US20140356128A1

US20140356128A1 - Method and device for stabilizing a compressor current

Info

Publication number: US20140356128A1
Application number: US14/372,589
Authority: US
Inventors: Stefan Bindl; Marcel Stossel; Reinhard Niehuis; Bastian Muth
Original assignee: Universitaet der Bundeswehr Muenchen
Current assignee: Universitaet der Bundeswehr Muenchen
Priority date: 2012-01-16
Filing date: 2012-12-20
Publication date: 2014-12-04
Also published as: EP2805059A1; DE102012100339A1; WO2013107489A1; CN104114875A

Abstract

The present invention relates to a method for providing a fluid flow to a compressor system of a first turbo machine, wherein the compressor system includes at least one compressor housing in which at least one impeller is arranged and through which a compressor flow flows. The method includes feeding a primary fluid flow to a mixing region of the compressor system. The method further includes feeding a secondary fluid flow from an outside region of the compressor housing to the mixing region so that the secondary fluid flow mixes at least in part with the primary fluid flow to form a resulting fluid flow so that between the primary fluid flow and the secondary fluid flow a momentum exchange takes place, and so that the secondary fluid flow is promoted by the primary fluid flow. The method further includes feeding the resulting fluid flow to the compressor flow upstream of the impeller in the direction of the impeller.

Description

FIELD OF THE INVENTION

The present invention relates to a method and a device for providing a fluid flow to a compressor system of a turbo machine, in particular for stabilizing a compressor flow to or in an aircraft engine.

