Problem with plotting the Massflow in 2D-Axisymmetric

Bando · June 20, 2012, 12:10

Hello

i'm simulating a venturi nozzle. because of it's axisymmetric geometrie i'm only simulating it in 2D but with the centerline beeing an axis i choose the axisymmetric option instead of just 2D.

now for the problem i'm having:
i want to calculate the massflow at the throat. therefore i inserted a derived parts -> plane at the right location.
when i create a massflow report at the plane it computes me massflows that are about 6 times smaller than the measured ones.
when i define my own massflow user field function as density*velocity*(throat-cross-section-area) and plot that in an X-Y Plot with the centerline representing the X-Axis und my own massflow as the Y-Axis it should plot me the right massflow at the location of the throat. but this time i get an massflow that is about 3 times higher than the measured one.

so can anyone tell me what i'm doing wrong? ore even better how to get the right massflow?

Bando · June 21, 2012, 06:09

ok, solved the problem...the massflow measured with my own user field function is exactly by that amount higer by witch i scaled my geometrie with star ccm.

so the imported geometrie had ha diameter at the throat of 5mm, i scaled it down to 1,5mm so the scaling faktor is about 3,3. now if i divide my massflow by 3,3 i get the right result.

June 20, 2012, 12:10	Problem with plotting the Massflow in 2D-Axisymmetric	#1
Bando New Member Join Date: Jun 2012 Posts: 6 Rep Power: 14	Hello i'm simulating a venturi nozzle. because of it's axisymmetric geometrie i'm only simulating it in 2D but with the centerline beeing an axis i choose the axisymmetric option instead of just 2D. now for the problem i'm having: i want to calculate the massflow at the throat. therefore i inserted a derived parts -> plane at the right location. when i create a massflow report at the plane it computes me massflows that are about 6 times smaller than the measured ones. when i define my own massflow user field function as densityvelocity(throat-cross-section-area) and plot that in an X-Y Plot with the centerline representing the X-Axis und my own massflow as the Y-Axis it should plot me the right massflow at the location of the throat. but this time i get an massflow that is about 3 times higher than the measured one. so can anyone tell me what i'm doing wrong? ore even better how to get the right massflow?

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
question about the volume integral in axisymmetric problem	Renold	FLUENT	0	December 7, 2009 12:28
boundary conditions for axisymmetric problem	eers	Main CFD Forum	0	June 19, 2009 15:52
2d axisymmetric: nozzle--> massflow too low?!	Friederike	FLUENT	2	May 9, 2005 05:51
problem in plotting cl curve	kiran	FLUENT	5	August 11, 2004 12:04
y+ - plotting problem -cfx5.4.1	joseph	CFX	2	September 7, 2001 11:06

June 21, 2012, 06:09		#2
Bando New Member Join Date: Jun 2012 Posts: 6 Rep Power: 14	ok, solved the problem...the massflow measured with my own user field function is exactly by that amount higer by witch i scaled my geometrie with star ccm. so the imported geometrie had ha diameter at the throat of 5mm, i scaled it down to 1,5mm so the scaling faktor is about 3,3. now if i divide my massflow by 3,3 i get the right result.