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Dear Flash-Users,<br><br>I'm currently injecting a jet through a few cell boundaries on one side of a 3D box. <br>The jet has variable velocity, regulated by some near density-temperature condition. <br>And here come some problems with the split hydro (ppm).<br><br>1) If I let vary the jet every timestep, when the velocity is increasing the sim crashes, because<br>the timestep (CFL condition) is fixed for 2 consecutive dt. To circumvent this I let vary vjet<br>only in the "second" dt (essentially fixing it also for the next one).<br>First question: is there another (clever) simple method to avoid this and let vjet vary every dt?<br><br>2) When vjet reaches 10^4 km/sec and also when I increase resolution, the sim easily becomes<br>unstable at some dt (under smallest min values possible). I have to lower CFL number to 0.1 and it goes<br>better, but it can in any case crash in longer evolutions. Now, am I doing something wrong with jet<br>injection (and above set up)? 0.1 and lower make my sims almost impossible to evolve for some Gyr, is<br>it really possible that with ppm strang split method I have to adjust CFL to 0.1 or lower?<br>Again, is there any clever way to avoid this? (I know someone else has done jets with FLASH).<br><br>3) To try another way I've begun to use unsplit hydro solvers. This way the jet can be regulated<br>every timestep. What kind of solver do you suggest for Jet ignition (I have not much knowledge of them)? <br>I'm using HLLC and with 0.3 CFL the sims never crashes, also with high vel and resolution.<br>How can it be possible such a difference between split and unsplit method?<br><br>4) How much are the unsplit solvers in FLASH "reliable"?<br>Have you done some tests or are they still in a "beta" phase?<br>Again, are they adequate to study a jet ignition? <br><br>5) Last point. I need also the evolution of a MASS_SCALAR and it seems that it is not<br>evolving with the flow with the unsplit solvers (HLLC). How can I use them? (In Flash.h it is present)<br>Is it possible? If not, is it easy to implement (or someone else has done this)?<br><br>Thank you very much in advance for any help.<br>In literature I've seen many flash-users implementing jets; hope that someone has interesting way to attach<br>the problems I mentioned (maybe yet solved), or also completely different approaches for jets.<br><br><br><br>Max<br><br><br>(Massimo Gaspari, University of Bologna, ITA)<br> <br /><hr />Novità dai Social Network e i tuoi account di posta... <a href='http://www.windowslive.it/hotmail/UnicaCasellaDiPosta.aspx' target='_new'>Tutto su Hotmail!</a></body>
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