Boundary condition not respected

Fluidic · March 21, 2018, 20:15

Hi everyone,

I used CFX (Ansys 18) and I imposed a total pressure at the inlet boundary, the calculation seems to be converged and when I do a total pressure mass-flow average in the CFD-Post, I don't have the same value of total pressure that I imposed in the boundary. Did I miss something?

@++

Gert-Jan · March 22, 2018, 04:05

How do you calculate the pressure in Post? Do you use areaAve(Total Pressure)@inlet or massFlowAve(Total Pressure)@inlet ?

Fluidic · March 22, 2018, 09:57

Hi,

Yes, I use massflowAve(Total pressure)@Inlet

Fluidic · March 23, 2018, 13:42

Hi,

Nobody have an idea?

++

Opaque · March 23, 2018, 14:17

May I ask why massFlowAve(Total Pressure)@Inlet ?

Total Pressure is not an advected quantity..

What kind of Total Pressure profile are you imposing? Uniform distribution of Total Pressure at an inlet?

Gert-Jan · March 23, 2018, 16:42

Indeed, Total Pressure is not advected. But it is a different kind of weighing. If differs from area average. My experience is that Mass Flow Average quanties are more in inline with measurements than area averages.

But this has nothing to do with the underlying question: why the difference? I don't know. How large is the difference? Could it be that it has to do with the (small) difference between node and cell based values?

Antanas · April 4, 2018, 04:55

Quote:

Originally Posted by Fluidic

Hi everyone,

I used CFX (Ansys 18) and I imposed a total pressure at the inlet boundary, the calculation seems to be converged and when I do a total pressure mass-flow average in the CFD-Post, I don't have the same value of total pressure that I imposed in the boundary. Did I miss something?

@++

What type of value you compare - hybrid or conservative?

March 21, 2018, 20:15	Boundary condition not respected	#1
Fluidic New Member Join Date: Mar 2018 Posts: 3 Rep Power: 8	Hi everyone, I used CFX (Ansys 18) and I imposed a total pressure at the inlet boundary, the calculation seems to be converged and when I do a total pressure mass-flow average in the CFD-Post, I don't have the same value of total pressure that I imposed in the boundary. Did I miss something? @++

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March 22, 2018, 04:05		#2
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,928 Rep Power: 28	How do you calculate the pressure in Post? Do you use areaAve(Total Pressure)@inlet or massFlowAve(Total Pressure)@inlet ?

March 22, 2018, 09:57		#3
Fluidic New Member Join Date: Mar 2018 Posts: 3 Rep Power: 8	Hi, Yes, I use massflowAve(Total pressure)@Inlet

March 23, 2018, 13:42		#4
Fluidic New Member Join Date: Mar 2018 Posts: 3 Rep Power: 8	Hi, Nobody have an idea? ++

March 23, 2018, 14:17		#5
Opaque Senior Member Join Date: Jun 2009 Posts: 1,880 Rep Power: 33	May I ask why massFlowAve(Total Pressure)@Inlet ? Total Pressure is not an advected quantity.. What kind of Total Pressure profile are you imposing? Uniform distribution of Total Pressure at an inlet?

March 23, 2018, 16:42		#6
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,928 Rep Power: 28	Indeed, Total Pressure is not advected. But it is a different kind of weighing. If differs from area average. My experience is that Mass Flow Average quanties are more in inline with measurements than area averages. But this has nothing to do with the underlying question: why the difference? I don't know. How large is the difference? Could it be that it has to do with the (small) difference between node and cell based values?