Learning Forum

[Gius86]

Hello everyone, i am facing a Flow induced vibrations problem. In particular Flow induced pulsations due to a deadleg of a main header pipe. I am running a transient simulation to catch the pressure oscillation on the deadleg but I want to understand if there is an acoustic resonance condition and which is the magnitude of the pressure in this condition. The solver works well without acoustics one but when i activate it the solver diverges.

[ErKo]

To study resonacnes you need to use the acoustic FE modules in Workbench - Modal acoustics say.

All the best

 

EK

[Gius86]

thank you but this is not my target. I already done a modal acoustics but my target is to quantify the pressure amplification when i have a vortex detachment

[RG]

HI, 

As I understand, you are running transient flow simulation. However when you include Acoustic as Fluent Physics modelling, simulation gets diverged. Generally, enabling or disabling acoustic option doesnt interfere with CFD simulation. Therefore it doent impact convergence or divergence. For your case, you need to look at mesh (it is is well ressolved to acount for flow fluctuation). If you want to predict noise generated then you should look at time step size if it is resolving frequency in interest. Also as per turbulence model used, check if mesh satisfy its criteria. Additionally, check any acoustic condition getting switched on at inlet or outlet like "NRBC". If so need to check if you acoustic courant number greater than 1 on inlet or outlet. If ACFL is less than 2 then need to coarsen the mesh. These are few checks to avoid divergence.

 

 

[Gius86]

just to update. I found the solution. i run a compressible model such that the acoustic response is included in the pressure output.