US3385374A - Marine propeller - Google Patents

Description

May 28, 1968 P. KAPLAN ETAL 3,385,374

MARINE PROPELLER Filed Jan. 23, 1967 5 sheets-sneek 1 May 28, 1968 P. KAPLAN ETAL 3,385,374

MARINE PROPELLER Filed Jan. 2s, 1967 s sheets-sheet a ff fame Thrust Farce Flc-5.2

Bray Farce FIG.3B

lNvENToRs- Paz/Z Kapla BY Huff/.sf Zeman Hyg/yay Afro/wins May 28, 1968 P, KAPLAN ETAL MARINE PROPELLER 3 Sheets-Sheet 5 Filed Jan. 23, 1967 FIG.6

INVENTORS United States Patent O 3,385,374 MARINE PROPELLER Paul Kaplan, Jericho, and August F. Lehman, Centerport, N.Y., assignors to Oceanics, Inc., Plainview, N.Y., a corporation of Delaware Filed Jan. 23, 1967, Ser. No. 616,999 4 Claims. (Cl. 170-135.4)

ABSTRACT OF THE DISCLOSURE A marine screw propeller having internal ducting connected to a huid-pressure source by means of which lluid is discharged as a jet sheet at a predetermined velocity and angle from critical locations on the blade surface in the area of the trailing edge. The parameters of the blade and jet are so arranged that a condition of super-circulation is induced resulting in a lift force which exceeds the theoretical maximum obtainable due to camber and angle of attack.

Many attempts have been made to improve the efciency of propellers, particularly when the propeller develops high thrust. Due to the occurrence of cavitation or the separation of the water from the blades, or a cornbination of both, there is a limitation on the thrust and etliciency which can be normally obtained under any given operating conditions. For any given propeller geometry, rotational speed, inflow velocity and depth of submergence, there is, in addition to a predetermined relation between thrust and eliciency, a maximum thrust beyond which the propeller can not be operated without the occurrence of the adverse eiects of separation and/ or cavitation.

It is an object of the present invention to provide an improved marine screw propeller and propeller system, capable of operating with higher thrust and eiliciency than are attainable under present techniques and designs.

It is another object of the invention to provide a method for achieving super-circulation conditions in a marine screw propeller.

Still another object of the invention is to provide a marine screw propeller design which can be made structurally strong without making it susceptible to cavitation and decreased eiciency.

In accordance with the present invention, increased thrust and eiciency are obtained from marine screw propellers through the control of the pressure distribution on the blades by inducing a condition of super-circulation, which is defined as a means of developing a lift force which exceeds the theoretical maximum attainable with any given propeller blade geometry by virtue of changes in camber and angle of attack. By discharging a jet of predetermined size and velocity, and at a predetermined angle from critical locations on the blade, super-circulation is attained which enables the blade to operate at high ciciency and thrust.

In accordance with one embodiment of the invention, the propeller is driven by a combination of torque applied to the propeller shaft and by the torque developed by the jet momentum reaction which occurs as a result of the discharge of jets from the trailing edges of the blades. Propellers driven by drive shaft torque 'or jet momentum reaction generated by fluid discharge from the blades, as well as a combination of the two, are known in the art. In all cases, however, the total lift force which can be generated by the blades is limited by the phenomena of cavitation and/or separation of the liquid operating medium from the surfaces ot' the blades. The present invention utilizes a jet discharge in the form of a jet ap in the vicinity of the trailing edges of the blades which is critically shaped in width, length, angle of discharge, and veice locity, to induce super-circulation, in addition to the benefit which results incidentally from the jet momentum recovery of the jet. There results augmented thrust without the danger 0f a decrease of eliciency resulting from cavitation or separation associated with high blade loadings. This is achieved with the jet ilap by modifying the chordwise pressure distribution of the foil so as to reduce the pressure peaks occurring with normal distributions while increasing the overall load developed by the pressure distribution profile.

Preferred embodiments of the invention, as well as other features and advantages thereof, will be understood from the following specification taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a view of one of the blades and a portion of the hub of a marine screw propeller in plan view, i.e., looking in the direction of the drive shaft of the propeller;

FIGURE 2A is a chord section view in enlarged scale of the blade, taken on the line 2 2 of FIGURE 1 looking in the direction of the arrows, showing the lift and thrust force vectors of both the foil eiiect and the jet-induced super-circulation effect, the latter vector including a relatively small jet momentum reaction component;

FIGURE 2B is a partial chord section similar to FIG- URE ZA but in larger scale to illustrate the jet slot width limits;

FIGURE 2C is a chord section view corresponding to FIGURE 2A showing the lift and thrust yforce vectors of a propeller in which there is a jet discharge aligned with the nose-tail line of the blade section so that super circulation does not occur although the jet momentum reaction torce remains;

FIGURE 3A is a diagrammatic view of a chord section of a blade or foil showing, superimposed thereon, a plot of the pressure distribution which occurs when the blade is driven at incidence without the present invention;

FIGURE 3B is a view of the blade of FIGURE 3A, showing a plot of the upper surface pressure distribution utilizing a jet ilap deflection in accordance with the present invention;

FIGURE 4 is a View in longitudinal section of the stern of a ship taken through the axis of the drive shaft and including a propeller and drive shaft assembly embodying the present invention;

FIGURE 5 is a view in horizontal section through the stern of the ship of FIGURE 4, illustrating one representative mechanism for introducing fluid under pressure into the propeller blades; and

FIGURE 6 is a plan or full-face view, looking the direction ofthe axis ofthe drive shaft of the propeller of FIG- URE 4 and having one of is four blades illustrating internal ducting by a section passing through all of the chord lines of the blade.

