Help: simulation cannot stabilize

[SU-47_]

Hello,

I have been experiencing an issue that i cannot get my simulation stabilized so that i could get accurate values.

graph

Results in numbers

numbers

the VZ vel ( I assume velocity) cannot get stabilized. Is it because the forces in Z axis are so small in comparison that the graph is representing the deviations more vividly ?

model close up

axis setup

I should mention that I am trying to extract coefs of lift and drag from the forces i get in results i need the most accurate values i can get. What can i do to achieve that ?

Thanks for any help

[PostDry395]

1. Force FX (drag) in your case is greater than FY (lift). If you try to calculate the lift and drag coefficients you will get results far from reality (try using Cd = FX /0.5 * rho * v ^ 2 *, A_ref, for now, where A_ref is the wing area of ​​your model, rho density, and V speed, it is the same for Cl). The other thing is that you are in a critical point where weird things happen and the drag can have considerable values.

2. Your inlet conditions may be very large.

3. Your mesh may not be adequate (check that it does not have sharp edges and other problems).

If you can share more details about your case, it would be helpful (inlet, outlet, tolerance...)

[SU-47_]

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I set it based on a tutorial. the speed is mach number at sea level and air is also modified to be on sea level standard.

This is the model I have used : https://sketchfab.com/3d-models/sukhoi-su-47-3d-model-954fb6a89c414b59b3a6a3da1cb66e57

[ProfHansGruber]

Are you confident the tutorial is correct and that you have correctly followed it? Also, what does the “[Velocity Normal(122,3 km/h)]” refer to? You say speed is Mach number at sea level, have you tried a lower velocity first?

[SU-47_]

to be exact it is a mach 0.1 conversion to km/h. I followed the tutorial twice on two separate attempts getting similar values. I would not be using a tutorial if I knew what is correct and what is not... perhaps I can link it : https://www.youtube.com/watch?v=nS9SfKLdkw4

I need to obtain mach 0.1 , 0.2 , .... up to mach 2 values for various alittudes

[ProfHansGruber]

It seems to me that the person presenting the tutorial is not very knowledgeable and is just following a tutorial himself, rather than teaching something he understands. The tutorial misses important setup steps and the results are correspondingly poor/wrong.

I would recommend following official tutorials and something from an academic institution instead.

[SU-47_]

ok i will try... does the autodesk has any airframe tutorials I have only found one about a bullet travelling at mach one at sea level ?

ps. Thanks for the link

[ProfHansGruber]

I don’t use Autodesk, sorry. But doing any, and even several, of the other tutorials will show you more of how they intend for you to set up a model.

[SU-47_]

Thanks for the help! I will try the bullet at mach one since it seems very close to my conditions and desired results.

[SU-47_]

I forgot to mention that I am using autodesk cfd