Time step help in Explicit method

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

 August 13, 2013, 13:06 Time step help in Explicit method #1 Member   sandy Join Date: May 2013 Posts: 81 Rep Power: 6 Hello everyone , I have wrote a code for solving compressible navier stokes code over a flat plate (same as given in the Anderson CFD Book) . when i tried simulating it with free stream conditions at higher altitude for example Plate length of 1e-5 encounters slip regime above 10km altitude , which means that slip boundary conditions should be incorporated to get proper results , and the code blows up for free stream conditions above 20km (because transition regime comes into play ) Am i correct guys ? Navier stokes equation works only for continuum regime right ? So i am using MACCORMACK Method with the time step given in book . Its because of the time step , which brings up complex numbers and its causes the program to stop . What should i do now ? Any suggestion will be of great help Thanks in advance

 August 13, 2013, 13:28 #2 Senior Member     Alex Join Date: Jun 2012 Location: Germany Posts: 1,663 Rep Power: 26 While the NS equations are only valid in the continuum regime, a NS solver should still be able to produce a (wrong) solution in the rarefied regime. If your NS code diverges for higher Knudsen numbers, there must be something wrong with the code.

 August 13, 2013, 13:31 #3 Member   sandy Join Date: May 2013 Posts: 81 Rep Power: 6 Alex, I checked the code and i find that i implemented the time step (stability criteria) wrong . This produces the complex number first which makes the solver to blow up for higher Knudsen numbers

 August 13, 2013, 13:35 #4 Member   sandy Join Date: May 2013 Posts: 81 Rep Power: 6 Take a look at my time step , I implemented it wrong . Code: ```function delt=Tstep(u,v,T,rho,mu) % K -Fudge factor 0.5

 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 Lord Kelvin OpenFOAM Running, Solving & CFD 8 March 28, 2016 11:08 mbay101 OpenFOAM Running, Solving & CFD 13 December 28, 2013 14:12 sharonyue OpenFOAM Running, Solving & CFD 6 June 10, 2013 09:34 Heroic OpenFOAM Running, Solving & CFD 26 December 17, 2012 04:34 danny123 OpenFOAM 19 October 24, 2012 07:44

All times are GMT -4. The time now is 06:05.