HIGH PRESSURE CENTRIFUGAL COMPRESSOR

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.

Inventors: LIOR DAVID, LIOR, DAVID
Applicants: LIOR DAVID, TECHNION RES & DEV FOUNDATION, LIOR, DAVID, TECHNION RESEARCH & DEVELOPMENT FOUNDATION LTD.
Application year: 1998
Main classification: F04D25
IPC codes: F04D17, F04D25