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Hi all,

I have a few questions regarding spectral vanishing viscosity and hope somebody can help me out. I read in section 9.3.2.2 of Prof. Sherwins book Spectral/hp element methods for computational fluid dynamics that:

  1. only the upper one-third of the spectrum should be treated with SVV
  2. the optimal SVV amplitude level (called diffusion parameter in the user guide) is unknown a priori.

Since according to the user guide SVV is activated for modes higher than the product of the cut-off ratio and the expansion order, 1. means the cut-off ratio shouldn't fall below a value of 2/3. I wonder why the default value for all SVV kernels is 0.75 and 2/3?

Furthermore, since again according to the user guide, the diffusion parameter is scaled by h/p, how is h evaluated and which value is used for p if different expansions are used for different flow variables? Is p always corresponding to the expansion used for velocity?

In section 9.4.2.3 of the book a possible dynamic SVV model formulation is presented. Another question I am interested in, is whether it is possible to activate such a dynamic SVV model within the incompressible N-S solver of Nektar and if not, which procedure would you recommend in order to optimally tune SVV diffusion for a given flow problem?

Thanks in advance and all the best
Alex

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