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Old 06-04-2019, 04:37 PM   #1
DerNerf
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Question Simulation of Transsonic effects

Hello everyone,

I'm currently working on the simulation of the re-entry of a lifting capsule. I already have decently working aerodynamics and all that stuff, but I found somehing i can't quite explain:

The callback function for aerodynamic coefficients works fine and generally the results in the simulation meet the literature data. One thing however does not:

The angle of attack doesn't match the literature value for the entire flight duration. In particular, when the vessel flies at the transsonic regime around Mach 1, the angle of attack is too high (or actually low, since it's a negative angle of attack).

Therefore I have a simple question: To what degree does Orbiter simulate transsonic effects?
In another thread I've read, that Orbiter does simulate the drag induced due to compression shock. From my understanding, this is added to the drag vector, that has it's origin in the centre of pressure. However, since these compression shocks are locally limited, they should also produce a momentum, because they act on the surface and not the centre of mass or pressure.
Does Orbiter simulate the resulting momentum and the resulting attitude change, or does it "only" simulate the quantity of drag?

This would help me very much in finding the source of error.
Thanks in advance for your help

Best regards,
DerNerf
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Old 06-04-2019, 05:27 PM   #2
Urwumpe
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Quote:
Originally Posted by DerNerf View Post
 Therefore I have a simple question: To what degree does Orbiter simulate transsonic effects?
In another thread I've read, that Orbiter does simulate the drag induced due to compression shock.

Orbiter supplies a simplified helper function to use in your coefficient function. That is all. You are free to use it or use a better function, if you have one.
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Old 06-04-2019, 06:46 PM   #3
DerNerf
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First of all, thanks for the answer.

Just so I get it right: Orbiter does NOT simulate transsonic efects by itself from the mesh. All aerodynamic effects, like transsonic or hypersonic effects, have to implemented via the aero coefficients. And if I want to I can use the Orbiter helper function .
Is that correct?
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Old 06-04-2019, 07:44 PM   #4
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Quote:
Originally Posted by DerNerf View Post
 First of all, thanks for the answer.

Just so I get it right: Orbiter does NOT simulate transsonic efects by itself from the mesh. All aerodynamic effects, like transsonic or hypersonic effects, have to implemented via the aero coefficients. And if I want to I can use the Orbiter helper function .
Is that correct?

Yes, that is correct. Orbiter's physics do not care about the mesh at all. You can create a mesh of a Concorde and give it the aerodynamics of the Hindenburg.



For implementing the transsonic or hypersonic effects, you can trivially use Mach number and reynolds number. You can also use the context parameter of the coefficient function to store variables for more complicated functions (eg, centre of pressure shifts calculated in pre or post step)
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Old 06-04-2019, 08:51 PM   #5
DerNerf
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Okay, got it,

Thank you very much, then I know what I'll go after next.
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