fsi and cavitation in cfx

mortazavi · April 9, 2016, 02:05

hi,
To simulate cavitation on a flexible (FSI) hydrofoil I am using Ansys+CFX.
there are two tutorials in cfx for cavitation around a hydrofoil and fsi(oscillating plate). In the first one the reference pressure is set to zero while in the second one pref=1atm. To habe both fsi and cavitation what do you recommend???
I have tried cavitation whith pref=1atm and modified the outlet pressure according to the new ref pressure. the same for fsi with pref=0. but none of them works. I mean the results are different.
ANY SUGGESTION???
thanks,

mortazavi · April 15, 2016, 23:29

Any help please?!!!!!!!!!!!!!

ghorrocks · April 16, 2016, 07:39

What type of FSI are you proposing? 1 or 2 way? Cavitation models are hard and FSI models are hard, 2-way FSI are hard^2 so cavitation and FSI are hard^3. I hope you have plenty of time to get this model working as you are going to need it.

To answer your question: set the reference pressure to the ambient pressure present in the domain. That is probably 1 atm but you might be running in unusual conditions (or submerged) which could change that.

As this is a REALLY hard simulation it does not surprise me that small changes (eg reference pressure) make big differences to the results. It means you are miles away from an accurate simulation. All I can recommend is a careful approach:
* Do a single phase, no FSI model until you can model an airfoil accurately.
* Then add cavitation and get that working accurately
* Then do FSI on a single phase airfoil
* Only once everything is working and accurate should you consider combining it all together into a simulation which does everything.

April 9, 2016, 02:05	fsi and cavitation in cfx	#1
mortazavi Member SMN Join Date: Jun 2009 Location: CANADA Posts: 71 Rep Power: 17	hi, To simulate cavitation on a flexible (FSI) hydrofoil I am using Ansys+CFX. there are two tutorials in cfx for cavitation around a hydrofoil and fsi(oscillating plate). In the first one the reference pressure is set to zero while in the second one pref=1atm. To habe both fsi and cavitation what do you recommend??? I have tried cavitation whith pref=1atm and modified the outlet pressure according to the new ref pressure. the same for fsi with pref=0. but none of them works. I mean the results are different. ANY SUGGESTION??? thanks,

April 16, 2016, 07:39		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,852 Rep Power: 144	What type of FSI are you proposing? 1 or 2 way? Cavitation models are hard and FSI models are hard, 2-way FSI are hard^2 so cavitation and FSI are hard^3. I hope you have plenty of time to get this model working as you are going to need it. To answer your question: set the reference pressure to the ambient pressure present in the domain. That is probably 1 atm but you might be running in unusual conditions (or submerged) which could change that. As this is a REALLY hard simulation it does not surprise me that small changes (eg reference pressure) make big differences to the results. It means you are miles away from an accurate simulation. All I can recommend is a careful approach: * Do a single phase, no FSI model until you can model an airfoil accurately. * Then add cavitation and get that working accurately * Then do FSI on a single phase airfoil * Only once everything is working and accurate should you consider combining it all together into a simulation which does everything. mortazavi likes this.

April 15, 2016, 23:29		#2
mortazavi Member SMN Join Date: Jun 2009 Location: CANADA Posts: 71 Rep Power: 17	Any help please?!!!!!!!!!!!!!