What term describes the point at which flow becomes turbulent?

What term describes the point at which flow becomes turbulent?

• A. Poiseuille's law
• B. Bernoulli's law
• C. Starling's law
• D. Reynolds number

Answer: (D)

Flow becomes turbulent when inertial forces in the fluid start to dominate over viscous forces, allowing disturbances to grow rather than be damped out. The Reynolds number captures this balance in one dimensionless quantity: Re = (rho * v * L) / mu. As Re increases, inertial effects rise and the flow is more likely to transition from smooth, laminar motion to chaotic, turbulent motion. While the exact threshold depends on the geometry and conditions, Reynolds number is the standard way to describe the onset of turbulence. The other options describe different principles: Poiseuille's law gives the pressure drop for laminar pipe flow; Bernoulli's law relates pressure and speed along a streamline in inviscid flow; Starling's law concerns fluid exchange across capillary walls.

Flow becomes turbulent when inertial forces in the fluid start to dominate over viscous forces, allowing disturbances to grow rather than be damped out. The Reynolds number captures this balance in one dimensionless quantity: Re = (rho * v * L) / mu. As Re increases, inertial effects rise and the flow is more likely to transition from smooth, laminar motion to chaotic, turbulent motion. While the exact threshold depends on the geometry and conditions, Reynolds number is the standard way to describe the onset of turbulence. The other options describe different principles: Poiseuille's law gives the pressure drop for laminar pipe flow; Bernoulli's law relates pressure and speed along a streamline in inviscid flow; Starling's law concerns fluid exchange across capillary walls.