Patent Application
20070292278
The present invention is directed to an axial flow pumping device and method, as well as an application thereof to achieve efficient marine propulsion.
In a multistage axial flow pump having two or more impeller stages, a certain amount of energy is transferred from a power plant to working fluid (e.g., water) at successive stages. Pressure is essentially stepwise increased at the succeeding stages until discharge of the working fluid through an outlet nozzle whereby to generate thrust. Increased pressure inside the pump suppresses damaging cavitation that may otherwise act upon the impellers. An axial flow pump differs from a more voluminous centrifugal or mixed-flow pump that is generally limited to single stage. Thus, an axial flow pump, if properly designed, may have a higher power density than conventional pumps. Apart from use in marine propulsion, other applications of the present invention include high volume pumps for fire or flood control, irrigation, and in large cooling towers requiring extremely high volumes or pressures.
In marine applications, design parameters of the propulsion pump are ideally matched with engine torque and speed, i.e., the engine power or performance curve. Most engines, however, have only a single optimum operating speed that delivers peak horsepower and another single operating speed for peak efficiency, which may not optimally match the desired thrust and/or hull speed of the vessel. Such desired hull speed or thrust generally varies with vessel loading, sea state conditions, and/or temperature and density of the ocean. Thus, certain inefficiencies inherently exist in conventional engine-propulsor combinations during operation of a vessel.
To compensate for such inefficiencies during the desired operating condition, it has been known to vary the pitch rotor blades in a pump's impeller section according to optimum torque, speed, or fuel efficiency of the engine. It is also known, but not necessarily applied to marine propulsion, to include fixed stator vanes between impeller sections of a multi-stage pumping device to counteract whirl or rotational velocity that rotor blades impart to the fluid, such as that disclosed by U.S. Pat. Nos. 5,755,554 and 5,562,405 (both issued to Ryall). The stator vanes has the effect of redirecting fluid flow to achieve a desired angle-of-attack of fluid acting on rotor blades in the succeeding stage, but such prior stator vane designs significantly increased internal friction. Ryall, for example, provides a substantially constant absolute velocity in flow passages between fixed stator blades. Due to their geometric structure, prior stator vane designs endured losses in efficiencies and generally operated, at best, around 65 to 72% propulsive efficiency.
The present invention, in part, takes advantage of the relationship between static and ram pressure, that is, the fact that the total pressure at within the pumping device (as well as at the pump's intake and discharge) comprises the sum of hydrostatic (static) of the pumped fluid plus the impact (ram) pressure imparted to the fluid by the impellers. It is also known the extent of internal frictional losses, due to barrier layer effects of the fluid transgressing internal components of the pump, increases exponentially with fluid speed. At the pump inlet, a diffuser may be used to alter static pressure before water enters the impeller section. Also, it was not heretofore known, among other things, to alter the static pressure component of total pressure between rotor stages (by impeller design or geometric shape of the pump housing); to provide a low pressure booster for pumping mechanism; or to provide variable pitch stator vanes or a variable inlet guide vanes that mechanically reconfigure the pump to compensate for variations or operating characteristics of the power plant, desired mission profile, ship velocity or loading, water density or water temperature changes.
Thus, one aspect of the invention comprises a multistage axial flow pump that includes an outer housing, a substantially annular chamber within the housing that conveys working fluid (e.g., water) from an inlet to an outlet, multiple stages within the chamber that may each include a rotor section and a stator section. Stator vanes in the stator section may be fixed relative to housing and have a geometrical shape to define a fluid flow path having a cross-sectional area that increases as the fluid transgresses the stator section in the downstream direction whereby to increase static pressure. Optionally, variable internal geometry may be provided to reconfigure the pump parameters to match desired operating conditions of a vessel. For example, the stator vanes may optionally have variable pitch and the chamber may optionally include a variable nozzle having a discharge area (i.e., throat) that is controlled to optimally match the water jet discharge speed with the vessel speed. In yet a further aspect of the invention, a set of variable inlet guide vanes controls inlet fluid flow by changing the inlet area and/or whirl angle of incoming fluid. Such variable geometry enables the propulsion device to match a wide range of prime movers of different power.
The invention also includes a method implemented by the pumping device. One aspect of the method includes providing an actuator that varies the throat area of the discharge nozzle, detecting respective pressures associated with the discharge velocity and speed of the vessel, and using the respective pressures to drive the actuator to an equilibrium position that defines a desired optimum throat area of the discharge nozzle according to the instantaneous speed of the vessel. Other aspects are set forth in the claims.
