Fluid Mechanics Flashcards

A submerged gate 1 m wide and 2 m tall has its top edge at 3 m depth. What is the total hydrostatic force on the gate? (ρ = 1000 kg/m³)

Answer: 78,480 N

F = ρg·ȳ·A where ȳ = 3 + 1 = 4 m (centroid depth); F = 1000×9.81×4×(1×2) = 78,480 N.

What does the water hammer phenomenon refer to in pipe systems?

Answer: Pressure surge caused by rapid valve closure

Water hammer is a pressure surge or wave caused when a fluid in motion is forced to stop or change direction suddenly, typically by rapid valve closure.

For a Venturi meter, which principle is used to determine flow rate?

Answer: Continuity and Bernoulli equations combined

A Venturi meter uses the continuity equation (A₁V₁ = A₂V₂) combined with Bernoulli's equation to relate pressure difference to flow velocity.

The net positive suction head (NPSH) is important in pump design primarily to avoid:

Answer: Cavitation

If the available NPSH falls below the required NPSH, the local pressure drops below vapor pressure and cavitation occurs, damaging the pump.

For laminar flow in a circular pipe (Hagen-Poiseuille flow), the velocity profile is:

Answer: Parabolic

Hagen-Poiseuille flow produces a parabolic velocity profile: u(r) = (ΔP/4μL)(R² - r²), with maximum velocity at the centerline.

Which of the following best describes the concept of 'specific energy' in open channel flow?

Answer: Total energy per unit weight relative to the channel bottom

Specific energy E = y + V²/2g, representing total energy per unit weight measured above the channel bed (not a fixed datum).

In Stokes' law for a small sphere settling in a viscous fluid, the drag force is proportional to:

Answer: The sphere's velocity (linear)

Stokes' drag law: F = 3πμDV, showing drag is linearly proportional to velocity for Re < 1 (creeping flow).