EIT Fluid Mechanics 5

Question 1

The bulk modulus of elasticity of a fluid is defined as:

Accepted Answer

K = −V(dP/dV)

Answer

Bulk modulus K = −V(dP/dV) = ρ(dP/dρ), measuring resistance to compression.

Question 2

A 0.05 m diameter pipe (f = 0.02, L = 100 m) carries water at 2 m/s. The major (friction) head loss is:

Accepted Answer

8.16 m

Answer

h_f = f(L/D)(V²/2g) = 0.02×(100/0.05)×(4/19.62) = 0.02×2000×0.204 = 8.16 m.

Question 3

For laminar flow between two infinite parallel plates (Couette flow with both plates stationary and a pressure gradient), the velocity profile is:

Accepted Answer

Parabolic

Answer

Pressure-driven flow between stationary plates (Poiseuille flow) produces a parabolic velocity profile u ∝ (h² − y²).

Question 4

The specific speed of a pump (Ns) is used to:

Accepted Answer

Classify pump type and predict performance at various scales

Answer

Specific speed Ns = N√Q/H^(3/4) classifies pumps (centrifugal, mixed-flow, axial) and enables similitude-based performance prediction.

Question 5

The Strouhal number is defined as St = fL/V, where f is the frequency of vortex shedding. It primarily relates to:

Accepted Answer

Periodic vortex shedding behind bluff bodies

Answer

The Strouhal number characterizes the periodic vortex shedding (Kármán vortex street) frequency behind cylinders and bluff bodies.

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