# Navier-Stokes Equation - unit problems

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

 April 24, 2002, 04:52 Navier-Stokes Equation - unit problems #1 Maciej Matyka Guest   Posts: n/a Hello. I have a problem with interpreting results of numerical calculations. Let say, than i'm solving full 2D NS equation. Somebody asked me what is really size of the tank. And.. let: WIDTH and HEIGHT are the screen calculations NX and NY are grid size (number of cells) now i calculate DX and DY as WIDTH/NX and HEIGHT/NY VIS is viscosity of the fluid GY is grawity vector DT is float delta time now let: WIDTH=320 HEIGHT=200 NX=32 NY=20 then DX = DY = 10 let: VIS = 0.1 GY = -9.8 DT = 0.01 now im asking: from where i know what is size of my tank and other physically properties of my fluid model? is that determined by GY unit (m/s^2)??? i really dont know what are units of my calculations, and my results are only qualitate not quatitate. Maciej Matyka, author of Fluid NS solver - available at http://panoramix.ift.uni.wroc.pl/~maq

 April 26, 2002, 09:44 Re: Navier-Stokes Equation - unit problems #2 Francisco Guest   Posts: n/a Hi Maciej. As far as I´m concerned, what really matters in such a calculation is the Reynolds number (as long as effects like surface tension are negligible). That is, once you have defined the Reynolds number (which is dimensionless) for your specific problem, the units of VIS, RHO, HEIGHT and the characteristic velocity are irrelevant (take the flow between parallel plates for instance Re=U*RHO*HEIGHT/VIS). The result will be a function of Re number only. You can prove this to yourself by writing the NS equations in dimensionless form. This can be found in any book of Fluid Mechanics. Best regards, Francisco.

 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 ashtonJ CFX 3 January 15, 2011 07:32 prashant FLUENT 0 March 7, 2008 08:05 selim Main CFD Forum 0 July 6, 2007 11:24 Jose Choy Main CFD Forum 3 October 24, 2003 02:28 Jose Choy Main CFD Forum 2 May 18, 2000 05:45

All times are GMT -4. The time now is 17:24.