EP0040769A1

EP0040769A1 - Arrangement for lowering the surge limit of a rotary type compressor

Info

Publication number: EP0040769A1
Application number: EP81103727A
Authority: EP
Inventors: Keiichi Nakanishi
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1980-05-23
Filing date: 1981-05-14
Publication date: 1981-12-02
Also published as: JPS56165796A

Abstract

To lower the surge limit of a gas turbine compressor, a movable member (16) is disposed in the induction passage (12) and adapted to be projectable into the induction flow as the induction volume approaches the surge limit, to produce a turbulent or eddy flow which acts as a quasi-solid body and throttles the passage. The remaining essentially laminar flow is accelerated and directed against the blades (28) of the compressor wheel (10) at a reduced angle of incidence. This suppresses surging and stabilizes compressor operation.

Description

The present invention relates generally to a turbo compressor for use with gas turbines or the like and more specifically to an arrangement for lowering the surge limit of such a compressor.
Figs. 1 to 3 show a previously proposed arrangement for lowering the surge limit of a compressor of a gas turbine. Figs. 1 and 2 show the arrangement disposed with a centrifugal type compressor having an "asymmetrical" induction port (Viz., an induction port having a mouth which lies on an essentially flat plane which is spaced from and non-intersecting with the axis of rotation of the compressor wheel), while Fig. 3 shows the same arrangement disposed with a compressor having a "symmetrical" induction port (Viz., a port which has an essentially annular mouth surrounding the compressor wheel axis). With this arrangement, during low volume induction the incomming flow of air (or other gas) is induced to swirl, through the use of a plurality of movable flow control vanes 1, about the axis of the compressor wheel 2 so that the angle of incidence of the incomming fluid flow on the blades 3 of the wheel is reduced. This reduction in the angle of incidence has lowered the surge limit of the compressor but has created the problem that when applied to a compressor having an "asymmetrical"induction port, the flow of air passing between some of the plurality of movable flow control vanes 1 has a velocity differential due to the curved nature of the swirled flow. That is to say, as seen in Fig. 1 due to the curvature of the flow between given guide vanes 1 the flow velocity of flow OF is greater than that of IF. Hence the situation arrises wherein a high flow rate occurs on one side of a vane 1 while a slower flow occurs on the other. This flow velocity difference induces a pressure differential at the trailing edge of the vane which in turn produces eddy or turbulent flow downstream thereof. The turbulent or eddy flow thus produced creates a resonace vibration which, at given flow velocities and rotational speeds of the compressor wheel is apt to break the blades of the wheel.
Hence, this arrangement has been effectively limited to use in compressors having a "symmetrical" induction port such as shown in Fig. 3. However, even in this case the arrangement has still suffered from the drawback of being overly complex. Viz., the arrangement includes a plurality of radially disposed adjustable vanes each of which is connected to a control ring 4 through a linkage 5, the production, assembly and disposition of which in the extremely cramped environment of the compressor housing, are time consuming and expensive while not being entirely effective.
The present invention takes the form of a simple annular member or the like which can be selectively projected into a laminar flow of gas moving toward a compressor wheel to create a turbulent or eddy flow along an inner peripheral wall of the induction passage. This turbulent flow functions to throttle the flow or air (or other gas) passing through the induction passage to the compressor wheel and accordingly increase the velocity thereof. Accordingly, during low volume induction operation of the compressor the member is projected to increase the velocity and lower the angle of incidence of the flow impinging on the blades of the compressor wheel and thus lower the surge limit of the compressor.
The features and advantages of the arrangement of the present invention will become more clearly appreciated from the following description taken in conjunction with the accompanying drawings in which

Fig. 1 is a sectional view of a centrifugal type compressor having an "asymmetrical" induction port which is equipped with a swirl generating arrangement discussed under the heading of "Description of the Prior Art";
Fig. 2 is a sectional view taken along the section line II-II of Fig. 1;
Fig. 3 is sectional view of a centrifugal type gas turbine having a "symmetrical" induction port which is equipped with a swirling device as described under the heading of "Description of the Prior Art";
Fig. 4 is a sectional view of a preferred embodiment of the present invention as applied to a centrifugal type compressor having an "asymmetrical" induction port by way of example; and
Fig. 5 is a vector diagram of showing the effect of the present invention.

