JPH07279894A - High speed rotary blade device - Google Patents

Abstract

PURPOSE:To prevent a rotor blade from lowering due to cavitation so as to rotate the blade at a high speed by providing an air introduction port in a casing, which faces a negative pressure area of the rotor blade, and by incorporating an air feed valve for controlling the supply of feed onto the negative pressure area of the rotor blade, in the air introduction port. CONSTITUTION:An air introduction port 10 is formed in a suction casing 2, facing a negative pressure area at the tip end of an impeller 6 where the pressure is lowest. An air feed valve 11 communicated with the air introduction port 10 is opened and closed in accordance with a negative pressure in the negative pressure area so as to control the flow rate of air into the negative pressure area. Further, the air is led into the negative pressure area of the impeller from the air introduction port 10 by way of an air passage 9 as indicated by the arrow 22 so as to eliminate a part whose pressure is lower than an evaporating pressure in order to prevent occurrence of cavitation. With this arrangement, it is possible to prevent the impeller 6 from lowering its function due to cavitation which is generated during high speed operation of the impeller 6, thereby it is possible to rotate the impeller at a high speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid machine having rotary blades such as a pump using a liquid as a working fluid and a propeller for a ship, and more particularly to a high speed rotary blade device intended for high speed use.

[0002]

2. Description of the Related Art Conventionally, in a fluid machine using a liquid as a working fluid such as a turbo pump or a marine propeller, when the liquid is accelerated by a rotor (impeller, propeller),
When the pressure is reduced, bubble nuclei contained in the liquid grow and cavitation occurs.This cavitation causes machine performance deterioration, machine surface erosion, noise and vibration. The airfoil and the mechanical shape around it are designed to prevent cavitation.

In another prior art, a super cavitating blade shown in FIG. 6 has been developed as an airfoil intended for use at high speed, and this airfoil actively causes cavitation, so that at high speed. The cavity 18 has a cross-sectional shape 24 suitable for a super cavitation state in which the length of the cavity 18 is longer than the length of the blade, and the leading edge of the blade is edged to cause cavitation. The suction surface from the trailing edge to the trailing edge is entirely contained in the cavity 18, so that the pressure in the negative pressure region 17 is approximately equal to the vapor pressure, and the lift 21 is designed to depend largely on the pressure in the positive pressure region 16. By using such an airfoil, it is possible to use a rotating blade in a high-speed range where cavitation is not avoided, and a fluid machine is accelerated.

[0004]

However, there is a speed limit in the design of the airfoil that does not cause cavitation and the mechanical shape around it in the conventional fluid machine, and it is not possible to use the blade at a higher speed than this limit. This is not possible, and therefore, the speeding up of fluid machines having rotating blades is being pursued.

Further, although the fluid machine using the above-mentioned super cavitating blade can be used at high speed, the performance of the blade is largely changed by the shape of the blade, and the performance of the blade is small when the cavity 18 is small due to the use at low speed. It is extremely bad, and it is sensitive to changes in the angle of attack 15. If it is used at a speed outside the design point, the performance drops sharply, and there are casings, fixed blades, rudders, etc. at the position where the cavitation bubbles collapse downstream of the blade. Has the problem that its surface is damaged by severe erosion.

According to the present invention, the blade can be rotated at a high speed by exceeding the speed limit due to cavitation, and therefore, the speed of the fluid machine can be increased, and it is possible to prevent the performance from being drastically deteriorated due to the change in the usage state. It is an object of the present invention to provide a high-speed rotary blade device that can prevent damage to the machine due to the erosion effect of cavitation.

[0007]

In order to solve the above-mentioned problems, in a high-speed rotary blade device of the present invention, an air inlet opening facing the negative pressure region of the rotary blade is provided in a casing surrounding the rotary blade. The air inlet is provided with means for controlling the supply of air to the negative pressure region of the rotary blade.

