yplus value in two phase flow

P.R.Naren

How is the wall y plus value computed for a two phase gas solid flow of given operating conditions of say superficial gas velocity = 10m/s and superficial solid particle velocity = 3.5 m/s of particle density = 2500 kg/m3 and particle size = 150micron

Referring to FLUENT 6.2 documentation, it is given that yplus value is computed based on y value [ distance of cell adjacent to wall] and frictional velocity

Now how is the frictional velocity computed in case of two phase flows??

Can someone cite a suitable reference if any??

Regards Naren