Question

Fully developed, steady, incompressible laminar flow of a viscous fluid exists between two large parallel horizontal plates separated by 5 mm. The bottom plate is fixed and the top plate moves at U=4 m/s with no pressure gradient. Density of fluid is 800 kg/m³, kinematic viscosity is 1.25×10⁻⁴ m²/s. The average shear stress in the fluid is ___ Pa (round off to the nearest integer).

Accepted Answer

The correct answer is 80 Pa (± 1). For plane Couette flow, τ=μ(U/h), constant across the gap. μ=ρν=800×1.25×10⁻⁴=0.1 Pa·s. τ=0.1×(4/0.005)=0.1×800=80 Pa.

Explanation