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2D Flow Simulation "Thickness"

Question asked by Josiah Lund on Jan 1, 2015
Latest reply on Jan 4, 2015 by Jared Conway

I am trying to learn more about reading results out after running a simulation. I have done a couple of 2D simulations with a thin plate at 5 deg angle of attack, with a freestream velocity of 100 ft/s. I chose this because I wanted something simple that I could check with hand calculations, but I am running into some differences that seem fairly substantial to me.

 

Theoretically, the lift coefficient for a thin, flat plate at low angles of attack should be 2*π*alpha (rad). This says that the lift coefficient for a flat plate at 5 deg should be about 0.548. Lift is given as (0.5*ρ*v²)*S*Cl, where rho is air density, v is freestream velocity, S is the wing or airfoil area, and Cl is the lift coefficient.

 

When doing a 2D simulation, the thickness of the simulation was automatically set to what is equal to 0.2 inches giving the plate an area of 0.01667 ft^2 yielding a theoretical lift of 0.109 lbs, or exactly 1/5 of the lift of the entire plate. This does not match my findings for either case. Please see attachments for my setup and results.

 

The table below shows the collected data

Theoretical CL0.548311
Lift (lb)
fluid regionArea (ft2)TheoreticSimulation
partial0.0166670.1086110.073
complete0.0833330.5430570.3763

 

Thank you in advance for any information on why these approximations and simulations are not in better agreement.

Josiah

boundary region.PNG

Above is the computation region for both simulations

 

narrow region.PNG

Above is the section view showing the narrower section 0.2 inches across

 

complete region.PNG

Above is the section view showing the wider region 1 in. wide

 

mesh quality.PNG

Above is the view of the lower quality mesh. For the wider region, I was running into some computation errors that estimated 50 hours to solve, so I lowered the resolution to what is shown above.

 

surfaces partial.PNG

Above are the surface forces for the narrower region

 

surfaces complete.PNG

Above are the surface forces for the wider region

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