EP0417433A1 - Axial turbine - Google Patents

Axial turbine Download PDF

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Publication number
EP0417433A1
EP0417433A1 EP90113994A EP90113994A EP0417433A1 EP 0417433 A1 EP0417433 A1 EP 0417433A1 EP 90113994 A EP90113994 A EP 90113994A EP 90113994 A EP90113994 A EP 90113994A EP 0417433 A1 EP0417433 A1 EP 0417433A1
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EP
European Patent Office
Prior art keywords
guide vanes
flow
turbine according
blades
ribs
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Granted
Application number
EP90113994A
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German (de)
French (fr)
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EP0417433B1 (en
Inventor
Franz Kreitmeier
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ABB Asea Brown Boveri Ltd
ABB AB
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ABB Asea Brown Boveri Ltd
Asea Brown Boveri AB
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D17/00—Regulating or controlling by varying flow
    • F01D17/10—Final actuators
    • F01D17/12—Final actuators arranged in stator parts
    • F01D17/14—Final actuators arranged in stator parts varying effective cross-sectional area of nozzles or guide conduits
    • F01D17/16—Final actuators arranged in stator parts varying effective cross-sectional area of nozzles or guide conduits by means of nozzle vanes
    • F01D17/162—Final actuators arranged in stator parts varying effective cross-sectional area of nozzles or guide conduits by means of nozzle vanes for axial flow, i.e. the vanes turning around axes which are essentially perpendicular to the rotor centre line
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D25/00—Component parts, details, or accessories, not provided for in, or of interest apart from, other groups
    • F01D25/30—Exhaust heads, chambers, or the like

