How to set initial pressure

KevNo · February 14, 2020, 08:24

Hello! I'm a newby in Fluent and have a question:
I want to model a countercurrent-flow tube heat exchanger.

The flow through the tubes has an initial pressure of 250000 Pascal (temperature 40 degrees) - velocity inlet.
The flow around the tubes has an initial pressure of 450000 Pascal (temperature 15 degrees) - velocity inlet.
I have two corresponding pressure outlets. I want to simulate the flow and the temperature gradient (energy equation and viscous flow are activated). I'm using a pressure-based solver in the steady case.

So, where can I set the initial pressure? In the inlets are only supersonic pressure and in the outlets backflow pressure given...

Thank you!

LuckyTran · February 14, 2020, 11:02

In the initialization pane. It looks like so.

vinerm · February 14, 2020, 13:29

There are multiple ways to initialize at different pressure values, however, the initialization would have no effect if the system is incompressible. You can initialize with same pressure. If the system, however, is compressible, you have to initialize all domains at same pressure, say lower of the two, using the initialization dialogue box, as shown by Lucky and then use the patch within the same dialogue box to initialize the other domain at higher pressure.

KevNo · February 17, 2020, 05:59

Thank you both!
I have incompressible flow with water on both sides. So, I don't need to initializie with the pressure? But where can I setup this information?

vinerm · February 17, 2020, 07:09

For an incompressible system, pressure has no relevance. Only its drop is important. Therefore, you do not need to set different pressure values. However, if you have some model, e.g., evaporation-condensation or cavitation, where value of pressure is important, then you have to set pressure accordingly. You can use patch option for the same.

LuckyTran · February 17, 2020, 12:19

You still need to initialize the pressure field. The point is that the value of pressure has a slightly different meaning for an incompressible fluid. Regardless, Fluent is a compressible N-S solver even when the Fluid is incompressible.

February 14, 2020, 08:24	How to set initial pressure	#1
KevNo New Member KevNo Join Date: Oct 2019 Location: Germany Posts: 2 Rep Power: 0	Hello! I'm a newby in Fluent and have a question: I want to model a countercurrent-flow tube heat exchanger. The flow through the tubes has an initial pressure of 250000 Pascal (temperature 40 degrees) - velocity inlet. The flow around the tubes has an initial pressure of 450000 Pascal (temperature 15 degrees) - velocity inlet. I have two corresponding pressure outlets. I want to simulate the flow and the temperature gradient (energy equation and viscous flow are activated). I'm using a pressure-based solver in the steady case. So, where can I set the initial pressure? In the inlets are only supersonic pressure and in the outlets backflow pressure given... Thank you!

February 14, 2020, 13:29	Initial Pressure	#3
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	There are multiple ways to initialize at different pressure values, however, the initialization would have no effect if the system is incompressible. You can initialize with same pressure. If the system, however, is compressible, you have to initialize all domains at same pressure, say lower of the two, using the initialization dialogue box, as shown by Lucky and then use the patch within the same dialogue box to initialize the other domain at higher pressure. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

February 17, 2020, 07:09	Incompressible	#5
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	For an incompressible system, pressure has no relevance. Only its drop is important. Therefore, you do not need to set different pressure values. However, if you have some model, e.g., evaporation-condensation or cavitation, where value of pressure is important, then you have to set pressure accordingly. You can use patch option for the same. Haitham Osman CFD likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

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February 14, 2020, 11:02		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 66	In the initialization pane. It looks like so.

February 17, 2020, 05:59		#4
KevNo New Member KevNo Join Date: Oct 2019 Location: Germany Posts: 2 Rep Power: 0	Thank you both! I have incompressible flow with water on both sides. So, I don't need to initializie with the pressure? But where can I setup this information?

February 17, 2020, 12:19		#6
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 66	You still need to initialize the pressure field. The point is that the value of pressure has a slightly different meaning for an incompressible fluid. Regardless, Fluent is a compressible N-S solver even when the Fluid is incompressible.