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Old   September 30, 2011, 12:31
Default Turbulent Jets in Water and Air
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Hi all, I have started out with FLUENT for a while in air studies but recently required to perform simulations on submerged turbulent jets


The problem is to replicate the results from experiment studies, a horizontal turbulent jet at the bottom of a water tank. I was unable to get results similar to the experimental setup (way off, not even the jet shape). So I decided to do it in air, with the velocity scaled up based on Re similarity. It worked very well for air in most models.

I was trying to find out the differences for many days but still unable to.

Differences I have made from Air to Water:

1. Surface of water I have changed to pressure outlet with 0 pascal, I=0.05% and use the tank top view's hydraulic diameter. I have tried several different BC but the differences are small.

2. Gravity is a must now. 9.81 towards the bottom of tank (Can someone confirm if its a must for to turn on gravity? Cos it seems hard to converge with gravity turned on)

3. Reference pressure location at the bottom of the tank near the inlet. Operating Pressure = atm + pgh

4. Variable density parameters-haven tried with it on.


Thanks in advance for any advice. Please correct me if I am wrong, much appreciated.

Last edited by haze_1986; September 30, 2011 at 12:47.
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Old   October 3, 2011, 14:20
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Quote:
Originally Posted by haze_1986 View Post
Hi all, I have started out with FLUENT for a while in air studies but recently required to perform simulations on submerged turbulent jets


The problem is to replicate the results from experiment studies, a horizontal turbulent jet at the bottom of a water tank. I was unable to get results similar to the experimental setup (way off, not even the jet shape). So I decided to do it in air, with the velocity scaled up based on Re similarity. It worked very well for air in most models.

I was trying to find out the differences for many days but still unable to.

Differences I have made from Air to Water:

1. Surface of water I have changed to pressure outlet with 0 pascal, I=0.05% and use the tank top view's hydraulic diameter. I have tried several different BC but the differences are small.

2. Gravity is a must now. 9.81 towards the bottom of tank (Can someone confirm if its a must for to turn on gravity? Cos it seems hard to converge with gravity turned on)

3. Reference pressure location at the bottom of the tank near the inlet. Operating Pressure = atm + pgh

4. Variable density parameters-haven tried with it on.


Thanks in advance for any advice. Please correct me if I am wrong, much appreciated.



I'm simulating a similar case, but I have water + particles entering a domain filled of water, and mixing with still water. Activating the gravity field, and using a pressure inlet, means that the hydrostatic pressure automatically accounts for the stratification of the pressure, and the contribution of ro*g*h is added to the reference pressure. Probably, including the gravity depends on the dimensions of the domain; in my case, the dimensions are of the order of tens of meters, so I cannot neglect it. Anyway, I'm having some problems (take a quick look if you can, two lines above your post, ''how simulating a water-particle current into sea).
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Old   October 3, 2011, 21:08
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I have also tried changing the water surface boundary to 0 shear stress wall, and it seems that my results are getting better (no reversed flows) but my ratio of lateral spread is still to large now.
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