JPH0849696A - Impulse wave generation preventing structure of impeller blade of high pressure ratio centrifugal compressor - Google Patents

Abstract

PURPOSE:To increase the operation area of a centrifugal compressor and to improve performance by preventing the generation of an impulse wave from the end part of a leading edge without lowering of performance of the centrifugal compressor. CONSTITUTION:The meridian plane of an impeller blade 16 is formed in a shape in such a manner that the corner part 18 of the outer peripheral side 17a of the end part 17 of a leading edge is cut obliquely based on the end part 17 of the leading edge so that the magnitude of the speed component, flowing in vertically to the impeller blade 16, of a sucked air flow is reduced to a value lower than a speed at which an impulse wave is generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shock wave generation preventing structure for an impeller blade of a high pressure ratio centrifugal compressor, and the relative inflow velocity of gas at the end of the leading edge of the impeller blade exceeds the shock wave generation velocity. Also, it is possible to prevent the generation of shock waves starting from the end of the leading edge.

[0002]

2. Description of the Related Art A centrifugal compressor is one of turbo compressors that is equipped with a plurality of impeller blades, sucks gas by a rotating impeller, and pressurizes the sucked gas while flowing it outward in a radial direction of the impeller blades. It is used by being incorporated in an air compressor of a gas turbine or a supercharger of a diesel engine for ships or automobiles.

Recently, the impeller of a centrifugal compressor has been promoted to have a high rotation speed for the purpose of widening the operating range and improving the performance of the centrifugal compressor by further increasing the pressure ratio.

In such a high pressure ratio centrifugal compressor, the relative inflow speed M _w, which is the combined speed of the peripheral speed of the impeller blade of the centrifugal compressor and the flow speed of the gas sucked into the impeller blade, exceeds Mach 1. Impeller blades that are supersonic have also been put to practical use.

FIG. 2 is an explanatory view showing an example of the structure of a turbocharger mounted on an automobile diesel engine. Basically, this turbocharger is a mixed flow turbine 1, a high pressure ratio centrifugal compression. The machine 2 and the shaft 3 that coaxially connects these machines.

The mixed flow turbine 1 has a turbine wheel 5 which is axially supported by a shaft 3 in a turbine housing 4, and an exhaust gas inlet 6 is provided on a wall surface of the turbine housing 4.
An exhaust gas flow path 7 through which the exhaust gas supplied to the chamber flows is communicated with the internal space and is provided in a circumferential shape. The exhaust gas sent from the exhaust gas inlet 6 is accelerated while flowing in the exhaust gas passage 7 in a circumferential shape, and is sprayed on the turbine wheel 5 to rotate the turbine wheel 5. After this, the exhaust gas is discharged from the exhaust gas outlet 8 toward the outside.

The high pressure ratio centrifugal compressor 2 has an impeller 10 which is axially supported by a shaft 3 in a compressor housing 9, and a suction air flow path through which a sucked air flows on a wall surface of the compressor housing 9. 11 communicates with the internal space and is provided circumferentially. Intake air inlet 12 by rotation of impeller 10
The air sucked from the air collides with the impeller 10, the inflow direction is changed by 90 degrees, is guided to the intake air flow passage 11, and is accelerated / pressurized while flowing in the intake air flow passage 11 in the circumferential direction.

The shaft 3 connecting the turbine wheel 5 and the impeller 10 is pivotally supported by bearings 19, 19 provided in the center housing 13.

The turbocharger configured as described above is
When exhaust gas from the engine is blown to the turbine wheel 5 and the turbine wheel 5 rotates, the impeller 10 coaxially connected to the turbine wheel 5 rotates to form compressed air, which is sent to the engine.

FIG. 3 is an enlarged longitudinal sectional view showing the meridional surface shape of the upper half of the impeller blade of the impeller used in this high pressure ratio centrifugal compressor.