[0008]

In the high-speed rotary blade device of the present invention, the casing surrounding the rotary blade is provided with the air inlet facing the negative pressure region of the rotary blade, and the negative pressure generated by rotating the blade at high speed is provided. By controlling the supply of air to the area, air is supplied according to its negative pressure to prevent performance deterioration due to cavitation, and to prevent a sharp decrease in performance even when the usage condition of the fluid machine changes. In addition, erosion due to cavitation is prevented and damage to the machine is prevented.

[0009]

1 is a sectional view of an axial flow pump according to an embodiment of the present invention, FIG. 2 is a sectional view of an air inlet provided in the pump, and FIG. 3 is a sectional view of FIG. It is sectional drawing of the rotary blade (impeller) along a chain line AA.

As shown in FIG. 1, the axial flow pump 1 has a liquid passage 3 formed by a suction casing 2 and a discharge casing 2a, and the discharge casing 2a has a plurality of fixed blades radially in the radial direction thereof. 4 is provided, and an impeller 6 is rotatably supported by a bearing 5 arranged at the center thereof, and the impeller 6 is supported by an impeller shaft 8 which is introduced through a bearing water sealing portion 7 of the suction casing 2. The power of a prime mover (not shown) connected to the impeller shaft 8 is transmitted and rotationally driven.

Suction casing 2 and discharge casing 2a
2, an air passage 9 is formed on the outer periphery of the suction casing 2 as shown in FIG. 2, and an air inlet 10 communicating with the air passage 9 is provided so as to surround the blade tip of the impeller 6. The air passage 9 is connected to one or a plurality of air supply valves 11, and this air supply valve 11 is connected to the air inlet 1
It is a means of controlling the supply of air to zero.

When the impeller 6 is rotationally driven, as shown in FIG. 3, the rotational speed 12 of the impeller 6 and the liquid inflow speed 1
3, the impeller 6 and the liquid flow at a relative velocity of 14 and the liquid flows into the impeller 6 at an attack angle of 15. As a result, the positive pressure of the liquid is applied to both sides of the impeller 6 as indicated by the + and − symbols in the figure. A zone 16 and a negative pressure zone 17 are formed, and in the negative pressure zone 17, cavitation occurs in a portion whose pressure is lower than the vapor pressure of the liquid.

When cavitation occurs, the flow is peeled off from the surface of the impeller 6 by the growth of the cavity 18 to cause separation, which causes a vortex 19, and also causes a pressure fluctuation, which rapidly increases the drag 20 and decreases the lift 21. As a result, the performance of the pump is deteriorated, and cavitation bubbles are discharged from the impeller 6 and the discharge casing 2.
If the surface of a, the fixed wing 4 or the like collapses, the surface will be damaged by the erosion effect of cavitation.

Therefore, in the present invention, the suction casing 2 faces the negative pressure area 17 at the blade tip of the impeller 6 where the speed of the impeller 6 is high and therefore the pressure in the negative pressure area 17 is the lowest.
Is provided with an air introduction port 10, and an air supply valve 11 communicating with the air introduction port 10 is opened / closed according to the negative pressure in the negative pressure region 17 to control the inflow amount of air. The air flows from the air inlet 10 through the passage 9 into the negative pressure region 17 of the impeller 6 as indicated by an arrow 22 in FIGS. 2 and 3, and a portion lower than the vapor pressure is eliminated to prevent cavitation.

Cavitation is unavoidable in a high-speed operating region where the impeller 6 is rotated at a higher speed. However, even if the flow separates from the surface of the impeller 6 due to the cavity 18, separation of the impeller 6 occurs due to the introduction of air. By suppressing the increase of the vortex 19 by covering the surface with a gas phase whose pressure is higher than that of the cavity 18 by the amount of introduced air,
In addition, the vortex 19 can be moved rearward to reduce the eddy resistance and the pressure fluctuation due to the vortex, to prevent the drastic increase of the drag force 20 and the decrease of the lift force 21 to prevent the deterioration of the pump performance. Since the impact pressure at the time of the collapse of the cavitation bubbles is reduced by introducing, it is possible to prevent the mechanical surface from being damaged by the erosion effect of the cavitation.

