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.
Read the first 7 Computational Fluid Dynamics Theory & Principles flashcards as text
In Direct Numerical Simulation (DNS), the minimum mesh spacing required scales approximately as:
Answer: Re^(3/4)
DNS must resolve down to the Kolmogorov length scale η ~ Re^(-3/4)L, so mesh point counts scale as Re^(9/4) in 3D, making DNS prohibitively expensive at high Re.
The Lax-Wendroff scheme achieves second-order accuracy in both space and time by:
Answer: Replacing the time derivative with spatial derivatives via the PDE itself before discretizing
Lax-Wendroff substitutes the second time derivative with spatial derivatives using the governing PDE, enabling a single-step second-order scheme.
Which boundary condition type specifies the gradient (flux) of a variable normal to the boundary, rather than its value?
Answer: Neumann condition
A Neumann boundary condition prescribes the normal derivative (flux) of the variable at the boundary, commonly used for symmetry planes or fully developed outflow.
The concept of 'numerical diffusion' as opposed to 'numerical dispersion' refers to:
Answer: Smearing of sharp gradients caused by truncation error in the dissipative part of the scheme
Numerical diffusion arises from even-order truncation error terms that act like additional viscosity, smearing gradients, while numerical dispersion comes from odd-order terms causing phase errors.
In the Finite Volume Method, the divergence theorem is used to convert the volume integral of a divergence term into:
Answer: A surface (face) integral of fluxes
Gauss's divergence theorem converts ∫_V ∇·F dV into ∮_S F·n dS, transforming volume divergence integrals into face flux integrals in FVM.
The 'realizability' requirement in turbulence modeling ensures that:
Answer: The turbulent kinetic energy k remains non-negative and normal stresses are positive
Realizability constraints guarantee physically admissible turbulence statistics, such as non-negative normal stresses and satisfaction of the Schwarz inequality for shear stresses.
Which method is commonly used to handle moving boundaries or fluid-structure interaction in CFD by re-meshing the domain at each time step?
Answer: Arbitrary Lagrangian-Eulerian (ALE) method
The ALE method moves the mesh with the boundary to maintain mesh conformity while allowing interior nodes to move independently, combining Lagrangian and Eulerian descriptions.