CPCE CPCE Turbulence Modeling & Numerical Methods 3

Question 1

What is the Boussinesq hypothesis used for in RANS turbulence modeling?

Accepted Answer

Relating Reynolds stresses to the mean rate of strain via turbulent viscosity

Answer

Relating turbulent heat flux to temperature gradient

Answer

Defining the wall shear stress in turbulent flows

Answer

Calculating the turbulent Prandtl number

Question 2

In which scenario is a Detached Eddy Simulation (DES) approach most appropriate?

Accepted Answer

Flows with large separated regions where RANS is inaccurate but full LES is too costly

Answer

Fully laminar pipe flow

Answer

Steady-state heat conduction problems

Answer

Low Reynolds number microfluidics

Question 3

What is the significance of the y+ (y-plus) value in wall-bounded turbulent CFD simulations?

Accepted Answer

It is a non-dimensional wall distance indicating whether the first cell is in the viscous sublayer

Answer

It measures the Mach number at the wall

Answer

It quantifies the turbulent kinetic energy at the wall

Answer

It defines the pressure coefficient at the wall surface

Question 4

Which finite volume method property ensures that the sum of fluxes across all faces of a control volume equals zero, maintaining mass conservation?

Accepted Answer

Conservativeness

Answer

Consistency

Answer

Stability

Answer

Boundedness

Question 5

What is 'false diffusion' in CFD and under what conditions is it most pronounced?

Accepted Answer

Numerical diffusion error from upwind schemes; most pronounced when flow is oblique to the mesh

Answer

Extra diffusion added by the user for stability; pronounced in high-viscosity flows

Answer

Diffusion caused by round-off errors; most pronounced at high Reynolds numbers

Answer

Boundary layer diffusion; most pronounced in laminar flows

Question 6

In implicit time integration for unsteady CFD, what is the main computational advantage over explicit schemes?

Accepted Answer

It allows larger time steps without violating stability constraints

Answer

It requires no iteration within each time step

Answer

It is more accurate per time step

Answer

It eliminates the need for pressure-velocity coupling