Analysing Lift for NACA0012 through range of angles of attack.

wrb · March 1, 2018, 10:23

I am currently trying to find coefficients of lift for a NACA 0012 (2D) airfoil operating at a Reynolds number of 6million, mach number of 0.3 and with a chord length of 1m through a range of angles of attack to determine Clmax and dCl/dAoA.

Through fluent i am operating a density based solver, viscous k-omega SST and using a 2nd order flow solution. To alter angle of attack I am altering the x & y velocity components while also altering the force vectors on the monitors to ensure the lift and drag properties are measured perpendicular and parallel to the free stream.

My mesh is a structured mesh designed to deal with the boundary layer across the airfoil.

I am having issues with obtaining solutions for AoA above 12 degrees. Typically energy and continuity residuals are not converging and tend to hover around the 10^-2. (I have my residuals set to 10^-3) despite running to near 30,000 iterations. Looking through NACA0012 data https://turbmodels.larc.nasa.gov/naca0012_val_sst.html it seems the Clmax occurs at approximately 16 degrees however i can not get my residuals to converge and hence obtain Cl values.

To obtain a value at 12degrees Fluent ran for 12,000 iterations but after 30,000 at 14 degrees there was no convergence.

If the flow has began to separate over the airfoil will this prevent the solution from converging? if this is the case, how do I obtain a value for Cl?

How do I check for flow separation? Do I run the solution and stop it after x amount of iterations, then use post processing to get a mach contour and go from there?

Would a transient solver be better to analyse higher angles of attack?

ICEMgod · March 6, 2018, 08:33

Set the drag and lift as monitor plots. In that way you can obtain the value during calculation and judge the convergence. You can see if the values settle after an amount of iterations or if the solution changes over time.

Could be possible, that separation occurs. Save your results after x iterations and look at the velocity contour.

Residuals alone are not a criterion for convergence.

March 1, 2018, 10:23	Analysing Lift for NACA0012 through range of angles of attack.	#1
wrb New Member Finlay Join Date: Mar 2018 Posts: 2 Rep Power: 0	I am currently trying to find coefficients of lift for a NACA 0012 (2D) airfoil operating at a Reynolds number of 6million, mach number of 0.3 and with a chord length of 1m through a range of angles of attack to determine Clmax and dCl/dAoA. Through fluent i am operating a density based solver, viscous k-omega SST and using a 2nd order flow solution. To alter angle of attack I am altering the x & y velocity components while also altering the force vectors on the monitors to ensure the lift and drag properties are measured perpendicular and parallel to the free stream. My mesh is a structured mesh designed to deal with the boundary layer across the airfoil. I am having issues with obtaining solutions for AoA above 12 degrees. Typically energy and continuity residuals are not converging and tend to hover around the 10^-2. (I have my residuals set to 10^-3) despite running to near 30,000 iterations. Looking through NACA0012 data https://turbmodels.larc.nasa.gov/naca0012_val_sst.html it seems the Clmax occurs at approximately 16 degrees however i can not get my residuals to converge and hence obtain Cl values. To obtain a value at 12degrees Fluent ran for 12,000 iterations but after 30,000 at 14 degrees there was no convergence. If the flow has began to separate over the airfoil will this prevent the solution from converging? if this is the case, how do I obtain a value for Cl? How do I check for flow separation? Do I run the solution and stop it after x amount of iterations, then use post processing to get a mach contour and go from there? Would a transient solver be better to analyse higher angles of attack?

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March 6, 2018, 08:33		#2
ICEMgod New Member Join Date: Feb 2016 Posts: 2 Rep Power: 0	Set the drag and lift as monitor plots. In that way you can obtain the value during calculation and judge the convergence. You can see if the values settle after an amount of iterations or if the solution changes over time. Could be possible, that separation occurs. Save your results after x iterations and look at the velocity contour. Residuals alone are not a criterion for convergence.