Assignment 6 Solutions

1. Large eddies get their energy from

a) Small eddies

b) Mean flow

c) Large eddies

d) Turbulent flow

Ans: (b)

2. In low Re turbulence model, we

i) Solve governing equation near the wall with fine mesh

ii) Eddy viscosity is damped

iii) Wall function is used

a) (i) and (iii)

b) (i) and (ii)

c) (ii) and (iii)

d) (i), (ii) and (iii)

Ans: (b)

3. Relation among 𝑘, 𝜀 and 𝜇𝑇 is

a) 𝜇𝑇 = 𝜌𝑘2/𝜀

b) 𝜀 = 𝜌𝑘/𝜇𝑇

c) 𝜇𝑇 = 𝑘2/𝜀

d) 𝜀 = 𝑘2/𝜇𝑇

Ans: (a)

4. The smallest scale of turbulent flow is called

a) Small eddy scale

b) Boussinesq scale

c) Kolmogorov scale

d) None of these

Ans: (c)

5. In turbulent boundary layer, the sequence of difference regions starting from the wall is

a) Viscous sublayer, buffer layer, log layer

b) Buffer layer, viscous sublayer, log layer

c) Log layer, buffer layer, viscous sublayer

d) Buffer layer, log layer, viscous sublayer

Ans: (a)

Assignment 6 Solutions

6. Select the odd one out

Turbulent flow is/has

a) Non-periodic fluctuations

b) Small scale of length and time

c) Irregular

d) Unsteady

Ans: (b)

7. Turbulent viscosity is a property of ___________, whereas dynamic viscosity is a property of

_______.

a) Flow, fluid

b) Flow, flow

c) Fluid, flow

d) Fluid, fluid

Ans: (a)

8. Wall functions are not used in

a) Standard 𝑘 − 𝜔 model

b) High Re model

c) Standard 𝑘 − 𝜀 model

d) DNS

Ans: (d)

9. If the decomposition principle and averaging is to be applied the product of density and u-

velocity, the resulting terms are,

a) �̅��̅� + �̅�𝑢′ + �̅�𝜌′ + 𝜌′𝑢′̅̅ ̅̅ ̅

b) �̅��̅�̅̅̅̅ + �̅�𝑢′̅̅ ̅̅̅ + �̅�𝜌′̅̅ ̅̅ ̅

c) �̅��̅� + 𝜌′𝑢′̅̅ ̅̅ ̅

d) �̅��̅� + 𝜌′𝑢′̅̅ ̅̅ ̅ + 2�̅�𝜌′̅̅ ̅̅ ̅

Ans: (c)

10. In turbulence models, which term of RANS equation is modelled?

a) Pressure fluctuations

b) Viscous stresses

c) Velocity fluctuations

d) Reynold’s stresses

Ans: (d)