mean velocity through area

tobi1492 · February 6, 2014, 09:31

Hey guys,

is there any possibility to calculate a mean velocity through an area (not a plane), see figure.

I have an solution, but this is very very uncomfortable. I export a data file with the velocity values in normal direction to that plane. I have to import this file in Matlab and over an script file i can filter the values outside my area. with the velocity values of the area i can calculate my mean velocity.

is there any possibility to draw a polyline on my plane normal to the flow direction that describes my area A in CFX?

http://www.directupload.net/file/d/3...n5hf9x_png.htm

thank you guys

khoopes · February 6, 2014, 09:59

I would try a user surface in CFD-Post. You could use your matlab script to generate a csv file in the right format that you could then use in CFD-Post. This would create a surface just like any other surface in CFD post that you could use all the functions on. It seems straight forward from the help, the only trouble would be getting the connectivity information, but matlab has some triangulation functions that can help you there.

TrII4d · February 6, 2014, 10:07

hi,

did u test the usage of user surface for ur problem ? in CFD-Post guide chapter 10.1.11.1

is the area of interest always on the same position ?

### edit ###
sorry for the repetition ... i did not update the site and saw the post of khoopes after i posted reply ... and finally i found no way to delete the post

ghorrocks · February 6, 2014, 16:56

Can't you calculate the mass flow rate over any arbitrary surface? There is built in calculator in CFX-Post to get that. And if you know your density you can get velocity from that.

singer1812 · February 6, 2014, 17:10

Just thinking off the top of my head, and I assume you have the area in your model and it is not aligned with the coord system or is of odd shape/alignment:

1) In CFX post you can create an expressions:

Normal X*Velocity u
Normal Y*Velocity v
Normal Z*Velocity w

2) Create a vector variable with components of each of the above expressions.

3) Calculate area average of the vector magnitude

If your area is aligned with the coord system, then there is no need to create the above, as I hope you know.

February 6, 2014, 09:31	mean velocity through area	#1
tobi1492 New Member Deutschland Join Date: Dec 2013 Posts: 4 Rep Power: 12	Hey guys, is there any possibility to calculate a mean velocity through an area (not a plane), see figure. I have an solution, but this is very very uncomfortable. I export a data file with the velocity values in normal direction to that plane. I have to import this file in Matlab and over an script file i can filter the values outside my area. with the velocity values of the area i can calculate my mean velocity. is there any possibility to draw a polyline on my plane normal to the flow direction that describes my area A in CFX? http://www.directupload.net/file/d/3...n5hf9x_png.htm thank you guys

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February 6, 2014, 09:59		#2
khoopes Member Kevin Hoopes Join Date: Oct 2010 Posts: 43 Rep Power: 16	I would try a user surface in CFD-Post. You could use your matlab script to generate a csv file in the right format that you could then use in CFD-Post. This would create a surface just like any other surface in CFD post that you could use all the functions on. It seems straight forward from the help, the only trouble would be getting the connectivity information, but matlab has some triangulation functions that can help you there.

February 6, 2014, 10:07		#3
TrII4d Member Join Date: Nov 2011 Location: Germany Posts: 40 Rep Power: 14	hi, did u test the usage of user surface for ur problem ? in CFD-Post guide chapter 10.1.11.1 is the area of interest always on the same position ? ### edit ### sorry for the repetition ... i did not update the site and saw the post of khoopes after i posted reply ... and finally i found no way to delete the post

February 6, 2014, 16:56		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Can't you calculate the mass flow rate over any arbitrary surface? There is built in calculator in CFX-Post to get that. And if you know your density you can get velocity from that.

February 6, 2014, 17:10		#5
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 20	Just thinking off the top of my head, and I assume you have the area in your model and it is not aligned with the coord system or is of odd shape/alignment: 1) In CFX post you can create an expressions: Normal XVelocity u Normal YVelocity v Normal Z*Velocity w 2) Create a vector variable with components of each of the above expressions. 3) Calculate area average of the vector magnitude If your area is aligned with the coord system, then there is no need to create the above, as I hope you know.