BACKGROUND AND STATE OF THE ART

Turbo compressors form essential components of turbo machines, for example of aircraft engines, gas turbines in power stations, or other process plants.
An aero engine essentially comprises a compressor, a combustion chamber, a turbine and a thrust nozzle. These components are arranged one behind the other in the direction of flow. The compressor has the task of compressing ambient air that has been drawn into the engine and forwarding it to the combustion chamber. In the combustion chamber the compressed air is mixed with fuel, and the mixture is ignited. The gas that expands in this process escapes and drives the turbine, which in turn is connected to the compressor by way of a shaft in order to drive said compressor. The expanding gas escapes by way of a thrust nozzle, thus producing propulsion.
Compressors that are used in aero engines usually comprise a cylindrical housing whose interior defines a flow channel for the compressed air. The housing comprises an air inlet opening at its axial forward end, and an air outlet opening, preferably to the combustion chamber, at its axial rear end. The shaft, on which several impellers that are driven by the turbine are arranged one behind the other in the axial direction, extends along the housing axis. Each impeller comprises a multitude of essentially identical profiled blades whose plane is inclined relative to the axial direction. When the blades rotate on the shaft, due to the geometry of the blades air is conveyed through the compressor channel, and the air downstream of the impeller is compressed relative to the air upstream of the impeller. Thus in the operating state on each impeller there is a certain pressure ratio between the air pressure downstream of the impeller and the air pressure upstream of the impeller. This pressure ratio depends, for example, on the impeller geometry and/or the rotational speed of the impeller.
Usually in practical application multi-stage compressors are used in which several impellers are arranged one behind the other in the compressor channel in order to incrementally compress to the desired pressure level the air flowing into the compressor.
Increasing the efficiency of the components of the compressor provides considerable potential for the entire turbo machine. Engine manufacturers therefore endeavour, by means of modern design methods, to further optimize the design of the compressor stages, in particular of the blade contours, in order to in this manner achieve improved energy conversion to the flowing fluid. However, this endeavour encounters physical limits. Compressor geometries that are subjected to excessive aerodynamic loads have an increased tendency to flow separation on the compressor blades, which flow separation can result in damage to the engine or to engine failure. Therefore, in the design of compressors an adequate safety buffer must always be provided so that even under high engine load and in extreme flight situations flow separation can always be prevented. Reducing the stable operating line to far below the stability limit of the engine provides sufficient protection against safety-critical operating states; however, it reduces the achievable compression ration and thus limits the efficiency of the system.
Stable operation of a turbo compressor is limited by various factors. Inflow interference or transient load changes can have an unfavourable influence on the flow in the engine. An ex-panding gap between the housing and the rotor (so-called radial gap), which is frequently observed with ageing engines, is a further cause of deterioration of the stability behaviour. These factors can cause improper local incident flow to the impellers, which can result in flow separation on the suction side of the compressor profile. Consequently the particular blade passage can be blocked. Usually, at first only the region near the housing is affected by the blockage, which results in a reduction in the flow both in the radial direction and in the circumferential direction. As soon as this state is reached, because of the lack of performance, the compressor pressure ratio is significantly reduced in this blade passage, and at the outlet of said blade passage a highly disturbed flow results. The pressure loss continuously increases downstream across the stages of the compressor.
FIG. 1 diagrammatically shows such flow separation in a compressor grate. As a result of the flow deflection described above, the incidence angles α differ from one blade profile to the other until finally in the adjacent profile a critical angle of incidence is achieved, which results in flow separation on this profile. Evasion by the fluid results in the initially affected blade passage then being subjected to adequate flow again and being relieved, and consequently the separation and thus blockage of the passage being able to be reversed. The disturbance continues to the next blade and moves against the direction of rotation of the rotor through the compressor grate. Such a disturbance, in which areas of a reduced mass flow rate rotate at a speed that is less than the rotor speed is commonly referred to as a rotating stall.
Injecting additional air in the blade tip region, as described, for example, in S. Bindl et al., “Active Stall Elimination by Air Injection onto the Tip Region of Compressor Blades”, ISABE-2009-1105, Proceedings of the 19th International Symposium on Air Breathing Engines, Montreal, September 2009 provides an effective method for stabilizing the flow of air through the compressor and for counteracting the rotating stall. As a result of the targeted injection of air the flow in proximity of the housing is energized and thus stabilized. The injected air can be taken from a higher-order compressor stage of the compressor, from a further engine, or from some other external source. However, if the air is taken from another engine or a downstream compressor stage of the compressor, the efficiency of said compressor is reduced because the air that has been removed is no longer available for generating thrust. Likewise, in the case of recirculation and utilization of the dethrottling effect during removal of the air in the rear compressor stages it is expedient to limit the quantities of air. Otherwise the efficiency of the downstream components of the engine is greatly impaired. Furthermore, due to compression the air bled from the downstream compressor stages can already reach high temperatures, for which the upstream compressor stages are often not designed. Moreover, the undesired heating limits the recirculated air mass flow and thus the stabilizing effect of air injection.
In view of the above-mentioned problems it is thus the object of the invention to provide an improved method or an improved device for stabilizing the air flow through the compressor, and thus to increase the efficiency of the compressor.
Presentation of the Invention
This object is met by a method and a device for providing a fluid flow to a compressor system of a turbo machine with the characteristics of the independent claims 1 and 11. The dependent claims relate to improvements to the invention.
