Ship

Details Ship Ship

1996-11-25

1998-05-19

Sotelo, Jesus D.

Marine propulsion

Screw propeller

Having means to control flow around propeller

416189, B63H 116

Patent

active

057528659

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a ship equipped with a circular nozzle in front of a propeller of the ship to improve the propulsion performance of the ship.


BACKGROUND ART

Circular nozzles respectively mounted in front of the ship's propeller include a wedge-shaped one 3a as shown in FIG. 9 and a trapezoidal one (not shown) when they are viewed from a side.
The nozzle, particularly the one shown in FIG. 9, can reduce the development of three-dimensional separated vortices broken out from bilges on both sides of a hull to concentratedly settle the flow portion having a large wake coefficient w (w=(Vs-Va)/Vs) flowing into the region in the proximity of the upper part of the propeller disc area.
The nozzle can decrease the hull resistance and can improve the propulsion efficiency .eta. (.eta.=.eta..sub.h .multidot..eta..sub.o .multidot..eta..sub.R). Here, V.sub.s is the speed of the ship, and Va is a propeller inlet velocity .eta..sub.h is called a hull efficiency, and is given by
.eta..sub.o is the open propeller efficiency in the state that the influence of the hull does not exist. .eta..sub.R is called a relative rotative efficiency, and is the ratio of the propeller efficiency to the open propeller efficiency .eta..sub.o in the state the propeller operates in the wake near the stern. Further, the symbol t is the thrust deduction fraction.
In order to allow the nozzle to display its performance described above, a circulation .GAMMA. acting on the nozzle is increased. As shown in FIG. 10, to increase this nozzle circulation .GAMMA., the angle of attach .alpha. of the flow flowing into the nozzle 3a is increased and the chord length L of the nozzle 3a is increased, too.
In the recent full-bodied ships, however, the wake has a flow distribution on the propeller disc area as shown in FIG. 11, and the in-plane flow in the propeller plane has a direction shown in FIG. 12.
In the case of a wedge-shaped nozzle 3a shown in FIG. 9, therefore, the flow has a distribution having an angle of attack .alpha. and a velocity Va at the nozzle leading edge LE (refer to FIG. 10), as shown in FIG. 13. The abscissa of FIG. 13 represents the angle in the nozzle circumferential direction, when the angle is measured clockwise when the nozzle is viewed from the bow from the position of 0 o'clock when the nozzle is looked on as a clock. It can be seen from FIG. 13 that the field of flow is symmetric with respect to the line representing 180.degree..
The propulsion force F.sub.N acting on the nozzle is the sine component of the angle .beta. of the lift L.sub.N acting on the nozzle as shown in FIG. 10 and is expressed as
On the other hand, the lift L.sub.N is proportional to the circulation .GAMMA. of the nozzle, and the circulation .GAMMA. is proportional to the angle of attack .alpha. and the chord length L of the nozzle.
Therefore, the propulsion force F.sub.N acting on the nozzle is:
A frictional resistance Df also acts on the nozzle section. This frictional resistance Df is written as
The force F.sub.T acting on the nozzle is given by .multidot.L.ident.A.multidot.Va.sup.2 .multidot.L
In the above equation, C.sub.1 and C.sub.2 are proportional constants.
In order to improve the propulsion efficiency .eta., therefore, it is understood that the chord length L of the nozzle must be increased at the part at which the angle of attack .alpha. is great and A is positive, and must be decreased at the part at which the angle of attack .alpha. is small and A is negative.
FIG. 14 shows the distribution of the force F.sub.T acting on the wedge-shaped nozzle shown in FIG. 9. When the diameter of the aft end of the nozzle becomes smaller than the diameter of the propeller, however, the distribution of the angle of attack .alpha. and the flow velocity Va at the fore end of the nozzle becomes the ones shown in FIG. 15, and the force F.sub.T acting on the nozzle becomes the one shown in FIG. 16.
As shown in FIGS. 14 and 16, the nozzle becomes a resistance near 90.degree. and 270.degree. measured from the nozzle apex 0.degree. in the

Affiliated with

Also associated with

Rating

Ship does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Ship, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ship will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1847849