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Old   June 24, 2022, 20:56
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Kartini Ganesha
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Hello everyone, now I have been learning CFD since 6 months back. I have I a couple of doubts regarding the basic setup and comparison between the solution. Please kindly help me to solve my doubts below:

1. Do you think the steady approach would be sufficient to get the force coefficients? What would be the gain in terms of computational time?
2. Why is the Cd more sensitive to the simulation parameters than the Cl?
3. Do you think the behavior of the boundary layer is well modeled on the hydrofoil when a wall function is used?
4. Why do you think the C-type mesh is more widely used for hydrofoils?
5. What is the effect of the domain size on the results?
6. The flow Reynolds number is 700,000, do you think the flow is turbulent everywhere?
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Old   June 25, 2022, 14:03
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1. You don't "gain time" per se but steady simulations are an order of magnitude less complex then transient ones, so it is safe to say you will get the answer in one-tenth the time. For a lot of people, steady simulations are sufficient and it depends how you plan on using the CFD.

2. Because its very easy to produce drag and much harder to produce lift.

3. A good wall function, yes.

4. It's not. It's very easy to teach someone how to generate a C-type mesh and put this into a youtube video but that is not what people actually use when they get serious about simulating airfoils.

5. Bigger is always better.

6. Any flow can always be either and sometimes both.
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Old   June 29, 2022, 16:56
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I don't have much to add to the answers from LuckyTran, however, it is my opinion that you should try to relate the physics to the computational stuff.

For example, your question number 2, consider what you really need to calculate lift and what it takes to calculate drag. What parameters feed into the calculation each of them.

Same with the 1st question. There's no clear-cut answer.
I have examples that I've proven to people that their steady state approach is not appropriate at all for the kind of problem under investigation. So you need to consider the physics again.

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cfd, cfl, reynold, steady, transient

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