did is use a 1 Pa gauge pressure at each boundary. Then, I had use a user-specified bulk density. After making these changes, I was able to get a solution with the air moving in the correct direction. I have a feeling there were not enough specified parameters within my problem initialization to come up with a proper solution.

December 9, 2012, 16:43	Flow Reversed from what is expected	#1
fatirishman53 Member Matt Join Date: Oct 2012 Posts: 39 Rep Power: 13	Hello, I am running a simulation of a firebox and I have it configured as follows: Inlet: pressure-inlet with 0 gauge pressure, initial velocity 0 m/s, and temperature of 300 K. Outlet: pressure-outlet with 0 gauge pressure, initial velocity 0 m/s, and temperature of 400 K. (400 K is just an estimate to try to get flow moving in the correct direction) Heat Source: wood at constant temperature of 922 K Walls: steel at 300 K, adiabatic Analysis method: Pseudo-Transient What I am trying to do is allow FLUENT to begin heating air within the interior, making it more buoyant and flowing out of the outlet stack until a steady state condition is reached. However, for some reason it is flowing in from the outlet and out through the inlet. I've tried reducing flow area at the inlet and increasing flow area at the outlet, among trying other computation techniques. However, I haven't found out why the flow is reversed from what I know to be true in reality. If anyone could help me, I would certainly appreciate it! By the way, the mesh is composed of > 400000 elements. Unfortunately, with the student version of the sofware, I cannot increase this much more.

December 11, 2012, 07:37		#4
RodriguezFatz Senior Member Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 26	Can you post a picture, that shows all boundaries and boundary conditions? __________________ The skeleton ran out of shampoo in the shower.

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December 10, 2012, 07:04		#2
thousand New Member khalil Join Date: Jul 2012 Posts: 21 Rep Power: 13	hi i think your inlet boundary condition isnt valid u should use velocity inlet with v=0

December 11, 2012, 06:38		#3
idil New Member idil tezcan Join Date: Oct 2012 Posts: 13 Rep Power: 13	I'm struggling from the same issue, I have a micro reactor with velocity inlet= 5m/s pressure outlet =0 gauge p. nothing wrong with mesh. what should I do to fix it?

December 21, 2012, 23:46		#5
fatirishman53 Member Matt Join Date: Oct 2012 Posts: 39 Rep Power: 13	I found a solution to my issue. After doing some research using the help files, I found that using 0 gauge pressure B.C.'s is not preferable. So what I did is use a 1 Pa gauge pressure at each boundary. Then, I had use a user-specified bulk density. After making these changes, I was able to get a solution with the air moving in the correct direction. I have a feeling there were not enough specified parameters within my problem initialization to come up with a proper solution.