turbulent Prandtl number

TEXSTAN uses the Kays turbulent Prandtl number model, developed in detail in our textbook CHMT. The model evolved from a simple conduction model for Prt that includes heat conduction to or from the turbulent element (eddy) as it moves. The following equation fits the available experimental data reasonably well Kays Prt model
where Pet = (εM/ν) Pr is a turbulent Péclet number. C is an experimental constant equal to 0.3. The far-field value of the turbulent Prandtl number, Prt,∞ , is set equal to 0.86 for gases and light liquids, and for Pr< 0.6 (liquid metals), the Weigand correction is applied Weigand Prt correction for liquid metals

The Prt model has been calibrated for equilibrium turbulent boundary layers for use with the mixing-length turbulence model. It works equally well for turbulent flows with one- and 2-equation turbulence models. This option is not recommended for transitional boundary layer flows or flows with pressure gradients, or for liquids with Pr > 10-20.

Note, for turbulent mass transfer, the turbulent mass flux would be specified through a turbulent Schmidt number. However, there is currently no provision in TEXSTAN to input a turbulent Schmidt number.

The flag ktme identifies the turbulent Prandtl number model choices for computing the turbulent conductivity.

 ktme  turbulence model for the energy equation
 = 1  constant turbulent Prandtl number; =0.85
 = 2  constant turbulent Prandtl number, = fxx
 = 3  Kays variable turbulent Prandtl number model

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