As shown in FIG. 3, the impeller blade 14 that rotates about the axis of rotation L has a peripheral speed at each end 15 of the leading edge of the impeller blade 14 from the front (left in the drawing). And impeller blade 14
The air is sucked in the direction of the arrow at a relative inflow velocity M _w that is a combined velocity with the flow velocity of the air sucked in. Since each part of the leading edge end 15 has a different radius of gyration, the peripheral speed of each part also differs, and the relative inflow velocity M _w also differs for each part of the leading edge end 15 as indicated by the size of the arrow. .

The flow direction of the sucked air is changed by 90 degrees by the impeller blade 14 and
The pressure is increased while flowing outward in the radial direction, but as described above, the outer peripheral side 15a, which is the outer side of the end 15 of the leading edge of the impeller blade 14, has a larger relative inflow velocity than the inner peripheral side 15b, The relative inflow velocity M _w of the air sucked in the vicinity of the outer peripheral side 15 a easily exceeds Mach 1.

[0013]

As described above, in the high pressure ratio centrifugal compressor, the air flow whose relative inflow velocity exceeds the velocity at which a shock wave is generated at the outer peripheral side 15a of the end 15 of the leading edge of the impeller blade 14 is obtained. When a collision occurs, a shock wave is generated in a spherical shape starting from this collision part. The generation of the shock wave is dominated by the magnitude of the velocity component of the airflow flowing into the impeller blade 14 which vertically collides with the end portion 15 of the leading edge, and theoretically occurs when Mach 1.0 is exceeded. Empirically, this occurs when the magnitude of this velocity component exceeds approximately Mach 1.1.

The shock wave thus generated interferes with the boundary layer formed on the surface of the rotating impeller blade 14 to separate the boundary layer from the surface of the impeller blade 14. When the boundary layer peels off from the impeller blade 14 in this way, the impeller blade 14 is designed on the assumption that the boundary layer does not peel off, so that the design performance (particularly the target flow rate) cannot be exhibited, Performance will decrease.

Further, in the high pressure ratio centrifugal compressor, when the boundary layer is separated from the surface of the impeller blade 14, the surging area is expanded, so that the usable low flow rate area is reduced, and the high pressure ratio in the low flow rate area is reduced. The specific centrifugal compressor cannot be used.

The present invention has been made in view of the above problems of the prior art. Even if the relative inflow velocity of air at the end of the leading edge of the impeller blade exceeds the velocity at which a shock wave is generated, By preventing the generation of a shock wave starting from the end of the leading edge, the high pressure ratio centrifugal compressor is intended to have a wide operating range and high performance.

[0017]

A shock wave generation preventing structure for an impeller blade of a high-pressure ratio centrifugal compressor according to the present invention has a meridional surface shape of an impeller blade of a high-pressure ratio centrifugal compressor, in which an end portion of a leading edge is The corners on the outer peripheral side should be oblique to the end of the leading edge so that the magnitude of the relative inflow velocity component perpendicular to the end of the leading edge of the inhaled airflow is smaller than the velocity of the shock wave. It is characterized by having a cut shape.

[0018]

In general, the air flow sucked into the impeller of a high-pressure ratio centrifugal compressor has a velocity at which a shock wave is generated on the outer peripheral side of the end of the leading edge of the impeller blade, while at the same time the end of the leading edge of the impeller blade is On the inner peripheral side of the section, each end collides with the leading edge at a speed that does not generate a shock wave.

At this time, in the shock wave generation preventing structure for the impeller blade of the high pressure ratio centrifugal compressor according to the present invention, the corner portion on the outer peripheral side of the leading edge end portion is at a predetermined angle with respect to the leading edge end portion. Since it is cut obliquely, the magnitude of the relative inflow velocity component perpendicular to the end of the leading edge of the sucked airflow becomes smaller than the velocity at which the shock wave is generated.

Therefore, in the high pressure ratio centrifugal compressor, the generation of shock waves from the outer peripheral side of the leading edge of the impeller blade is prevented, so that the shock wave is not generated in the entire region of the leading edge of the impeller blade. .

