NICOP-ONR R&D PROJECT “Energy Efficient Contracted-Loaded Tip (CLT) Propellers for Naval Ships”
SISTEMAR has received a grant from the OFFICE OF NAVAL RESEARCH of the U.S. NAVY (ONR) to perform a two years R&D project on CLT propellers within the framework of the NICOP (National International Cooperative Opportunities in Science and Technology Program).
There are renewed worldwide interests in the energy-efficient contracted loaded tip (CLT) propellers due to steadily increasing oil cost and uncertain future of the oil supply. Reducing fuel consumption through increased propeller efficiency is an obvious means to reduce life cycle cost of ships. Propellers are designed to satisfy a host of requirements, including efficiency, cavitation inception, thrust breakdown, radiated noise, hull vibration, structural integrity, weight, and maintainability. Improving one performance metric, such as propeller efficiency, typically must be traded off against one or more other metrics, such as cavitation and noise.
One propeller concept which shows promise in increasing efficiency without sacrificing cavitation performance is the contracted loaded tip (CLT) propeller. The application of CLT propellers for naval ships would pose major challenges to the propeller designers due to different performance requirements. For example, naval ships may have more stringent cavitation performance requirements.
The objectives of this NICOP project are two-fold: (1) develop and demonstrate CLT-type propellers for naval ships that would improve efficiency by the comparable range demonstrated for commercial ships (i.e., 4-8%) over conventional open propellers without sacrificing cavitation performance, and (2) develop a scaling method for full-scale CLT propeller performance based on model-scale testing in the water tunnel.
Through collaborative efforts, SISTEMAR and NSWCCD will develop a set of design requirements for a new propeller design for a naval ship. These requirements will address tip vortex, suction side and root cavitation inception, required thrust coefficient, diameter, and pressure pulse severity. Once these requirements are set and agreed upon, engineers at SISTEMAR will develop a CLT design which meets these requirements using their standard practices while engineers at NSWCCD will do the same, using standard USN practices for propeller design.
SISTEMAR will act as project coordinator and will subcontract the work performed at CEHIPAR; both propeller models will be manufactured and tested in the variable pressure cavitation tunnel at CEHIPAR. Computations will be made both by NSWCCD and SISTEMAR/CEHIPAR for the two propeller designs using RANS methods at model and full-scale Reynolds numbers. Computational results obtained by two organizations will be compared in detail to understand the physics of tip flow of CLT-type propellers and the scale effects.
The US Navy has never built the CLT-type propellers. The NICOP efforts will provide the US Navy with an energy-efficient propeller concept for their consideration for retrofit or for new construction.