In another aspect of the present invention, it was recognized that if a trade-off is made between static and ram pressure by increasing static pressure and reducing ram pressure using a diffuser-type annular chamber between stages of a multi-stage pumping device (with total pressure remaining constant), inherent frictional losses can be significantly lowered since friction exponentially decreases with fluid speed. This results in a more efficient propulsion device. Thus, an aspect of the invention also comprises a multi-stage pumping device, such as that described in U.S. patent application Ser. No. 10/801,705, having diffuser-like chamber between stages to control static and ram pressures according to desired a relationship. Construction of either the housing or the annular chamber may be varied where the effective area of the chamber in a direction normal to fluid flow is progressively increased or decreased. The height of the stator and rotor blades is correspondingly varied according to the height (clearance between the shaft wheel and housing) within the annular chamber.
Other aspects of the invention are pointed out by the appended claims.
Concatenated wheels are driven in unison by drive shaft 20, which may be coupled to any one of a number of conventional engines. Mounting flange 24 couples device 10 to a fluid conduit that supplies working fluid to device 10. Forward and aft sets of thrust bearings 15 and 17 support the shaft along axis 13 within casing or housing 12. Thrust bearings 15 and 17 also absorb or counteract a relatively large opposing axial force between housing 12 and shaft 20 developed by multiple rotor sections during operation of the device. Preferably, each of the rotor blades 30, 32, and 34 radially extends from axis 13 of an associated rotating wheel to a given design height, width, thickness, and twist angle so as to impart maximum energy to a working fluid.
Stator vanes 40, 42, and 44 lay in respective stator sections following respective rotor sections but instead are fixedly attached relative to wall 11 of the casing or housing 12, rather than being attached to a rotating wheel. Vane design is similar to the blade design of the rotors. Stator vanes 40, 42, and 44 serve to redirect and/or diffuse the flow of working fluid from the rotor blades, e.g., rotor blades 30, 32, and 34, in the preceding section. In operation, rotor blades impart energy to the working fluid by accelerating fluid in a partial tangential and partial axial direction relative to axis 13, thus increasing the ram or impact pressure of the fluid as it enters the next stage. The stationary vanes redirect the working fluid in an opposed tangential direction, e.g., to counteract whirl imparted by the preceding rotor section, as the fluid flows in annular chamber 19 along axis 13 towards outlet 18.
According to an important aspect of the invention, the stator vanes are arranged to effectively reduce the velocity of the working fluid but retaining total pressure therein by providing an expanding area between vanes as fluid flows through the stator section. In part, this is accomplished by providing, in embodiments illustrated in
Preferably, device 10 has three or more stages although two stages may also suffice. Each rotor section may or may not include a subsequent stator section. Fluid enters the next or succeeding stage at essentially the same total pressure of the fluid being discharged from the preceding stage. The rotor sections impart additional pressure to the fluid at each stage. Stepwise increases in pressure is repeated as many times as necessary to attain the desired design point pressure at region 21, which supplies pressurized fluid to an annular discharge nozzle. The discharge nozzle includes an axially variable plug 60 that controls the size of the area of throat 28 between deflector 52 and plug 60. Preferably, region 21 defines an annular nozzle that is convergent to eject water at an increased velocity thereby generating propulsive thrust. Thrust, which can be measured in pounds, equals mass flow times velocity.
In a preferred embodiment, the size or area of throat 28 in the annular discharge nozzle is variable and controllable, and may be used to trim the water jet discharge velocity to maximize boat velocity.
Inlet 16 of device 10 preferably includes a series of inlet guide vanes 46 that serve to control, redirect, or throttle incoming fluid flow and/or to change the angle of attack of incoming fluid. This alters the load on the rotor blades in the first stage of device 10. Due to differential cross-sectional areas of inlet duct 26, the velocity of water at entry into the inlet duct is lower than the velocity of the water entering the casing of device 10. In the inlet duct, there is a transition section 23 from larger to smaller area so that the difference is not so abrupt as to cause losses from eddies thereby maintaining streamline fluid flow. A principal embodiment of the invention does not require inlet guide vanes 46 in the first stage although other embodiments do. In a fixed inlet guide vane embodiment, the vanes direct water flow into the first rotor-stator stage 30, 40 at a prescribed angle and function as a flow director. In an embodiment utilizing variable inlet guide vanes, i.e. variably controlled vanes actuated by actuator ring 48 and actuator 47, the flow angle of water entering the first rotor stage of blade 30 is variable. This not only changes the incidence angle of the working fluid entering the pump but also changes the amount of flow and therefore the inlet guide vanes function as a throttling mechanism. Thus, guide vanes 46 provide mass flow throttling of the working fluid, and include control linkage to rotate the vanes 46 about ±30° from a neutral position according to a desired mass flow rate.