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a shock wave generation preventing structure for an impeller blade of a high pressure ratio centrifugal compressor according to the present invention is applied to a centrifugal compressor used in a supercharger of an automobile diesel engine is described below with reference to the drawings. The details will be described.

In this embodiment, the only structural difference from the conventional high pressure ratio centrifugal compressor described with reference to FIGS. 2 and 3 is the structure of the leading edge of the impeller blade. Therefore, also in the description of this embodiment, the difference in the structure of the end portion of the leading edge will be mainly described, and the description of the portions overlapping with FIGS. 2 and 3 will be omitted.

FIG. 1 is an explanatory view showing a meridional shape of an impeller blade to which a shock wave generation preventing structure for an impeller blade of a high pressure ratio centrifugal compressor according to the present invention is applied.

As shown in the figure, the shock wave generation preventing structure of the impeller blade 16 has a leading edge portion 1
A corner portion 18 (shown by a broken line) on the outer peripheral side 17a of 7 has a shape cut obliquely and linearly so as to form an angle θ with respect to the end portion 17 of the leading edge.

The shape in which the corner portion 18 is cut is that the end portion 17 (reference numeral 17) of the leading edge included in the cut portion is formed.
Since the relative inflow velocity of the air current impinging on a (between a and the reference numeral 17c) is the velocity at which a shock wave is generated, as will be described later, by inclining this portion, the inflow is made perpendicular to the cut portion. This is to prevent the generation of the shock wave from the end portion 17 of the leading edge by setting the magnitude of the velocity component to the speed at which the shock wave is not generated.

The end 17 of such a leading edge
The cutting of the corner portion 18 is performed similarly for all other impeller blades.

The range of the corner portion 18 is defined by the impeller blade 16
Is rotated about the rotation axis L, so that the airflow having a relative inflow velocity (empirically set to Mach 1.1 in this embodiment) that generates a shock wave is set to the end portion 17 of the impeller leading edge.

In the present embodiment, in FIG. 1, the relative inflow velocity M _w of the airflow flowing into the outer peripheral side 17a of the end portion 17 of the leading edge is Mach 1.0 or more and a shock wave is generated, but the inner peripheral side 17b. The relative inflow velocity number M _w of the airflow flowing into is less than Mach 1.0 and no shock wave is generated. Therefore, the outer peripheral side 17a of the end portion 17 of the leading edge
The relative inflow Mach number is 1.
There is a boundary point 17c that is 0. The impeller blade 16 is cut from this boundary point 17c as a starting point.

When the angle formed by the cutting portion and the leading edge 17 is θ degrees, θ degrees is determined as follows.
The largest inflow relative velocity of the airflow flowing into each part of the end 17 of the leading edge is that which flows into the outer peripheral end of the end 17 of the leading edge,
When this inflow relative velocity is M _w1s , the magnitude of the velocity component perpendicular to the cut portion when this airflow collides with the cut portion is M _w1s cos θ. If the velocity component has a magnitude that does not generate a shock wave, all the airflows flowing into the cutting portion will not generate a shock wave.

In the present embodiment, the relative inflow velocity for generating a shock wave is empirically set to Mach 1.1, and M _w1s × cos θ
From <1.1, cos θ <1.1 / M _w1s is satisfied θ
And

As described above, the shock wave generation preventing structure of the impeller blade of the high pressure ratio centrifugal compressor according to the present invention does not generate a shock wave over the entire length of the leading edge and the cutting portion, and the centrifugal compressor Even if the relative inflow velocity of the sucked air flow exceeds the velocity at which the shock wave is generated, the shock wave is not generated from the end portion of the leading edge.

A high pressure ratio centrifugal compressor having an impeller to which the shock wave generation preventing structure of the impeller blade of the high pressure ratio centrifugal compressor according to the present invention is applied, which is constructed as described above, and a conventional normal shape compressor are used. A compressor characteristic curve determined by the pressure ratio and the weight flow rate was obtained for a high pressure ratio centrifugal compressor incorporating an impeller of an impeller blade. The respective compressor characteristic curves are shown graphically in FIG.

