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

Potential theory

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 15, 2007, 16:15
Default Potential theory
  #1
Martin
Guest
 
Posts: n/a
Hi! I have a question about the potential theory. I donīt understand why one property of potential flows is to be irrotational. When I have a foil with a certain angle and Kutta-condition, this causes a lift due to rotation, right? For me thatīs a contradiction. Thank you! Martin
  Reply With Quote

Old   January 15, 2007, 20:48
Default Re: Potential theory
  #2
Bren
Guest
 
Posts: n/a
When you're dealing with potential flows about an airfoil you do indeed require circulation in order to deal with non-symmetrical systems or airfoils at an angle of attack.

In some potential theories there needs to be a jump in the solution (a branch cut) to ensure that your solution isn't multi-valued. Across this branch cut the potential can jump - the circulation around the airfoil is related to the jump in the potential. The flow is still irrotaional though - which is required in order to use potential theory in the first place. The concept of rotationality (is that even a word!) is related to rotation but only in a local sense. A good discription of rotational flows can be found in Achieson's: "Introductory fluid mechanics".

I'm unsure of whether this is the case for ALL potential flows - this is certainly the case in my own work (2D transonic flow) however. Hope this vague explanation is of some use - not bad for 1am though!

B
  Reply With Quote

Old   January 31, 2007, 20:06
Default Re: Potential theory
  #3
Ionut Popescu
Guest
 
Posts: n/a
Hi !

Irrotational doesn't mean that you don't have circular motion.Take the vortex equation... The pure vortex in potential theory is called irrotational vortex. The word "irrotational" says that that the vorticity is zero. But the vorticity is nothing but: omega = C * nabla X V = C * curl(V). In potential theory velocity comes from a potential function: V=nabla(phi) Now, results that omega=C * nabla X nabla (phi) = curl(nabla(phi)) = 0, therefore the flow is irrotational.

  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
Potential flow Laith Mohammed Main CFD Forum 1 November 14, 2013 12:26
Spalart-Allmaras model in Ansys Fluent 12.0 theory guide macfly FLUENT 0 February 7, 2010 18:03
udf electronic potential boundary. shuqin FLUENT 0 February 22, 2006 10:16
Potential Flow Swapnil CFX 5 February 26, 2003 08:33
Question on 3D potential flow Adrin Gharakhani Main CFD Forum 13 June 21, 1999 05:18


All times are GMT -4. The time now is 15:26.