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8.5 Scalable Wall Functions

Scalable wall functions ensure that the wall distance employed in the wall functions is such that y+≥11.126 irrespective of the level of near-wall grid refinement. This value of y+ marks the intersection of the linear and logarithmic velocity profiles. It is evident that the scalable wall function will produce identical results to the standard wall function for values of y+≥11.126.

The use of standard equilibrium and non-equilibrium wall functions implies that the near-wall grid node resides entirely within the log-law region, but this can be difficult to realise in general applications because of varying geometrical and velocity scales associated with the flow. Scalable wall functions avoid erroneous modelling of the laminar and buffer regions of the boundary layer by effectively shifting the near-wall mesh point to y+=11.126 regardless of the close it is to the wall.

Scalable wall functions can be activated in the "Sources" dialog box under "Menu", or by putting SCALWF=T in the Q1 input file.

Scalable wall functions can be activated for all high-Reynolds-number turbulence models that employ equilibrium wall functions without surface roughness. They are not currently implemented for use with non-equilibrium wall functions or with the Reynolds Stress Transport Model.

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