Referring to the drawings, the invention is illustrated as embodied in a marine screw propeller 10 (FIGURES 4 and 6) attached to a hollow tail or drive shaft section 11 in a ship 12 (illustrated only diagrammatically to show the underwater portion of the stern). One of the blades 19a of the propeller lil is illustrated in enlarged scale in FIGURE 1 and in still larger scale in FIGURES 2A and 2B.

IEach of the four blades, 10a' b, c and a' of the propeller 10 includes internal ducting of the type indicated generally by the numeral 13 in the blade section 19a. For purposes of tlow control, the ducting 13 is preferably divided into discrete ducts 13a, b and c by means of contoured inner partitions 14a and b, terminating at the trailing edge 1S of the blade in an elongated discharge opening or series of openings 16, best seen in FIGURES 1 and 6, adapted to discharge a iluid jet sheet I (FIGURE 4) from the surface of the blade opposite the suction or low pressure side of the blade. The inner hub openings and the iluid passageways are so designed so as to control the exit velocity of the uid at the trailing edge. It will be observed that the slot 16 extends over a substantial length of the trailing edge of the blade from a point near the central hub 17 to a point near the blad-e tip to approximately the 0.85 radius of the blade.

The drive shaft section 11 to which the propeller 10 is affixed is hollow and includes, in its portion disposed within the propeller, radial ports or openings I8 which place the interior conduit Ila of the shaft 11 in communication with the ducts 13a, b and c of each of the blades. In accordance with the invention, the jet velocity at any given point along lthe length of the jet ap discharge J should exceed the magnitude of the local water velocity at the particular point. Thus the sizes of the ports `1'8 as lwell as the sizes of the ducts t13a, b and c can be selected and arranged to achieve this result. The low path from the interior of the shaft l1 into each of the blades is further controlled by a tapered plug 18a.

The drive shaft il, between the main propulsion motor (not shown) of the ship and the propeller, passes through a stationary collector box 19 having seals 19a and 1913. The collector is connected by suitable conduits 20 and 21 to the output sides of pumps 22 and 23, the pumps having their input sides connected by conduits 24 and 25 to suitable openings in the ships hull beneath the water line, preferably at points having high pressures. The hollow drive shaft section 11, within the collector box 19, is formed with radial openings 26 communicating with the hollow interior. A contoured plug 27 can be included within the hollow shaft within the collector 19 to promote uniform flow.

In operation, torque is applied to the drive shaft in the conventional manner by means of the main propulsion engine and, in addition, uid is pumped through the ducts 113 and out of the slots 16 in a jet flap. The pumps 22 and 23 are used to supply and to adjust 4the ow rate of the jets to the optimum value, recognizing that some pumping action will occur automatically, as the propeller rotates, due to the centrifugal force generated by the turning propeller.

The function of the jet flap emitted from the slots is so arranged in its shape, positioning and flow rate, in accordance with the present invention, that super-circulation is induced. The concept of circulation is the basis of airfoil and propeller blade theory. Assuming a finite span foil, the lift per unit length of span varies directly with circulation. Lift is expressed as follows:

wherein L equals lift, p equals mass density of the fluid, V equals fluid velocity, and I equals circulation. Normally the total lift force which can be obtained is limited by the adverse effects of cavitation and separation which occur when certain pressure distributions over the foil exist. Super-circulation is a term used to describe the creation of a large lift force by increasing the pressure distribution magnitude over the foil surface through an increase in I over and above the I which can normally be induced. In the case of the jet ilap produced in accordance with the present invention, there is a significant augmentation of the total resulting lift relative to the lift increase resulting from the jet momentum force alone.

Referring to FIGURES 3A and 3B, it will be seen that the pressure distribution on a foil due to super-circulation induced by the jet iiap (FIGURE 3B) differs considerably from that created by the foil at incidence (FIGURE 3A). In the case of the pressure distributions resulting from the jet ilap, it will be seen that a total lift force from the pressure distribution is achieved without the pressure peak associated with the generation of the same total lift through foil incidence. The limit of the maximum thrust obtained with incidence, camber, or both, is exceeded significantly by -the jet flap induced super-circulation effect. Also, the reduction in the maximum pressure peak magnitude for the case of the jet flap pressure pattern acts to inhibit the possibility of separation as well as the susceptibility to cavitation.