The invention relates to a method for providing a fluid flow to a compressor system of a turbo machine, wherein the compressor system comprises at least one compressor housing in which at least one impeller is arranged, through which housing a compressor flow flows, with the method-related steps of feeding a primary fluid flow to a mixing region of the compressor system and of feeding a secondary fluid flow from an outside region of the compressor housing to the mixing region so that the secondary fluid flow mixes at least in part with the primary fluid flow to form a resulting fluid flow, and of feeding the resulting fluid flow from the mixing region to the compressor flow upstream of the impeller in the direction of the impeller.
The inventors have recognized that by feeding a secondary fluid flow from the outside region of the compressor housing, a primary fluid flow that is compressed to a greater extent than the secondary fluid flow can be enriched so that the resulting fluid flow effectively stabilizes the compressor flow in the region of the impeller. Because of feeding the secondary fluid flow effective stabilization can be achieved already with a comparatively small primary fluid flow so that the disadvantages described with reference to the state of the art, namely a reduction in the efficiency of the compressor system and excessive heating of the front compressor stages, are reduced.
In this process, mixing the primary fluid flow with the secondary fluid flow can take place in such a manner that the primary fluid flow promotes the secondary fluid flow, in particular by means of momentum exchange. In particular, in the mixing region the secondary fluid flow can establish contact with the primary fluid flow and can be accelerated by the primary fluid flow so that after at least partial mixing of the primary fluid flow with the secondary fluid flow the resulting fluid flow arises. Generally-speaking this effect is referred to as the ejector effect.
The primary fluid flow passes through the mixing region before being fed to the compressor flow by way of the impeller or upstream of the impeller, and, depending on the design of the compressor system and on the flow rate, can aspirate a secondary fluid flow whose mass flow corresponds to a multiple of the primary mass flow. The secondary fluid flow is fed to the mixing region from the outside, i.e. preferably by way of an external supply line rather than by way of the upstream stages of the compressor system or the main inlet aperture of the compressor housing, thus increasing the mass flow available for stabilizing the compressor flow, without this resulting in a reduction in the efficiency of the compressor system. According to a preferred embodiment the secondary fluid flow differs from the compressor flow.
In the context of the invention the terms “upstream” and “downstream” are to be interpreted in relation to the compressor flow by which the compressor housing is impinged. Thus the upstream end of the impeller is the end facing the inlet of the compressor system or of an upstream compressor stage. Correspondingly, the downstream end of the impeller is the end of the impeller facing the outlet or a downstream compressor stage.
The impeller separates that region downstream of the impeller, from which region the primary fluid is diverted, from that region upstream of the impeller, to which region, after the admixture of the secondary fluid flow the resulting fluid flow is fed back to the compressor flow. In embodiments of the invention these regions can also comprise more than one impeller, or can be separated from each other by several compressor stages. The pressure differential between the region in which the primary fluid flow is diverted and the region to which the resulting fluid mixture is fed is then correspondingly greater so that the flow speed and the mass flow rate of the primary fluid flow also increase accordingly. This can reinforce the ejector effect.
In the context of the invention the terms “inside region” and “outside region” of the compressor housing can relate to a radial direction perpendicular to the housing axis or shaft of the compressor. In this case the inside region is closer to the housing axis or the shaft than the outside region and comprises, in particular, the flow channel for the compressor flow. The outside region of the compressor housing comprises the region outside the compressor housing or the environment in which the compressor system is operated.
The medium of the secondary fluid flow can resemble the medium of the primary fluid flow. In particular, both media can be air. The primary fluid flow can be more highly compressed than the secondary fluid flow.
In a preferred embodiment the primary fluid flow is diverted from the compressor flow of the first turbo machine downstream of the impeller. In this configuration part of the compressor flow is also recirculated as the primary fluid flow.
In one embodiment the primary fluid flow is diverted from a compressor flow of a further turbo machine. This embodiment is particularly advantageous if the first turbo machine and the further turbo machine are aircraft engines respectively. Depending on the flight attitude, flow instabilities can often occur to a different extent in the different engines of an aircraft. The invention then makes it possible to stabilize the compressor flow of the first, more unstable, engine by means of the ejector effect and by means of a primary mass flow fed from the compressor system of the second, more stable, engine.
The second turbo machine can, for example, also be an auxiliary gas turbine or auxiliary power unit of the aircraft.
In a further embodiment the primary fluid flow can be fed from an external pressure accumulator. This embodiment is advantageous in particular in an application of the invention in process plants.
Preferably, the primary fluid flow and/or the secondary fluid flow are introduced into the mixing region in such a manner that the resulting fluid flow at least in part impinges the impeller. In particular, the resulting fluid flow can be directed in a targeted manner onto the impeller.
In a preferred embodiment the impeller comprises several blades, and the resulting fluid flow is fed to the compressor flow in such a manner that the resulting fluid flow impinges the impeller in the region of the blade tips.
As mentioned above, the rotating stall is usually particularly pronounced in the region of the blade tips. Stabilizing intervention in the flow conditions is particularly promising at this location.
In a preferred embodiment the resulting fluid flow is fed to the compressor flow along a peripheral region of the compressor flow. In particular, the resulting fluid flow can be fed to the compressor flow along a circumferential region of the compressor flow or along a circumferential region of a flow channel defined by the compressor housing. In this manner, feed-in of the stabilizing fluid mixture flow over the entire region near the housing, which region is subjected to high aerodynamic loads, is achieved, and a rotating stall in the region of the blade tips is effectively prevented.
