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## Simulation Mechanical and Multiphysics

Active Member
Posts: 6
Registered: ‎03-21-2012

# Lift/Drag Forces

459 Views, 4 Replies
04-09-2012 03:46 PM

Im currently doing some analysis on aerofoils and trying to vary angle of attack etc and calculate lift and drag coefficients. I've set up a 2D planar unsteady fluid flow analysis in Simulation Multiphysics 2012, and I dont know how to convert the reaction forces into one value (or two in y and z components) on the aerofoil, is there any way of doing this?

Below is a picture of the kind of results I'm getting.

Also, for the legend, what is the reaction force measured in? eg per unit width, it seems wierd to have a reaction force in N for flow that is in an infinitely thin plane.

Thanks

Employee
Posts: 259
Registered: ‎06-14-2010

# Re: Lift/Drag Forces

04-10-2012 06:16 AM in reply to: sam_melvin

Reaction force is the integration from surface pressure and shear stress, where shear stress is from surface velocity gradient and assumed viscous fluid.

For 2D planar fluid flow analysis, the reaction force is calculated according the unit length thickness (i.e. =1 with your current length unit). Note that reaction force calculation is from postprocessor; please distinguish the basic 2D planar assumption which assumes infinite thickness.

Jianhui Xie, Ph.D
Principal Engineer
MFG-Digital Simulation
Active Member
Posts: 6
Registered: ‎03-21-2012

# Re: Lift/Drag Forces

04-13-2012 03:20 PM in reply to: Joey.X

Is there any way to get it to integrate the reaction forces over the surface? Just so I can calculate Lift and Drag forces. Cheers

Active Member
Posts: 6
Registered: ‎03-21-2012

# Re: Lift/Drag Forces

04-14-2012 05:20 AM in reply to: sam_melvin

To calculate lift/drag forces select all nodes that are on the surface you are interested in, in the results window (it doesn't matter if you select nodes that are in the flow, as long as they're not on another surface). Set the display type to reaction forces > vector plot (or z / y magnitude if you are only interested in one direction). Select Results Inquire > Current Results, which will open a pop up window with a list of the nodes selected and the forces on them. Select Sum from the drop down menu labelled 'Summary', which will then display the force on the selected surface in x, y and z components.

Employee
Posts: 492
Registered: ‎03-25-2010

# Re: Lift/Drag Forces

04-16-2012 05:42 AM in reply to: Joey.X

The reaction force is for a model depth of 1 length in the model units. It is not for a model depth of 1 length in the current display units. For example, imagine the model was created in units of pounds (lbf) and inches (in), and the reaction force is 1 lbf. That really means 1 lbf per inch of depth. However, when the display units are changed to metric MKS, the reaction force is 4.448 N ( = 1 lbf) which indicates 4.448 N per inch of depth, not 4.448 N per m of depth!

Sincerely,
John Holtz, P.E.
Senior User Experience Designer, Simulation
Autodesk, Inc.

Current version of Mechanical & Multiphysics: 2013 SP1 (2013.01.00.0012 28-Jun-2012)