Type 1 vs Type 2 Polar like in XFLR5

Kailee71 · May 14, 2023, 11:21

Hi all,

I'm just getting into Star-CCM+ and as a training exercise I'm going to do some 2D comparisons of airfoils for model aircraft. I have some experience in using XFLR5 to so similar comparisons and found the Type 2 polars that it produces very intuitive and helpful. In other places these polars are called dynamic polars. In a nutshell, it will adjust flow velocity such that for a particular airfoil and chord length, it produces plots of Cl/Cd for a particular Re*sqrt(Cl), which essentially means that for lower Cl values you're using higher free stream velocities. It's trivial generating Cl/Cd vs Cl plots using the design manager, but this would generate plots at constant Re, which is not what usually happens in real, equilibrated flight (you'll have lower Re at higher Cl unless you're pulling up at elevated speeds for instance).

I've tried to do this in Star-CCM+ but am failing; I thought to make reference velocity and cell initiation velocity dependent on Cl, but Cl only comes out of the sim itself... Ideally the input would be an actual value of Re*sqrt(Cl), which would then generate a flow velocity for that particular design (AoA & v), which would then be the basis for the mentioned plot.

Would anybody have any pointers as to how a plot like this could be generated in Star-CCM+?

Best of thanks in advance for any pointers,

Kai.

f-w · May 15, 2023, 16:29

To do this semi-auto, pick and fix AOA, then iterate using a macro on velocity until the calculated report value of Re*sqrt(Cl) hits your target, within tolerance. End result is a single data point for your plot. Within reason, start at a low AOA, and repeat in desired # of increments until you reach high AOA (or until you can't sufficiently converge); each of these is a data point.

For iterating on velocity, adapt the macro provided in the following knowledge base article:
https://support.sw.siemens.com/knowl...00031937_EN_US

You can use Design Manager to automate the whole process; it will iterate through AOA, the macro will iterate on velocity, while all you have to do is specify/pass through Re*sqrt(Cl) to the macro.

Cheers

Kailee71 · May 15, 2023, 20:22

Hi f-w,

yes I thought it would get to something like this. It'll be a good learning experience with design manager, I've only done some trivial AoA sweeps, so it's a step ahead!

Best of thanks for the pointer!

Kai.

May 14, 2023, 11:21	Type 1 vs Type 2 Polar like in XFLR5	#1
Kailee71 Member Kailee Join Date: Dec 2019 Posts: 35 Rep Power: 6	Hi all, I'm just getting into Star-CCM+ and as a training exercise I'm going to do some 2D comparisons of airfoils for model aircraft. I have some experience in using XFLR5 to so similar comparisons and found the Type 2 polars that it produces very intuitive and helpful. In other places these polars are called dynamic polars. In a nutshell, it will adjust flow velocity such that for a particular airfoil and chord length, it produces plots of Cl/Cd for a particular Resqrt(Cl), which essentially means that for lower Cl values you're using higher free stream velocities. It's trivial generating Cl/Cd vs Cl plots using the design manager, but this would generate plots at constant Re, which is not what usually happens in real, equilibrated flight (you'll have lower Re at higher Cl unless you're pulling up at elevated speeds for instance). I've tried to do this in Star-CCM+ but am failing; I thought to make reference velocity and cell initiation velocity dependent on Cl, but Cl only comes out of the sim itself... Ideally the input would be an actual value of Resqrt(Cl), which would then generate a flow velocity for that particular design (AoA & v), which would then be the basis for the mentioned plot. Would anybody have any pointers as to how a plot like this could be generated in Star-CCM+? Best of thanks in advance for any pointers, Kai.

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May 15, 2023, 16:29		#2
f-w Senior Member Join Date: Apr 2009 Posts: 154 Rep Power: 17	To do this semi-auto, pick and fix AOA, then iterate using a macro on velocity until the calculated report value of Resqrt(Cl) hits your target, within tolerance. End result is a single data point for your plot. Within reason, start at a low AOA, and repeat in desired # of increments until you reach high AOA (or until you can't sufficiently converge); each of these is a data point. For iterating on velocity, adapt the macro provided in the following knowledge base article: https://support.sw.siemens.com/knowl...00031937_EN_US You can use Design Manager to automate the whole process; it will iterate through AOA, the macro will iterate on velocity, while all you have to do is specify/pass through Resqrt(Cl) to the macro. Cheers

May 15, 2023, 20:22		#3
Kailee71 Member Kailee Join Date: Dec 2019 Posts: 35 Rep Power: 6	Hi f-w, yes I thought it would get to something like this. It'll be a good learning experience with design manager, I've only done some trivial AoA sweeps, so it's a step ahead! Best of thanks for the pointer! Kai.