A Design Method and an Application for Contrarotating Propellers

A design methodology for contrarotating propellers bas been developed based on rational hydromechanics. Three fundamental principles need to be satisfied: momentum, mass, and circulation conservation. Momentum conservation requires the net force generated by the contrarotating propeller to be balanced by the drag of the bare body and the drag due to hull-propulsor interaction. Mass conservation determines the circulation distribution of the aft propeller once the forward propeller circulation distribution is specified. Circulation conservation determines the magnitude of the circulation distribution of the aft propeller to ensure the proper thrust and torque ratios. The effects of the hub boundaries have been taken into account in the design and analysis methods. A contrarotating propeller set was designed for uniform flow at the operating point of the propeller for a high-speed surface ship. Open water results show that the performance predictions agree well with the measurements.