What is the significance of Reynolds number?

Streamline flow is more likely for liquids with

In deriving Bernoulli’s equation, we equated the work done on the fluid in the tube to its change in the potential and kinetic energy. What is the largest average velocity of blood flow in an artery of diameter $2 \times {10}^{-3} \mathrm{m}$ if the flow must remain laminar? (Viscosity of blood, $\mathrm{\eta } = 2.084 \times {10}^3 \mathrm{Pa} \mathrm{s}$, Density of blood, $\mathrm{\rho } = 1.06 \times {10}^3 \mathrm{kg}/{\mathrm{m}}^3$)

A fire hydrant (as shown in the figure) delivers water of density $\mathrm{\rho }$ at a volume rate $L$. The water travels vertically upward through the hydrant and then does $90°$ turn to emerge horizontally at speed $V\mathit{.}$ The pipe and nozzle have uniform cross-section throughout. The force exerted by the water on the corner of the hydrant is