ADVANCED COMPACT WATERJET PROPULSION FOR HIGH-SPEED SHIPS
David R. Lavis1, Brian G. Forstell1 and John G. Purnell1
The paper describes the development and validation of a compact waterjet propulsion system for high-speed vessels. The development was conducted in four discrete phases: 1) Comparison ofWaterjet Types, 2) Pump Detail Design & Sealift Ship Concept Design, 3) Cavitation Tunnel Model Tests, and 4) Self-Propulsion Model Tests. The focus of the paper is on phases 2 and 3.
Waterjet; Propulsion; High-Speed Vessels; Computational Fluid Dynamics; Cavitation; Model; Tests
CDI Marine Systems Development Division (CDIM-SDD) (formerly Band, Lavis & Associates, Inc.)9th International Marine Design Conference 2006 Ann Arbor, MI, 16-19 May 2006
Symbol CFD D g GPM H Htot H0 IVR JVR Kram LDV NPSH Nss Q Qd RPM SHP UTIP Vaxial Vo φ ψtip Definition Computational Fluid Dynamics Impeller or Duct Diameter Gravitational Constant Gallons per Minute Headrise Pump Total Headrise Initial Headrise Inlet Velocity Ratio Jet Velocity Ratio Ram Recovery LaserDoppler Velocimeter Net Positive Suction Head Suction Specific Speed Volume Flow Rate Design Point Volume Flow Rate at Design RPM Shaft Rotational Speed Shaft Horsepower Impeller Tip Velocity Axial Inflow Velocity Craft Velocity Flow Coefficient (Phi) Pump Head Coefficient Units -ft ft/sec2 gal/min ft ft ft ------ft3/sec ft3/sec revs/sec horsepower ft/sec ft/sec knots Vaxial / UTIP 2gHtot / UTIP 2INTRODUCTION
High-ship speeds generally require the use of slender hullforms (to reduce the ship’s wave drag) and efficient, but compact, propulsion systems (to minimize the total installed power and installation space required). For this application, waterjets are often a preferred choice since: • • they have no appendage drag (with a flush-mounted waterjet inlet); and they have high efficiency(because they recover part of the ship’s frictional drag by ingesting the low momentum boundary layer at the waterjet inlet).
However, today’s commercially available large waterjets, above 10,000 horsepower, are large mixed-flow pumps. For these pumps, the installation flange diameter is 70 to 85 percent larger than the diameter of the inlet flow duct, and this large flange diameter is oftenincompatible with the slender hulls required for high-speed ships. Increasing the hull’s beam to accommodate the size and number of mixed-flow waterjets required could result in significant increases in drag, which leads to a spiraling increase in ship displacement and the power that must be installed. Axial-flow waterjet pumps, however, have installation flange diameters that are only about 15 to20 percent larger than the inlet duct and, since they are also much lighter in weight, they are a potential solution to this problem. Thus, in 2002, The Center for Commercial Deployment of Transportation Technologies (CCDoTT) of California State University at Long Beach funded CDIM-SDD for a four-year program to examine technology options and eventually to focus on the RDT&E to develop and validatecompact axial-flow pumps, as illustrated in Figures 1, 2 and 3.
9th International Marine Design Conference 2006 Ann Arbor, MI, 16-19 May 2006
Figure 1: Pump & Ship Design, Phases 1 and 2
Figure 2: Cavitation Test, Phase 3
Figure 3: Self-Propulsion Tests, Phase 4 The objective of this four-phase project for CCDoTT is to develop and validate the attributes of a preferred compactwaterjet propulsor suitable for high-speed sealift applications where waterjet propulsion is the only realistic choice. The four phases of the project are:
9th International Marine Design Conference 2006 Ann Arbor, MI, 16-19 May 2006 Phase 1: Exploration and Comparison of Waterjet Propulsion System Types, completed Aug. 02 Phase 2: Concept Design of Sealift Ship and Propulsion System, completed...