This paper presents the results of flow measurements in the nozzle opening of ducted propellers operating in both open and behind conditions. The open-water test measurements show the propeller induced velocities in nozzle opening differ from the results from conventional propeller measurements. It is shown that both can be correlated to the induced velocity calculated from momentum theory.

This correlation is expressed as a function of a modified advance coefficient which enables the results of propellers with a wide range of pitch/ diameter ratios to collapse into a single curve. This approach gives an accurate estimate of the effective speed of advance and/or the effective wake fraction of ducted propellers operating in the behind condition using the propeller thrust identity to interpret the open water propeller curves.

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