At the discharge end of device 10, the axial position of nozzle plug 60 is controllable to effectively open or restrict the water jet throat area 28. When plug 60 is extended, as shown in
When deployed in marine applications, steering may be accomplished by redirecting the water jet at the discharge nozzle. In the embodiment of
In an alternative design, rather than providing an effective area of annular chamber 216 that progressively decreases in the downstream direction, the effective area of the annular chamber in the downstream direction may increase (rather than decrease) while transgressing the rotor-stator sections and then merge with a region 217 in a less abrupt transition. Such alternative design may be accomplished by varying the blade height or housing geometry, as explained in the earlier embodiment. Thus, the invention embraces various geometrical designs that take advantage of diffuser designs to trade off static and ram pressures, while maintaining constant total pressure, to improve efficiencies of a multi-stage axial flow pumping device.
In the exemplary embodiment of
Instead of using a segmented vane structure, vanes 80, 82 may take on the form 86, as depicted in
The material of the vanes and stator may comprise any of a variety of materials known in the art such as titanium, bronze, a high carbon stainless steel, a composite material, or other material that is preferably non-corrosive and/or adapted for marine applications.
In addition, there is provided a “fixed pitch” exit guide vane 84 (
As apparent from the illustrated actuating mechanism, control of the stator vanes and the inlet guide vane 46 occur in unison for simultaneous pitch angle changes. Pitch angle changes alter the angle of attack of, and hence, the torque applied against or energy delivered to the working fluid by the rotor blades of the following section. Each rotor section thus stepwise increases the energy imparted to the working fluid. Control of the inlet guide vanes of ring 124 may, however, be separated from control of the stator vanes of rings 120 and 122. As control arm 104 axially translates, linkage 110 pivots about pivot point 111 to advance and retract turnbuckle 112, which drives control ring 124 via flange 126. Control ring 126 couples the shaft of inlet guide vane via actuating arm 150. Preferably, actuator 100 is controlled in a way to attain peak power output or peak propulsive efficiency of the pumping device as working fluid enters the inlet 16.
Thus, according to the structure of
Thrust T=W/g*(Vj−Vb) (1)
where thrust T=mass flow rate in weight of working fluid (i.e., water) per unit volume per second, g=gravitational acceleration constant (e.g., expressed as 32 ft/sec2), velocity Vj=exit velocity of the fluid jet at the discharge nozzle, and velocity Vb=exit velocity of the vessel relative to the water. The exit velocity exerts a dynamic pressure Pd equal to ½ the density Rho of the working fluid times the velocity squared divided by two times the acceleration of gravity, or
Pd=(Rho*V2)/2g (2)
It is known that dynamic pressure Pd at the discharge nozzle is directly proportional to the velocity squared V2 of the fluid. Propulsive efficiency (Np) equals the useful thrust output divided by the combination of useful thrust output and losses (e.g., frictional losses). So, if Vb represents the velocity of boat and Vj represents the velocity of the water jet at the discharge nozzle, then the Absolute (or effective) Discharge Velocity Va equals Vj−Vb. Therefore, propulsive efficiency
Np=((W/g)*Va*Vb)/{(W/2g)*(Vj2−Vb2)} (3)
Simplifying the expression of Np, then
Np=2/(1+Vj/Vb) (4)
Therefore, it is seen that the propulsive efficiency Np is indirectly proportional to the ratio of the water jet and boat velocities. Propulsive efficiency Np is also proportional to the ratio of the dynamic pressures generated by the jet and boat velocities, i.e., Np=Pd(jet)/Pd (boat). Using equation (4) above, the propulsive efficiency Np is 67% for a hull design speed of 30 knots at a water jet speed of 60 knots.
A balance in the opposing forces is achieved when the individual products of pressure and area equalize, which drives piston 202, and consequently nozzle head 200, to an equilibrium position (e.g., from position indicated by phantom nozzle 201) thereby providing a mechanism and method to optimize water jet speed for a given boat speed, assuming the operator has knowledge of characteristics of the boat, e.g., optimum hull speed. In mechanical construction, the diameter d of neck 205 defines the areas of respective surface 203a and 204a, which due to their respective areas automatically effects equilibrium at the appropriate nozzle head position. In the exemplary device, the area of surface 203a is 1.88 times the area of surface 104a.
