[lcbarreto]

Hi guys,

I am simulating the flow over a aircraft wing and came across a doubt. I need to simulate the whole angle of attack range of my aircraft, so that includes the stall region. My question is: after the stall, where the separation is strong enough to make the unsteadiness of my flow worthing simulating, is there a problem to simulate it as steady considering that I am only interested on the mean values of lift, drag and momentum.

Another thing, at a certain point my simulation will start oscillating around a certain value, would it be wrong to get this mean value and consider it as my answer?

Sorry if it is a simple question, but I really haven't found the answer.

Thanks in andvance.

[Foxhunter]

Originally Posted by lcbarreto

Another thing, at a certain point my simulation will start oscillating around a certain value, would it be wrong to get this mean value and consider it as my answer?

I don't understand what you mean with the other question, but if your residuals start oscillating you can decrease your relaxation factors(if you are using the Steady State solver).

[lcbarreto]

Originally Posted by Foxhunter

I don't understand what you mean with the other question, but if your residuals start oscillating you can decrease your relaxation factors(if you are using the Steady State solver).

Hi FoxHunter, thanks for your response.

Usually reducing relaxation factor works, however in the stall region my flow is unsteady, so if I simulate it as steady, my simulation will oscillate around a value. That will also happens when I simulate as unsteady, my CL, CD and CM will oscillate with time, usually also around a value. My question was if I could use the mean values of my steady solution as my answer, considering that I am only after the mean values of CL, CD and CD, not interested on its behavior along time.

Thanks in advance

[Foxhunter]

Originally Posted by lcbarreto

Hi FoxHunter, thanks for your response.

Usually reducing relaxation factor works, however in the stall region my flow is unsteady, so if I simulate it as steady, my simulation will oscillate around a value. That will also happens when I simulate as unsteady, my CL, CD and CM will oscillate with time, usually also around a value. My question was if I could use the mean values of my steady solution as my answer, considering that I am only after the mean values of CL, CD and CD, not interested on its behavior along time.

Thanks in advance

I am not proficient enough in Fluent to answer that question, but I'm sure an expert of this forum knows the answer. If you use the Transient solver and it still oscilates perhaps you could decrease the time steps?

[lcbarreto]

Originally Posted by Foxhunter

I am not proficient enough in Fluent to answer that question, but I'm sure an expert of this forum knows the answer. If you use the Transient solver and it still oscilates perhaps you could decrease the time steps?

When I simulate with URANS my residuals converge, but my values of CD, CL and CM converge to different values every time step. Considering that my flow is unsteady, it makes sense right? I need to have values varying with time, otherwise it would be a steady flow.

[Foxhunter]

Originally Posted by lcbarreto

When I simulate with URANS my residuals converge, but my values of CD, CL and CM converge to different values every time step. Considering that my flow is unsteady, it makes sense right? I need to have values varying with time, otherwise it would be a steady flow.

Again, I'm not an expert at all, but that makes sense. However, there should be some average there right? The values should not jump all over the place, there should be a value that they jump around.

[lcbarreto]

Originally Posted by Foxhunter

Again, I'm not an expert at all, but that makes sense. However, there should be some average there right? The values should not jump all over the place, there should be a value that they jump around.

Yes, it is jumping around a value, it goes up and down. I am sending an example of my lift and residual curves obtained considering my flow as steady.

[Foxhunter]

Originally Posted by lcbarreto

Yes, it is jumping around a value, it goes up and down. I am sending an example of my lift and residual curves.

I think that you have found your values, but again, I am no expert!

[lcbarreto]

Originally Posted by Foxhunter

I think that you have found your values, but again, I am no expert!

I hope so haha.

Thank you very much for your help.

[mostafa kareem]

Originally Posted by lcbarreto

Yes, it is jumping around a value, it goes up and down. I am sending an example of my lift and residual curves obtained considering my flow as steady.

please, if you found answer, could you share it