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CHAPTER
6 TURBULNACE

MODELING

In this Chapter
6.1 Introduction 6.4 k-ω Model
6.2 Spalart-Allmaras Model 6.5 Shear Flow Corrections
6.3 k-ε Model

6.1 Introduction

Turbulent flows are characterized by fluctuating velocity fields. These fluctuations mix transported
quantities such as momentum, energy, and species concentration, and cause the transported
quantities to fluctuate as well. Since these fluctuations can be of small scale and high frequency, they
are too computationally expensive to simulate directly in practical engineering calculations. Instead,
the instantaneous (exact) governing equations can be time-averaged, ensemble-averaged, or
otherwise manipulated to remove the resolution of small scales, resulting in a modified set of
equations that are computationally less expensive to solve. However, the modified equations contain
additional unknown variables, and turbulence models are needed to determine these variables in
terms of known quantities.

ANSYS FLUENT provides the following choices of turbulence models:
1. Spalart-Allmaras model
2. k-ε models
a. Standard k- ε model
b. Renormalization-group (RNG) k- ε model
c. Realizable k- ε model
3. k-ω models
a. Standard k-ω model
b. Shear-stress transport (SST) k-ω model
4. V2-f model (add-on)
5. Transition k-kl-ω model
6. Transition SST model
7. Reynolds stress models (RSM)
a. Linear pressure-strain RSM model
b. Quadratic pressure-strain RSM model
c. Low-Re stress-omega RSM model

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