# help in ANDERSON text...

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 July 14, 2009, 01:20 help in ANDERSON text... #1 Senior Member     ATM Join Date: May 2009 Location: United States Posts: 104 Rep Power: 10 i`m going through anderson`s 'CFD and its applications",and i`m stuck on pg. 308 (analysis of quasi one dimensional subsonic-supersonic nozzle). here the initial condition of density,temperature and velocity is given by the equations p = 1 - 0.3146x T = 1 - 0.2314x . initial conditions at t = 0 V = (0.1 + 1.09x)T^1/2 where 'x' is the axis where the grid points are evenly spaced forgive me if dis question`s stupid, but what is the origin of these eqns? there is no explanation offered in the text as to what are the governing principles behind these. are these just taken arbitrarily or what... please help. thanks in advance, atm

 July 14, 2009, 09:58 Initial Conditions #2 Senior Member     Richard Smith Join Date: Mar 2009 Location: Enfield, NH, USA Posts: 138 Blog Entries: 4 Rep Power: 10 The subsonic-supersonic nozzle appears in Modern Compressible Flow, 2nd Edition, Anderson, pp. 365 (The Time-Marching Technique) with the following quote: "...the guessed initial temperature distribution at time t=0. It is arbitrarily taken as linear variation." I presume it's likely the same example in your book "CFD and its Application." So I believe all the initial values are based on knowing the solution, so they have no theoretical foundation. They are probably chosen to be just close enough to the final (known) solution to make your solver work, but not far enough away to cause problems. If you are following along and writing your own solver I would suggest substituting fixed values and see what converged solution you get. __________________ Symscape, Computational Fluid Dynamics for all

 July 14, 2009, 11:26 #3 Senior Member     ATM Join Date: May 2009 Location: United States Posts: 104 Rep Power: 10 thank u very much... is it better if i write my computer code in C++ or MATLAB? how do the 2 differ? thanks in advance. atm

 July 14, 2009, 14:09 #4 Member   Join Date: Mar 2009 Posts: 62 Rep Power: 10 Since your problem is 1D you can use C++ or Matlab. For 2D and 3D problems Matlab is simply to slow. Use the language you are more familiar C++ or Matlab for this simple problem.

 July 15, 2009, 01:11 #5 Senior Member     ATM Join Date: May 2009 Location: United States Posts: 104 Rep Power: 10 oh... thank u very much.i guess C++ is better.

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