Hi, I am new to CFD and have a question relating to the convergence plots:
In my simulation, I am simulating laminar flow over a cylinder.
The Forces and Coefficients plots all converge nicely along with the residuals, but when looking at the inlet and outlet plots there a heavy oscillations. I understand that we are not trying to obtain the same trend as the residuals plots, but moreover have the inlet and outlet stay around the same value. Is this oscillating nature acceptable? It seems to oscillate back to the same value each time. I’ve moved the inlet and outlet boundaries way far away from the object inside the enclosure region by a large mutiple (probably to large, but to isolate that issue from the plots was the main goal). I found another post like this, but there was never a response to the oscillating flow question within that post.
The flow around the cylinder seems to look as what I would expect in Run 4 and the drag coefficients seem around what I would expect also
Here is the link to the simulation and a picture:
[Drone Arm FEA and CFD | SimScale]
Hello,
It’s slightly unusual to see such oscillations (specially given the high frequency that you are getting). Have you already tried using a “Fixed value” for the velocity inlet, instead of “Freestream”?
Cheers
Hi,
Check out Incompressible 2 with Run 1 and Run 2. I used a smaller enclosure size and ran fixed value and freestream velocity inlets and the inlets/outlets look much better now. Making the enclosure smaller improved the outlets/inlets which seems interesting to me. Seems odd that a smaller enclosure would work better. I also remeshed at the exact same settings and same mesh fineness.
I have tried using fixed value and currently still get those high frequency oscillations. I’m running A CFD for the entire drone body and those oscillations are still present. I’m not entirely sure what else to do at this point.
I have done the following:
Activated potential flow to ease convergence
Physics-based meshing
Refinement regions around the body ( A larger one and a smaller one)
The upstream and downstream lengths are 5 times the length of the drone and 10 times the length of the drone respectively.
Boundary conditions make sense to me.
