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

stagnation pressure on a water droplet

Register Blogs Community New Posts Updated Threads Search

Like Tree2Likes
  • 1 Post By piu58
  • 1 Post By piu58

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 7, 2018, 07:04
Default stagnation pressure on a water droplet
  #1
New Member
 
Hussain
Join Date: Mar 2018
Posts: 4
Rep Power: 8
mformazhar is on a distinguished road
Hi,
I am modeling a free falling of a water droplet through air. the issue is that i want to estimate the deformation rate and for that it seems like i need to calculate the stagnation pressure. by looking at the equation (wiki) it is not clear to me what values to choose. for example should i choose the density of air or density of water droplet in that equation, similarly what velocity should i consider. is it the velocity of water droplet or the air? i appreciate if you could help me route me to a correct forum. thanks!

Best regards
Hussain
mformazhar is offline   Reply With Quote

Old   March 7, 2018, 07:24
Default
  #2
Senior Member
 
piu58's Avatar
 
Uwe Pilz
Join Date: Feb 2017
Location: Leipzig, Germany
Posts: 744
Rep Power: 15
piu58 is on a distinguished road
You have to use the density of the air. Formula given in textbooks are valid for solid bodies too, which don't deform.

The velocity is the relative one between the droplet and the air. It doesn't play any role if the air is moving or the droplet. It is the difference hat counts.
mformazhar likes this.
__________________
Uwe Pilz
--
Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)
piu58 is offline   Reply With Quote

Old   March 7, 2018, 08:19
Default
  #3
New Member
 
Hussain
Join Date: Mar 2018
Posts: 4
Rep Power: 8
mformazhar is on a distinguished road
HI Pilz
Thanks for a quick reply. how about the static pressure in the equation. can i just use the atmospheric pressure?

Regards
Hussain
mformazhar is offline   Reply With Quote

Old   March 7, 2018, 08:32
Default
  #4
Senior Member
 
piu58's Avatar
 
Uwe Pilz
Join Date: Feb 2017
Location: Leipzig, Germany
Posts: 744
Rep Power: 15
piu58 is on a distinguished road
> can i just use the atmospheric pressure?

I think so. I need your reference to check this.
__________________
Uwe Pilz
--
Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)
piu58 is offline   Reply With Quote

Old   March 7, 2018, 08:40
Default
  #5
New Member
 
Hussain
Join Date: Mar 2018
Posts: 4
Rep Power: 8
mformazhar is on a distinguished road
The droplet is falling through the air at atmospheric pressure of 1 atm. do you have any reading suggestions regarding my problem because i want to estimate the deformation rate of the droplet while it is falling?
thanks!

Regards
Hussain..
mformazhar is offline   Reply With Quote

Old   March 7, 2018, 09:27
Default
  #6
Senior Member
 
piu58's Avatar
 
Uwe Pilz
Join Date: Feb 2017
Location: Leipzig, Germany
Posts: 744
Rep Power: 15
piu58 is on a distinguished road
In this case I would simulate an aerial flow around the droplet. With changing the speed the droplet gets deformed (more or less slightly), but the cf values change fast. Your solution is the one where the drag equals the gravity.
mformazhar likes this.
__________________
Uwe Pilz
--
Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)
piu58 is offline   Reply With Quote

Old   March 7, 2018, 09:55
Default
  #7
New Member
 
Hussain
Join Date: Mar 2018
Posts: 4
Rep Power: 8
mformazhar is on a distinguished road
Thank you Pilz. I will try to dig down more on that suggestion of yours.

regards
Mazhar..
mformazhar is offline   Reply With Quote

Reply

Tags
bernoulli's equation, droplet simulation, falling drops, stagnation pressure


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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Periodic flow using Cyclic - comparison with Fluent nusivares OpenFOAM Running, Solving & CFD 30 December 12, 2017 06:35
How to patch a water droplet with smooth surface? Hossein1 FLUENT 0 January 13, 2017 10:25
CFX Solver stopped with error when requested for backup during solver running Mfaizan CFX 40 May 13, 2016 07:50
stagnation pressure boundary problem mbgnfrx2 STAR-CD 2 November 26, 2012 00:55
what the result is negatif pressure at inlet chong chee nan FLUENT 0 December 29, 2001 06:13


All times are GMT -4. The time now is 14:15.