[Lukeyfish]

Under reference values what does depth represent and how can I determine what to set my depth value to? If you want any specific details I can provide upon request.

Also curious about length. I am doing external flow over a multi element airfoil
Thank you!

[moh_zain]

tall me more about your airfoil send picture

[LuckyTran]

For hitting the calculate button and getting an answer, the depth can be ignored. The reference depth does not affect in any way the flow that you get (i.e. you always get the same velocity, pressure, temperature, etc.).


If you choose to do surface integrals (say to get the force) then the integral over the line is multiplied by the depth. If you try to calculate the lift/drag coefficient, then the reference depth also comes into play. Many users set the reference depth to the unit depth (1 meter or 1 ft). But there are situations where one might want to give the reference depth a specific value (for comparison with equivalent 3D objects).

[Lukeyfish]

Thank you that answers my question perfectly.

Just to be sure, would I set my length value to be the arc length of whatever I am simulating or the "chord line".

And for area, that is just the actual surface area of my 2d object. Or is it the surface area of the object if it were 3d with a depth of 1?

[LuckyTran]

The reference length should be the reference length that goes in the definition of the lift and drag coefficients or whatever value you're trying to post-processing (i.e. hydraulic diameter if you're after Nusselt number). However you define these coefficients, your length is in their definition.

Originally Posted by Lukeyfish

And for area, that is just the actual surface area of my 2d object. Or is it the surface area of the object if it were 3d with a depth of 1?

That is actually a good question because I forgot to point it out earlier. Yes in 2D simulations your reference area needs to be consistent with your reference length. The force is line integral of pressure*dl multiplied by the reference depth. But if you calculate drag or lift coefficient, there is a reference area. Fluent doesn't use the arc length * reference depth as the area, it uses exactly what you enter for the reference area to calculate the drag coefficient. You can imagine you put zero or a negative number for the reference area, you will get very funny looking lift/drag coefficients.


If you want to interpret your 2D object as a 3D object w/ 1m depth, then specify your reference area accordingly. This is what is usually done (but of course not always).