Preferably, the direction of the resulting fluid flow substantially coincides with the direction of the primary fluid flow. The directional effect of a fast, high-pressure, primary fluid flow can be used in this manner in order to impinge in a targeted manner the blades, in particular the blade tips, of the impeller.
In one embodiment the mixing region can at least in part be outside the compressor housing and/or outside an outer wall of a flow channel defined by the compressor housing. Preferably, the mixing region is situated completely outside the flow channel. In this case the resulting fluid flow can be channeled, by way of a feed line, from the mixing region to the compressor flow and in the direction of the impeller. This configuration is associated with an advantage in that the flow channel remains largely or completely free, and disturbing effects on the compressor flow during feed-in of the resulting fluid flow are avoided or at least reduced.
In a preferred embodiment the mixing region is completely outside the flow channel and is connected to the flow channel by way of openings in the outer wall of the flow channel.
However, in one embodiment of the invention the mixing region can also, at least in part, be situated in a flow channel that is defined by the compressor housing. This configuration provides an advantage in that feeding the resulting fluid flow to the compressor flow and in the direction of the impeller is facilitated. In particular, it is possible to a large extent to dispense with separate lines for feeding the resulting fluid flow from the mixing region to the compressor flow, and consequently the design of the air-assisted injection system is particularly simple and economical. Moreover, such a system can be integrated with little effort and expenditure into existing compressor housings.
In a preferred improvement the compressor housing defines a flow channel, wherein the mixing region is closed off, at least in part, from the flow channel. In particular, the mixing region can comprise a mixing chamber that is preferably closed off at least in part from the flow channel. A closed-off mixing region promotes the ejector effect and the formation of a stable resulting fluid flow.
In one improvement the mixing region comprises several mixing chambers that are preferably arranged along a circumferential region of the compressor flow. Feeding-in the resulting fluid flow by way of several mixing chambers along the circumferential region of the compressor flow promotes particularly effective stabilization of the compressor flow in the peripheral region of the compressor housing.
In a preferred embodiment the method comprises impingement of the impeller at a predetermined angle, in particular at a variable angle.
Preferably, the resulting fluid flow can be aligned in such a manner that it impinges the blade essentially perpendicularly or at an angle δ to a blade axis of a blade of the impeller and/or at an angle γ to a plane of the impeller.
In this arrangement an angle γ of zero degrees can mean that the resulting fluid flow is directed in the direction of rotation of the blade. An angle of 180 degrees can mean that the resulting fluid flow is directed against the direction of rotation of the blade.
The angle γ is preferably in a range of 20° to 160° and particularly preferably in a range of 90° to 140°.
In a preferred embodiment the angle can be varied, depending on a rotational speed of the impeller, preferably in a range of 20 degrees to 160 degrees and particularly preferably in a range of 90 degrees to 140 degrees.
By varying the angle at which the resulting fluid flow impinges the impeller the air injection and thus the stabilization of the compressor flow can be precisely adjusted to the operating state of the compressor.
In a preferred embodiment an admixing ratio of a quotient of a mass flow of the secondary fluid flow and of a mass flow of the primary fluid flow is at least one, preferably at least three, and particularly preferably at least ten.
A device according to the invention for providing a fluid flow to a compressor system of a turbo machine comprises a compressor housing that defines a flow channel in which at least one impeller is arranged, and a first supply line for a primary fluid flow, wherein the first supply line comprises a first inlet for the primary fluid flow, and comprises a first outlet, wherein the first outlet upstream of the impeller is in fluidic communication with the flow channel, as well as a second supply line for a secondary fluid flow, wherein the second supply line comprises a second inlet that is in fluidic communication with an outside region of the compressor housing, and comprises a second outlet that upstream of the impeller is in fluidic communication with the flow channel, wherein the first outlet and the second outlet are arranged in such a manner relative to each other that the secondary fluid flow mixes at least in part with the primary fluid flow to form a resulting fluid flow directed onto the impeller.
In the context of the invention the terms “upstream” and “downstream” relate to a compressor flow that in operation of the turbo machine is conveyed through the compressor housing of the compressor system. The configuration of the compressor system or of the impeller defines the direction of flow which during operation flows through the compressor housing.
In a preferred embodiment the first inlet is in fluidic communication downstream of the impeller with the flow channel of the turbo machine.
In a further embodiment the first inlet is in fluidic communication with a compressor stage of a further turbo machine.
In one embodiment the first inlet is in fluidic communication with an external pressure source.
In a preferred embodiment the first outlet and the second outlet are arranged relative to each other in such a manner that the primary fluid flow promotes the secondary fluid flow, in particular by promoting momentum exchange.
The second outlet can be arranged so as to be adjacent to the first outlet, in particular directly adjacent. Preferably, the first outlet and/or the second outlet are/is arranged in a peripheral region of the flow channel.
Preferably, the first outlet is directed to the impeller so that the resulting fluid flow impinges the impeller. In this manner a particularly effective ejector injection and a reduction in the rotating stall can be achieved.
In a preferred embodiment the second supply line is separate from the flow channel, in particular different from the flow channel.
Preferably, the first outlet is arranged within the flow channel. In particular, the first outlet can be aligned in the direction of the impeller.
In a preferred embodiment the device comprises a mixing line that comprises a third inlet and comprises a third outlet, wherein the third inlet faces the first outlet, and the third outlet is in fluidic communication with the flow channel.
In one improvement the third outlet can be situated in the flow channel and can be aligned in the direction of the impeller.
