Maximizing the Operations of Compensated Fuel/Ballast Ships by Redesigning their Fuel Tanks and Fuel Systems

摘要

Compensated fuel/ballast systems are used by thernUS Navy in three of its combatant classes, as well asrnLHD 7, to maintain uniform trim and draft. In suchrnships, when fuel is consumed, it is replaced byrnseawater which is discharged overboard duringrnrefueling. The discharged compensating water mayrncontain concentrations of (fuel) oil in excess ofrnapplicable environmental regulations because thernhigh refueling rates and internal structure withinrncompensated fuel/ballast tanks promote fuel/waterrnmixing and entrainment of fuel into therncompensating water. In addition, water hideout,rnwherein water remains trapped in tanks whenrnrefueling is terminated, reduces fuel capacityrnsignificantly. The US Navy has undertaken anrnextensive research and development effort atrnCarderock Division, Naval Surface Warfare Centerrn(NSWCCD) to assess the current performance ofrncompensated systems during refueling operationsrnand to develop and propose improvements to theirrndesign which may be implemented in either existingrnor future ship classes. This paper describes therncomputational fluid dynamics (CFD) analysis andrn1/8-scale physical model experimental efforts tornassess the performance of the Arleigh Burkern(DDG 51) class of US Navy guided missilerndestroyer mid-group compensated fuel/ballast tankrn5-300-2-F. The amounts of water hideout, the timesrnfor the termination of refueling and mass fuelrndischarge, and two-fluid dynamics are compared forrnthe baseline point-to-point, point-to-diffuser, andrndiffuser-to-diffuser inlet-outlet piping configurationsrncommonly found in this tank. Results show thatrnbaseline configurations can have mass fuelrndischarge before refueling is terminated due tornnon-uniformities in tank filling. The tanks also haverna high potential for fuel/water mixing particularlyrnwhere buoyant jets impinge on the tank top. Variousrnmodifications to the tank structure and diffuserrnpiping have been assessed. Results show that waterrnhideout and problems with mass fuel discharge canrnbe minimized or eliminated with relatively minorrnmodifications to the structure. CFD results showrnthat these modifications can also reduce the potentialrnfor fuel/water mixing by eliminating buoyant jets.rnThe quantification of effluent fuel concentrationsrnduring refueling is the ultimate objective of thisrnproject. This capability is necessary to assessrnwhether modifications to existing tanks or designsrnfor new tanks comply with environmentalrnregulations. A series of fuel/water experiments, inrnwhich various compensated fuel/ballast tank flowsrnare isolated and studied in-depth, are beingrnconducted to provide the physical data necessary forrncomputational sub-model development. These datarnare being used to develop, validate and calibraterncomputational sub-models which parameterize fuelrndroplet formation, entrainment and advection.rnThese experiments and sub-model development arernsummarized.