Further, in the conventional pump, the pressure difference between the both surfaces of the impeller is large at the blade tip of the impeller 6, and leakage from the gap between the blade tip and the casing has a great influence on the performance of the pump. According to the above, since air is introduced from the minimum pressure portion of the negative pressure region 17 by introducing air from the blade tip, the pressure difference between both surfaces of the blade at the blade tip is reduced and leakage from the gap with the casing is reduced. , The air from the air inlet 10 forms a gas phase film along the casing due to the Coanda effect in this gap, so that the frictional resistance is reduced and the rotational drag of the impeller 6 can be reduced. The blade tip vortices 23 are also reduced to prevent the pump performance from being deteriorated. Furthermore, as for the vortex cavitation generated in the blade tip vortices 23, the introduction of air causes the cavitation bubbles to collapse as described above. It is possible to prevent damage of that machine surface.

Further, in order to operate the impeller 6 at an extremely high speed, the super cavitating blade shown in FIG. 6 can be used. According to the present invention, not only the operation at an extremely high speed is possible, but also at a low speed. When the pressure in the negative pressure region 17 is high and the cavity 18 is small in use, air is introduced at a predetermined low speed region by means of controlling the supply of air (described later), and the cavity 18 is enlarged to cause the same flow as in the super cavitation state. It is possible to prevent the deterioration of performance by suppressing the increase of the vortex by the introduced air even when the separation vortex is generated due to the change of the angle of attack 15 and to move the vortex to the rear to reduce the shape resistance of the blade. The pressure fluctuation can be prevented, and the performance of the super cavitating blade can be prevented from dropping sharply, and the cavitation bubble collapses at high speed operation. Located on the fixed wing 4, by the introduction of air even when the discharge casing 2a and the like facing the damage of the machine surface by erosion of cavitation can be prevented that.

The means for controlling the air supply is the impeller 6
The air supply valve 11 that opens and closes according to a predetermined pressure so that an appropriate amount of air is supplied according to the negative pressure in the negative pressure region 17 can be used, and when a super cavitating blade is used, In order to introduce air in a predetermined low speed range like the above, a rotational speed (speed) detecting device of the impeller 6 or a pressure (flow velocity) detecting device in the suction casing 2 is provided, and from these detection signals, the blade in the use state is provided. It is preferable to adjust the air supply amount by opening and closing the air supply valve 11 by a drive device that is controlled by an output signal of the arithmetic device, using a device that calculates the optimal air amount according to the characteristics of.

Regarding the air supply amount, if a large amount of gas is mixed, the incompressibility of the fluid will decrease, and the efficiency as a machine using a liquid as a working fluid will decrease, so there is a limit to the amount of air that can be introduced. When the impeller 6 is operated at a higher speed, the air is supplied at a pressure higher than the atmospheric pressure by a compressor or the like, the cross-sectional area of the air inlet 10 is reduced, and a small amount of high speed air is injected to further increase the speed. It becomes possible to operate in the region, and the air supply can be controlled by controlling the operation of the compressor and the like.

As described above, the high-speed rotor device of the present invention can be used at a higher speed because it can prevent the performance from being deteriorated by cavitation caused by high-speed operation.
By increasing the speed of the pump, it is small and lightweight, and the flow rate per weight can be increased, and it can be operated by a high-speed prime mover such as a gas turbine without going through a speed reducer, making it possible to greatly reduce the size and weight of the entire device. For example, when it is used as a pump for a water jet propulsion device of a ship, the high speed performance of the ship can be improved by reducing the speed and weight of the propulsion device.

Although this embodiment shows an example of an axial flow pump, the present invention can be applied to a mixed flow pump and a centrifugal pump, which is effective for increasing the speed of these fluid machines, and further, Even in a fluid machine used at a low speed, cavitation is likely to occur when the rotor blade receives a large load, and temporary or periodic cavitation due to pressure fluctuation of the inflowing liquid is prevented to prevent machine damage. Since the service life can be extended, it can be effectively used as a safety protection device against cavitation.

FIG. 4 shows a side view of an outboard motor of another embodiment of the present invention and a cross section of a part of a propeller casing, and FIG. 5 is a cross sectional view showing another embodiment of an air inlet.

