Mass-average V.S Area-average

rikio · March 19, 2009, 07:59

Hi, all,

I am facing a problem, the total pressure increased before entering the comprossor wheel. Yes, I am doing an analysis on a compressor. Total pressure was area-averaged. And it decreases if mass averaged. Obviously, the later is the right trend we should get.
Well, which qualities could be weighted by mass? And which by area? I can not figure it out. Please show me the differences between the two methods.
Thanks for any information, thank you !

pratikmehta · March 20, 2009, 16:12

hi,

There was a similar question or doubt before and here is the link for the same

http://www.cfd-online.com/Forums/cfx...a-average.html

I hope this will make i clear for you

Best of luck
pratik

rikio · March 20, 2009, 21:19

Pratik，
Thanks for your information. I know more about them now. But I am not sure that I could make the right decision on other qualities next time. Do you think this is related to the intensive & extensive parameters? Saying, if the quality is a intensive parameter, area-average could be used, and mass-average for extensive parameter. Do you agree with me?

pratikmehta · March 23, 2009, 03:58

Hi,

When you take an average of certain quatity like Total Pressure in your domain where there exist recirculations or separations like in wake region, under such case area averaging will not give you correct output numerical value, but when you are considering abs mass flow averaging , it is the correct method . I believe this is specifically true for Total Pressure calculations.

When you want to know say velocity values, you have to always take area average over the cut plane. Here Mass flow averaging will give you very high value, using which you cannot retrieve the mass flow value ( if you want you can cross check it ).

I hope this info helps , regarding you concern of intensive properties , ya i think taking an area averaging or mass flow averaging shouldn`t make any change when you want to derive a numerical value of an intensive properties.

But for extensive properties you have to careful .

Best regards
pratik

rikio · March 24, 2009, 00:47

Pratik, thanks very much for your kindly help...

Best regards to you.

March 19, 2009, 07:59	Mass-average V.S Area-average	#1
rikio Senior Member Rikio Join Date: Mar 2009 Location: SH, China Posts: 182 Blog Entries: 1 Rep Power: 17	Hi, all, I am facing a problem, the total pressure increased before entering the comprossor wheel. Yes, I am doing an analysis on a compressor. Total pressure was area-averaged. And it decreases if mass averaged. Obviously, the later is the right trend we should get. Well, which qualities could be weighted by mass? And which by area? I can not figure it out. Please show me the differences between the two methods. Thanks for any information, thank you !

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March 20, 2009, 16:12		#2
pratikmehta Member Pratik Mehta Join Date: Mar 2009 Posts: 32 Rep Power: 17	hi, There was a similar question or doubt before and here is the link for the same http://www.cfd-online.com/Forums/cfx...a-average.html I hope this will make i clear for you Best of luck pratik

March 20, 2009, 21:19		#3
rikio Senior Member Rikio Join Date: Mar 2009 Location: SH, China Posts: 182 Blog Entries: 1 Rep Power: 17	Pratik， Thanks for your information. I know more about them now. But I am not sure that I could make the right decision on other qualities next time. Do you think this is related to the intensive & extensive parameters? Saying, if the quality is a intensive parameter, area-average could be used, and mass-average for extensive parameter. Do you agree with me?

March 23, 2009, 03:58		#4
pratikmehta Member Pratik Mehta Join Date: Mar 2009 Posts: 32 Rep Power: 17	Hi, When you take an average of certain quatity like Total Pressure in your domain where there exist recirculations or separations like in wake region, under such case area averaging will not give you correct output numerical value, but when you are considering abs mass flow averaging , it is the correct method . I believe this is specifically true for Total Pressure calculations. When you want to know say velocity values, you have to always take area average over the cut plane. Here Mass flow averaging will give you very high value, using which you cannot retrieve the mass flow value ( if you want you can cross check it ). I hope this info helps , regarding you concern of intensive properties , ya i think taking an area averaging or mass flow averaging shouldn`t make any change when you want to derive a numerical value of an intensive properties. But for extensive properties you have to careful . Best regards pratik

March 24, 2009, 00:47		#5
rikio Senior Member Rikio Join Date: Mar 2009 Location: SH, China Posts: 182 Blog Entries: 1 Rep Power: 17	Pratik, thanks very much for your kindly help... Best regards to you.