ANS:C - Froude

The number that determines whether the fluid flow in an open channel is supercritical, critical, or sub-critical is the Froude number. The Froude number (Fr) is defined as the ratio of inertial forces to gravitational forces and is given by: Fr=gd​V​ Where:

• V is the velocity of the flow,
• g is the acceleration due to gravity, and
• d is the characteristic length (typically the depth of flow in open channel flow).

• Fr<1: Subcritical flow (flow velocity is less than the wave velocity).
• Fr=1: Critical flow (flow velocity is equal to the wave velocity).
• Fr>1: Supercritical flow (flow velocity is greater than the wave velocity).