Simple Water Tank Transient

88phil88 · February 21, 2011, 08:58

I've been stuck for a while modelling a water tank in transient flow. The tank itself runs fine for steady state.

I want to model the tank for transient flow when initially the tank is empty and fills up with water. I've specified two fluids water and air and set initial conditions to water volume fraction 0, air volume fraction 1. The inlet is set to 5ms^-1 and the outlet to static pressure 0 Pa (inlet and outlet are at the top of the tank). Whatever i try i end up with the tank's absolute pressure at interval 1 being the same as the last interval which makes me think the tank is full of water the whole time!

I've worked through lots of the tutorials including the transient flow of the smoke in the air i've tried using all of them to help me but its not working

Any help would be greatly appriciated!

Thanks

Phil

Bmolaie · March 16, 2014, 06:49

I think u should consider atmosphere pressure in the outlet zone instead of 0.

ghorrocks · March 16, 2014, 17:34

I assume you mean a reference pressure of 1 atmosphere and 0 relative pressure at the outlet.

But to help you, you will need to show some images of what you are doing and your CCL. Your output file would also help.

Bmolaie · March 17, 2014, 01:17

Baffle 2.jpg

Baffle 4.jpg
inlet volume flow rate is 0.111 m3/sec from a 1 m^2 hole
and out let is 6 m^2 in the bottom end
I don't know what type of output you wanted to see... if u tell me specificly I will send it
I'm really stock! this just isn't logical!
if u have a manual for this type of modeling or you can give me some points that u think is important it will help a lot

Bmolaie · March 17, 2014, 01:24

No Baff.jpg
this one is with no baffle... the velocity vectors are flying all over the place...

I want to put a baffle in a optimum location that we could get more low velocity length for sedimentation...
(p.s. I think I made a mistake, I thought this is my post, and i thought u were talking to me

, sorry for that)

ghorrocks · March 17, 2014, 03:48

The final simulation moght not be converged, or there could be other weirdness giong on.

But this all looks like basic CFD technique to me. If I was you I would choose a relevant benchmark simulation (maybe flow over a backwards facing step) and compare your simulation results against a good benchmark solution (either a quality CFD simulation or experimental results). This will be a good exercise in CFD accuracy. If you cannot do basic simulations accurately then you have no chance to get good answers with a more complex flow.

February 21, 2011, 08:58	Simple Water Tank Transient Flow HELP!!	#1
88phil88 New Member phil fenna Join Date: Feb 2011 Posts: 14 Rep Power: 15	I've been stuck for a while modelling a water tank in transient flow. The tank itself runs fine for steady state. I want to model the tank for transient flow when initially the tank is empty and fills up with water. I've specified two fluids water and air and set initial conditions to water volume fraction 0, air volume fraction 1. The inlet is set to 5ms^-1 and the outlet to static pressure 0 Pa (inlet and outlet are at the top of the tank). Whatever i try i end up with the tank's absolute pressure at interval 1 being the same as the last interval which makes me think the tank is full of water the whole time! I've worked through lots of the tutorials including the transient flow of the smoke in the air i've tried using all of them to help me but its not working Any help would be greatly appriciated! Thanks Phil ajithjec likes this. Last edited by 88phil88; February 21, 2011 at 09:34. Reason: just to add help to it

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March 16, 2014, 06:49		#2
Bmolaie New Member Baharan Molaie Join Date: Feb 2014 Posts: 6 Rep Power: 12	I think u should consider atmosphere pressure in the outlet zone instead of 0.

March 16, 2014, 17:34		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,696 Rep Power: 143	I assume you mean a reference pressure of 1 atmosphere and 0 relative pressure at the outlet. But to help you, you will need to show some images of what you are doing and your CCL. Your output file would also help.

March 17, 2014, 01:17		#4
Bmolaie New Member Baharan Molaie Join Date: Feb 2014 Posts: 6 Rep Power: 12	Baffle 2.jpg Baffle 4.jpg inlet volume flow rate is 0.111 m3/sec from a 1 m^2 hole and out let is 6 m^2 in the bottom end I don't know what type of output you wanted to see... if u tell me specificly I will send it I'm really stock! this just isn't logical! if u have a manual for this type of modeling or you can give me some points that u think is important it will help a lot

March 17, 2014, 01:24		#5
Bmolaie New Member Baharan Molaie Join Date: Feb 2014 Posts: 6 Rep Power: 12	No Baff.jpg this one is with no baffle... the velocity vectors are flying all over the place... I want to put a baffle in a optimum location that we could get more low velocity length for sedimentation... (p.s. I think I made a mistake, I thought this is my post, and i thought u were talking to me , sorry for that)

March 17, 2014, 03:48		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,696 Rep Power: 143	The final simulation moght not be converged, or there could be other weirdness giong on. But this all looks like basic CFD technique to me. If I was you I would choose a relevant benchmark simulation (maybe flow over a backwards facing step) and compare your simulation results against a good benchmark solution (either a quality CFD simulation or experimental results). This will be a good exercise in CFD accuracy. If you cannot do basic simulations accurately then you have no chance to get good answers with a more complex flow.