Hello, I'm eagerly and gradually learning PyFR. I've run the 2D Couette flow tutorial in the examples folder bundled with PyFR 1.8. Now I'm struggling to interpret the behaviour.
1. The example is setup with order p = 2 and a timestep size of dt = 0.00004. When I increase the order to p = 4, the code spits a NaN error. By trial/error, I've found the following timestep sizes are required for solution convergence: p = 2 dt = 4e-5 p = 3 dt = 3e-5 p = 4 dt = 2e-5 p = 5 dt = 1e-5 p = 6 dt = 5e-6 *Question 1: How does the polynomial order affect the time step required for solution stability?* 2. For the above runs, I have plotted the solution residuals below: [image: residuals.png] The largest decay rate is with p=1. For p=2 to p=5, the residual drops at nearly identical rates. This was unexpected; I expected the residual to converge at a rate proportional to the polynomial order. *Question 2: How does the polynomial order relate to the residuals produced in the tutorial and their convergence rate?* 3. The wallclock times for the solution runs is not predictable. For the above cases, the wallclock time to run for a total of 4 s simulation time is below: Order Elapsed time p=1 00:46:11 p=2 00:16:56 p=3 00:12:36 p=4 00:19:19 p=5 00:44:35 p=6 70+ hrs estimated (it took 13 hours to reach 0.6 s then I stopped it) Granted, the time step sizes were marginally different (as per Q1) so it isn't a completely consistent comparison. But the solution times are tremendously different and unpredictably so. *Question 3: Why do I see non-monotonic variation in the solution time for different polynomial orders?* Notes about my solution: - Backend = OpenMP (8 threads; single cpu). - I adjusted p and dt, but left everything else the same in the *.ini file. - I used the tutorial-supplied *.msh file. Thanks! Joshua -- You received this message because you are subscribed to the Google Groups "PyFR Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to pyfrmailinglist+unsubscr...@googlegroups.com. To post to this group, send an email to pyfrmailinglist@googlegroups.com. Visit this group at https://groups.google.com/group/pyfrmailinglist. To view this discussion on the web, visit https://groups.google.com/d/msgid/pyfrmailinglist/CALkBc_drE3CnLD0E4b%3DGtUw30tW8WgiuGA6iwyNV4oK5L0JkFw%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
