|The Keulegan-Carpenter number is important for the computation of the wave forces on offshore platforms.|
In fluid dynamics, the Keulegan-Carpenter number, also called the period number, is a dimensionless quantity describing the relative importance of the drag forces over inertia forces for bluff objects in an oscillatory fluid flow. Or similarly, for objects that oscillate in a fluid at rest. For small Keulegan-Carpenter number inertia dominates, while for large numbers the (turbulence) drag forces are important.
The Keulegan-Carpenter number KC is defined as:
The Keulegan-Carpenter number is named after Garbis H. Keulegan (1890-1989) and Lloyd H. Carpenter.
with A the excursion amplitude of fluid particles in oscillatory flow and L a characteristic diameter of the sediment material. For sinusoidal motion of the fluid, A is related to V and T as A = VT/(2?), and:
Dividing these two acceleration scales gives the Keulegan-Carpenter number.
A somewhat similar parameter is the Strouhal number, in form equal to the reciprocal of the Keulegan-Carpenter number. The Strouhal number gives the vortex shedding frequency resulting from placing an object in a steady flow, so it describes the flow unsteadiness as a result of an instability of the flow downstream of the object. Conversely, the Keulegan-Carpenter number is related to the oscillation frequency of an unsteady flow into which the object is placed.