Blood becomes turbulent when Reynolds number exceeds which value?

• A. >1000
• B. >2000
• C. >3000
• D. >4000

Answer: (B)

Reynolds number tells you whether flow is smooth or chaotic by comparing inertial forces to viscous damping. When Re is low, viscosity dominates and the flow stays laminar; as Re increases, inertial effects dominate and disturbances can grow into turbulence. In blood vessels, the transition to turbulence typically starts around Re of about 2000. Once Re exceeds this value, turbulence can begin, especially at sites where the vessel geometry changes abruptly or where flow is disturbed.

So the onset is around 2000, which is why the correct choice is the value greater than 2000. Values much lower (like 1000) stay laminar in most cases, and while turbulence becomes more pronounced at higher Re (3000–4000 and beyond), the earliest onset is around 2000.