Numerical Investigation on Ship Podded Propulsion

2021

JMSE

Self Cite

The hydrodynamic effect exerted by a nozzle placed in front of a KP505 propeller on the propulsive performances is studied by using extensive numerical simulations. The influence of a NACA 0015 nozzle with a chord length of 0.3 of the propeller diameter, D, mounted at 0.2 D in front of the propeller plane is studied for a various range of relevant nozzle diameters and different angles of attack. A detached eddy simulation (DES)-based hybrid technique implemented on the ISIS-CFD finite volume solver of the Numeca’s FineTM/Marine environment is proposed to fit the purpose. Systematically conducted simulations have proven that the net thrust reflecting the overall drag, which includes the nozzle, depends on the duct size. The duct presence determines two regions of the inflow into the propeller. One is the inner region of the nozzle where the high-speed flow exists because of the contraction of the duct. The other is the outer region of the nozzle where the flow decelerates due to the duct wake. Lower- and higher-pressure coefficients on the suction and pressure sides, cover a significantly wider area than those of the case without the nozzle, leading therefore to greater thrust and torque. The existence of a critical attack angle for which the magnitude of the relative axial force becomes maximum for the smallest nozzle diameter has been noticed.

Section: Introductionmentioning

confidence: 99%

Energy-Saving Devices in Ship Propulsion: Effects of Nozzles Placed in Front of Propellers

2021

JMSE

Self Cite

Overall performances of a propeller operating near the free surface

IOP Conf. Ser.: Mater. Sci. Eng.

2020

The paper describes a numerical study on the effects of the interaction of the free surface with a marine propeller operating close to it, including the effects of the immersion on the cross flow. Extensive simulations using the ISIS-CFD naval hydrodynamics computational fluid dynamics solver are conducted to study the open water characteristics (POW hereafter), transient blade loads, and flow behavior around the DTMB 4119 three-bladed propeller, with comparisons to the fully submerged experimental data at two different immersions in respect to the undisturbed free-surface. Computations and experiments for the deeply submerged case show that the cross flow results in an increase of the energy spent and lower efficiency relative to the uniform inflow. Near the water surface, numerical solutions show that effects on thrust and torque increase significantly as the propeller load increases. Furthermore, the presence of the free surface breaks the symmetry resulting in highest blade force losses when the blade is near top dead center. As the propeller approaches the surface, not only the amplitude of the blade higher harmonics increases, but also the efficiency drops down.

Hydrodynamic loads and wake dynamics of a propeller working in oblique flow

IOP Conf. Ser.: Mater. Sci. Eng.

2020

Most of the small crafts and navy ships are equipped with propellers mounted on inclined shafts as thrusters. In spite of its importance, the information on the forces generated by inclined shaft propellers is scarce. To help the designers of small craft and navy ships, the present research describes a systematic numerical program undertaken to evaluate the propeller performances when inclined in respect to the oncoming flow. Scale resolved incompressible Detached Eddy Simulation (DES hereafter) or Delayed Detached Eddy Simulation (DDES) technique are employed by using a volume of fluid approach to study the four-blade propeller recommended in 2015 Tokyo Workshop on CFD Ship Hydrodynamics for the ONR tumblehome ship model 5613. A series of three working conditions are numerically analyzed over a range of shaft inclinations and advance coefficients. Besides, the usual shaftline thrust and torque, horizontal and vertical side forces are computed. The results of these simulations confirm the expectations that a propeller mounted on an inclined shaft produces less thrust than the same propeller on a horizontal shaft. This paper contains propeller characteristic curves and lift- and side-force data which are directly applicable in the design of both high-performance small craft and commercial ships.