The mixing line can serve to connect a mixing region, in which the secondary fluid flow mixes with the primary fluid flow, to the flow channel, and to align the resulting fluid flow to the impeller. The mixing line can also serve as a diffuser.
In one improvement of the invention the third inlet has a diameter D, and a distance a between the first outlet and the third inlet is at least −3D, preferably at least 0 and particularly preferably at least 2D, wherein a negative distance indicates that the third inlet is situated upstream of the first outlet. The inventors have recognized that in this distance range a particularly high admixture ratio can be achieved.
In one improvement of the invention the distance a does not exceed 5D, preferably does not exceed 4D.
In one embodiment of the invention a ratio of a cross-sectional area of the third inlet to a cross-sectional area of the first outlet is at least 1 to 1, preferably at least 5 to 1 and particularly preferably at least 10 to 1.
In one improvement of the invention the ratio of the cross-sectional area of the third inlet to the cross-sectional area of the first outlet does not exceed 100 to 1, preferably does not exceed 60 to 1 and particularly preferably does not exceed 40 to 1.
The inventors have recognized that with these cross-sectional ratios a particularly effective ejector effect and a high admixing ratio can be achieved.
In a preferred embodiment the first outlet and/or the third outlet are/is aligned so as to be essentially perpendicular to a blade axis of a blade of the impeller and/or at an angle to a plane or axis of the impeller.
The device can, in particular, be equipped to vary the angle depending on a rotating speed of the impeller, preferably in a range of 20 degrees to 160 degrees, particularly preferably in a range of 90 degrees to 140 degrees.
Preferably, the device according to the invention can comprise several first outlets and/or several second outlets that are arranged along a circumferential region of the flow channel. In particular, the first outlets and/or the second outlets can be arranged along an inside periphery of the compressor housing.
Several first and/or second outlets make it possible to lead the resulting fluid flow in a distributed manner over the entire peripheral region of the compressor flow or flow channel onto the impeller so that particularly effective stabilization of the flow can be achieved. One main ejector can feed several air-assisted injection nozzles.
The several first outlets can be connected to a common first supply line for a primary fluid flow. Likewise, several first supply lines for the primary fluid flow can be provided which in each case are in fluidic communication with a pressure source, in particular with the flow channel downstream of the impeller, and provide primary fluid flows at the corresponding outlets.
Accordingly, the several second outlets can be in fluidic communication with an outside region of the compressor housing by way of a common second supply line or in each case by way of separate second supply lines.
In one improvement the device according to the invention comprises a mixing region that upstream of the impeller is in fluidic communication with the flow channel, and into which mixing region the first outlet and the second outlet lead.
As previously explained with reference to the method according to the invention, the mixing region makes it possible to mix the secondary fluid flow, which has been fed from the outside region of the compressor housing, with the primary fluid flow which has been bled from the compressor system, for example downstream of the impeller, to the resulting fluid flow that can be led from the mixing region to the compressor flow and in the direction of the impeller. The device according to the invention can therefore alternatively be characterized by way of this mixing region and its embodiment.
The invention therefore also relates to a device for providing a fluid flow to a compressor system of a turbo machine with a compressor housing that defines an flow channel in which at least one impeller is arranged, and with at least one mixing region which upstream of the impeller is in fluidic communication with the flow channel, and with a first supply line for a primary fluid flow, wherein the first supply line on a first inlet is in fluidic communication with a pressure source, and an on a first outlet is in fluidic communication with the mixing region, and with a second supply line for a secondary fluid flow, wherein the second supply line on a second inlet is in fluidic communication with an outside region of the compressor housing, and on a second outlet is in fluidic communication with the mixing region.
In a preferred embodiment the first supply line at its first inlet downstream of the impeller is in fluidic communication with the flow channel.
In another embodiment the first supply line at its first inlet is in fluidic communication with a flow channel of a further turbo machine.
However, the pressure source can also be an external pressure source.
In an improvement according to the invention the mixing region comprises a mixing chamber that at least in part is situated within the flow channel.
In a preferred embodiment the mixing chamber comprises a chamber wall that separates the mixing chamber from the flow channel.
The mixing region can also comprise a mixing chamber that at least in part is situated within the compressor housing and outside the flow channel.
In one improvement the mixing chamber can comprise a chamber outlet that is preferably arranged within the flow channel.
The mixing region can comprise a mixing line that comprises a third inlet and a third outlet, wherein the third inlet faces the first outlet and the third outlet is in fluidic communication with the flow channel, in particular is situated in the flow channel and is aligned in the direction of the impeller.
In one improvement the third inlet can have a diameter D, and a distance a between the first outlet and the third inlet can be at least −3D, preferably at least 0, and particularly preferably at least 2D, wherein a negative distance shows that the third inlet is situated upstream of the first outlet.
In one improvement of the invention, a does not exceed 5D, preferably does not exceed 4D.
In a preferred embodiment the third outlet is aligned so as to be essentially perpendicular to a blade axis of a blade of the impeller and/or at an angle to a plane of the impeller.
The angle is preferably in a range of 20° to 160°, particularly preferably in a range of 90° to 140°.
The device can be equipped to vary the angle depending on a rotating speed of the impeller, preferably in a range of 20 degrees to 160 degrees, particularly preferably in a range of 90 degrees to 140 degrees.
The mixing chamber can be a chamber inlet area Aein, formed by a cross-sectional area of the second outlet, and a chamber outlet area Aaus, formed by a chamber outlet that is preferably arranged within the flow channel, wherein Aein/Aaus is ≧1, preferably Aein/Aaus is ≧3, and particularly preferably Aein/Aaus is ≧10.
In a preferred embodiment the compressor system is an axial compressor.
The compressor can, in particular, be used in an engine, preferably in an aircraft engine.