Referring now to FIGURE 2A, the jet ilap is discharged at an angle 1- to the nose tail line of the blade 10a. The angle 1- is illustrated as being approximately 30 degrees, although as described below it can vary over a range of angles. It should be noted that there is a component of the jet momentum which reacts in the direction of rotation of the blade and a component which acts in the direction of travel of the vehicle. The latter component less the drag loss constitutes a net thrust gain of relatively small magnitude and is insignificant for practical and achievable ilow rates that would yield etiicient operation. U.S. Patent No. 2,511,156, discloses a marine screw propeller in which this reaction component is utilized to augment the thrust of the propeller. The component in the direction of rotation of the propeller is also insignificant for practical and achievable ow rates. This force has also been used in the prior art as a means of driving the propellers and is described in U.S. Patent No. 2,705,- O51. These two effects which necessarily result in the practice of the present invention are, as stated, relatively insignicant when reduced 4to practice.

The lift force to which the present invention is directed is that indicated by the vector bearing the legend Additional Lift Due to Super-Circulation. To achieve supercirculation:

(a) the width of the jet ap or stream,

(b) the angle of the jet flap or stream,

(c) the velocity of the jet Hap or stream, and

(d) the radial location on the blade of the jet flap or stream,

are interrelated and must be coordinated. In accordance with the invention, the thickness of the jet sheet, i.e. the slot width, must be between approximately 0.005 and 0.03 of the blade chord as shown in FIGURE 2B; the jet stream angle must be between approximately 15 and 75 degrecs from the nose tail line of the blade prole at each particular radial section of the propeller as shown in FIGURE 2A; the velocity of the jet stream must be greater than the resultant water velocity at each parti-cular radial section of the propeller; and the majority of the jet stream must be emitted between the blade root and approximately the 0.85 radial section as shown in FIGURE 1, with the jet slot being located in the region of the trailing edge of the blade or inward up to a distance of 0.15 chord as also shown in FIGURE 2A. While any combination of the above parameters will induce some degree of super-circulation about the blade, it will be understood that for a particular propeller design the parameters can be optimized to achieve a loading per unit area of the blade which can be increased tive to ten times over conventional average design loadings (loadings obtainable without the jet ap action) without increasing cavitation susceptibility. The driving torque of the propeller is supplied by the main drive shaft and the increase in thrust loading is achieved without a corresponding increase in shaft torque. Thus, the eiciency of the propeller is increased for any given required amount of total thrust.

While the invention has been described above having reference to preferred embodiments thereof, it will be understood that it can take various other forms and arrangements within the scope of the invention. Thus, for example, the means for supplying fluid to the ducts within the blade can be widely varied, as can the geometry of the blades and the internal ducting. Also, while the jet fluid used in the embodiment of the invention described herein is water, other liquids can be used as can gasses such as steam, air, machinery exhaust gas and the like. The invention should not, therefore, be regarded as limited except as defined by the following claims.

We claim:

1. A marine screw propeller comprising a hub portion and a plurality of blades extending radially therefrom, each having a curvilinear foil surface, fluid duct means in the blades, and uid discharge openings disposed adja- -cent the trailing edges of the blades and disposed primarily in the space between the blade root and the'0.85 radial section of the blade to discharge fluid from said duct means in a shaped jet stream, said iluid duct means having inlet means communicating with said hub portion, said openings being shaped and arranged to direct the jet stream at an angle of between approximately 15 and 75 degrees to the nose-tail line of each radial profile of the blades and in a direction having a component opposite to the direction of thrust of the blades, and means to pass iluid through said duct means from the openings at a velocity greater than the resultant water velocity at each radial section of the blade, and having a predetermined magnitude to achieve predetermined local loading thereon and to establish super-circulation about the blades.

2. Apparatus as set forth in claim 1, the width of the openings being between approximately 0.005 and 0.03 of the blade chord.

3. Apparatus as set forth in claim 1, said duct means in each blade comprising a plurality of generally coplanar ducts separated by internal partitions, and ports in the hub communicating with the ducts, with the said duct and port dimensions and contours controlling the uid discharge velocity along the length of shaped jet discharge.

4. Apparatus as set forth in claim 1 said discharge openings being disposed on the side of the blade Opposite the suction surface and in the space within a distance of approximately 0.15 chord length from the trailing edge.

References Cited UNITED STATES PATENTS 736,952 8/1903 Fox 170-172 1,119,178 12/1914 Krantz 170--172 X 1,190,755 7/1916 Hahn 170--172 2,169,325 8/1939 Novak 170-172 X 3,109,495 11/1963 Lang.

3,209,714 10/1965 Bowles.

FOREIGN PATENTS 505,082 8/1954 Canada.

774,396 5/ 1957 Great Britain.

124,583 4/ 1949 Sweden.

EVERETTE A. POWELL, I R., Primary Examiner.

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