ENH: New wall-function blending approaches

Summary

This merge request is a discussion placeholder for two topics:

• Potential improvements to the wall-function hierarchies
• Wall-function blending treatments between viscous and inertial sublayers

Wall-function hierarchy

Arguably, the wall-function hierarchies need a reexamination as the relations have "grown organically" in the course of time. One recent problem is that {omega,epsilon,k}Wall functions use data members from nutWallFunction base class even though the former group is not derived from the latter.

One practical consequence is that {omega,epsilon,k}Wall always require a nut wall function is defined in the nut dictionary, otherwise simulation in question noisily fails without informing the user with useful information, e.g. CFD-Online:Error with k-omega SST and simpleFoam (21-Feb-20), and the bug-fix:55776069.

Wall-blending treatments

• Four wall-function blending treatments were introduced:

  • STEPWISE
  • MAX
  • BINOMIAL
  • EXPONENTIAL

• .. For the following wall functions:

  • epsilonWallFunction
  • omegaWallFunction
  • nut{k,U}WallFunction

• The header-file documentations were improved for the following wall functions for which the blending treatments were not applicable (e.g. due to the continuous treatment in nutUSpaldingWallFunction):

  • nutU{Spalding,Tabulated,Blended}WallFunction
  • nut{k,U}RoughWallFunction
  • nutLowReWallFunction
  • {kLowRe,kqR}WallFunction

• Based on:

  • Viegas and Rubesin (1983); Viegas et al. (1985) (i.e. the option: STEPWISE)
  • Menter and Esch (2001) (i.e. the option: BINOMIAL)
  • Popovac and Hanjalić (2007) (i.e. the options: MAX, EXPONENTIAL)
  • Knopp et al. (2006) (i.e. the option: TANH only for omega)

Resolved bugs

N/A

Risks

High risk, yet bitwise backward compatibility, and regression were verified for each modified functionality.

@mark @Sergio @Mattijs