Pressure Boundary at Outlet

AS_Aero · March 10, 2017, 13:04

Hi All

I was doing a simple RANS simulation of circular Pipe flow with diffuser at one end using CFX.
The
Inlet Boundary was given massflow rate and
Outlet as static pressure =zero
Reference Pressure = 1 atm

The data sheet of the diffuser says that at inlet the operating pressure of 10 bar has a flow rate of 4 l/min.

But when I post process my results at inlet where I gave 4 L/min shows a pressure less than that or around 5 bar which makes me doubt about the boundary condition. Could someone help me to explain what could have gone wrong or is it quiet natural ? or should I do something with the reference pressure or at the outlet ?

Thanks in advance

ghorrocks · March 11, 2017, 05:43

Have you done the standard checks for accuracy? https://www.cfd-online.com/Wiki/Ansy..._inaccurate.3F

AS_Aero · March 11, 2017, 06:04

YEs No I would say !! There is the problem. I am doubtful about the BC'ns I have applied. Or either I am confused what to give. And yes with the other parameters YEs I did play around.. Not much of a difference. I am confused about this pressure thing !!
In the experiment when you give 10 bar from the pump (barometer reading) to the pipe it has a flow rate of 5L/min. So in the simulation I gave the 5L/min so I expect a 10 bar pressure as the inlet maximum pressure right ? But thats no the case here.

Jiricbeng · March 14, 2017, 09:10

Moreover make sure about static/total pressure.

March 10, 2017, 13:04	Pressure Boundary at Outlet	#1
AS_Aero Senior Member Join Date: Mar 2013 Location: Germany Posts: 357 Rep Power: 15	Hi All I was doing a simple RANS simulation of circular Pipe flow with diffuser at one end using CFX. The Inlet Boundary was given massflow rate and Outlet as static pressure =zero Reference Pressure = 1 atm The data sheet of the diffuser says that at inlet the operating pressure of 10 bar has a flow rate of 4 l/min. But when I post process my results at inlet where I gave 4 L/min shows a pressure less than that or around 5 bar which makes me doubt about the boundary condition. Could someone help me to explain what could have gone wrong or is it quiet natural ? or should I do something with the reference pressure or at the outlet ? Thanks in advance

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March 11, 2017, 05:43		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 18,011 Rep Power: 146	Have you done the standard checks for accuracy? https://www.cfd-online.com/Wiki/Ansy..._inaccurate.3F

March 11, 2017, 06:04		#3
AS_Aero Senior Member Join Date: Mar 2013 Location: Germany Posts: 357 Rep Power: 15	YEs No I would say !! There is the problem. I am doubtful about the BC'ns I have applied. Or either I am confused what to give. And yes with the other parameters YEs I did play around.. Not much of a difference. I am confused about this pressure thing !! In the experiment when you give 10 bar from the pump (barometer reading) to the pipe it has a flow rate of 5L/min. So in the simulation I gave the 5L/min so I expect a 10 bar pressure as the inlet maximum pressure right ? But thats no the case here.

March 14, 2017, 09:10		#4
Jiricbeng Senior Member Jiri Join Date: Mar 2014 Posts: 228 Rep Power: 14	Moreover make sure about static/total pressure.