# Doubt about calculating the frictional velocity over an airfoil

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 LinkBack Thread Tools Display Modes
 November 13, 2012, 21:14 Doubt about calculating the frictional velocity over an airfoil #1 New Member   Jorge Join Date: Jul 2012 Posts: 16 Rep Power: 5 Hi there, Recently I read a post in a blog about estimating the initial cell height in a simulation of an aerofoil, this estimation includes the calculation of the frictional velocity over the aerofoil wall but the equation is not clearly written and I don't know if the right form is: Vt = Vinf*2*(Cf)^0.5 or: Vt = Vinf*(Cf*2)^0.5 Vinf : is the flow velocity Cf : is the skin friction coefficient Any help will be appreciated!

November 14, 2012, 01:32
#2
Senior Member

Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 678
Rep Power: 13
Quote:
 Originally Posted by Jorg Hi there, Recently I read a post in a blog about estimating the initial cell height in a simulation of an aerofoil, this estimation includes the calculation of the frictional velocity over the aerofoil wall but the equation is not clearly written and I don't know if the right form is: Vt = Vinf*2*(Cf)^0.5 or: Vt = Vinf*(Cf*2)^0.5 Vinf : is the flow velocity Cf : is the skin friction coefficient Any help will be appreciated!
It looks mostly correct, however, I think it should be:

Vt = Vinf(Cf/2)^0.5

Starting with definition of Cf
Cf(0.5*density*Vinf^2) = Tau

Vt = sqrt(Tau/density) = sqrt ( 0.5*Cf*Vinf^2) = Vinf*sqrt(Cf/2)

That particular work may have used a different definition of friction coefficient so that a factor of 4 may have been introduced. Which would yield the formula you already provided.

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post wanna88 FLUENT 2 October 1, 2012 22:34 lakhi FLUENT 5 July 18, 2012 16:28 Chander CFX 3 March 11, 2012 22:18 Harry Main CFD Forum 3 July 31, 2005 11:24 Sergei Chernyshenko Main CFD Forum 0 September 12, 2003 12:27

All times are GMT -4. The time now is 10:22.

 Contact Us - CFD Online - Top