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AcuSolve Training Manual
Introduction of background knowledge regarding flow physics and CFD as well as detailed information about the use of AcuSolve and what specific options do.
Theoretical Background
Turbulence
This section on turbulence covers the topics describing the physics of turbulence and turbulent flow. It also covers the modeling of turbulence with brief descriptions of commonly used turbulence models.
Modeling of Turbulence
This section covers the numerical modeling of turbulence by various turbulence models, near wall modeling and inlet turbulence parameters specified for turbulence models.
Reynolds-Averaged Navier-Stokes (RANS) Simulations
For incompressible turbulent flow the instantaneous velocity field can be decomposed into a time averaged velocity and its corresponding fluctuation.
Two Equation Eddy Viscosity Models
Two equation turbulence models are perhaps the most commonly used in industrial flow applications.

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AcuSolve Training Manual
Introduction of background knowledge regarding flow physics and CFD as well as detailed information about the use of AcuSolve and what specific options do.
- Introduction to CFD
- Theoretical Background
  - Mathematical Background
    This section on mathematical background covers the various notations and operators used to formulate and define the equations of fluid flow.
  - Basics of Fluid Mechanics
    This section on basics of fluid mechanics covers topics describing the fundamental concepts of fluid mechanics, such as the concept of continuum, the governing equations of a fluid flow, definition of similitude and importance of non-dimensional numbers, different types of flow models and boundary layer theory.
  - Turbulence
    This section on turbulence covers the topics describing the physics of turbulence and turbulent flow. It also covers the modeling of turbulence with brief descriptions of commonly used turbulence models.
    - Physics of Turbulent Flows
      This section on physics of turbulence introduces a brief history of turbulence and covers the theory behind turbulence generation, turbulence transition and energy cascade in fluid flows.
    - Modeling of Turbulence
      This section covers the numerical modeling of turbulence by various turbulence models, near wall modeling and inlet turbulence parameters specified for turbulence models.
      - Challenges in Simulating Turbulent Flows
        In order to set the context for the modeling of turbulent flow it is essential to understand why turbulent flow simulations are challenging.
      - The Navier-Stokes Equations
        The Navier-Stokes (NS) equations are the set of equations that govern the motion of a fluid.
      - Direct Numerical Simulation
        Direct Numerical Simulation (DNS) solves the time dependent Navier-Stokes equations, resolving from the largest length scale of a computational domain size to the smallest length scale of turbulence eddy (Kolmogorov length scale).
      - Turbulence Modeling
        Three-dimensional industrial scale problems are concerned with the time averaged (mean) flow, not the instantaneous motion. The preferred approach is to model turbulence using simplifying approximations, and not resolve it.
      - Reynolds-Averaged Navier-Stokes (RANS) Simulations
        For incompressible turbulent flow the instantaneous velocity field can be decomposed into a time averaged velocity and its corresponding fluctuation.
        General Form of Turbulence Models
        One Equation Eddy Viscosity Models
        One equation Reynolds-averaged Navier-Stokes (RANS) models solve a single scalar transport equation to compute the eddy viscosity.
        Two Equation Eddy Viscosity Models
        Two equation turbulence models are perhaps the most commonly used in industrial flow applications.
        Standard k-ε Model
        Launder and Spalding (1974) proposed the standard k-ε turbulence model utilizing the relationships described below.
        Renormalization Group (RNG) k-ε Model
        The RNG k-ε turbulence model (Yakhot and Orszag, 1986) deduces the behavior of large scale eddies from that of the smaller ones by utilizing the scale similarity properties that are inherent in the energy cascade (Bradshaw, 1997).
        Realizable k-ε Model
        The standard k-ε turbulence model and RNG k-ε turbulence model do not satisfy mathematical constraints on the Reynolds stresses for the consistency with physics of turbulence.
        Wilcox k-ω Model
        Since all three k-ε turbulence models cannot be integrated all the way to walls, wall damping wall functions must be employed to provide correct near wall behavior. It is also known that the standard k-ε turbulence model fails to predict the flow separation under adverse pressure gradients.
        Menter Shear Stress Transport (SST) k-ω Model
        Menter (1994) suggested the SST model to overcome the freestream value sensitivity of the standard k-ω turbulence model by transforming the k-ε model into the k-ω model in the near-wall region, and by utilizing the k-ε model in the turbulent region far from the wall.
        Shear Stress Transport (SST) Model with Rotation/Curvature Correction
        Since the SST model relies on the Boussineq approximation, it also has poor performance for the prediction of flows with streamline curvature and system rotation because the Reynolds stress tensor is aligned to the mean strain rate tensor.
      - Turbulent Transition Models
        All of the previously described models are incapable of predicting boundary layer transition. To include the effects of transition additional equations are necessary.
      - Large Eddy Simulation (LES)
        LES is often regarded as an impractical tool for industrial CFD applications as it requires large computational resources.
      - Hybrid Simulations
        In recent years, hybrid methods have increasingly been employed for the simulation of unsteady turbulent flows.
      - Near-Wall Modeling
        For internal wall bounded flows, proper mesh resolution is required in order to calculate the steep gradients of the velocity components, turbulent kinetic energy, dissipation, as well as the temperature.
      - Inlet Turbulence Parameters
        CFD simulations require specification of turbulence variables at inlet boundaries.
      - Summary
        During the past decades turbulence models of various complexities have been developed. Turbulence models that employ the most assumptions are typically the least demanding from a CPU cost standpoint.
  - Numerical Approximation Techniques
    This section on numerical approximation techniques covers topics, which describe the numerical modeling of the fluid flow equations on a computational domain, such as spatial discretization using finite difference, finite element and finite volume techniques, temporal discretization and solution methods.
- AcuSolve
- Guidelines for Quality CFD Modeling
AcuSolve Validation Manual
Collection of AcuSolve simulation cases for which results are compared against analytical or experimental results to demonstrate the accuracy of AcuSolve results.
AcuSolve Command Reference Manual
AcuSolve command descriptions and corresponding examples.
AcuSolve Programs Reference Manual
AcuSolve utility programs covering preparatory and post-processing as well as user-defined functions and utility scripts.
AcuSolve User-Defined Functions Manual
Customization of AcuSolve allowing you to customize certain capabilities of the solver.
AcuTrace Command Reference Manual
Commands of AcuTrace, a particle tracer that runs as a post-processor to or a co-processor with AcuSolve.
AcuTrace User-Defined Functions Manual
Instructions to define additional solution quantities of AcuTrace called user equations.
AcuReport Reference Manual
Instruction of the AcuReport tool, a standalone post-processor batch tool used to generate a report from an AcuSolve solution database.
AcuSolve Surface Processing

Two Equation Eddy Viscosity Models

Two equation turbulence models are perhaps the most commonly used in industrial flow applications.

Although there are many two equation models available, some of the more popular ones include:

$k - ε$ model, Renormalized Group (RNG) $k - ε$ model, Realizable $k - ε$ model,
$k - ω$ model, Shear Stress Transport (SST) model.