Fluid Flow & Heat Transfer Analysis 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 Fluid Flow & Heat Transfer Analysis flashcards as text
In CFD, what is the primary purpose of the wall y+ value in turbulent boundary layer modeling?
Answer: To ensure appropriate mesh resolution for the chosen near-wall treatment
The dimensionless wall distance y+ determines whether the near-wall mesh is fine enough to resolve the viscous sublayer or whether wall functions should be used.
What is the physical significance of the thermal entry length in duct flow?
Answer: The duct length over which the thermal boundary layer grows to fill the duct
The thermal entry length is the downstream distance from the inlet where the thermal boundary layer fully develops and heat transfer transitions to the fully-developed profile.
Which CFD boundary condition is most appropriate for a fully-developed flow outlet in an internal flow simulation?
Answer: Zero-gradient (outflow) condition for all variables
A zero-gradient (outflow) condition assumes that flow variables do not change in the streamwise direction at the outlet, appropriate for fully-developed exit conditions.
In the energy equation for CFD, what does the viscous dissipation term represent?
Answer: Conversion of kinetic energy to heat through viscous stresses
Viscous dissipation represents the irreversible conversion of mechanical energy to thermal energy due to viscous stresses within the fluid, becoming important at high velocities or in highly viscous flows.
What is the key characteristic of a pressure-based CFD solver compared to a density-based solver?
Answer: Uses pressure as the primary variable for incompressible and low-speed flows
Pressure-based solvers use the pressure field as the primary variable and are well-suited for incompressible and mildly compressible flows where density variations are small.
In heat exchanger CFD analysis, what does the NTU (Number of Transfer Units) method help predict?
Answer: Heat exchanger effectiveness from inlet conditions
The NTU-effectiveness method calculates heat exchanger performance using the number of transfer units and capacity rate ratio without requiring outlet temperatures.
For multiphase flow CFD, what distinguishes the Volume of Fluid (VOF) method?
Answer: It uses a volume fraction to capture sharp interfaces between phases
The VOF method uses a volume fraction field (0 to 1) to represent the interface between immiscible phases, making it effective for capturing sharp free-surface flows.