To automatically control or override the pressure-driven equilibrium position of nozzle head 200, automated computer control may be implemented to actuate servos according to sensed pressure at pitot tubes 210 and 212, or conventional transducers and amplifiers may be deployed to produce appropriate control signals to drive a servo or actuator. Instead of using pitot static pressure, the axial position of nozzle 200 in larger propulsion devices may be electrically or hydraulically actuated. In addition, a pressure regulator may be interposed on either or both lines 211, 213 (or elsewhere) to alter the equilibrium position of or control piston 202.
The illustration of
V1/V2=1.15 to 1.0 (5)
Due to a decreasing area of the flow path between the inlet guide vanes 412, 414 and 418, which define the respective flow paths, the velocity of the working fluid for a given mass flow rate increases as it flows through section 408. As seen, the cross-sectional area between inlet guide vanes 412 and 414 decreases in downstream direction 416 because the vane geometry provides a wider width W1 at its section entry and a narrower width W2 at its section outlet. The cross-sectional area of the flow path between vanes is measured by width multiplied by vane height, assuming the guide vanes have the same twist angle and constant height throughout the section. As measured in a plane normal to flow path 400, the area of the flow path between the vanes decreases in the downstream direction. According to an aspect of the invention, the flow path area between the inlet guide vanes can be altered by changing the pitch angle of the inlet guide vanes, as shown by exemplary vane 418, for example.
As known in the art, total or absolute pressure of the working fluid in an axial flow device includes two components, i.e., a ram or impact pressure component and a static pressure component. The rotor blades impart ram or impact pressure to the fluid. Static pressure is ambient. Assuming total or absolute pressure remains constant throughout the inlet guide stage, an increase in fluid flow speed after passage through the inlet guide stage 408 necessarily decreases the static pressure component of the working fluid if total pressure is to remain the same. Thus, the variable inlet guide vanes enable altering of pressure and whirl angle of the fluid before entering the first rotor stage. This provides an additional level of control of the performance of the pumping or propulsion device.
In stages 402-410, however, the area of the flow passage between rotor blades and stator vane increases from an entry point to an exit point of each section thereby decreasing the speed of the work fluid as it flows through the pumping or propulsion device. In the succeeding stages 402-410, the width W1 at the entry point between rotor blades 422 and 424 is less than the width W2 at the exit point of these blades—resulting in expanding flow path area when blade height is constant in the direction of axis 13. Likewise, the width W1 at the entry point between stator vanes 426 and 428 is less than the width W2 at the exit point of these vanes—resulting in expanding flow path area when vane height remains constant in the direction of axis 13. A similar decrease in working fluid velocity occurs in stages 404-410. Given a constant overall mass flow rate through the pumping or propulsion device, it is seen that the velocity of the working fluid decreases at each section. The decreased velocity over the succeeding stages also lowers internal frictional and eddy (non-laminar) flow losses (which exponentially increases with speed) that are typically encountered in axial flow devices, thus further improving efficiency.
Advantageously, the difference in magnitude of W1 and W2, and consequently the relative entry and exit speeds as well as the extent of whirl of the working fluid when passing the stator section, may be changed by altering the pitch angle of the stator vanes 426 and 428, as indicated by variable pitch stator blade 430. Changing the angle of attack of the fluid prior to the rotor stage, i.e., changing the amount of whirl, alters the load placed on the engine, or energy imparted to the fluid. Thus, this aspect of the invention substantially improves the overall operating efficiency at various operating set points of the vessel, or at various engine speeds, torque or power. Although W1 and W2 designate entry and exit point width of each section shown in
The exit guide vanes 440, 442, and 442 serve to straighten fluid flow at the discharge nozzle. Their pitch angle may be fixed or variable. A mechanism similar to that use to vary the stator vanes may be employed to vary the pitch angle of the exit guide vanes. This provides an additional layer of control.
