[vara.b1991]

hi,

i am relatively new to fluent, so pls help me with this. my problem is:

i am running a transient simulation of "starting" phenomenon of a Mach 5 nozzle, in a diffuser-ejector system. first i ran a steady state analysis of only the ejector running so that it evacuated the whole system, then gave a steady state pressure of 9 bar at nozzle-inlet using SST-kw turbulence model and density based explicit solver. result was satisfying with a clear mach cone forming in the nozzle divergent. -
then i loaded the transient pressure input file (varying from 9 bar to 30 bar in 1.4 s) at the pressure-inlet of the nozzle. As the pressure increases, the shock wave moves from divergent into the diffuser at some point which comprises the diffuser start phenomenon.
at first i used implicit time stepping with 10^-5 time step, which led to abnormal pressure (10^20,10^26 )and mach no (60,200) values at around 0.13s. then i changed to explicit time stepping which was using its own timestep of 10^-10s. but this is taking very long on my home pc. can u suggest any other method or atleast verify if am using correct formulations/solver for the given problem?