- **Main CFD Forum**
(*https://www.cfd-online.com/Forums/main/*)

- - **Time step help in Explicit method**
(*https://www.cfd-online.com/Forums/main/122166-time-step-help-explicit-method.html*)

Time step help in Explicit methodHello 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 |

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. |

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 |

Take a look at my time step , I implemented it wrong .
Code:
`function delt=Tstep(u,v,T,rho,mu)` |

All times are GMT -4. The time now is 22:04. |