GB2355768A

GB2355768A - Turbine/compressor rotor with helical blade

Info

Publication number: GB2355768A
Application number: GB9925856A
Authority: GB
Inventors: Kofi Abaka Jackson
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-11-01
Filing date: 1999-11-01
Publication date: 2001-05-02
Anticipated expiration: 2019-11-01
Also published as: GB9925856D0; GB2355768B

Abstract

A rotor for a steam turbine, gas turbine, axial flow compressor or the like comprises helical blades. The blades may have a smaller radial extent at a high pressure end of the rotor than at the low pressure end, and they may be surrounded by a shroud (3, fig. 1b) to which they are connected so that the shroud rotates with the rotor. A rotor for a gas turbine engine (figs. 2a,2b,3a,3b,3c) may comprise both compressor and turbine rotor portions, each comprising helical blades. The compressor blades may be extended beyond the diameter of the engine core (fig. 3c) to serve as turbofan blades (TF). Alternatively turbofan blades may be mounted on a shroud. The blades may be cambered to provide a concave surface facing upstream. The blade leading edges may be drooped, from root to tip, in the direction of blade rotation.

Description

2355768 TURBINE ENGINES

Technical Field

The invention relates to turbine engines and similarly acting rotary fluid machines of the kind usually combining stator vanes and rotor blades.

Backaround

Turbine engines convert the energy of high pressure steam or gases into rotational mechanical force for doing work as employed on ships, power stations andjet aircraft.

A turbine typically has alternate rings of fixed guide vanes (stator vanes) fastened to the 15 outer casing and revolving blades (rotor blades) arranged on wheels that form the dnim of the turbine shaft.

Steam directed into the turbine of a steam turbine unit is deflected by the leading stator blades so that the steam strikes the first rotor blades at the most effective angle. As the steam leaves the first ring of rotor blades, its direction is similarly changed by the next set of stator vanes onto the next set of rotor blades. This continues along the entire length of the turbine druni so that energy is taken from the steam and converted, through the rotors, into rotational force for doing work. Some steam turbines have over twenty sets of rotating wheels or stages. A typical steam turbine system is 35% to 40% efficient.

Gas turbines work like steam turbines but use hot gases instead of steam. However, gas turbines usually drive their own compressors for supplying air for combustion. Also, an aircraft turbine engine may have only one, two or three turbine wheels or stages. This allows the efflux of hot gases to gush out at a high velocity giving a jet effect to propel the aircraft. The turbine takes energy from the escaping hot gases to drive the compressor and engine accessories. Its tiny blades are scathed continuously by the heat of combustion and 2 therefore its material strength limits the temperature ceiling. But the hotter a gas or a steam turbine runs, the more efficiently it operates. On a jet engine, straightening vanes are provided beyond the turbine wheel(s) to straighten the whirling gases so as to achieve straight flow out. Some energy is lost to the straightening vanes.

An axial-flow compressor is like a gas turbine turned front to back. The compressor sucks in air and compresses it. Fuel is added to the compressed air and burnt in the combustion chamber. The burning gases expand and rush through the turbine, spinning the turbine wheel(s).

Assessment of today's turbines Today's steam and gas turbines, axial-flow compressors and similarly acting machines have numerous stator vanes that direct the steam or hot gases onto equally numerous rotor blades. A side view of the turbine or axial compressor shows a maze of tiny blades closely arranged. A front view shows a solid plane of overlapping tiny blades.

With an arrangement of this kind:

a) The hot gas or steam follows a zigzag path strMng the stator vanes and the rotor blades thus imparting energy to both: a substantial amount of energy is therefore lost to the stator vanes.

b) The very high engineering precision and close tolerances employed make it difficult and expensive to manufacture.

c) The tiny blades are subjected to high temperatures and high rotational stresses so the permissible top temperature is limited, although the hotter they run the more efficiently they perform.

3 d) The fine thin blades which are closely arranged are highly susceptible to damage or deterioration resulting from intake of dirt or sand, and foreign objects may cause serious darnage.

e) The turbine is very expensive to acquire, costly to repair and very costly to overhaul.

f) The numerous tiny blades spinning at high speed create loud high frequency noise io and therefore create environmental pollution.

g) The combination of tiny stator vanes and tiny rotor blades perfonn best only when run at 75% to 100% of full power: efficiency drops rapidly with reduction in load.

