EP0995039A1

EP0995039A1 - High pressure centrifugal compressor

Info

Publication number: EP0995039A1
Application number: EP98966759A
Authority: EP
Inventors: David Lior
Original assignee: Technion Research and Development Foundation Ltd
Current assignee: Technion Research and Development Foundation Ltd
Priority date: 1997-07-08
Filing date: 1998-07-02
Publication date: 2000-04-26
Also published as: IL121256A0; WO1999002864A1; AU1550499A

Abstract

A multi stage compressor includes a first stage centrifugal compressor (1) with an axial inducer (2) and a number of radial outlets (4), and a second stage centrifugal compressor (6) with a rotating vaned disk (15) mounted to rotate coaxially with the first stage centrifugal compressor (1). The second stage compressor includes radial inlets (5).

Description

HIGH PRESSURE CENTRIFUGAL COMPRESSOR

FIELD AND BACKGROUND OF THE INVENTION

In state of the art high pressure air compressing machines, compression is

done by using several compressor stages, either axial compressors or centrifugal

compressors. In order to attain a 1 :30 pressure ratio, i.e. compressed air pressure at

the outlet is increased 30 times over the air pressure in the inlet, the axial compressor

requires up to 15 stages. Therefore, the multi stage axial compressor is heavy and

complicated with many moving parts which makes it very expensive to manufacture.

The current technology centrifugal compressor can attain pressure ratio of 1 :30 by

combining 2 to 3 centrifugal stages in cascade. However this arrangement has a

drawback since the diffuser between the first stage and the second stage has to redirect

the flow from outward radial direction where it leaves the outlet of the first stage, into

inward radial direction in order to direct it into the axial inlet of the next stage

centrifugal compressor, resulting in a pressure drop due to slowed air, decreased

efficiency, increased weight and a cumbersome arrangement. Another major problem

in centrifugal compressor is the supersonic flow at the outlet which causes shock

wave and energy and efficiency losses, resulting a maximum pressure ratio of about

1 :4. There is one exception done by Pratt & Whitney Canada which includes a special

shape static diffuser which is optimized to specific design point and therefore not

satisfactory in off design points which limits the high efficiency region of the

operating envelope of the engine. SUMMARY OF THE INVENTION

The invention disclosed here is a multi stage centrifugal compressor including

a first stage centrifugal compressor having an axial inducer and a plurality of radial

outlets; and a second stage centrifugal compressor including a rotating vanes disk

mounted to rotate coaxially with the first stage centrifugal compressor, the second

stage compressor having radial inlets.

Both centrifugal stages operate in the same plane, see Fig 1. The first stage 1

has an axial inducer 2 which is a typical design. However, unlike known multi stage

centrifugal compressors where all stages have axial inducers and therefore require

long and bent diffusers to redirect the radial flow coming from the forward stage inlet

to the next stage axial inlet, according to this invention, the second stage rotor 6 has a

radial inlet 5 ( any single part relates to Fig 1 could represents identical parts due to

radial symmetry), thus a short vaneless radial diffuser 3 directs the compressed air

coming from an outlet 4 of the first stage 1 into radial inlet 5 of the second rotating

centrifugal compressor 6. Since the second stage is rotating in the same direction as

the first stage, the relative Mach number of the flow in the second stage inlet 5 is

reduced to subsonic speed. This eliminates shock waves and energy losses which are

a major factor in limiting the exit Mach number of current state of the art centrifugal

compressors. Thus, in this invention a much higher rotating speed of first stage 1 can

be used to attain a higher pressure ratio, high adiabatic efficiency, and high mass flow

in a compact low weight device which has advantages for any airborne usage such as

turbojet engines and turbocharger devices. Another important advantage of this

invention is its simple design which lowers the manufacturing cost. Obviously this

new invention can be used in any other machines using compressors. The compressed air leaving the outlet 7 of the second stage 6 has a high subsonic

velocity due to the high static temperatures of the air, resulting in a low Mach number

and eliminating shock wave at the inlet of the outer diffuser which includes a first

vaneless diffuser 8 followed by a static vane diffuser 9 which is part of the housing.

