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-   -   Simulating aircraft- my l-d values (http://www.cfd-online.com/Forums/fluent/117319-simulating-aircraft-my-l-d-values.html)

 C_K May 6, 2013 13:50

Simulating aircraft- my l-d values

Would simulating an accurately created airplane give you the lift and drag values it should achieve in real life?

For example making an airbus a320 which has a weight of say 62000kg-608220N

Should the lift value i get in fluent be around that value in newtons or does Ansys fluent only give the correct cl and cd value that i should expect?

My sim has given me 150000N for half the aircraft- 300000N for full aircraft which is half the value needed to lift the aircraft.

Thanks

Are you sure that you have the right AoA (angle of attack) ? Lift or cl is much easier to predict so that the result of your simulation should not differ much from the real world if you have the same AoA as it cruises. If you have the right AoA but still the lift is incorrect, then you should check your simulation.

 C_K May 7, 2013 04:38

Quote:
 Originally Posted by blackmask (Post 425707) Are you sure that you have the right AoA (angle of attack) ? Lift or cl is much easier to predict so that the result of your simulation should not differ much from the real world if you have the same AoA as it cruises. If you have the right AoA but still the lift is incorrect, then you should check your simulation.
This is at 8 degrees AoA.

The Cl number is correct however the lift force is too low, i am not looking for correct lift force to be honest just the cl and cd.

So Ansys is supposed to give values of lift force of a model close to the real world?

The angle is correct but the mesh because its such as large model has an orthogonal quality of around 0.02. Is that the problem?

How could cl be correct if the lift is too low?
CL = lift/(1/2*rho*U^2*Area)

 Far May 7, 2013 11:28

Quote:
 The angle is correct but the mesh because its such as large model has an orthogonal quality of around 0.02. Is that the problem?
minimum allowed quality is 0.01. Would you like to post some pics of mesh?

 C_K May 7, 2013 19:26

I don't know why the lift force is wrong when the cl is correct.

Cl max for the aircraft at the angle im simulating is 2.1 i got 2.5 which isnt far off.

So is my original question, the lift force should be fairly accurate for the real life model or not? Im new to ansys so please excuse my questions, i though the lift to drag force would just be a component in calculating the cl and cd. Also the cl/cd ratio is good too.

The cl cd values are quite realistic. But not the lift force in newtons.

I dont have the mesh file with me will post it when i do. thanks

 Aeronautics El. K. May 8, 2013 11:38

Have you analyzed the forces properly? In the monitors panel you have to adjust the direction of the forces.

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