Turbulence Modeling – The Gist

The attached presentation is a concise description of turbulence modeling approaches, based on the portion of Turbulence Modeling of past CFD courses I have had the opportunity to lead. It has many links to more elaborated blog posts relating to specific turbulence models and its foundations. Update 29/3/18: Stress-Blended Eddy Simulation (SBES) (slides 86-87) Update …

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Know Thy Mesh – Mesh Quality – Part I

Many would argue that your CFD solution is as good as the mesh behind it. Many aspects of the mesh have a vital contribution to simulation accuracy, and include among others the type of physics models simulated, the details of the solution to the particular simulation, chosen discretization scheme and geometric mesh properties having to …

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Numerical Schemes in CFD: Upwinding and The Cell-Reynolds Problem

There are three broad methods employed for discretizing the governing partial differential equations of a fluid flow: Finite Difference Methods (FDM) Finite Element Methods (FEM) Finite Volume Methods (FVM) Finite element and finite volume methods (FEM and FVM) are both based on dividing the flow domain into small cells, or volumes. These may possibly take any shape …

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Know Thy Solver – Part III: Pressure Equation Methodologies for Incompressible Flow

In compressible flows the continuity equation can be used to determinethe density and the pressure can be calculated from an equation of state. This approach is not appropriate for incompressible or low Mach number flows. When considering the incompressibility assumption as valid, Navier-Stokes equations supplemented by continuity take the following recognizable form (body forces neglected): …

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Law of the Wall

We begin our discussion by noting that there are three quite general and distinct types of turbulent flows: namely, Homogeneous and/or isotropic turbulence, free shear flows and wall-bounded shear flows. Homogeneous and/or Isotropic Turbulence Homogeneous turbulence is such that statistics are invariant under spatial translations, while isotropic turbulence is invariant under rotations and reflections. As rotations and reflections can …

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The Prince of RANS: k-ω SST Turbulence Model

"Every mathematician believes that he is ahead of the others. The reason none state this belief in public is because they are intelligent people" - Andrey Kolmogorov Most of nowadays CFD simulations are conducted with the Reynolds Averaging approach. Reynolds-Averaged Navier-Stokes (RANS) simulation is based on the Reynolds decomposition according to which a flow variable …

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Going Hybrid

Nothing is as beneficiary for the flight industry as the ability to cut substantially on fuel budget. From a CFD perspective, such a goal could potentially be achieved by high fidelity simulation for a detailed design full airborne vehicle . A naive approach for the highest physical fidelity could be a Direct Numerical Simulation (DNS) of Navier-Stokes equations. …

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