Disclosure of Invention

The invention as claimed in claim I is intended to remedy these drawbacks and improve efficiency. The preferred inventive rotor comprises spirally curved, tapering rotor blades in the place of the stator vanes and rotor blades combination. The invention solves the problem of how to design an axial compressor or steam or gas turbine engine or similarly acting rotary fluid machines in which the compression or the extraction of energy is done in a smooth and continuous rotary action of only rotor blades without the intervention of stator vanes, thereby averting losses of energy to stator vanes, improving efficiency and reducing noise.

Like the blades of existing steam or gas turbines and axial compressors, the blades of the inventive rotor are preferably shorter from root to tip (providing a smaller throat or flow area) at the high pressure end and longer (providing a wider throat area) at the low pressure end.

4 Description of the Preferred Embodiments

Illustrative embodiments of the invention are described below with reference to the drawings in which:

Fig la is a side view of four spiral rotor blades (1) on a conical shaft (2) illustrating a steam turbine provided with a rotor in accordance with the invention.

Fig I b is the same as Fig I a but shrouded by tip-fairing which forms a unitary casing (3) io that spins with the rotor assembly and prevents tip fluid energy losses.

Fig 2a is a side view of a gas turbine engine. The compressor (C) is like the turbine (T) turned front to back. The turbine turns the compressor.

Fig 2b is an illustration of a gas turbine engine similar to that of Fig. 2a, but with its compressor and turbine shrouded by tip-fairing (3) as for Fig lb above.

Fig 3a is an illustration of an aircraft jet engine. The compressor (C) is a normal compressor for a gas turbine as shown in Fig 2a. However, the Turbine (T) which is for taking just enough energy from the escaping gases for driving the compressor and the engine accessories has only two blades which are spirally curved through 180 degrees round the conical turbine shaft or drum.

Fig 3b is a shrouded version of aircraft engine illustrated at Fig 3a.

Fig 3c is one embodiment of a turbofan blade (TF) arrangement on the jet engine's compressor. A few centimetres of the blade, from the leading edge towards the rear, are extended radially so that they extend beyond the diameter of the engine core, like the fan blades of known turbo-fan engines do.

Fig 3d is the front view of turbofan arrangement showing the engine cowling (EC), fan blades (FB) and engine core diameter (CD).

Fig 4 is an illustration of an embodiment of a gas turboshaft engine for rail or road use.

The compressor (C) is a turbofan arrangement. The turbine (T) has a wider diameter to allow maximum expansion of gases, achieve higher absorption of energy ftom the gases and produce slower, less noisy exhaust and maximum shaft power.

On an aircraft jet engine, the turbine may comprise only two to four blades curved round a conical shaft. Fig 3a shows a two bladed jet engine turbine (T). Each blade is curved through 180 degrees forming a half thread of a screw. While an end view of the blades shows two semi-circular blade parts interfaced to forin a complete disc across the path of the jet efflux, its actual frontal area at any particular point along the shaft is the crosssectional area of the blades. Obstruction to the gas efflux is therefore minimal.

The turbine blades may be cambered thus forming "spiral bow blades" around the drum of the shaft, i.e. the pitch of the spiral decreases from the inlet towards the exhaust.

To minimise or eliminate tip fluid energy losses, the rotor blades may be completely shrouded. The unitary casing so formed will rotate with the rotor blades.

To create turbofan effects, stubby winglets can be mounted on the shroud near its front end like the mounting of unducted ultra bypass blades. Alternatively, a short length of each spiral blade, ftorn the leading edge a few centimetres towards the rear, is extended diametrically so that it extends beyond the diameter of the core engine, like the fan blades of today's by-pass engines. This will then be covered by the normal engine cowling as done for known bypass engines.

6 Operation of the invention A column of steam or hot gases delivered to the turbine strikes the spiral blades at a predetermined angle and continues to exert pressure as it moves along the length of the 5 blades and the blades also "unwind" in rotation.

In the case of the axial compressor, the rotary action of the curved blades sucks in air. The spiral blades arrangement screws in the air axially and compresses it as it forces it through a narrowing path along the compressor drum. During forward movement, the pressure of io the in-coming air on the compressor blades makes the compressor and turbine assembly tend to spin like a pin-wheel.

