Fluid Mechanics Flashcards

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

Answer: K = −V(dP/dV)

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

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

Answer: 8.16 m

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

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

Answer: Parabolic

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

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

Answer: Classify pump type and predict performance at various scales

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

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

Answer: Periodic vortex shedding behind bluff bodies

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

For a pump operating in a piping system, the operating point is determined by:

Answer: The intersection of the pump curve and the system curve

The operating point is where the pump head-flow curve intersects the system resistance curve (static head + friction losses).

The net positive suction head available (NPSHA) is calculated as:

Answer: NPSHA = (P_s − P_v)/(ρg) + V_s²/(2g)

NPSHA = (P_s/ρg + V_s²/2g) − P_v/(ρg), representing the absolute suction head minus the vapor pressure head.