From the graph shown in FIG. 4, the surging with the shock wave generation preventing structure of the impeller blade of the centrifugal compressor according to the present invention while maintaining the pressure ratio equal to or higher than that of the conventional high pressure ratio centrifugal compressor. It can be seen that the occurrence of the above can be prevented even in a lower flow rate range and can be used.

Next, FIG. 1 having the above configuration and performance.
The centrifugal compressor having the impeller blades 16 shown in Fig. 2 was applied to a supercharger for an automobile diesel engine having the structure shown in Fig. 2.

As a result, the basic performance is completely the same as that of the conventional centrifugal compressor, and even in the low flow rate range where the conventional operation could not be performed due to the surging, the operation is performed without the surging. I was able to do it.

Further, in the shock wave generation preventing structure for the impeller blade of the high pressure ratio centrifugal compressor according to the present invention, the inclination angle of the leading edge with respect to the gas inflow direction is changed in order to increase the flow rate and increase the natural frequency. Compared with the conventional one (shown in FIG. 3 by a broken line as a modified example), the corners of the leading edge are simply cut, so that the performance of the impeller blade is hardly changed, and It could be easily achieved by cutting a part of the existing impeller blade.

[0037]

As described above in detail, in the shock wave generation preventing structure for the impeller blade of the high pressure ratio centrifugal compressor according to the present invention, the meridional surface shape of the impeller blade is the outer peripheral side of the end of the leading edge. The corners were cut diagonally with respect to the end of the impeller leading edge so that the magnitude of the velocity component of the inhaled airflow that flowed perpendicularly to the impeller blade was smaller than the velocity at which the shock wave was generated. Because of the shape, the relative inflow velocity of the airflow flowing vertically to the end portion of the leading edge including the cut portion can be suppressed below the velocity at which the shock wave is generated. Therefore, even if the relative inflow velocity to the impeller exceeds the velocity at which the shock wave is generated, it is possible to prevent the shock wave from being generated from the end portion of the leading edge. Therefore, surging does not occur even when the centrifugal compressor is used in a lower flow rate range than in the past, and the usage range of the centrifugal compressor is expanded.

Further, in the shock wave generation preventing structure for the impeller blade of the centrifugal compressor according to the present invention, the shape change relating to the basic performance of the impeller blade can be achieved by using the impeller blade having a shape obtained by cutting a part of the impeller blade. Since it is not performed, the basic performance was not inferior to the conventional centrifugal compressor.

Further, the shock wave generation preventing structure for the impeller blade of the centrifugal compressor according to the present invention can be easily realized by cutting a part of the existing impeller blade.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a meridional surface shape of an impeller blade to which a shock wave generation preventing structure for an impeller blade of a high pressure ratio centrifugal compressor according to the present invention is applied.

FIG. 2 is an explanatory view showing an example of the structure of a turbocharger mounted on a diesel engine for automobiles.

FIG. 3 is an explanatory view showing an enlarged meridional surface shape of an impeller blade of a conventional high pressure ratio centrifugal compressor.

FIG. 4 shows a high pressure ratio centrifugal compressor incorporating an impeller to which a shock wave generation preventing structure for an impeller blade of a high pressure ratio centrifugal compressor according to the present invention is incorporated, and an impeller of a conventional normal shape impeller blade. It is a graph which shows the compressor characteristic curve respectively calculated | required about a high pressure ratio centrifugal compressor.

[Explanation of symbols]

 16 Impeller Blade 17 Leading Edge 17a Outer Side 17b Inner Side 17c Boundary Point 18 Corner

Claims (1)

[Claims] 1. A meridional surface shape of an impeller blade of a high pressure ratio centrifugal compressor is such that an outer peripheral corner of an end of a leading edge is perpendicular to the end of the inhaled airflow. A structure for preventing shock wave generation of an impeller blade of a high pressure ratio centrifugal compressor, characterized in that it has a shape cut obliquely so that the magnitude of the relative inflow velocity component becomes smaller than the velocity at which a shock wave is generated.