The "half-thread" turbine of the jet engine extracts energy from the escaping hot gases and also helps to expel the gases. VVhile the shallow concave surfaces facing upstream extract energy from the efflux, the convex surfaces facing down-stream help to push the gases with a "rifling twisf '.

Advantages of the invention and its pLqferred embodiments a) Most of the energy normally lost to stator vanes is captured by the spiral rotor blades so efficiency rises dramatically.

b) The cambered blades generate "aerodynamic IiJW' type of force favouring both shaft rotation and axial flow thus enhancing efficiency when used either in a compressor or in a turbine.

C) By its heavy blading and continuous construction, the spiral rotor blades can withstand higher working temperatures therefore they can be operated at higher temperatures for improved efficiency.

7 d) The heavy gauge spiral blades with unobstructed passages between pairs are less susceptible to damage or deterioration resulting from intake of dirt, sand or other materials.

e) The unobstructed passages between the rotor blades also facilitate easy intake and flow of air, steam or gases for improved efficiency.

f) The blades roll with the flow instead of spinning across the flow-path so the typical high frequency noise from the compressor and turbine blades is averted. The io turbine or compressor is therefore relatively quiet and thus more environmentally friendly.

g) As load is reduced, pressure does not fall rapidly. Efficiency is therefore maintained over a wider range of load. The turbine or compressor is therefore more flexible in operation than prior art turbines on ships and trains and for other applications where a high percentage of the installed power is not required most of the time. Throttle response is also sharper.

h) The inventive jet engine may use the pin-wheel principle to an advantage. At high forward speeds, the pressure of the incoming air on the rotor blades of the compressor will make the compressor and the turbine unit tend to spin like a pin- wheel. This contributes substantially towards the energy required for compression. The turbine unit therefore requires less energy to drive the compressor. More efficiency is thus achieved.

i) Because the rotor blades can be built of heavy gauge material, it is possible to build small turbine engines that can withstand normal high operating temperatures and stresses.

j) Turbine engines will be less expensive to build, less costly to maintain, have longer life, be extremely efficient, and be environmentally ftiendly.

8 The preferred turbine or compressor arrangement using the inventive rotor is like a multiple thread screw with a wider opening at one end and smaller opening at the other. A number of spirally curved, parallel, tapering, blades (1) are formed round the shaft or drum (2) of the turbine to replace the prior art tiny stator vanes and rotor blades combination.

Typically, the blades are cambered thus forming "spiral bow blades" with the convex surfaces facing downstream and the concave surfaces facing upstream, the spiral pitch decreasing in the downstream direction.

to The number of blades, their angle of inclination to the axis of the turbine shaft, and the length of the screw so formed, will be according to choice or requirement. However, as few as six or eight blades having their chord set at 45 degrees to the shaft axis and curved through 360 degrees will run satisfactorily. A four-blade-configuration is illustrated in figs. I a, I b, 2a and 2b of the drawings. Another possibility is to droop the blade leading edge progressively from the root to the outer casing or tip in the direction of blade rotation, to facilitate smooth intake of fluid and even out the angle of attack along the leading edge, as is done for a propeller or the blade of a centrifugal compressor. The leading edges of any blade extensions or winglets, used to obtain bypass flow may be similarly drooped.

9

Claims

1. A rotor for a steam turbine, gas turbine, axial flow compressor or a similarly acting machine, said rotor having a spirally curved blade extending axially along its 5 length, whereby the need for stator vanes in the machine is obviated.

2. A rotor as defted in claim I wherein the blades are smaJIer in radius at the high pressure end and of larger radius at the low pressure end.

io

3 A rotor as claimed in Claims I or 2 wherein a leading edge of the blade is extended radially beyond the core diameter to serve as a by-pass or turbofan blade.

4 A rotor as defined in any preceding claim wherein the blade is cambered to provide a concave surface facing upstream.

A rotor as claimed in any preceding claim, wherein the tip of the blade is shrouded in a casing that rotates as part of the rotor assembly to reduce tip losses.

6. A rotor as defined in claim 5 wherein fan blades are mounted on the casing to 20 produce by-pass turbofan effects.

7. A rotor as defined in any preceding claim wherein the blade leading edge is drooped from the root to the tip in the direction of blade rotation.