Marine propulsion – Jet drive
Reexamination Certificate
2002-06-07
2004-02-17
Avila, Stephen (Department: 3745)
Marine propulsion
Jet drive
C440S047000, C415S191000
Reexamination Certificate
active
06692318
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the field of pumps, and in particular, to improved mixed flow pumps for marine propulsion and hydraulic applications.
BACKGROUND OF THE INVENTION
Conventional propulsors include numerous propeller, pumpjet and water jet propulsion devices. These devices are typically powered by an engine at a distance from the propulsor that is connected by a shaft to the propulsor. The engine is typically contained within a ship hull or pressure hull. Usually, a drive shaft extends from the engine through the pressure hull to the propeller, and bearings and a pressure seal are required to support the shaft and provide water-tight integrity for the engine and hull. These conventional propulsors contain motors that are located inside the pressure hull and that are directly coupled to a propeller that is located outside the pressure hull, with the flow being an external, rather than an internal flow.
Some examples of prior art patents include U.S. Pat. Nos. 6,273,768; 6,267,632; 6,203,388; 6,168,485; and 3,939,794. For example, U.S. Pat. No. 6,273,768 teaches that it is known to propel a boat or other watercraft using a water jet apparatus mounted to the hull, with the powerhead being placed inside (inboard) or outside (outboard) the hull. The drive shaft of the water jet apparatus is coupled to the output shaft of the motor. The impeller is mounted on the drive shaft and installed in a housing, the interior surface of which defines a water tunnel having a convergent nozzle. The impeller is designed such that during motor operation, the rotating impeller impels water rearward through the water tunnel and out the convergent nozzle. The reaction force propels the boat forward.
Conventional pumps include radial, axial, and mixed flow pumps. In a typical axial flow pump, the radial distance of a fluid particle from the pump centerline is constant from the pump inlet to the pump outlet. In radial and mixed flow pumps, the radial distance of a fluid particle from the pump centerline increases along the length of the pump because these types of pumps typically include a scroll or spiral type casing. Mixed flow pumps typically have a discharge that is perpendicular to the axis of impeller rotation.
A problem with conventional propulsors is that they typically do not include any flow conditioning of the fluid flow entering the pump impeller. For example, it may be desirable to condition the inlet flow to affect pump performance in some way, such as to reduce cavitation and improve acoustic performance of the propulsor, increase the head rise potential of the pump, and the like. Cavitation is generally undesired in conventional pumping systems because cavitation results in lost thrust and acoustic noise.
For example, U.S. Pat. No. 5,947,680 discloses turbomachinery with variable angle inlet guide vanes and variable angle diffuser vanes. However, the turbomachinery disclosed in U.S. Pat. No. 5,947,680 only teaches straight inlet guide vanes that are controlled in conjunction with the diffuser vanes to control the angle of the vanes to suit an operating condition. Also, the turbomachinery disclosed in U.S. Pat. No. 5,947,680 has variable geometry vanes, not fixed geometry guide vanes. This design is to adjust the performance to an optimum over a range of operating points and does not, for example, provide superior performance at one operating point. The device disclosed in U.S. Pat. No. 5,947,680 also includes a scroll discharge casing.
Another problem is flow conditioning of the outlet flow exiting the pump impeller. For example, in radial and mixed flow pumps, the rotating impeller imparts swirl to the flow as the impeller rotates and this swirl velocity decreases the pump performance.
Conventional propulsion pumps include various means for straightening the fluid flow exiting the impeller. For example, U.S. Pat. No. 4,427,338 discloses thrust control vanes for waterjets. The flow straightening vanes of the waterjets pump are designed to produce a low-pressure area, and the downstream side of the rotor drum is located inside the low-pressure area to eliminate the need for an axial thrust control seal. Also, U.S. Patent No. 4,929,200 discloses fixed flow-correction guide vanes positioned downstream of a rotating impeller. A number of gas injection slots are situated in the area of the trailing edges of the vanes for introducing a volume of gas into the flow in the tail pipe section of the pump in order to reduce internal drag resulting from pressure exercised by the water against the pump casing. U.S. Pat. No. 6,102,757 discloses a water jet propulsion device for a marine vessel having guide vanes provided in the water passage in the rear of the impeller for converting the guided swirl flows exiting the impeller into straight flows. U.S. Pat. No. 5,417,547 discloses a vaned diffuser for centrifugal and mixed flow pumps having two rows of radially displaced vanes to more efficiently convert the kinetic energy of the fluid flowing out from the impeller into static pressure. In addition, U.S. Pat. No. 5,480,330 discloses using a second impeller located rearward of a first impeller and which serve to straighten the rearwardly directed water flow.
Therefore, a need exists for a mixed flow pump having improved pump performance, reduced cavitation, and improved acoustics performance. The need also exists for a co-axial mixed flow pump.
SUMMARY OF THE INVENTION
The present invention is directed to a co-axial mixed flow pump system having one or more of improved pump performance, reduced caviatation, and reduced acoustic noise. The mixed flow pump includes an outer casing having a longitudinal centerline axis and a central body aligned co-axially within the outer casing along the longitudinal centerline axis. An axial forward looking inlet is formed along the longitudinal centerline axis for receiving a flow of fluid. A mixed flow pump having an impeller rotatably mounted to a forward end of the central body. The mixed flow impeller includes a hub, a plurality of blades extending outward from the hub, and a plurality of flow passages formed between adjacent blades. The mixed flow pump impeller rotates about the longitudinal centerline axis to draw a flow of fluid into the mixed flow impeller through the inlet and imparts energy to the fluid flow. An annular passageway is formed between the outer casing and the central body on a downstream side of the mixed flow pump impeller for receiving the fluid flow exiting the mixed flow impeller. The annular passageway is aligned axially. A plurality of stator vanes are disposed between and connecting the outer casing and the central body to condition the flow exiting the mixed flow impeller to flow generally in the axial direction. The mixed flow pump system also includes an axial rearward looking outlet formed along the longitudinal centerline axis for discharging the flow of fluid from the mixed flow pump system.
According to one aspect of the invention, the mixed flow pump, further includes an inlet section extending forward of the axial forward looking inlet. The inlet section has a distal inlet opening at a forward end and a length of inlet ducting connecting the inlet opening to the mixed flow pump impeller. In an alternate embodiment, the inlet section can further include a flush type inlet upstream of the axially aligned inlet to the mixed flow pump.
According to another aspect of the invention, the mixed flow pump can further include a plurality of inlet flow conditioning vanes disposed in the inlet section to condition a fluid flow flowing into the mixed flow pump impeller. The inlet flow conditioning vanes can be connected at a first end to the inlet ducting and extending into the inlet ducting to a distal end. The inlet flow conditioning vanes can comprise straight vanes attached to and extending radially inward from the outer casing into the fluid flow to eliminate any distortions in the fluid flow.
According to another aspect of the invention, the inlet flow conditioning vanes can comprise curved vanes
Avila Stephen
The Penn State Research Foundation
Woodcock & Washburn LLP
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