Define Driving pressure

cheetthe1 · May 29, 2019, 13:28

Technically I would like to define a driving pressure above a mass flow inlet.
I want to increase values of density and pressure in a certain domain, any advice?

fluid23 · May 29, 2019, 14:55

Driving pressure above mass flow inlet? Can you clarify what you are asking, this isn't 100% clear.

cheetthe1 · May 29, 2019, 19:52

Jet fluid is supposed to be pushed into a chamber with a certain driving pressure, which may partially dissipate by the end of the jet inlet duct. The density/pressure combination the model gibes me automatically for this domain is too low, I want both values higher. Any way to get there?

Thanks,
Bernie

me3840 · May 29, 2019, 20:14

Use a pressure condition and adjust the simulation backpressure to get the correct massflow.

cheetthe1 · May 29, 2019, 20:33

Quote:

Originally Posted by me3840

Use a pressure condition and adjust the simulation backpressure to get the correct massflow.

The entire crossflow chamber is at constant pressure, just the jet domain should be at higher pressure to get more penetration. I think I can not use a pressure outlet, it is reacting flow and I do not want to specify outlet parameters. Am thus running an open outlet.

What is a pressure condition? The only pressure-related inlet BC star ccm+ has would be a stagnation inlet, which does not make sense as I would figure.

LuckyTran · May 30, 2019, 13:21

Use a stagnation inlet and specify the inlet stagnation pressure.

You can't have a static pressure inlet unless the flow is supersonic at the inlet.

cheetthe1 · May 30, 2019, 14:03

Okay, sounds like a plan, thank you will try.

I got another idea in mind, can I superimpose two boundaries? For example by using a little extrusion domain and then using pressure and massflow separately.

cheetthe1 · May 31, 2019, 11:03

So actually I found that at the outlet BC, you could specify a mass flow rather than a split ratio of 1. To my understanding, knowing two mass flows (main inlet and outlet) should set the third mass flow, unfortunately star has great trouble to get there, it would not converge well in the jet inlet domain. Any advice?

May 29, 2019, 13:28	Define Driving pressure	#1
cheetthe1 Member Bernhard Stiehl Join Date: Oct 2018 Posts: 30 Rep Power: 7	Technically I would like to define a driving pressure above a mass flow inlet. I want to increase values of density and pressure in a certain domain, any advice?

May 30, 2019, 14:03		#7
cheetthe1 Member Bernhard Stiehl Join Date: Oct 2018 Posts: 30 Rep Power: 7	Okay, sounds like a plan, thank you will try. I got another idea in mind, can I superimpose two boundaries? For example by using a little extrusion domain and then using pressure and massflow separately. Last edited by cheetthe1; May 30, 2019 at 23:49.

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May 29, 2019, 14:55		#2
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	Driving pressure above mass flow inlet? Can you clarify what you are asking, this isn't 100% clear.

May 29, 2019, 19:52		#3
cheetthe1 Member Bernhard Stiehl Join Date: Oct 2018 Posts: 30 Rep Power: 7	Jet fluid is supposed to be pushed into a chamber with a certain driving pressure, which may partially dissipate by the end of the jet inlet duct. The density/pressure combination the model gibes me automatically for this domain is too low, I want both values higher. Any way to get there? Thanks, Bernie

May 29, 2019, 20:14		#4
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 24	Use a pressure condition and adjust the simulation backpressure to get the correct massflow.

May 30, 2019, 13:21		#6
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,675 Rep Power: 66	Use a stagnation inlet and specify the inlet stagnation pressure. You can't have a static pressure inlet unless the flow is supersonic at the inlet.

May 31, 2019, 11:03		#8
cheetthe1 Member Bernhard Stiehl Join Date: Oct 2018 Posts: 30 Rep Power: 7	So actually I found that at the outlet BC, you could specify a mass flow rather than a split ratio of 1. To my understanding, knowing two mass flows (main inlet and outlet) should set the third mass flow, unfortunately star has great trouble to get there, it would not converge well in the jet inlet domain. Any advice?