# calculation of drag coefficients

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

 May 5, 2000, 00:42 calculation of drag coefficients #1 Longbin Tao Guest   Posts: n/a Sponsored Links I have trouble to figure it out how to derive the formulae that calculates viscous drag coeffient using vorticity. Any one can help me?

 May 5, 2000, 12:08 Re: calculation of drag coefficients #2 Nishikawa Guest   Posts: n/a Viscous Drag D = integral of stress tensor T over the body. For incompressible flows, T = mu*(def(u)). (mu is viscosity assumed to be constant and u is velocity vector) So, D = mu * integral of def(u)*dS -------(a) def(u) is the deformation tensor defined by grad(u)+(grad(u))^t where t means transpose, and dS is the outward normal area vector on the body surface. Using the facts that (1)div(u)=0 on the surface (2)(w)x(dS)=[grad(u)-(grad(u))^t]*dS where w is the vorticity vector and "x" means a cross product (3)(grad(u))^t*dS=0 on the surface, you can show that D = (a) = mu * integral of (w)x(dS) which is the desired result. I learned this a long time ago, but the professor said that this formula was impractical since measuring vorticity vector was difficult. Would you tell me more about what kind of problem you are dealing with? Why do you not compute velocities?

 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 lc05 Main CFD Forum 2 November 1, 2010 08:50 abcdef123 Main CFD Forum 1 May 9, 2010 23:00 ArtyB Main CFD Forum 1 January 10, 2010 19:18 Prachi CFX 3 August 14, 2007 14:05 AB CD-adapco 6 November 15, 2004 05:41