DETAILED DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS

The characteristics and the numerous advantages of the invention are best understood from a detailed description of preferred exemplary embodiments with reference to the accompanying drawings in which:

FIG. 1 diagrammatically illustrates the rotating stall in a compressor grate;

FIG. 2 diagrammatically illustrates the principle of ejector air-assisted injection for stabilizing a compressor flow according to one embodiment of the present invention;

FIG. 3 shows a compressor system with an air-assisted injection system for feeding a stabilizing fluid flow along the peripheral region of the flow channel according to one embodiment of the present invention;

FIG. 4 with reference to a diagrammatic sectional drawing illustrates the angular relationship between the impeller blades of the impeller and the resulting impinging fluid flow;

FIG. 5 shows a diagrammatic sectional drawing of the air-assisted injection system of the embodiment according to FIGS. 3 and 4; and

FIG. 6 shows a diagrammatic sectional drawing of an alternative air-assisted injection system according to one embodiment of the present invention.

Below, the method according to the invention and the device according to the invention for providing a resulting fluid flow to a compressor system are explained using the example of a compressor system for an aircraft engine. However, the invention is not limited to this application. The use, according to the invention, of the ejector effect makes it possible to achieve a stabilization of the compressor flow or a reduction of flow instabilities as represented, for example, by the rotating stall, in all conventional gas compressor systems. This includes, in particular, compressor systems as they are used in large numbers in process plants, in particular in stationary gas turbines used in power generation.
Based on the known state of the art for the stabilization of the compressor flow by injecting air into the blade tip region, as described, for example, in S. Bindl et al. (cited above), the invention is based on the recognition that with the use of the ejector effect the air-assisted mass injection flow, preferably at a constant recirculation flow, can be increased multiple times. Consequently, even with comparatively small recirculation flows and thus small losses in terms of efficiency, improved stabilization of the compressor flow can be achieved.
The ejector effect is based on a fast primary mass flow accelerating and conveying the surrounding fluid by means of momentum transfer. The ejector effect is characterised by the so-called admixing ratio μ, the quotient of the secondary mass flow (sek) and of the primary mass flow (prim),
The admixing ratio μ describes the efficiency of the ejector.
The ejector effect is utilized in various industrial applications. Detailed numeric simulation and experimental studies relating to the basic effect of ejectors have been described by the inventors in the articles B. Muth et al., “Basic Study of the Ejector Effect, Part 1: CFD”, 47th AIAA/ASMI/SAE/ASEE Joint Propulsion Conference and Exhibit, 31.07.-03.08.2011, San Diego, and M. Stossel et al.: “Basic Study of the Ejector Effect, Part 2: Experimental Approach”, ibid., but not in the context of the stabilization of a compressor flow. The invention is based on the new and surprising recognition that an ejector effect can advantageously also be utilized for the stabilization of the compressor flow.
The principle of utilizing the ejector effect to increase the air-assisted injection flow on a compressor system is shown in FIG. 2. The air-assisted injection system 10 is arranged upstream of an impeller 12 of a compressor stage, of which for the sake of clarity only the blades 14 are shown. The impeller 12 is rotatably mounted on an axis of rotation A that coincides with the axis of symmetry of the compressor system. The plane of the impeller blades 14 (shown in section view in FIG. 2) is in each case inclined relative to the direction A.
The air-assisted injection system 10 guides a primary fluid flow 16 through a nozzle 18 in the direction of the blades 14 of the impeller 12. The primary fluid flow 16 is removed from the compressor system downstream of the impeller 12 (not shown in FIG. 2). The air-assisted injection system 10 further comprises a supply line from the outside region of the compressor, of which supply line only the outlet openings 20 are shown in FIG. 2. Through the supply line and its outlet opening the primary fluid flow 16, as it flows from the nozzle 18, aspirates a secondary fluid flow 22. In a mixing tube 24 that is arranged between the outlet of the nozzle 18 and the blades 14 of the impeller 12 the secondary fluid flow 22 establishes contact with the primary fluid flow 16 and is accelerated by the primary fluid flow 16. In this process the mixing tube 24 can additionally act as a diffuser. The primary fluid flow 16 and the secondary fluid flow 22 mix in the mixing tube 24 to form a resulting fluid flow that impinges the blades 14 of the impeller 12.
The ejector effect in which the primary fluid flow 16 conveys a secondary fluid flow 22 from the outside region of the compressor system results in a significant increase in the total mass flow of air-assisted injection, and thus in increased efficiency of the power plant process.
FIG. 3 is a perspective partial section view of a compressor system of an aircraft engine with an air-assisted injection system according to the invention. Generally-speaking, a compressor system of a turbo machine comprises several compressor stages with a multitude of impellers 12 arranged along the flow channel or the common axis of rotation A, and respective stators arranged downstream. The basic design of such a compressor system as described in the introduction with reference to the state of the art is known to the average person skilled in the art, and for the sake of clarity is not shown in every detail in FIG. 3.
The compressor system comprises an essentially cylindrical compressor housing 26 whose interior defines a flow channel 28 which in operation is impinged by the compressor flow 30. In the flow channel 28 the impeller 12 with the blades 14 is rotatably held. The blade surfaces are inclined relative to the axis of rotation A of the impeller 12. In operation of the compressor system the impeller 12 is rotated and because of the profile of the blades 14 conveys the air entering the flow channel 28 in the direction of a downstream stator or of downstream compressor stages so that a compressor flow 30 through the flow channel 28 occurs. In this process the air is compressed so that the pressure downstream of the impeller 12 exceeds the pressure upstream of the impeller.
To utilize the ejector effect the primary fluid flow 16 is diverted from the compressor flow 30 downstream of the impeller 12, and by way of first supply lines 32, which are in part arranged in the compressor housing 26, is returned to a mixing region upstream of the impeller 12. The mixing region comprises a multitude of mixing chambers 34 arranged equidistantly along the circumference of the inner wall of the compressor housing 26. Each one of the mixing chambers 34 comprises inlet openings 20 for a secondary fluid flow 22 which aspirates the primary fluid flow 16 from the outside region of the compressor housing 26.
The design and configuration of the mixing chambers is shown in further detail in the enlarged sectional view of FIG. 3. The mixing chambers 34 comprise a mixing-chamber wall 36 which closes off a chamber interior from the flow channel 28. The outlet of the first supply line 32 leads to the chamber interior in which the primary fluid flow 16 mixes with the secondary fluid flow 22. The resulting fluid flow is guided by way of chamber outlet openings 38 at a predetermined angle in the direction of the impeller 12 so that it impinges the blades 14. The chamber outlet openings 38 can, in particular, also be designed so as to be adjustable so that the blades 14 of the impeller 12 can be impinged by the flow at different angles.
FIG. 4 illustrates the angular relationship during impingement of the blades 14 with reference to a sectional view along the line B-B of FIG. 3. The impeller 12 rotates along a circumferential direction U in a rotational plane 40 that is situated so as to be perpendicular to the shaft axis A or to the compressor flow 30. The blades 14 are inclined by an angle β relative to the rotational plane 40, which angle can depend on the configuration of the compressor system and of the compressor stage. The resulting fluid flow provided from the mixing chambers 34 by way of the chamber outlet openings 38 impinges the blades 14 of the impeller 12 essentially perpendicularly to a blade axis 42 and at an angle γ to the rotational plane 40 of the impeller 12. The adjustable chamber outlet openings 38 make it possible to select or vary the inflow angle γ depending on the rotational speed of the blades 14 and/or depending on the operating state of the compressor system in order to in this manner make it possible to achieve dynamic stabilization of the compressor flow 30. In this process the resulting fluid flow can be directed onto the blades 14 with one component in the direction of rotation, or with one component against the direction of rotation. An angle γ=0 indicates that the resulting fluid flow impinges the blade 14 in the direction of rotation U. An angle γ=180° indicates that the resulting fluid flow is directed against the direction of rotation U of the blade 14. Preferably, the inflow angle γ can be varied in a range of 20° to 160°, particularly preferably in a range of 90° to 160° and in particular in a range of 90° to 140°.
In an exemplary configuration the chamber outlet openings 38 are arranged in such a manner that the impeller blades 14 are impinged in the axial direction.
In one embodiment of the invention the chamber outlet openings 38 can also be aligned in such a manner that the impeller blades 14 are impinged at an angle δ (not shown), as measured in the radial direction of the blade axis 42. Preferably, the angle δ is in the range between 45° and 135°.
The plurality of mixing chambers 34 arranged along the circumferential region of the flow channel 28 make it possible to feed the stabilizing ejector flow almost uniformly over the entire circumferential region of the impeller 12 and thus in the blade tip region of the blades 14, which region because of its proximity to the housing and because of the high rotational speed is aerodynamically particularly highly loaded, to intervene in a stabilizing manner in the flow conditions and to prevent flow separation.
FIG. 5 shows a diagrammatic cross-sectional drawing of the air-assisted injection device described above with reference to FIGS. 3 and 4. In the illustration the flow channel 28, which is delimited by a housing wall of the compressor housing 26, during operation of the compressor system is subjected to a compressor flow 30 from left to right. In the flow channel 28 several impellers 12, 12′, 12″, whose design and function correspond to those of the impeller 12 described with reference to FIG. 3, are arranged in series in the direction of flow. Together, said impellers 12, 12′, 12″ form a compressor system. For the sake of clarity the stators, which in each case can be arranged downstream of the impellers 12, 12′, 12″, are not shown in FIG. 5.
FIG. 5 further shows the first supply line 32 for the primary fluid flow 16 with a first inlet 44 for diverting the primary fluid flow 16 from the flow channel 28 downstream of the impeller 12, 12′, 12″. The first supply line 32 leads the primary fluid flow 16, which enters at the inlet 44, outside the wall of the flow channel 28 past the impellers 12, 12′, 12″ and then through the wall of the flow channel 28 by way of a diversion section 46 and an outlet 48, which can be designed as a nozzle, into the mixing chamber 34, which is situated upstream of the impeller 12 on the inside wall of the compressor housing 26 and which is separated from the flow channel 28 by the mixing chamber wall 36.
After diverting in the diversion section 46 the primary fluid flow 16 exits from the outlet opening 48 in the direction of the blade tip region of the impeller 12. The outlet opening 38 of the mixing chamber 34 forms a mixing tube 24 whose inlet aperture 50 is arranged so as to preferably be concentrically opposite the outlet opening 48, with the outlet opening 52 of said mixing tube 24 facing in the direction of the blade tips of the impeller 12.
By way of a second supply line 54 the mixing chamber 34 is in fluidic communication with an outside region of the compressor housing. By way of the second supply line 54, the primary fluid flow 16, which exits from the nozzle 48 at high speed, draws air from the outside region of the compressor housing 26 as a secondary fluid flow 22 into the mixing chamber 34. In the mixing tube 24 the secondary fluid flow 22 establishes contact with the primary fluid flow 16, is accelerated by the primary fluid flow 16, and mixes with it to form a resulting fluid flow 56 that leaves the mixing tube 24 through the outlet opening 52 in the direction of the impeller 12.
The mixing tube 24 can act as a diffuser; it comprises a cross-sectional area that exceeds the cross-sectional area of the outlet 48 of the first supply line 32 twice, preferably more than twice or more. The distance between the outlet 48 of the first supply line 32 and the inlet aperture 50 of the mixing tube 24 is preferably in the range of between 2D and 4D, wherein D designates a diameter of the mixing tube 24. As shown in FIG. 5, the distance can, however, also be selected to be shorter. In particular, the outlet 48 of the first supply line 32 can also project into the mixing tube 24 so that the distance becomes negative. The compact design of an aero engine can considerably limit the ratio.
With the configuration described it is possible to achieve an admixing ratio μ=2 or greater, i.e., the primary fluid flow 16 is increased by the secondary fluid flow 22 from the outside region of the compressor housing 26 by more than twice. The mixing tube 24 can comprise movable components (not shown) at its outlet opening 52 in order to, depending on the operating state of the compressor system, direct the resulting fluid flow 56 at a predetermined angle γ onto the blades 14 of the impeller 12, as has been described above with reference to FIGS. 3 and 4.
FIG. 6 shows an alternative embodiment of a compressor system according to the invention, which essentially resembles the embodiment described above with reference to FIG. 5 and which differs only in the design of the mixing region.
In contrast to the embodiment of FIG. 5, in which the mixing chamber 34 is formed in the flow channel 28, the mixing region in the embodiment of FIG. 6 is situated at least in part outside the flow channel 28 and inside the compressor housing 26. In this configuration the first supply line 32 leads within the compressor housing 26 into the mixing chamber 34. When exiting from the nozzle aperture 48 of the first supply line 32 the primary fluid flow 16 aspirates a secondary fluid flow 22 by way of a second supply line (not shown) into the mixing chamber 34.
The mixing chamber 34 again comprises a mixing tube 24′ in which the secondary fluid flow 22 mixes with the primary fluid flow 16 to form the resulting fluid flow 56. In contrast to the embodiment of FIG. 5 the mixing tube 24′ passes through the wall of the compressor housing 26 and diverts the resulting fluid flow 56 in the direction of the impeller 12. In terms of its dimensions, its arrangement relative to the outlet 48 of the first supply line 32 and in its effect, the mixing tube 24′ of the embodiment of FIG. 6 does not otherwise, however, differ from the mixing tube 24 as described above with reference to FIG. 5.
There is an advantage of the configuration of FIG. 6, in which the mixing chamber is arranged at least in part outside the compressor housing 26, in that the air-assisted injection system requires no intervention, or only minimal intervention, in the flow channel 28.
In one improvement of the embodiment of FIG. 6 the chamber outlet openings 38 can be mere slots in the wall of the flow channel 28, which slots are designed and arranged in such a manner that they guide the resulting fluid flow 56 in the direction of the impeller 12. This configuration is associated with an advantage in that the flow channel 28 remains completely free.
The embodiments described above and the drawings have been provided exclusively to illustrate the invention and thus the advantages achieved by it; however, they are not to be interpreted as limiting the invention. The scope of the invention is derived solely from the following claims.

Claims

1. A method for providing a fluid flow to a compressor system of a first turbo machine, wherein the compressor system comprises at least one compressor housing in which at least one impeller is arranged and through which a compressor flow flows, with the method comprising:

feeding a primary fluid flow to a mixing region of the compressor system;

feeding a secondary fluid flow from an outside region of the compressor housing to the mixing region so that the secondary fluid flow mixes at least in part with the primary fluid flow to form a resulting fluid flow so that between the primary fluid flow and the secondary fluid flow a momentum exchange takes place, and so that the secondary fluid flow is promoted by the primary fluid flow; and

feeding the resulting fluid flow to the compressor flow upstream of the impeller in the direction of the impeller.

2. The method according to claim 1 in which the primary fluid flow is diverted from a compressor flow of a second turbo machine, preferably from the compressor flow of the first turbo machine downstream of the impeller.

3. The method according to claim 1 in which the impeller comprises several blades, and the resulting fluid flow is fed to the compressor flow in such a manner that the resulting fluid flow impinges the impeller in the region of the tips of the blades.

4. (canceled)

5. The method according to claim 1 in which the compressor defines a flow channel, and the mixing region is situated at least in part outside the flow channel, preferably completely outside the flow channel.

6. The method according to claim 1 in which the compressor housing defines a flow channel, and the mixing region is situated at least in part in the flow channel.

7. The method according to claim 1 in which the compressor housing defines a flow channel, and the mixing region is closed off at least in part from the flow channel.

8. The method according to claim 1 with the alignment of the resulting fluid flow in such a manner that the resulting fluid flow impinges the blade essentially perpendicularly to a blade axis of a blade of the impeller and/or at an angle to a plane of the impeller.

9. The method according to claim 8 in which the angle is varied depending on a rotating speed of the impeller, preferably in a range of 20° to 160°, particularly preferably in a range of 90° to 140°.

10. The method according to claim 1, in which an admixing ratio of a quotient of a mass flow of the secondary fluid flow and of a mass flow of the primary fluid flow is at least 1, preferably at least 3, and particularly preferably at least 10.

11. A device for providing a fluid flow to a compressor system of a first turbo machine, the device comprising:

a compressor housing that defines a flow channel in which at least one impeller is arranged;

a first supply line for a primary fluid flow, wherein the first supply line comprises a first inlet for the primary fluid flow and a first outlet, wherein the first outlet upstream of the impeller is in fluidic communication with the flow channel; and

a second supply line for a secondary fluid flow, wherein the second supply line comprises a second inlet that is in fluidic communication with an outside region of the compressor housing, and comprises a second outlet that upstream of the impeller is in fluidic communication with the flow channel;

wherein the first outlet and the second outlet are arranged in such a manner relative to each other that the secondary fluid flow mixes at least in part with the primary fluid flow to form a resulting fluid flow directed onto the impeller so that between the primary fluid flow and the secondary fluid flow a momentum exchange takes place, and so that the secondary fluid flow is promoted by the primary fluid flow.

12. The device according to claim 11 in which the first inlet is in fluidic communication with a compressor stage of a second turbo machine, preferably is in fluidic communication, downstream of the impeller, with the flow channel of the first turbo machine.

13. The device according to claim 11 or 12 in which the first outlet and/or the second outlet are/is arranged in a peripheral region of the flow channel.

14. The device according to claim 11 in which the first is arranged inside the flow channel and is preferably aligned in the direction of the impeller.

15. The device according to claim 11 with a mixing line that comprises a third inlet and a third outlet, wherein the third inlet faces the first outlet, and the third outlet is in fluidic communication with the flow channel, and is aligned in the direction of the impeller.

16. The device according to claim 15 in which the third inlet has a diameter D, and a distance a between the first outlet, and the third inlet is in a range of −3D≦a≦5D, preferably 0≦a≦4D, particularly preferably 2D≦a≦4D, wherein a negative distance indicates that the third inlet is situated upstream of the first outlet.

17. The device according to claim 15 in which a ratio of a cross-sectional area of the third inlet to a cross-sectional area of the first outlet is between 1:1 and 100:1, preferably between 5:1 and 50:1 and particularly preferably between 10:1 and 40:1.

18. The device according to claim 11 in which the first outlet and/or the third outlet are/is aligned so as to be essentially perpendicular to a blade axis of a blade of the impeller and/or at an angle to a plane of the impeller.

19. The device according to claim 18 which is equipped to vary the angle depending on a rotating speed of the impeller, preferably in a range of 20° to 160°, particularly preferably in a range of 90° to 140°.

20. (canceled)

21. The device according to claim 11 with a mixing region that upstream of the impeller is in fluidic communication with the flow channel, and into which mixing region the first outlet and the second outlet lead.

22. The device according to claim 21 in which the mixing region comprises a mixing chamber that at least in part is situated within the flow channel.

23. (canceled)