Turning now to the drawings and in particular Fig. 4, a preferred embodiment of the present invention is shown. In this arrangement a driven compressor wheel 10 is disposed in the induction passage 12 of a gas turbine or the like. A trumpet or bell shaped mouth 14 is formed in the induction passage 12 for promoting laminar flow toward the compressor wheel which in this case is of the centrifugal type.
An annular or ring-like member 16 is disposed in a mating recess 18 formed in the inner peripheral wall 26 of the induction passage. The ring-like member is arranged to have a cross section so that it blends smoothly into the profile of the induction passage 12 when in the fully retracted position so as to facilitate smooth or laminar flow thereover in this state. This position is shown in the part of the drawing located above the axis of rotation of the compressor wheel.
An actuator 22 is connected to the ring-like member 16 through a suitable connecting rod or rods 24. With this arrangement upon the induction volume of the compressor falling to a level where unstable operation or surging thereof is apt to occur, the actuator 22 is energized to move the ring-like member 16 out of its recess 18 to project into the flow moving toward the compressor wheel. In this state (shown in the drawing below the rotational axis of the compressor wheel) the ring-like member disturbs the flow in the vicinity of the inner peripheral wall 26 of the induction passage inducing turbulent flow downstream thereof. This turbulent flow has a velocity lower than that of the remainder of the laminar flow and tends to act a quasi-solid member which reduces the effective area through which the incomming air can flow. That is to say, the turbulent flow partially throttles the induction passage and accordingly accelerates the flow of air impinging on the blades 28 of the compressor wheel 10. The increase in flow velocity causes a reduction in the angle of incidence of the flow on the blades 28 and thus extends the lower limit of the compressor operation.
The actuator may be arranged to move the surge suppressing ring-like member 16 into the induction passage either stepwisely or continuously in accordance with the induction volume and maybe responive to a control unit 30 which outputs a suitable control signal in response to the input from an air flow meter, RPM sensor or the like 32. The actuator may be pneumatic, hydraulic or electric as best suits the situation.
With the arrangement of the present invention although a small amount of fluid having little kinetic energy is permitted to enter .the root portion of the bladed compressor wheel, at this portion the blades tend to turn both radially and outwardly so that stalling of the compressor is highly unlikely.
Fig. 5 shows in vector form the relationship between the flow velocity of the fluid in the induction passage, the peripheral velocity of the wheel and the relative velocity of the gases entering to the compressor wheel. Thus, in this diaphragm VPS denotes the peripheral velocity of the turbine wheel, IS the induction velocity in a region close to the outer periphery of the bladed compressor wheel and RIS the relative induction velocity of the air entering the peripheral region of the compressor wheel. In this diagram, the broken lines indicate the surge limit of the compressor without the provision or use of the present invention while the solid line diagram shows the extended limit via the use of the invention. As shown by the solid line diagram, when the surge supressing arrangement of the present invention is put into use, RIS increases while the angle of incidence on the blades 28 of the compressor wheel decreases. Accordingly surging is suppressed.
In summery the present invention, through the unique use of turbulent flow, increases the inflow velocity of the fluid inducted into the the compressor wheel and simultaneously reduces the angle of incidence of the flow on the blades of the wheel. Hence, the problems caused by the unwanted turbulent flow in the prior art are solved via the use thereof in the present invention. Moreover, the present invention may be used with turbo compressors having either "symmetrical" or "asymmetrical" induction ports with equal effect.

Claims

1. Compressor, comprising

an induction passage through which an essentially laminar fluid flow occurs and

a driven vaned rotary compressor wheel disposed in said induction passage for inducting and compressing fluid,
characterized by

a device (16) disposed upstream of said vaned wheel (10) for selectively generating turbulent flow in a portion of said laminar fluid flow, which turbulent flow throttles said induction passage (12) to increase the flow velocity of the laminar fluid flow and reduce the angle of incidence of said flow on the blades of said bladed wheel.

2. Compressor as claimed in claim 1,
characterized by that

said device takes the form of an annular member (16) slidably disposed in said induction passage (12), and

an actuator (22) operatively connected to said annular member for moving same into said essentially laminar fluid flow flowing in said induction manifold in response to the induction volume approaching the surge limit of the compressor.

3. Compressor as claimed in claim 2,
characterized by that

the annular member (16) is axially movable between a first position where it is disposed in a mating recess (18) in the inner peripheral wall (26) of the induction passage (12) and a second position closer to the vaned wheel (10).