multiple exits

piyusharas · June 14, 2015, 07:01

I have systemin which i have a system in which a tank in present having inlet of water from top through a pipe. there are 6 exit slits symmetrically located .
I have given inlet boundary condition as velocity inlet and given it a velocity of -0.5m/s and i want to calculate the mass flow in all the exits. So i have kept them pressure outlet . But in post processing i am getting mass flow in some as positive and some as negative which is not possible as all liquid will flow in direction of inlet only that is under influence of gravity.
please help me out.

marauder · June 15, 2015, 06:35

Please post an image to understand the problem better.

Between, did you activate Gravity, Buoyancy effects?

piyusharas · June 18, 2015, 03:16

yes i am considering the effect of gravity .
here are some pictures of my model
https://drive.google.com/file/d/0B9c...ew?usp=sharing
https://drive.google.com/file/d/0B9c...ew?usp=sharing
https://drive.google.com/file/d/0B9c...ew?usp=sharing

liusuanyatong · June 18, 2015, 04:40

I think your inlet velocity has a problem.Your velocity inlet setting should be positive.If your velocity is negative，it does mean that fluid flow outside computational domain，not intside.I'm sorry my English is poor.I hope my answer will help you.

piyusharas · June 18, 2015, 04:42

but as you can see my y direction is opposite direction to flow to inlet .
so shouldn't i put negative velocity only.
and yes in inlet my fluid is flowing inside the tank.

marauder · June 19, 2015, 00:36

You are getting negative flow at some exits because you have recirculation zones near these exits. This can be observed from vector plots.

You have not allowed the flow to fully develop at the exit. Try extending the exits outwards so that the recirculation zone is fully captured and the flow at outlet fully develops.

Or else if your goal is to remove these recirculation zone try keeping baffles near the exits to control the flow direction.

June 14, 2015, 07:01	multiple exits	#1
piyusharas Member Piyush Aras Join Date: Jun 2015 Posts: 34 Rep Power: 10	I have systemin which i have a system in which a tank in present having inlet of water from top through a pipe. there are 6 exit slits symmetrically located . I have given inlet boundary condition as velocity inlet and given it a velocity of -0.5m/s and i want to calculate the mass flow in all the exits. So i have kept them pressure outlet . But in post processing i am getting mass flow in some as positive and some as negative which is not possible as all liquid will flow in direction of inlet only that is under influence of gravity. please help me out.

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June 15, 2015, 06:35		#2
marauder Member Anonymous Join Date: Mar 2014 Posts: 84 Rep Power: 12	Please post an image to understand the problem better. Between, did you activate Gravity, Buoyancy effects?

June 18, 2015, 03:16		#3
piyusharas Member Piyush Aras Join Date: Jun 2015 Posts: 34 Rep Power: 10	yes i am considering the effect of gravity . here are some pictures of my model https://drive.google.com/file/d/0B9c...ew?usp=sharing https://drive.google.com/file/d/0B9c...ew?usp=sharing https://drive.google.com/file/d/0B9c...ew?usp=sharing

June 18, 2015, 04:40		#4
liusuanyatong New Member liusuanyatong Join Date: Jun 2015 Posts: 7 Rep Power: 10	I think your inlet velocity has a problem.Your velocity inlet setting should be positive.If your velocity is negative，it does mean that fluid flow outside computational domain，not intside.I'm sorry my English is poor.I hope my answer will help you.

June 18, 2015, 04:42		#5
piyusharas Member Piyush Aras Join Date: Jun 2015 Posts: 34 Rep Power: 10	but as you can see my y direction is opposite direction to flow to inlet . so shouldn't i put negative velocity only. and yes in inlet my fluid is flowing inside the tank.

June 19, 2015, 00:36		#6
marauder Member Anonymous Join Date: Mar 2014 Posts: 84 Rep Power: 12	You are getting negative flow at some exits because you have recirculation zones near these exits. This can be observed from vector plots. You have not allowed the flow to fully develop at the exit. Try extending the exits outwards so that the recirculation zone is fully captured and the flow at outlet fully develops. Or else if your goal is to remove these recirculation zone try keeping baffles near the exits to control the flow direction.