## Simulation Mechanical and Multiphysics

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# Lift/Drag Forces

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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

Solved! Go to Solution.

# Re: Lift/Drag Forces

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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.

Principal Engineer

MFG-Digital Simulation

# Re: Lift/Drag Forces

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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

# Re: Lift/Drag Forces

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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.

# Re: Lift/Drag Forces

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One technicality to Joey's reply.

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__!

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)