The compressed air coming from diffuser 9 flows into a collector 10.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to

the accompanying drawings, wherein:

FIG. 1 shows a section in the plane of symmetry of the compressor of the

present invention;

FIG. 2 is a front view of the compressor of Fig 1. showing its major parts

schematically;

FIG. 3 shows a schematic section in the plane of symmetry containing the

rotating axis of a turbofan jet engine incorporating the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 shows the major parts of the compressor of the present invention. A

first stage centrifugal compressor rotor 1 is mounted on a shaft 11 which is supported

by two bearings 12 mounted on a stationary housing 13. Shaft 11 is driven by an

external power source ( not shown) which can be a turbine powered shaft or other

source. A typical rotating speed is about 70,000 rpm. A planetary transmission 14

mounted on main shaft 11 drives a second stage compressor housing 15 attached to a second stage compressor vane disk 6 ( any single part shown in Fig 1 could represent several identical parts due to radial symmetry). Thus, housing 15 and disk 6 rotate at

the same speed, he second stage speed is smaller than the speed of first stage rotor 1

but in the same angular direction. Housing 15 is mounted on shaft 11 by two

bearings. The left part of housing 15 is mounted on a left bearing 16 by a rotating

vane 17 which is used to direct the incoming air and may be used as pre compressor

stage.

First stage compressor rotor 1 sucks a gas such as air through an axial inducer

2. The air leaves the first stage at an outlet 4 into a vaneless diffuser 3 and enters a

second stage inlet 5. Second stage rotating vane disk 6 further compresses the air

which leaves through an outlet 7 into a vaneless diffuser 8 and then into a static vanes

diffuser 9, and then leaves diffuser 9 and flows into the collector 10. There are

several labyrinth seals 18 that prevent compressed air leakage.

Fig. 2 shows the compressing parts schematically from the front side. Main

shaft 11 is in the center line of the compressor encircled by axial inducer 2. First

stage rotor 1 rotates around shaft 11, expelling compressed air into vaneless diffuser

5. Second compressor vanes disk 6 rotates in the same direction as rotor 1. Air

leaving the tunnel between two adjacent vanes of disk 6 ( i.e. the second stage

centrifugal compressor) enters the vaneless diffuser 8 and later into the static vane

disk 9.

Fig 3. shows schematically how the new compressor of the present invention

can be combined into a conventional turbofan engines replacing a traditional

mulistage axial compressor. A half part of the engine is shown, not to scale. Air

flows into an engine inlet 21 formed by an engine hub 22 and an engine inlet outer

skin 27. A turbofan blade 23 forces the air into the engine where it passes a stator blade 24. Then, the air flow is divided into two flows. The outer flow moves through

a tunnel 26 and later on toward the engine exit nozzle (not shown). The inner flow

flows through a nozzle 25 into an axial inducer 2 of the compressor, which rotates

around an axis 20 which is the engine main axis, and then through a compressor first

stage 1, a second stage 6 which rotates at a different speed, and a diffuser 9. The

compressed air then enters a nozzle 29 which directs the flow to axial flow into a

combustor chamber 30.

It is obvious that the principles of the two stages centrifugal compressor of the

present invention can be applied to multi stages centrifugal compressor in a single

plane or in parallel planes. This can be done by adding extra systems of planetary

transmissions and rotating housing-compressor vanes disks as it is done in the second

stage, thus the air leaving the second compressor stage in a radial direction would

enter a third rotating compressor.

It also is possible to replace the planetary transmission with two turbine shafts

operating in different speeds which is typical in modern turbojet engines, one shaft

rotating the first stage centrifugal rotor 1 and the second shaft rotating the second

stage centrifugal compressor 6.

It is also possible to change the rotation direction of the other compressor

stages if desired by changing planetary transmission 14.

While the invention has been described with respect to a limited number of

embodiments, it will be appreciated that many variations, modifications and other

applications of the invention may be made.

Claims

WHAT IS CLAIMED IS

1. A multi stage centrifugal compressor comprising:

a first stage centrifugal compressor having an axial inducer and a plurality of

radial outlets; and

a second stage centrifugal compressor including a rotating vanes disk mounted

to rotate coaxially with said first stage centrifugal compressor, said

second stage compressor having radial inlets.

2. The compressor of claim 1, wherein said radial inlets of said second

stage compressor are radially beyond said radial outlets of said first stage compressor.

3. The compressor of claim 1 wherein said second compressor stage

includes a plurality of vanes mounted to rotate within said axial inducer.

4. The compressor of claim 1 wherein said second stage centrifugal

compressor includes a rotating housing.

5. The compressor of claim 1, further including:

a planetary transmission for driving said second stage compressor.

6. The compressor of claim 1, wherein said radial inlets of said second

stage compressor are axially parallel to said radial outlets of said first stage

compressor.

7. A method of compressing a gas, comprising the steps of:

(a) providing a multi-stage centrifugal compressor including:

a first stage centrifugal compressor having an axial inducer and a

plurality of radial outlets, and

a second stage centrifugal compressor including a rotating vanes disk

mounted to rotate coaxially with said first stage centrifugal

compressor, said second stage compressor having radial inlets;

(b) rotating said first stage compressor and said second stage compressor.

8. The method of claim 7, wherein said rotating of said second stage

compressor is effected more slowly than said rotation of said first stage compressor.