FSI/MFX: resutls after using fluid mass flux to achieve convergence
 

Dear all:

I'm working on a valveless pump FSI. The geometry is quite simple, with a circular vibrating membrane (500 micron thick and 30 mm in diameter)and a channel (400 micron wide) with two nozzle-difusser as regulators.
Orginally the model didn't run because of folded mesh, even after modification of sizes of mesh and time steps; the problem was overcome with adding fluid mass flux of zero and adjusting the mass flux pressure coeffecient (followed the suggestion from stumpy with ANSYS knowledge base 2022119).

Although the simulation finished the run, I have a question about the results.
The membrane vibrates in sinusodial waves, and I expect both the membrane deflection (in the out-of-plane direction) and the flow rate at the channel openings show as sinusoidal responses.
The membrane deflection seems to behave nicely; however, the flow rate seems to be all over the place, with no steady flow rate; please see the attached picture.
(the vibrating frequency is 50 Hz, and 15 clear sine waves can be seen in 0.3 sec from the membrane deflection)
I also noticed the flow rate changed significantly with different mass flux pressure coefficients.

What is the cause of the unsteady fluid response, and what can I adjust to have a more reasonable response from the fluid side?
And how do I pick the right coefficient to achieve the result?
Thank you very much for sharing your experince!

Sincerly,

Ryan