Real Fluids

Question 1

What is the difference between ideal and real fluids?

Answer 1

Ideal Fluid: No shear stress, only normal stress, slip at boundaries.
Real Fluid: Supports both shear and normal stresses, no slip at boundaries.

Question 2

How do solids respond to stress?

Answer 2

Solids: Support all stress components (tension, compression, shear) in static equilibrium.

Question 3

How do fluids respond to stress?

Answer 3

Fluids: Do not support tension, compression is supported, shear stress leads to continuous deformation (flow)

Question 4

What is the mass continuity equation for fluids?

Answer 4

The mass conservation equation ensures that mass is conserved in any fluid element
∂ρ/∂t +∇⋅(ρv)= 0

Question 5

What is the difference between unsteady and convective acceleration in fluid flow?

Answer 5

Unsteady acceleration: Change in velocity with respect to time at a point.
Convective acceleration: Change in velocity due to spatial variations as fluid moves through different areas.

Question 6

What is the significance of viscosity in real fluids?

Answer 6

Viscosity describes a fluid’s resistance to shear and its dependence on the velocity gradient. For Newtonian fluids, viscosity is constant regardless of the rate of shear

Question 7

What does it mean a fluid is incompressible?

Answer 7

Cannot squeeze more/less fluid into our element

Question 8

What factors affect viscosity in real fluids?

Answer 8

Temperature: Viscosity decreases with increasing temperature for most fluids.
Pressure: For incompressible fluids like water, pressure has little effect on viscosity

Question 9

How are stress components related to fluid motion in real fluids?

Answer 9

Stress in real fluids is related to the rate of strain. Shear stresses act on fluid particles and vary based on the velocity gradients within the fluid. Linear relationship

Question 10

What is pressure per unit volume?

Answer 10

∂P/∂x,y,z

Question 11

How is fluid driven through an area?

Answer 11

From high to low pressure

Question 12

What is pressure per unit mass?

Answer 12

1/ρ*∂p/∂x,y,z

Question 13

What is a body force?

Answer 13

All external forces -> f_x,y,z or g_x,y,z

Question 14

What does Euler’s equations describe?

Answer 14

The dynamics of an inviscid and incompressible flow. Viscosity not included

Question 15

How is kinematic viscosity related to dynamic viscosity?

Answer 15

v = mu/rho

Question 16

What is the level of molecular activity dependent on?

Answer 16

• Pressure
• Temp
• Chemical composition

Question 17

How is Euler equation related to Navier-Stokes equation?

Answer 17

For inviscid flows the NSE is reduced to the EE as mu = 0

Question 18

Where can NSE be applied?

Answer 18

Turbulent and laminar

Question 19

What assumptions are made in the NSE?

Answer 19

• Steady flow
• Flow fully developed
• Two large plates
• No flow in z direction
• Mass continuity
• Impermeable plates
• v = 0

Question 20

What happens to the maximum velocity when mu is large?

Answer 20

Decreases

Question 21

What happens to the maximum velocity when B is large?

Answer 21

Increases

Question 22

How do larger gradients and slope affect max velocity?

Answer 22

Increase