CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

cavitation

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   February 15, 2008, 12:32
Default cavitation
  #1
dc
Guest
 
Posts: n/a
hi,

does the default cavitation model take care of the effect of turbulence by changing the vapour pressure from that of the saturation pressure? or, do we need to write a udf for it? if so, how to write this udf?

thanks,

dc

  Reply With Quote

Old   February 16, 2008, 14:28
Default Re: cavitation
  #2
NRD
Guest
 
Posts: n/a
Hello,

The cavitation model in FLUENT is based on the model by Singhal et al, Journal of Fluids Engineering, 2002. This model accounts for turbulence by simply raising the phase change pressure threshold. The details are also given in the FLUENT manual.

My understanding is this effect is already accounted in the model.

For the turbulent case that I ran, I had to account for reduction in mixture viscosity due to cavitation using an UDF. If interested let me know and I can share my results.

  Reply With Quote

Old   February 16, 2008, 23:16
Default Re: cavitation
  #3
dc
Guest
 
Posts: n/a
thanks. it'll be great if you can share your results with me. you may mail me directly the same.

dc
  Reply With Quote

Old   February 16, 2008, 23:24
Default Re: cavitation
  #4
dc
Guest
 
Posts: n/a
i have read Singhal's paper as well as the Fluent User Manual. But I am confused about a statement given in the UDF manual of Fluent. I quote it for your consideration.

"The following UDF named user cav rate, is an example of a cavitation model for a multiphase mixture that is di erent from the default model in FLUENT. This cavitation model calculates the cavitation mass transfer rates between the liquid and vapor phase depending on liquid pressure (*p), turbulence kinetic energy (C K(c,t)), and the liquid vaporization pressure (*p v). In general, the existence of turbulence enhances cavitation. In this example, the turbulence e ect is taken into account by increasing the cavitation pressure by 0.195* C R(c,t) * C K(c,t)."

You may note that this UDF is different from that of the default cavitation mass transfer model and here turbulence is taken care of in accordance with Singhal's paper.

Looking forward to hear from you.

Thanks,

dc
  Reply With Quote

Old   February 17, 2008, 00:08
Default Re: cavitation
  #5
NRD
Guest
 
Posts: n/a
Thanks for the note.

I believe the UDF example that is given in the FLUENT manual is similar to Singhal's model (p_turb =0.195*rho*k instead of 0.39*rho*k) which is already included in the model.

I had run FLUENT simulations of cavitation in a converging-diverging geometry using k-eps RNG model. Formation of vapor leads to decrease in mixture viscosity. This is not accounted in the turbulence model. I wrote an UDF which calculates the viscosity as a function of density. When I did not account for this effect, the flow would laminarize.

A detailed explanation can be found in the paper by Coutier-Delgosha et al, Journal of Fluids Engineering, 2003.
  Reply With Quote

Old   March 8, 2008, 23:38
Default Re: cavitation
  #6
Karim
Guest
 
Posts: n/a
Dear NRD Could you please send the paper and your results to my email address: mdmk27.at.yahoo.com

mdmk
  Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Cavitation Problems Chris CD-adapco 4 July 17, 2005 16:47
Cavitation inception problem newuser FLUENT 3 May 13, 2003 11:14
Cavitation Simulation by CFD Liu, L. CFX 2 November 29, 2000 14:50
Cavitation Simulation by CFD Liu, L. CD-adapco 2 November 1, 2000 22:51
Cavitation Simulation by CFD Liu, L. Main CFD Forum 7 November 1, 2000 22:26


All times are GMT -4. The time now is 23:05.