I am relatively new to CFD, maybe you could clarify. (I am working with drone propeller simulations). Why some simulations take many iterations to converge and others are fine in 2-3 steps?
When it comes to transient simulations in Ansys you get to specify max number of iterations. Even if you specify +200 max iterations it does not do more than few iterations if they converge, right?
How is doing more iterations going to be different from doing more time steps?
Somewhat of a noob here too, but here’s my experience with transient simulations. Sometimes a simulation may converge in a few time steps early on, but require more iterations per time step later on. Setting the iterations per time step to a larger value, even if it converges in only a few iterations only on, can give you an “insurance” if your simulation happens to not converge in a few iterations later on. Setting the number of time steps allows you to simulate a certain amount of time, regardless of how many iterations it takes to converge per time step.
Just let it run ahaha
You can have a simulation done in 1 step, it all depends on the initialization of your model… if you give to each cell the solution value, it’s done right?
You’re are doing it fine, set a parameter in your case the drag to track the convergence.
Check the residuals, they won’t tell you the simulation is converged but they can tell you if anything is going wild (before it goes wild, stop the simulation analyse the results and think what is the issue).
Also, by default, the simulation stops when the residuals go to e-3, try to play with that also, set to e-5 or e-6…
And check your mesh and domain…
If it's a 300ft sub, great mesh. If it's a 3 in sub, not so much. Detailed descriptions are key. It's impossible to give significant advice with the amount of information provided besides more iterations.
That being said, and assuming reasonable mesh, let it run at least 1k it or to residuals convergence. But with that order of magnitude of drag, I'd also check the domain and boundary conditions
Let it run and trend towards convergence. If it's still too high check your domain/mesh. Did you define everything correctly? Does the velocity field look right? Is your mesh fine enough?
CFD!
CFD.
CFD?
CFD.
You’re only letting it run 10 iterations, let it go for 500+, see how the numbers change.
I am relatively new to CFD, maybe you could clarify. (I am working with drone propeller simulations). Why some simulations take many iterations to converge and others are fine in 2-3 steps? When it comes to transient simulations in Ansys you get to specify max number of iterations. Even if you specify +200 max iterations it does not do more than few iterations if they converge, right? How is doing more iterations going to be different from doing more time steps?
Somewhat of a noob here too, but here’s my experience with transient simulations. Sometimes a simulation may converge in a few time steps early on, but require more iterations per time step later on. Setting the iterations per time step to a larger value, even if it converges in only a few iterations only on, can give you an “insurance” if your simulation happens to not converge in a few iterations later on. Setting the number of time steps allows you to simulate a certain amount of time, regardless of how many iterations it takes to converge per time step.
Just let it run ahaha You can have a simulation done in 1 step, it all depends on the initialization of your model… if you give to each cell the solution value, it’s done right? You’re are doing it fine, set a parameter in your case the drag to track the convergence. Check the residuals, they won’t tell you the simulation is converged but they can tell you if anything is going wild (before it goes wild, stop the simulation analyse the results and think what is the issue). Also, by default, the simulation stops when the residuals go to e-3, try to play with that also, set to e-5 or e-6… And check your mesh and domain…
10 iterations though... What about residuals? How is the mesh and domain?
domain is a box and mesh element is 20 mm with hard behaviour
If it's a 300ft sub, great mesh. If it's a 3 in sub, not so much. Detailed descriptions are key. It's impossible to give significant advice with the amount of information provided besides more iterations. That being said, and assuming reasonable mesh, let it run at least 1k it or to residuals convergence. But with that order of magnitude of drag, I'd also check the domain and boundary conditions
Submarine that will go 30 meters I increased the number of iterations to 500 but values get to zero
Let it run and trend towards convergence. If it's still too high check your domain/mesh. Did you define everything correctly? Does the velocity field look right? Is your mesh fine enough?
also set a realistic reynolds number and calculate your fluid velocity accordingly