Propeller thrust coefficient assessment using the phenomenological theory of turbulence

The bed erosion induced by a ship propeller is a paramount issue in the management of harbor basins and navigation channels. The efflux velocity from the ship propeller is the parameter that mostly influences the maximum scour depth. Literature formulas for calculating the efflux velocity require the knowledge of the propeller thrust coefficient (ct), which in turn depends on the geometric characteristics of the propeller (i.e; external propeller diameter, number of blades, hub diameter, blades area, etc.).Most authors in their works directly provide ct by considering literature values found for the same propeller geometric characteristics, or by evaluating it from the thrust generated by the propeller. The present work, instead, aims at tracing a new way for calculating ct by applying the phenomenological theory of turbulence, which is physically based and independent of scale effects, to the case of a propeller jet. Thus, it is demonstrated that ct assumes a constant value for given geometric characteristics of the propeller (as the theory states).