Flow Past Immersed Bodies MCQ with answer and solution

Concept

Lift generation via asymmetric pressure distribution

Formula

L = C_L × (1/2) × ρ × V² × A

Step-by-step solution

1. When a hydrofoil moves through water with camber or angle of attack, flow velocity over the upper curved surface increases. 2. According to Bernoulli's principle, higher velocity over the top surface produces lower static pressure compared to the bottom. 3. The resulting pressure differential between upper and lower surfaces produces an upward hydrodynamic force known as lift. 4. Hence, lift is primarily generated by the pressure difference caused by asymmetric flow. Answer: C

Explanation

A hydrofoil moving through water generates lift primarily due to asymmetrical flow velocities across its upper and lower surfaces created by camber and angle of attack. In accordance with Bernoulli's principle, higher flow speed over the suction surface produces lower static pressure than beneath the foil, producing a net upward pressure differential that yields hydrodynamic lift.

Why the other options are wrong

A) Viscous shear forces act tangentially to the surface and cause drag, not primary vertical lift. B) Buoyancy is static displacement force, whereas hydrofoil lift is dynamic and velocity-dependent. D) Surface tension effects are negligible on large-scale hydrofoils.

Shortcut

Hydrofoil lift = Bernoulli pressure differential between upper (low P) and lower (high P) surfaces.

Common mistake

Attributing lift to buoyancy or viscous shear stress rather than asymmetrical pressure distribution.