# CFL condition

 Register Blogs Members List Search Today's Posts Mark Forums Read October 12, 2004, 11:39 CFL condition #1 Sergei Guest   Posts: n/a In the Anderson's Book of CFD, there is a CFL condition for the problem of supersonic flow over a flat plate. There, he use MacCormack explicit in a time-dependent approach. My problem is I've got a coordinate transformation, x=x(xi,eta), y=y(xi,eta), so that I don't know what to write instead of \Delta x and \Delta y in the CFL condition. Thanks in advance.  October 13, 2004, 09:47 Re: CFL condition #2 versi Guest   Posts: n/a Many papers have answers. Let \xi_X and \xi_Y be metrics of corrd. transformation, in a illustrative way, D t= CFL /( |u * \xi_X +v * \xi_Y| + C * sqrt( xi_X**2 +xi_Y**2)). where C is sound speed. Note that the dimenson is consistent with definition of CFL number. One can similarly get Dt from another direction \eta. The minimum of the two is what desired.  October 13, 2004, 16:38 Re: CFL condition #3 Sergei Guest   Posts: n/a Thanks versi, very useful! I will try that. I've got another question. If x=x(nxi,neta); y=y(nxi,neta); XI=XI(nxi,neta); ETA=ETA(nxi,neta); Could you confirm that the next sentence is calcutating the metrics? XI_x=zeros(nxi,neta); ETA_x=zeros(nxi,neta); XI_y=zeros(nxi,neta); ETA_y=zeros(nxi,neta); for i=2:nxi-1; for j=2:neta-1; XI_x(i,j)=(XI(i+1,j)-XI(i-1,j))/(x(i+1,j)-x(i-1,j)); ETA_x(i,j)=(ETA(i,j+1)-ETA(i,j-1))/(x(i,j+1)-x(i,j-1)); XI_y(i,j)=(XI(i+1,j)-XI(i-1,j))/(y(i+1,j)-y(i-1,j)); ETA_y(i,j)=(ETA(i,j+1)-ETA(i,j-1))/(y(i,j+1)-y(i,j-1)); end end Thanks if you try that. Thread Tools Search this Thread Show Printable Version Email this Page Search this Thread: Advanced Search Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded 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 Off Pingbacks are On Refbacks are On Forum Rules Similar Threads Thread Thread Starter Forum Replies Last Post Matt Umbel Main CFD Forum 19 June 30, 2020 09:20 bzz77 Main CFD Forum 3 August 24, 2011 16:12 violet FLUENT 0 November 5, 2009 18:33 Shyam Main CFD Forum 2 February 14, 2008 15:24 turb Main CFD Forum 4 August 16, 2005 13:56

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