CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > CFX

How to measure thrust ?

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   January 12, 2010, 05:52
Arrow How to measure thrust ?
  #1
Senior Member
 
Attesz's Avatar
 
Attesz
Join Date: Mar 2009
Posts: 355
Rep Power: 8
Attesz is an unknown quantity at this point
Hi all,

I'm simulating a quadrotor RC helicopters propeller:
Quadrotor helicopter propeller simulation

The main goal is to find the best blade shape. To get this, I have to measure thrust in CFX post.

Now, I define a plane behind the rotor, and let the CFX calculate the normal force on it. The CFD forces are smaller than measured. I know, it can caused by a lot of things, but maybe I'm wrong in force calculation.

So my question is: how to measure the thrust of the propeller?

Thanks,
Attesz

Last edited by Attesz; January 12, 2010 at 14:28.
Attesz is offline   Reply With Quote

Old   January 12, 2010, 18:04
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,929
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Most people are more interested in the thrust from the rotor, not a plate underneath the rotor. Why don't you calculate the thrust on the rotor blades?
ghorrocks is offline   Reply With Quote

Old   January 13, 2010, 04:27
Default
  #3
Senior Member
 
Attesz's Avatar
 
Attesz
Join Date: Mar 2009
Posts: 355
Rep Power: 8
Attesz is an unknown quantity at this point
Hi Glenn,

I've calculated normal force on the rotor blades, but the values are lower than on the plane measured, so more lower than real. I don't know why?

I think, CFX calculates the force on a plane from the equation massflow*velocity, which is the general equation for thrust calculation. To this equation comes the pressure difference member: area*(pressure@outlet-pressure@environment), which has a low value in my work.

Thanks for your reply,
Attesz
Attesz is offline   Reply With Quote

Old   January 13, 2010, 06:50
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,929
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
So let me paraphrase you: When you put in a feature which has nothing to do with the rotors the force acting on it is closer to what you think it should be so therefore you will use this force rather than the force on the rotors which is actually what you want.

Pardon my sarcasm but I think this line of logic is not helpful. If the force you want seems wrong then you should look at the accuracy of your simulation rather than doing some fudge on the results to make it appear better than it is.

Calculate the force on the rotor using the forceX/Y/Z() function, and if the answer is wrong then you have an error in your simulation and you should fix it.
ghorrocks is offline   Reply With Quote

Old   January 13, 2010, 07:17
Default
  #5
Senior Member
 
Attesz's Avatar
 
Attesz
Join Date: Mar 2009
Posts: 355
Rep Power: 8
Attesz is an unknown quantity at this point
Thank you Glenn,

but I didn't want to cheat, I didn't know how to measure force simply. I tought measuring that is more difficult, than measure it on the blades.
However, I'll examine the mesh, but also the measuring of the real quadrotor can be inaccurate (ground effect, the effect of rotors to each other, and also the "measuring device": a kitchen balance . it's a student team project).

Best regards,
Attesz
Attesz is offline   Reply With Quote

Reply

Tags
measure, quadrotor, thrust

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Thrust calculation Tony CFX 4 July 9, 2012 11:48
Thrust value, positive or negative? Emmanuel FLUENT 0 June 25, 2007 19:47
3D Ejector Thrust Calculation Emmanuel FLUENT 0 April 6, 2007 13:59
pressure measure in centrifugal pump vanes Patricio Torrejon FLUENT 1 December 16, 2005 18:10
Add Measure Markings or Coordinates to the Contour Colin FLUENT 4 August 25, 2004 09:54


All times are GMT -4. The time now is 04:56.