This embodiment is an example of an outboard motor in which the high-speed rotor device of the present invention is applied to a marine propeller, and the outboard motor 25 has an engine (not shown) mounted on a drive shaft housing 26. A gear case 27 is joined to the lower portion, and a skeg 28 is further joined to the lower portion thereof.
A propeller shaft 29, to which a propeller 6a is coupled, is rotatably supported on the drive shaft 7, and the rotational driving force of the engine drives the drive shaft 3 in the drive shaft housing 26.
0 is transmitted to the propeller shaft 29 via the bevel gear 31 to rotate the propeller 6a, and a propulsive force is obtained.

The propeller 6a is provided with a propeller casing 2b which forms a propeller guard on the outer periphery thereof. The propeller casing 2b is arranged so that a part 26a of the drive shaft housing 26 and a lower end 28a of the skeg 28 are rearward substantially horizontally. The propeller casing 2b is provided with an air introduction port 10 provided so as to surround the wing tip of the propeller 6a on the inner peripheral surface of the propeller casing 2b. It communicates with an air passage 9 that circulates in the cross section of the propeller casing 2b, and the air passage 9 communicates with an air supply valve 11 via a housing air passage 32 provided in a drive shaft housing protrusion 26a. 11 is provided facing the engine exhaust passage 33 formed in the drive shaft housing 26. Ri, the engine exhaust gas is exhausted from the exhaust port 36 is guided to the propeller hub exhaust passage 35 as indicated by arrows 34 in FIG. 4 from the engine exhaust passage 33 to the outside.

When the propeller 6a is rotationally driven, a negative pressure is generated on the back surface of the propeller 6a, and the air supply valve 11 communicating with the air introduction port 10 provided facing this negative pressure region responds to the negative pressure. The exhaust gas in the engine exhaust passage 33 flows through the housing air passage 32 and the air passage 9 from the air inlet 10 into the negative pressure region from the blade tip of the propeller 6a as shown by an arrow 37 in FIG. Prevents cavitation by eliminating the lower pressure area.

When the outboard motor 25 is operated at a higher speed,
The relative speed between the rotation of the propeller 6a and the inflow water 38 increases, and the occurrence of cavitation becomes unavoidable. In the conventional propeller propulsion device, the water flow from the surface of the propeller 6a due to the cavity generated in the negative pressure region of the propeller 6a. When the cavitation bubbles collapse on the surface of the propeller 6a, the surface resistance of the propeller 6a sharply increases and the propulsion efficiency decreases, and the surface is eroded and damaged, causing noise and vibration. However, in this embodiment, since the exhaust gas of the engine is introduced from the air introduction port 10 into the negative pressure region of the propeller 6a, the surface of the propeller 6a is covered with a gas phase having a high pressure by the amount of the introduced exhaust gas. This suppresses the increase of vortices due to separation, and also moves the vortices rearward to reduce vortex resistance and pressure fluctuations due to vortices, and thus the shape resistance of the propeller 6a is sharply increased. It is possible to prevent a large amount and prevent a decrease in propulsion efficiency. Further, since the frictional resistance of the portion covered with the gas phase is greatly reduced, the rotational drag of the propeller 6a is reduced and the efficiency of the shaft power can be improved. It is also possible to reduce the impact pressure when the cavitation bubbles collapse, to prevent damage to the surface of the propeller 6a due to the cavitation erosion action, and to prevent noise and vibration.

In order to operate the outboard motor 25 at an extremely high speed, the super cavitating wing shown in FIG. 6 can be used. Since the outboard motor has no stern or rudder in the wake of the propeller 6a, the It is suitable for high speed navigation in a cavitation state, and in the conventional outboard motor, there is a problem that the performance of the propeller 6a does not become super cavitation state at a low speed range and the performance of the propeller 6a is extremely deteriorated. By introducing the exhaust of the engine in the low speed range by means of controlling the
It is possible to prevent the performance of the propeller 6a from deteriorating, suppress the increase in the vortex even when the separation vortex is generated due to the change in the angle of attack, reduce the shape resistance of the propeller 6a, and prevent the pressure fluctuation. It is possible to prevent the performance of the propeller 6a from deteriorating. Therefore, by optimally controlling the introduction of the exhaust gas, an ultra-high speed propeller propulsion device that does not drastically reduce the performance even when the operating condition is changed from ultra-high speed to low speed is provided. Obtainable.

