Fluid Mechanics Flashcards

Cavitation in hydraulic machinery occurs when the local fluid pressure drops below the:

Answer: Vapor pressure of the fluid

Cavitation occurs when local static pressure falls below the fluid's vapor pressure, causing vapor bubble formation.

For compressible flow in a converging-diverging nozzle, a normal shock wave can appear in the:

Answer: Diverging section at supersonic conditions

Normal shocks form in the diverging section when back pressure is between the design (fully supersonic) and subsonic exit conditions.

The concept of 'fully developed flow' in a pipe means that:

Answer: The velocity profile no longer changes with downstream distance

Fully developed flow means the velocity profile shape is constant with axial position; only pressure continues to drop linearly.

The vorticity vector ω in a fluid flow field is defined as:

Answer: ω = ∇×V (curl of velocity)

Vorticity is ω = ∇×V, representing the local angular rotation rate of a fluid element.

Stokes' Law for the drag force on a slowly moving sphere in a viscous fluid is:

Answer: F_D = 3πμVD

For creeping (Stokes) flow (Re ≪ 1), the drag on a sphere is F_D = 3πμVD where D is diameter.

The critical depth in open channel flow is defined as the depth at which:

Answer: Flow velocity equals the wave speed (Froude number = 1)

Critical depth occurs when Fr = V/√(gy) = 1, meaning flow velocity equals the shallow-water wave speed.

The Euler turbine equation relates the torque produced by a turbomachine to:

Answer: Change in the tangential component of fluid velocity between inlet and outlet

Euler's equation T = ρQ(r₂Vθ₂ − r₁Vθ₁) shows torque depends on the change in angular momentum (tangential velocity × radius).