As apparent, the invention allows control of thrust either by controlling mass flow via inlet guide vane position, by altering the pitch of the stator vanes (in the variable pitch embodiment of the invention) and thus the pressure imparted to the fluid by each rotor section, by altering the discharge nozzle area or jet velocity to optimally match boat and water jet speed, or any combination thereof, for any given horsepower, torque, or drive speed applied to a multistage axial flow pump or propulsion device. Since it is desired to operate most turbine or piston engines (diesel or gasoline) at an maximum power, at maximum fuel efficiency, at an optimum constant engine speed for best hull speed or sea state condition, or on an optimum performance curve, inlet guide vane throttling (to control mass flow) and/or discharge jet velocity may advantageously be adjusted at the will or desire of the shipmaster to meet any varied performance characteristics of the vessel. The inlet guide vanes may be configured to rotate plus or minus thirty degrees, more or less, from a neutral position. This way, mass flow is positively controlled independent of the speed of the vessel.
For a long haul, the shipmaster may desire to operate on a best speed-range curve to travel the known distance in the shortest time. In other situations, the shipmaster may desire to travel the farthest distance given the amount of fuel onboard. In yet other situations, the shipmaster may desire to travel at the highest speed given the available horsepower, sea state condition, loading of the vessel, and/or design speed of the hull. The present invention meets all of these demands.
Dual-Flow Propulsion System
Booster section 502 enables higher flow rates to attain a higher propulsive achieve efficiency and greater acceleration with minimal impeller cavitation. In a typical installation, both sections of the dual-flow system are mounted inside the hull of a vessel above to water line for easy access and maintenance. A diffuser duct is typically used to channel water from the bottom of the hull, and such a diffuser duct may be used to channel water to the inlet of low pressure section 502. As vessel speed increases, a series of nozzles disposed about a periphery 504 of the booster section may be partially or completely closed, either gradually or stepwise, using a conventional mechanism, in order to control water flow towards the inlet guide vanes of high pressure section 500, explained above. In one embodiment, the extent of nozzle opening (or closure) may be control by rotating slip ring 515 clockwise or counter-clockwise, as illustrated in
At lower vessel speeds, nozzles 510 remain open to provide additional thrust around the periphery of the housing of high pressure section 500. Total thrust produced by the embodiment of
Split-Casing Construction
To implement such embodiment,
Tables in the appendix proposed design parameters of exemplary propulsors having both a low-pressure booster section and a high-pressure primary section.
Inlet Diffuser for Ram Pressure Recovery
A diffuser that might be adapted to an inlet duct might have a diffuser ratio of 0.666 (i.e., ratio of inlet to outlet cross-sectional area of the diffuser), which would recover 51.9 psi of 78.0 psi of ram pressure. Such a diffuser having a maximum allowable divergent angle between 6° and 11°, i.e., the angle from a central axis of diverging walls of the diffuser, may be unduly long in the axial direction, as indicated by the length of duct 702 extending behind vessel 706 of
To explain further,
According to further refined aspect of the present invention, the diffuser duct may be staggered in multiple, stepped stages, as shown in
In the illustrated diffuser, each set of vane groups 726, 727, and 728 may recover as much as 1/cos θ of the ram pressure (assuming θ is about 30°) preceding the respective group. The deflection angle, however, may range between a few degrees to less than ninety degrees. In certain circumstances, it may also be practicable to deflect flow up to 180° provided the net gain in efficiency exceeds duct losses. A diffuser having four sets of deflector groups, for example, would yield a recovery ratio of 1.8:1, or a total ram pressure recovery 0.77 instead of 0.666 using a longer diffuser without deflectors. Additional diffuser sections having additional stator vane groups may be incorporated to further increase ram recovery of a multi-section diffuser. Similar to the fixed stator vanes of the multistage propulsor described herein, the vanes of deflector groups 726, 727, and 728 are designed to increase the cross-sectional area of fluid flow in the downstream direction in order to convert ram pressure to static pressure. In one embodiment, this is accomplished by providing deflector vanes having an airfoil shape, like that illustrated by an airfoil of
Embodiments of the invention may be used to propel displacement or hydroplaning hulls, or in hydrofoil or submarine applications. The invention may also be deployed in water or fluid pumping applications to pump the greatest amount of water or other fluid at the highest pressure for a given horsepower input, or to control the amount of water or other fluid delivered by a pumping station. Thus, the invention embraces all such modifications and adaptations that may come to those skilled in the art in view of the teachings herein.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US05/08474 | 3/15/2005 | WO | 7/3/2007 |
| Number | Date | Country | |
|---|---|---|---|
| 60455578 | Mar 2003 | US | |
| 60606905 | Sep 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10801705 | Mar 2004 | US |
| Child | 10591025 | Jul 2007 | US |
