CPCE Mesh Generation & Boundary Conditions Flashcards
6 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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What is the 'pressure outlet' boundary condition used for in CFD, and what is commonly specified?
Answer: It specifies a gauge static pressure at the domain exit, allowing flow to leave the domain naturally
A pressure outlet boundary specifies the static gauge pressure at the exit, allowing the solver to compute the outflow velocity profile naturally while maintaining the specified back pressure.
What is 'mesh aspect ratio' and what problem arises when it is excessively large?
Answer: Ratio of longest to shortest cell dimension; very high ratios can cause solver ill-conditioning and inaccuracy
Aspect ratio is the ratio of a cell's longest edge to its shortest; extremely large aspect ratios can make the discretized equations ill-conditioned and reduce solution accuracy.
In what situation is a 'periodic' boundary condition used in CFD?
Answer: When the geometry and flow repeat spatially, allowing a section of the domain to represent the full geometry
Periodic boundary conditions are applied when the geometry repeats in space (e.g., a turbine blade passage or a pipe with repeating fins), so only one repeating unit needs to be simulated.
What is 'mesh independence' (or grid independence) in CFD and how is it verified?
Answer: The state where refining the mesh no longer significantly changes the solution; verified by comparing key results on successively finer meshes
Mesh independence means the solution has converged with respect to spatial discretization; it is verified by running simulations on progressively finer meshes until key quantities (drag, pressure drop, etc.) change by less than an acceptable tolerance.
What is the 'no-slip' wall boundary condition in CFD?
Answer: The fluid velocity at the wall equals the wall velocity (zero for stationary walls), enforcing viscous adherence
The no-slip condition sets the fluid velocity at a solid wall equal to the wall's own velocity (zero for a stationary wall), physically representing viscous adhesion of real fluids to surfaces.
What is a 'polyhedral mesh' and what is its advantage in CFD over tetrahedral meshes?
Answer: A mesh with cells having many faces; advantage is fewer cells needed for same accuracy, better gradient calculation
Polyhedral cells have many neighbors, providing better gradient estimates and typically requiring fewer cells than tetrahedral meshes for equivalent accuracy, reducing overall cell count and computational cost.