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

drag calulation over a square cylinder

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 26, 2001, 11:50
Default drag calulation over a square cylinder
  #1
sex00
Guest
 
Posts: n/a
i am using MAC method for incompressible flow in a 3-D channel with a square cylinder in it. the pressure and velocities fields have been computed. how do i calculate the drag on the cylinder ? how to extrapolate the values of pressure etc. on the cylinder surface as the MAC algorithm uses staggered grid? thanking u in advance. sex00
  Reply With Quote

Old   January 26, 2001, 22:13
Default Re: drag calulation over a square cylinder
  #2
John C. Chien
Guest
 
Posts: n/a
(1). The drag on the cylinder comes from the pressure drag and the viscous drag. (2). Since the pressure gradient normal to a wall is zero, the effect of the exact location where the pressure is evaluated will have little effect on the result. (except around the corner where the pressure variation is large). (3). In any case, if your are interested in the accurate evaluation of the pressure and the tangential viscous stress, then, you should just refine the mesh near the wall. (4). The normal force on the wall will produce the pressure drag, and the tangential viscous stress on the surface will give you the viscous drag.
  Reply With Quote

Old   January 27, 2001, 08:25
Default Re: drag calulation over a square cylinder
  #3
Senthil
Guest
 
Posts: n/a
To get the drag just integrate the pressure along the upstream side (Pa) and on the downstream side (Pb). drag=Pa-Pb. I hope this is correct and our friend John.C.CHien accepts this.If pressure had builded up to larger values normalise it with some pressure at entry.

By the by I also use MAC algorithm.I need to know how u r discretising the convection term asap bye
  Reply With Quote

Old   January 28, 2001, 15:05
Default Re: drag calulation over a square cylinder
  #4
sex00
Guest
 
Posts: n/a
dear senthil, the convection terms are discretised using a weighted average of second upwinding and space centered scheme (Hirt et al. a numerical solution algorithm for transient fluid flows ,LA-5852 ,Los Alamos Scientific Laboratory Report,1975) however for LES it seems that either pure central differecing or pure upwinding works best!

also, i am interested in knowing how to integrate the pressure (procedure)! and the extrapolation procedure! i too know that i have to integrate the pressure! sex00
  Reply With Quote

Old   February 2, 2001, 08:16
Default Re: drag calulation over a square cylinder
  #5
Michal Marcinkowski
Guest
 
Posts: n/a
Hi, Senthil- could you tell me please few words more about accuracy of this method ? There is similar way for model-researches called Jone's method in which you integrate pressures on plane located in 5-10% of chord-line downstream but tangent stress term and energy disipation are ommited cause of difficulties of measurement shear stresses on whole hull. How does it look like for finite volume method which gives anyhow approximate disribution of pressure in cells but over whole shape ? Is it worth ? Maybe the way you are thinking about is taking into account (implicite way) the shear stresses and they influence on the wake and next on the total forces? Thanks

Michal
  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
Drag coefficient of square cylinder tonka Main CFD Forum 2 April 2, 2014 21:42
Incorrect Drag and Drag Coefficient for flow over a cylinder ozzythewise Main CFD Forum 8 June 13, 2012 06:24
Drag on non-infinite cylinder between parallel walls deltaquattro Main CFD Forum 0 September 10, 2009 13:01
Solver and geometry choose for drag coefficient calculation around circular cylinder at large Re lin OpenFOAM Running, Solving & CFD 3 April 16, 2009 10:50
solving airfoil like square cylinder problem? zonexo Main CFD Forum 1 May 27, 2006 15:16


All times are GMT -4. The time now is 07:56.