CPCE Turbulence Modeling & Numerical Methods Flashcards

Which turbulence model is known as a two-equation model that solves transport equations for turbulent kinetic energy (k) and its dissipation rate (ε)?

Answer: k-ε model

The k-ε model solves two transport equations for turbulent kinetic energy k and its dissipation rate ε to close the Reynolds-averaged Navier-Stokes equations.

What does the acronym 'DNS' stand for in the context of CFD turbulence simulation?

Answer: Direct Numerical Simulation

DNS (Direct Numerical Simulation) resolves all turbulent length and time scales without any turbulence modeling, making it highly accurate but computationally expensive.

The Courant-Friedrichs-Lewy (CFL) condition is primarily a stability criterion for which class of numerical methods?

Answer: Explicit time-stepping schemes

The CFL condition restricts the time step size in explicit time-stepping schemes to ensure numerical stability by requiring that information does not travel more than one cell per time step.

In Large Eddy Simulation (LES), what role does the Sub-Grid Scale (SGS) model play?

Answer: It models the effect of eddies smaller than the grid size

The SGS model in LES accounts for the influence of small unresolved eddies (smaller than the grid cell size) on the resolved larger-scale flow.

Which numerical discretization scheme is second-order accurate in space and is commonly used for convection terms in CFD to balance accuracy and stability?

Answer: Central differencing

Central differencing is second-order accurate in space and provides a good balance between accuracy and stability for convection term discretization in CFD.

What is the primary advantage of the k-ω SST turbulence model over the standard k-ε model?

Answer: It performs better in adverse pressure gradient and separated flow regions

The k-ω SST model blends k-ω near walls and k-ε in freestream, giving it superior performance in adverse pressure gradients and separated flows compared to standard k-ε.