In the present embodiment, the means for controlling the supply of air introduces the engine exhaust from the engine exhaust passage 33 by controlling the opening / closing of the air supply valve 11, so that the exhaust pressure of the engine can be utilized and the engine speed can be controlled. Depending on the change, for example, an engine speed detection device, a boat speed and acceleration detection device,
It is preferable to electronically control the air supply suitable for the cruising condition by providing a device that calculates the optimum air amount according to the usage state of the propeller, an electromagnetic proportional air supply valve, etc., and when higher pressure air supply is required. Is provided with a pump or the like that works with the drive shaft 30, and the engine exhaust or the atmosphere can be pressurized and supplied.

It is desirable that the air inlet 10 is opened in a slit shape over the entire inner surface of the propeller casing 2b as shown in FIG. 4, but in order to reduce the resistance of the propeller casing 2b due to traveling, the casing is not covered. When making the cross section as small as possible, the air inlet 1
0 as shown in FIG. 5, small holes 10 arranged at predetermined intervals
By making it a, it is possible to secure the strength of the propeller casing, and if the cross-sectional shape of the propeller casing is made into a super cavitating airfoil as shown in FIG. Can be significantly reduced and the propulsion efficiency can be improved.

In this embodiment, the high-speed rotary blade device of the present invention is applied to an outboard motor as a marine propeller, but it can also be applied to a propeller propulsion device of a normal type shaft drive using a stern tube. In this case, it is possible to prevent the stern, rudder, etc. in the wake of the propeller from being damaged by the erosion effect of cavitation, and it is possible to prevent the generation of noise and vibration.

[0031]

According to the present invention, it is possible to prevent the blade performance from rapidly deteriorating due to cavitation caused by the high speed operation of the rotor blade, and to rotate the blade at a high speed. The machine can be made smaller and lighter, and the machine can be operated by a high-speed prime mover without a speed reducer, so that the entire apparatus can be made significantly smaller and lighter.

Further, it is possible to use an airfoil such as a super cavitating blade whose performance changes greatly depending on the use condition, and by controlling the supply of air, it is possible to prevent a sharp deterioration of the performance due to the change of the use condition. It is possible to speed up the fluid machine without narrowing the range of use.

Further, even if cavitation occurs due to high speed operation of the fluid machine, introduction of air can prevent damage to the machine due to erosion of the cavitation.
The generation of noise and vibration can also be prevented.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an axial flow pump 1 according to an embodiment of the present invention.

2 is a cross-sectional view of an air inlet 10 provided in the axial flow pump 1 shown in FIG.

3 is a cross-sectional view of the impeller 6 taken along the chain line AA in FIG.

FIG. 4 is a side view showing a partial cutaway view of an outboard motor 25 according to another embodiment of the present invention.

5 is a cross-sectional view showing another embodiment of the air introduction port 10 provided in the outboard motor 25 shown in FIG.

FIG. 6 is a cross-sectional view of a prior art super cavitating wing.

[Explanation of symbols]

 1 Axial flow pump 2 Suction casing 2a Discharge casing 2b Propeller casing 6 Impeller 6a Propeller 9 Air passage 10 Air inlet 11 Air supply valve 15 Angle of attack 16 Positive pressure area 17 Negative pressure area 18 Cavity 19 Vortex 25 Outboard motor

Claims (1)

[Claims] 1. A fluid machine for operating a rotating blade in a liquid, wherein a casing surrounding the rotating blade is provided with an air introducing port facing a negative pressure region of the rotating blade, and the air introducing port is the above-mentioned. A high-speed rotary blade device comprising means for controlling the supply of air to the negative pressure region of the rotary blade.