Definitions

  • the invention relates to an axially flow-through turbine, to the outlet rotor blades of which a diffuser is connected, means within the deceleration zone being provided for swirl removal of the swirled flow
  • Such a turbine is known from EP-A 265 633.
  • a rectifying grid is provided within the diffuser, which extends over the entire height of the flowed channel.
  • These means for swirl removal are three flow ribs with thick profiles which are arranged uniformly over the circumference and which are designed according to the knowledge of turbomachine construction and which should be as insensitive as possible to oblique flow. The flowed leading edge of these ribs is located relatively far behind the trailing edge of the last blades in order to avoid excitation of the last row of blades caused by the pressure field of the ribs.
  • This distance is dimensioned such that the front edge of the ribs is in a plane in which a diffuser area ratio of preferably three predominates.
  • the diffuser zone between the blading and the flow ribs should therefore remain undisturbed due to total rotational symmetry.
  • the fact that no interference effects between the ribs and the blades are to be expected is due to the fact that the Ribs only become effective on a level in which a relatively low energy level already prevails.
  • the diffuser is flowed at at idle under a speed ratio c t / c n of approximately 1.2, where c t means the tangential speed and c n the axial speed of the medium.
  • This oblique flow leads to a drop in the pressure recovery C p , as can be seen from FIG. 2 to be described later (curve A).
  • the pressure behind blading can usually be 0.98 at full load at 40% volume flow rise up to 1.15 bar. This back pressure means that at 40% volume flow, significantly more drive power has to be applied to the machine than if a well-acting diffuser is available.
  • the object of the invention is to design the diffusion zone in axially flow-through turbines of the type mentioned at the outset in such a way that the part-load behavior of the machine is further improved.
  • At least one row with adjustable guide vanes is arranged between the means for swirl removal and the outlet blades.
  • the guide blades have a straight skeleton line with a symmetrical profile.
  • the well-known properties of such grids on insensitivity in the inflow can be used for low-loss deflection.
  • the known gas turbine of which only the last three axially flowed stages are shown in FIG. 1, consists essentially of the bladed rotor 1 'and the blade carrier 2' equipped with guide vanes.
  • the blade carrier is suspended in the turbine housing 3 '.
  • the rotor is in a support bearing 4 ', which in turn is supported in an exhaust housing 5'.
  • This exhaust housing 5 ' consists essentially of a hub-side, inner part 6' and an outer part 7 ', which limit the diffuser 13'.
  • Both elements 6 'and 7' can be one-piece pot housings without an axial parting plane. They are interconnected by several welded supporting flow ribs 8 ', which are arranged evenly distributed over the circumference and whose profile is indicated by 9'. It can be seen that for the reasons mentioned at the outset, the flow ribs 8 'are arranged at a suitable distance from the blading.
  • the pressure recovery C p is plotted on the ordinate, which in a first approximation corresponds to the ratio (p A -p E ) / p * E -p E ), where p A is the static pressure at the outlet of the diffuser, p E is the static pressure at Entry of the diffuser and p * E mean the total pressure at the inlet of the diffuser and thus at the outlet of the blading.
  • Curve A shows the pressure recovery in a diffuser which is equipped with flow ribs which have a pitch to chord ratio of approximately 0.5. It can be seen that the drop is somewhat acceptable up to a c t / c n value, but that the pressure recovery deteriorates dramatically as the volume flow decreases.
  • Curve B shows the completely unreasonable course when flow ribs with a pitch to chord ratio of approximately 1 are used.
  • FIG. 3 The structure of the gas turbine shown there corresponds to that of FIG. 1, which is why the structure is not described again.
  • the same elements as in Fig. 1 are designated in Fig. 3 with the same reference numerals without (').
  • Evenly distributed over the circumference are the same Straightening flow ribs 8 with a straight skeleton line and with a ratio of division to tendon of 0.5. This ratio occurs in the middle section of the flow-through channel of the flow ribs, which run conically in the radial direction.
  • the guide vanes 11 are also symmetrical profiles with a straight skeleton line, as are known for example under the term NACA 0010.
  • these guide blades have a pitch to chord ratio of 0.5 in the middle section of the channel through which the flow passes.
  • Such blades are to a certain extent insensitive to inclined flow, (see article by N. Scholz, "Investigations on blade grids of turbomachines", Journal of Flight Sciences, No. 3, 1955).
  • the guide vanes 11 are tapered in the radial direction and are preferably twisted.
  • the adjustment of the guide vanes 11 in the grating takes place via actuating means, not shown, as are known, for example, from compressor construction.
  • the actual adjustment is preferably carried out automatically as a function of the operating parameters such as load, speed, etc.
  • the greatest pressure recovery is achieved when the guide vanes are adjusted so that the shaft power assumes the greatest possible value under all operating conditions. A permanent performance measurement is therefore suitable.
  • the greatest pressure recovery can also be achieved if the adjustment of the guide vanes takes place in such a way that the static pressure in front of the guide vanes 11, ie behind the outlet rotor blades 12, takes the smallest possible value.
  • a permanent differential pressure measurement p A -p E is therefore suitable.
  • the cylinder section in FIG. 4 shows, on an enlarged scale, the blade plan in the gas turbine zone under consideration.
  • the characters c in each case mean the absolute speed, w the relative speed and u the peripheral speed of the machine.
  • the individual grids have, for example, the following in order to indicate the order of magnitude in an executed example Data:
  • the chord of the guide vanes 11 is 125 mm, that of the flow ribs is approximately 700 mm.
  • the ratio of profile thickness to chord is 0.1 for the guide vanes and for the flow ribs.
  • the flow towards the guide vanes 11 is approximately the same under which they leave the outlet rotor vanes 12, i.e. with the speed c and an angle ⁇ of 60 °.
  • the exhaust gases thus leave the guide vane at an angle of approximately 40 °, with which they strike the front edges of the flow ribs 8, which are also insensitive to oblique flow, where they enter the axial, i.e. be aligned to 0 °.
  • Curve C in FIG. 2 now shows the effect of an optimally adjusted guide blading.
  • the pressure recovery is almost constant and only then drops to a modest extent, compared to the diffuser configuration without guide vanes.
  • the diagram also shows that at full load, ie in the range c t / c n between -0.1 and +0.1 (depending on the design of the blading), the diffuser configurations which are state of the art achieve a somewhat better pressure recovery. This is because the area around which the diffuser flows is less than that with guide vanes.
  • the new measure also makes it possible to allow a certain counter-swirl at the outlet from the last rotor blades 12, since an axial alignment takes place downstream in the diffuser through the guide blades and the flow ribs.
  • This counter-swirl would have the following advantages: - The step work can be increased with constant efficiency; or - The efficiency can be increased with constant step work; - The blades of the last row could be made less twisted, which leads to a reduction in price; - The deflection in the last turbine stage can be reduced, which is particularly important in the case of fluidized-bed-fired gas turbines because of the particle separation.
  • the invention is not limited to the exemplary embodiment shown and described, which relates to a diffuser with an axial outlet and thus greatly facilitates the arrangement of the flow ribs. It is also particularly applicable to steam turbines or the turbines of exhaust gas turbochargers, both of which generally have a so-called axial-radial exit from the blading. In such machines, the means for swirl removal are represented by the radial part of the outlet housing itself.
  • the skeleton shape of the guide vanes can also be curved, which would of course lead to a significant increase in the cost of this additional measure.

Abstract

An axial turbine, to whose exhaust rotor blades (12) a diffuser (13) is connected, has first means for absorbing vortex movement (8) of the flow which contains vortices within its deceleration zone. <??>A row of adjustable stator blades (11) is arranged between these first means for absorbing vortex movement, in the form of flow ribs, and the exhaust rotor blades. These stator blades (11) have a straight mean camber line with a symmetrical profile, run conically in the radial direction and are twisted. <??>As a result of this measure, in addition to considerably improved pressure recovery over a large load range, it is also possible to prevent the eddies which normally occur between rotor blades and flow ribs. <IMAGE>

Description

Technisches GebietTechnical field

Die Erfindung betrifft eine axialdurchströmte Turbine, an deren Austrittslaufschaufeln sich ein Diffusor anschliesst, wobei innerhalb dessen Verzögerungszone Mittel zur Drallwegnahme der drallbehafteten Strömung vorgesehen sindThe invention relates to an axially flow-through turbine, to the outlet rotor blades of which a diffuser is connected, means within the deceleration zone being provided for swirl removal of the swirled flow

Stand der TechnikState of the art

Eine derartige Turbine ist bekannt aus der EP-A 265 633. Um der dortigen Forderung nach bestmöglichem Druckrückgewinn bei Teillast gerecht zu werden, ist innerhalb des Diffusors ein gleichrichtendes Gitter vorgesehen, das sich über die ganze Höhe des durchströmten Kanals erstreckt. Es handelt sich bei diesen Mitteln zur Drallwegnahme um drei gleichmässig über dem Umfang angeordnete Strömungsrippen mit dicken Profilen, die nach den Erkenntnissen des Strömungsmaschinenbaus ausgelegt sind und die gegen Schräganströmung möglichst unempfindlich sein sollen. Die angeströmte Vorderkante dieser Rippen befin­det sich relativ weit hinter der Austrittskante der letzten Laufschaufeln, um eine durch das Druckfeld der Rippen verur­sachte Anregung der letzten Schaufelreihe zu vermeiden. Dieser Abstand ist so bemessen, dass sich die Vorderkante der Rippen in einer Ebene befindet, bei welcher ein Diffusorflächenver­hältnis von vorzugsweise drei vorherrscht. Die Diffusorzone zwischen Beschaufelung und Srömungsrippen soll damit infolge totaler Rotationssymmetrie ungestört bleiben. Die Tatsache, dass keine Interferenzeffekte zwischen Rippen und Beschaufe­lung zu erwarten sind, ist darauf zurückzuführen, dass die Rippen erst in einer Ebene wirksam werden, in der bereits ein relativ tiefes Energieniveau vorherrscht.Such a turbine is known from EP-A 265 633. In order to meet the demand there for the best possible pressure recovery at part load, a rectifying grid is provided within the diffuser, which extends over the entire height of the flowed channel. These means for swirl removal are three flow ribs with thick profiles which are arranged uniformly over the circumference and which are designed according to the knowledge of turbomachine construction and which should be as insensitive as possible to oblique flow. The flowed leading edge of these ribs is located relatively far behind the trailing edge of the last blades in order to avoid excitation of the last row of blades caused by the pressure field of the ribs. This distance is dimensioned such that the front edge of the ribs is in a plane in which a diffuser area ratio of preferably three predominates. The diffuser zone between the blading and the flow ribs should therefore remain undisturbed due to total rotational symmetry. The fact that no interference effects between the ribs and the blades are to be expected is due to the fact that the Ribs only become effective on a level in which a relatively low energy level already prevails.

In üblichen Gasturbinen wird der Diffusor bei Leerlauf unter einem Geschwindigkeitsverhältnis ct/cn von etwa 1,2 ange­strömt, wobei ct die Tangentialgeschwindigkeit und cn die Axialgeschwindigkeit des Mediums bedeutet. Diese schräge Anströmung führt zu einem Abfall im Druckrückgewinn Cp, wie aus der später zu beschreibenden Fig.2 ersichtlich ist (Kurve A).In conventional gas turbines, the diffuser is flowed at at idle under a speed ratio c t / c n of approximately 1.2, where c t means the tangential speed and c n the axial speed of the medium. This oblique flow leads to a drop in the pressure recovery C p , as can be seen from FIG. 2 to be described later (curve A).

Bei andern Maschinentypen, wie beispielsweise Dampfturbinen oder Gasturbinen für wirbelschichtfeuerung, kommt es durchaus vor, dass der Volumenstrom bis auf 40% reduziert wird und damit ct/cn Verhältnisse bis zu 3 vorliegen. Bei solchen Maschinentypen bietet sich die bekannte Diffusorkonfiguration nicht an, da der Druckrückgewinn sogar negativ werden könnte, wie in Fig.2 erkennbar. Dies gilt selbst für den Fall, bei dem das Verhältnis Teilung zu Sehne der Strömungsrippen 0,5 beträgt (Kurve A). Strömungsrippen mit Teilung/Sehne-Verhält­nissen von etwa 1 (Kurve B), welche gemäss Fig.2 bei Vollast, d.h. ct/cn = ca.0, zwar einen etwas grösseren Druckrückgewinn ergeben würden, sind bei derartigen Maschinen überhaupt nicht anwendbar.With other machine types, such as steam turbines or gas turbines for fluidized bed combustion, it is quite possible that the volume flow is reduced to 40% and thus there are c t / c n ratios of up to 3. The known diffuser configuration does not lend itself to such machine types, since the pressure recovery could even become negative, as can be seen in FIG. This applies even to the case where the ratio of pitch to chord of the flow ribs is 0.5 (curve A). Flow ribs with pitch / chord ratios of about 1 (curve B), which according to FIG. 2 would result in a somewhat greater pressure recovery under full load, ie c t / c n = approx. 0, cannot be used with such machines at all.

Neben dem grossen Abfall im Druckrückgewinn ist bei den genannten extremen Verhältnissen ein starker Wirbel zwischen Austrittslaufschaufeln und Strömungsrippen charakteristisch, wie in der ebenfalls später zu beschreibenden Fig.1 angedeu­tet. Der Wirbel wird durch die Strömungsrippen begrenzt, an denen die Tangentialkomponente der Geschwindigkeit dissipiert wird. Werden an der sich einstellenden Rückströmung feste Par­tikel, bspw. in Gasturbinen oder Wassertröpfchen, bspw. in Dampfturbinen mitgeführt, so kann eine akute Gefahr der Fuss­erosion an den Schaufeln der letzten Laufreihe entstehen.In addition to the large drop in the pressure recovery, a strong vortex between the outlet blades and flow ribs is characteristic in the extreme conditions mentioned, as indicated in FIG. 1, which will also be described later. The vortex is limited by the flow ribs on which the tangential component of the velocity is dissipated. If solid particles, for example in gas turbines or water droplets, for example in steam turbines, are carried along with the return flow, an acute risk of foot erosion can arise on the blades of the last row of runs.

Im Falle von Gasturbinen für wirbelschichtfeuerung kann der Druck hinter Beschaufelung von üblicherweise 0,98 bei Vollast bei 40% Volumenstrom auf bis zu 1,15 bar ansteigen. Dieser Ge­gendruck bedeutet, dass bei 40% Volumenstrom für die Maschine bedeutend mehr Antriebsleistung aufzubringen ist als bei Vor­handensein eines gut wirkenden Diffusors.In the case of gas turbines for fluidized bed combustion, the pressure behind blading can usually be 0.98 at full load at 40% volume flow rise up to 1.15 bar. This back pressure means that at 40% volume flow, significantly more drive power has to be applied to the machine than if a well-acting diffuser is available.

Darstellung der ErfindungPresentation of the invention

Der Erfindung liegt die Aufgabe zugrunde, bei axial durch­strömten Turbinen der eingangs genannten Art die Diffusions­zone so zu gestalten, dass das Teillastverhalten der Maschine weiter verbessert wird.The object of the invention is to design the diffusion zone in axially flow-through turbines of the type mentioned at the outset in such a way that the part-load behavior of the machine is further improved.

Erfindungsgemäss wird dies dadurch erreicht, dass zwischen den Mitteln zur Drallwegnahme und den Austrittslaufschaufeln min destens eine Reihe mit verstellbaren Leitschaufeln angeordnet ist.This is achieved according to the invention in that at least one row with adjustable guide vanes is arranged between the means for swirl removal and the outlet blades.

Der Vorteil der Erfindung ist unter anderem darin zu sehen, dass neben dem beträchtlich verbesserten Druckrückgewinn über einem grossen Lastbereich auch der oben erwähnte Wirbel, sofern er überhaupt noch auftritt, sich erst zwischen Leit­schaufeln und Strömungsrippen ausbildet und damit keinen schädlichen Einfluss auf die rotierenden Austrittsschaufeln ausüben kann.The advantage of the invention can be seen in the fact that, in addition to the considerably improved pressure recovery over a large load range, the above-mentioned vortex, if it still occurs, only forms between guide vanes and flow ribs and thus has no harmful influence on the rotating outlet vanes can.

Es ist besonders zweckmässig, wenn die Leitschaufeln eine gerade Skelettlinie mit symmetrischem Profil aufweisen. Mit dieser Massnahme können die hinlänglich bekannten Eigenschaf­ten solcher Gitter auf Unempfindlichkeit in der Anströmung zur verlustarmen Umlenkung genutzt werden.It is particularly expedient if the guide blades have a straight skeleton line with a symmetrical profile. With this measure, the well-known properties of such grids on insensitivity in the inflow can be used for low-loss deflection.

Kurze Beschreibung der ZeichnungBrief description of the drawing

In der Zeichnung ist ein Ausführungsbeispiel der Erfindung anhand einer Gasturbine mit axial/axialem Austritt darge­stellt.
Es zeigen:

  • Fig.1 eine schematische Prinzipskizze eines zum Stand der Technik gehörenden Diffusorsystems;
  • Fig.2 ein Schaubild Druckrückgewinn in Funktion von ct/cn;
  • Fig.3 einen Teillängsschnitt einer Gasturbine mit erfin­dungsgemässem Diffusor;
  • Fig.4 die teilweise Abwicklung eines zylinderschnittes auf mittlerem Durchmesser des durchströmten Kanals gemäss Fig.3
In the drawing, an embodiment of the invention is shown using a gas turbine with an axial / axial outlet.
Show it:
  • 1 shows a schematic diagram of a diffuser system belonging to the prior art;
  • 2 shows a graph of pressure recovery as a function of c t / c n ;
  • 3 shows a partial longitudinal section of a gas turbine with a diffuser according to the invention;
  • 4 shows the partial development of a cylindrical section on the medium diameter of the flowed channel according to FIG. 3

Es sind nur die für das Verständnis der Erfindung wesentlichen Elemente gezeigt. Nicht dargestellt sind von der Anlage bei­spielsweise der Verdichterteil, die Brennkammer sowie das vollständige Abgasrohr und der Kamin. Die Strömungsrichtung des Arbeitsmittels ist mit Pfeilen bezeichnet.Only the elements essential for understanding the invention are shown. The system does not show, for example, the compressor section, the combustion chamber and the complete exhaust pipe and chimney. The direction of flow of the working fluid is indicated by arrows.

Weg zur Ausführung der ErfindungWay of carrying out the invention

Die bekannte Gasturbine, von der in Fig.1 lediglich die drei letzten, axialdurchströmten Stufen dargestellt sind, besteht im wesentlichen aus dem beschaufelten Rotor 1′ und dem mit Leitschaufeln bestückten schaufelträger 2′. Der Schaufelträger ist im Turbinengehäuse 3′ eingehängt. Der Rotor liegt in einem Traglager 4′ ein, welches sich seinerseits in einem Abgasge­häuse 5′ abstützt. Dieses Abgasgehäuse 5′ besteht im wesentli­chen aus einem nabenseitigen, innenliegenden Teil 6′ und einem aussenliegenden Teil 7′, welche den Diffusor 13′ begrenzen. Beide Elemente 6′ und 7′ können einteilige Topfgehäuse ohne axiale Trennebene sein. Sie sind miteinander verbunden durch mehrere angeschweisste tragende strömungsrippen 8′, die gleichmässig verteilt über dem Umfang angeordnet sind und deren Profil mit 9′ angedeutet ist. Es ist erkennbar, dass aus den eingangs genannten Gründen die Stömungsrippen 8′ in gehö­rigem Abstand zur Beschaufelung angeordnet ist.The known gas turbine, of which only the last three axially flowed stages are shown in FIG. 1, consists essentially of the bladed rotor 1 'and the blade carrier 2' equipped with guide vanes. The blade carrier is suspended in the turbine housing 3 '. The rotor is in a support bearing 4 ', which in turn is supported in an exhaust housing 5'. This exhaust housing 5 'consists essentially of a hub-side, inner part 6' and an outer part 7 ', which limit the diffuser 13'. Both elements 6 'and 7' can be one-piece pot housings without an axial parting plane. They are interconnected by several welded supporting flow ribs 8 ', which are arranged evenly distributed over the circumference and whose profile is indicated by 9'. It can be seen that for the reasons mentioned at the outset, the flow ribs 8 'are arranged at a suitable distance from the blading.

Ebenfalls erkennbar ist der starke Wirbel 10, der sich bei unterer Teillast zwischen Austrittslaufschaufeln 12′ und Strö­mungsrippen 8′ ausbildet und den es mit der Erfindung zu ver­meiden gilt.Also recognizable is the strong vortex 10, which is formed between the outlet blades 12 'and flow ribs 8' at lower partial load and which is to be avoided with the invention.

Das Ergebnis eines derartigen Wirbels kann anhand des Schau­bildes in Fig.2 aufgezeigt werden. Es versteht sich, dass auf die Bekanntgabe von allen den Berechnungen und Versuchen zugrundeliegenden Absolutwerten verzichtet wird, da diese wegen ihrer Abhängigkeit von allzu zahlreichen Parametern ohnehin ungenügende Aussagekraft besitzen würden. Die darge­stellten Kurven sind demnach vor allem qualitativ auszulegen. Auf der Abszisse des Diagrammes ist der Wert ct/cn aufgetra­gen, der ein Mass für den Volumenstrom darstellt. Es handelt sich um den Tangens des Abströmwinkels α aus den letzten Aus­trittslaufschaufeln, wobei ct die Tangentialkomponente und cn die Normalkomponente bedeutet. Bei gleichbleibender Maschinen­drehzahl wird bei abnehmender Last und damit abnehmenden Volu­menstrom dieser Winkel immer grösser.
Auf der Ordinate ist der Druckrückgewinn Cp aufgetragen, der in erster Näherung dem Verhältnis (pA-pE)/p*E-pE) entpricht, worin pA der statische Druck am Austritt des Diffusors, pE der statische Druck am Eintritt des Diffusors und p*E der Total­druck am Eintritt des Diffusors und damit am Austritt der Beschaufelung bedeuten.
Die Kurve A zeigt den Druckrückgewinn in einem Diffusor, der mit Strömungsrippen bestückt ist, welche ein Verhältnis Tei­lung zu Sehne von etwa 0,5 aufweisen. Man erkennt, dass der Abfall bis zu einem ct/cn-Wert einigermassen tragbar ist, dass bei kleiner werdendem Volumenstrom sich der Druckrückgewinn jedoch dramatisch verschlechtert. Kurve B zeigt den völlig unzumutbaren Verlauf, wenn Strömungsrippen mit einem Verhält­nis Teilung zu Sehne von etwa 1 zur Anwendung gelangen.The result of such a vortex can be shown on the basis of the diagram in FIG. It goes without saying that the disclosure of all absolute values on which the calculations and tests are based is dispensed with, since these would in any case have insufficient informative value because of their dependence on too many parameters. The curves shown are therefore primarily to be interpreted qualitatively. The value c t / c n , which is a measure of the volume flow, is plotted on the abscissa of the diagram. It is the tangent of the outflow angle α from the last outlet blades, where c t is the tangential component and c n is the normal component. With the machine speed remaining the same, the angle increases with decreasing load and thus decreasing volume flow.
The pressure recovery C p is plotted on the ordinate, which in a first approximation corresponds to the ratio (p A -p E ) / p * E -p E ), where p A is the static pressure at the outlet of the diffuser, p E is the static pressure at Entry of the diffuser and p * E mean the total pressure at the inlet of the diffuser and thus at the outlet of the blading.
Curve A shows the pressure recovery in a diffuser which is equipped with flow ribs which have a pitch to chord ratio of approximately 0.5. It can be seen that the drop is somewhat acceptable up to a c t / c n value, but that the pressure recovery deteriorates dramatically as the volume flow decreases. Curve B shows the completely unreasonable course when flow ribs with a pitch to chord ratio of approximately 1 are used.

Um dem abzuhelfen, wird nun gemäss der Erfindung zwischen den Austrittslaufschaufeln 12 und den Strömungsrippen 8 eine Reihe verstellbarer Leitschaufeln angeordnet, wie in Fig. 3 ersicht­lich. Die dort gezeigte Gasturbine entspricht in ihrer Struk­tur jener von Fig. 1, weshalb auf eine nochmalige Beschreibung des Aufbaus verzichtet wird. Die gleichen Elemente wie in Fig. 1 sind in Fig. 3 mit den selben Bezugszeichen ohne (') be­zeichnet. Gleichmässig über den Umfang verteilt sind gleich­ richtende Strömungsrippen 8 mit gerader Skelettlinie und mit einem Verhältnis Teilung zu Sehne von 0,5. Dieses Verhältnis tritt im Mittelschnitt des durchströmten Kanals der in radi­aler Richtung konisch verlaufenden Strömungsrippen auf.In order to remedy this, a row of adjustable guide vanes is now arranged according to the invention between the outlet rotor blades 12 and the flow ribs 8, as can be seen in FIG. 3. The structure of the gas turbine shown there corresponds to that of FIG. 1, which is why the structure is not described again. The same elements as in Fig. 1 are designated in Fig. 3 with the same reference numerals without ('). Evenly distributed over the circumference are the same Straightening flow ribs 8 with a straight skeleton line and with a ratio of division to tendon of 0.5. This ratio occurs in the middle section of the flow-through channel of the flow ribs, which run conically in the radial direction.

Bei den Leitschaufeln 11 handelt es sich ebenfalls um symme­trische Profile mit gerader Skelettlinie, wie sie beispiels­weise unter dem Begriff NACA 0010 bekannt sind. Im vorliegen­den Fall weisen diese Leitschaufeln im Mittelschnitt des des durchströmten Kanals ein Verhältnis Teilung zu Sehne von 0,5 auf. Derartige Schaufeln sind bis zu einem gewissen Grad un­empfindlich gegen Schräganströmung, (s. Artikel von N. Scholz, "Untersuchungen an Schaufelgittern von Strömungsmaschinen", Zeitschrift für Flugwissenschaften, Nr. 3, 1955). Die Leit­schaufeln 11 verlaufen in radialer Richtung konisch und sind vorzugsweise verwunden.The guide vanes 11 are also symmetrical profiles with a straight skeleton line, as are known for example under the term NACA 0010. In the present case, these guide blades have a pitch to chord ratio of 0.5 in the middle section of the channel through which the flow passes. Such blades are to a certain extent insensitive to inclined flow, (see article by N. Scholz, "Investigations on blade grids of turbomachines", Journal of Flight Sciences, No. 3, 1955). The guide vanes 11 are tapered in the radial direction and are preferably twisted.

Die Verstellung der Leitschaufeln 11 im Gitter erfolgt über nicht dargestellte Betätigungsmittel, wie sie beispielsweise aus dem Verdichterbau bekannt sind. Die eigentliche Verstel­lung erfolgt vorzugsweise automatisch in Funktion der Be­triebsparameter wie Last, Drehzahl usw. Der grösste Druckrück­gewinn wird erzielt, wenn die Einstellung der Leitschaufeln so erfolgt, dass die Wellenleistung bei allen Betriebsbedingungen den grösstmöglichen Wert annimmt. Geeignet ist demnach eine permanente Leistungsmessung. Der grösste Druckrückgewinn kann auch erzielt werden, wenn die Einstellung der Leitschaufeln so erfolgt, dass der statische Druck vor den Leitschaufeln 11, d.h. hinter den Austrittslaufschaufeln 12 den kleinstmöglichen Wert annimmt. Geeignet ist demnach eine permanente Differenz­druckmessung pA-pE.The adjustment of the guide vanes 11 in the grating takes place via actuating means, not shown, as are known, for example, from compressor construction. The actual adjustment is preferably carried out automatically as a function of the operating parameters such as load, speed, etc. The greatest pressure recovery is achieved when the guide vanes are adjusted so that the shaft power assumes the greatest possible value under all operating conditions. A permanent performance measurement is therefore suitable. The greatest pressure recovery can also be achieved if the adjustment of the guide vanes takes place in such a way that the static pressure in front of the guide vanes 11, ie behind the outlet rotor blades 12, takes the smallest possible value. A permanent differential pressure measurement p A -p E is therefore suitable.

Der Zylinderschnitt in Fig. 4 zeigt in vergrössertem Massstab den Schaufelplan in der betrachteten Gasturbinenzone. Hierin bedeuten jeweils die Zeichen c die Absolutgschwindigkeit, w die Relativgeschwindigkeit und u die Umfangsgeschwindigkeit der Maschine. Zwecks Angabe der Grössenordnung bei einem aus­geführten Beispiel haben die einzelnen Gitter bspw. folgende Daten: Die Sehne der Leitschaufeln 11 beträgt 125 mm, jene der Strömungsrippen ca. 700 mm. Das Verhältnis Profildicke zu Sehne beträgt bei den Leitschaufeln und bei den Strömungsrip­pen 0,1.The cylinder section in FIG. 4 shows, on an enlarged scale, the blade plan in the gas turbine zone under consideration. The characters c in each case mean the absolute speed, w the relative speed and u the peripheral speed of the machine. The individual grids have, for example, the following in order to indicate the order of magnitude in an executed example Data: The chord of the guide vanes 11 is 125 mm, that of the flow ribs is approximately 700 mm. The ratio of profile thickness to chord is 0.1 for the guide vanes and for the flow ribs.

Die Leitschaufeln 11 werden näherungsweise unter den gleichen Bedingungen angeströmt, mit denen sie die Austrittslaufschau­feln 12 verlassen, d.h. mit der Geschwindigkeit c und einem Winkel α von 60°. Die Leitschaufeln 11 sind nunmehr unter einem Winkel β so angestellt, dass sie im Unempfindlichkeits­bereich arbeiten. Bei dem gewählten Verhältnis Teilung/Sehne = 0,5 beträgt dieser Bereich 20°. Die Abgase verlassen das Leit­gitter somit unter einem Winkel von annähernd 40°, mit welchem sie auf die Vorderkanten der gegen Schräganströmung ebenfalls unempfindlichen Strömungsrippen 8 auftreffen, wo sie in die Axiale, d.h. auf 0° ausgerichtet werden.The flow towards the guide vanes 11 is approximately the same under which they leave the outlet rotor vanes 12, i.e. with the speed c and an angle α of 60 °. The guide vanes 11 are now set at an angle β such that they work in the insensitivity range. With the selected ratio pitch / chord = 0.5, this range is 20 °. The exhaust gases thus leave the guide vane at an angle of approximately 40 °, with which they strike the front edges of the flow ribs 8, which are also insensitive to oblique flow, where they enter the axial, i.e. be aligned to 0 °.

In der Leitbeschaufelung erfolgt nicht nur eine Umlenkung der Strömung. Man erkennt anhand des Betrages der dargestellten Geschwindigkeitsvektoren am Eintritt und am Austritt der Leit­schaufeln, dass es auch zu einem zusätzlichen Verdichtungsvor­gang kommt.In the guide blading, the flow is not only redirected. It can be seen from the amount of the velocity vectors shown at the inlet and outlet of the guide vanes that there is also an additional compression process.

Die Kurve C in Fig. 2 zeigt nun die Wirkung einer jeweils optimal angestellten Leitbeschaufelung. Bis zum erwähnten ct/cn-Verhältnis von ca. 1 verläuft der Druckrückgewinn nahezu konstant und fällt erst danach in bescheidenem Masse ab, ver­glichen mit der Diffusorkonfiguration ohne Leitschaufeln.Curve C in FIG. 2 now shows the effect of an optimally adjusted guide blading. Up to the c t / c n ratio of approx. 1 mentioned, the pressure recovery is almost constant and only then drops to a modest extent, compared to the diffuser configuration without guide vanes.

Im Diagramm in Fig. 2 dargestellt ist gemäss Kurve D ebenfalls der nicht beschriebene Fall, dass die Strömungsrippen mit einem Verhältnis Teilung/Sehne = 1 ausgeführt sind. Dies bedeutet, dass im Vergleich zum beschriebenen Fall bei glei­cher Sehnenlänge die Anzahl der Strömungsrippen auf die Hälfte reduziert ist. Die Rippen könnten in einem solchen Fall mit einem entsprechend dickeren Profil ausgestattet werden, um ihrer Gleichrichteraufgabe besser nachkommen zu können. Da mit weniger Rippen auch weniger benetzte und Reibungsverluste ver­ ursachende Fläche im Diffusor vorliegt, ist bei Vollast, d.h. bei axialer Abströmung aus der Beschaufelung der Druckrückge­winn geringfügig höher als beim dargestellten Fall. Bei grös­ser werdender Schräganströmung der Strömungsrippen fällt jedoch zwangsläufig der Druckrückgewinn etwas steiler ab als jener bei grösserer Anzahl Rippen.According to curve D, the diagram in FIG. 2 also shows the case, not described, that the flow ribs are designed with a ratio pitch / chord = 1. This means that compared to the case described, the number of flow ribs is reduced by half with the same chord length. In such a case, the ribs could be equipped with a correspondingly thicker profile in order to be able to better fulfill their rectifying task. Because with fewer ribs, there is also less wetting and friction losses the cause of the area in the diffuser is slightly higher at full load, ie with axial outflow from the blading, than in the case shown. As the inclined flow of the flow ribs increases, the pressure recovery inevitably drops somewhat more steeply than that with a larger number of ribs.

Es versteht sich, dass in der Praxis das Verhältnis Teilung zu Sehne optimiert wird bezüglich der Bedeutung der Teillast, mit der die Maschine gefahren wird.It goes without saying that in practice the pitch to chord ratio is optimized with regard to the importance of the partial load with which the machine is operated.

Dem Diagramm ist ferner zu entnehmen, dass bei Vollast, d.h. im Bereich ct/cn zwischen -0,1 und +0,1 (je nach Auslegung der Beschaufelung) die zum Stand der Technik zählenden Diffusor­konfigurationen einen etwas besseren Druckrückgewinn erzielen. Dies daher, weil die im Diffusor umströmte Fläche insgesamt geringer ist als jene mit Leitschaufeln.The diagram also shows that at full load, ie in the range c t / c n between -0.1 and +0.1 (depending on the design of the blading), the diffuser configurations which are state of the art achieve a somewhat better pressure recovery. This is because the area around which the diffuser flows is less than that with guide vanes.

Aufgrund der bisherigen Ueberlegungen kann gefolgert werden, dass bei Vollast der Maschine die Leitschaufeln 11 mit ihrer Skelettlinie im Mittel axial ausgerichtet sind.Based on the previous considerations, it can be concluded that the guide vanes 11 are axially aligned with their skeleton line on average when the machine is at full load.

Die neue Massnahme ermöglicht es nun jedoch auch, am Austritt aus den letzten Laufschaufeln 12 einen gewissen Gegendrall zuzulassen, da stromabwärts im Diffusor eine axiale Ausrich­tung durch die Leitschaufeln und die Strömungsrippen stattfin­det. Dieser Gegendrall hätte folgende Vorteile:
- Die Stufenarbeit kann gesteigert werden bei gleichbleibendem Wirkungsgrad; oder
- Der Wirkungsgrad kann gesteigert werden bei gleichbleibender Stufenarbeit;
- die Schaufeln der letzten Laufreihe könnten weniger verwun­den ausgebildet werden, was zu einer Verbilligung führt;
- die Umlenkung in der letzten Turbinenstufe kann reduziert werden, was wegen der Partikelseparation insbesondere bei wirbelschichtgefeuerten Gasturbinen zum Tragen kommt.However, the new measure also makes it possible to allow a certain counter-swirl at the outlet from the last rotor blades 12, since an axial alignment takes place downstream in the diffuser through the guide blades and the flow ribs. This counter-swirl would have the following advantages:
- The step work can be increased with constant efficiency; or
- The efficiency can be increased with constant step work;
- The blades of the last row could be made less twisted, which leads to a reduction in price;
- The deflection in the last turbine stage can be reduced, which is particularly important in the case of fluidized-bed-fired gas turbines because of the particle separation.

Selbstverständlich ist die Erfindung nicht auf das gezeigte und beschriebene Ausführungsbeispiel beschränkt, welches einen Diffusor mit axialem Austritt zum Gegenstand hat und damit die Anordnung der Strömungsrippen stark erleichtert. