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Computational Fluid Dynamics Theory & Principles Flashcards

7 cards from real CPCE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. Which turbulence model solves two transport equations — one for turbulent kinetic energy and one for its dissipation rate?

    Answer: k-ε model

    The k-ε model solves transport equations for turbulent kinetic energy k and its dissipation rate ε, making it a two-equation RANS model.

  2. The CFL (Courant-Friedrichs-Lewy) condition states that for explicit schemes the time step must satisfy:

    Answer: CFL = u·Δt/Δx ≤ 1

    The CFL condition CFL = u·Δt/Δx ≤ 1 ensures that information cannot travel more than one cell per time step for explicit convection schemes.

  3. In Large Eddy Simulation (LES), the role of the subgrid-scale (SGS) model is to:

    Answer: Model the effect of unresolved small-scale eddies on the resolved flow

    LES explicitly resolves large eddies but models the energy drain from resolved scales to unresolved small eddies via SGS models.

  4. The QUICK scheme (Quadratic Upstream Interpolation for Convective Kinematics) is third-order accurate and uses:

    Answer: Two upstream and one downstream node for interpolation

    QUICK fits a quadratic through two upstream and one downstream node to interpolate face values, achieving third-order spatial accuracy.

  5. Which statement best describes the concept of 'multigrid' in CFD solvers?

    Answer: Accelerating convergence by solving residual equations on coarser grids

    Multigrid methods use a hierarchy of coarser grids to efficiently damp error modes of all wavelengths, dramatically accelerating iterative solver convergence.

  6. The divergence-free constraint for incompressible flow (∇·u = 0) is enforced in pressure-based solvers by:

    Answer: Both B and C

    Pressure-based incompressible solvers derive a Poisson equation for pressure (or pressure correction) whose solution, when applied to the velocity, projects it onto the divergence-free space.

  7. In CFD, 'grid sensitivity study' is performed to:

    Answer: Demonstrate that results are independent of mesh resolution

    A grid sensitivity (or mesh independence) study verifies that further mesh refinement does not significantly alter key solution quantities, confirming discretization error is acceptable.