11 August 2011

ça marche (mal?)

Suzerain, my pseudospectral, compressible DNS code, is coming along.  After some manufactured solution love I'm onto channel problems.  With some added solenoidal velocity perturbations my laminar solutions transitioned to turbulent ones quite nicely.

However, I'm currently puzzling over why my Coleman-like case is showing stationary mean state behavior...

 ...but momentum fluctuations that grow in time:

Currently suspect things are:
  1. Inadequate resolution ('tis quite lousy)
  2. Pressure growing in time (a probable symptom I need to check but not a root cause)
  3. Funkiness associated with the discrete mass conservation fixes (my numerics are not conservative and holding mass constant requires some integral constraint futzing)
  4. Inadequate dealiasing (unlikely, currently using enough to handle quadratic nonlinearities in my Fourier directions but my equations are worse-than-cubic).
 Thank you to Nick Malaya for poring over plots with me this morning.

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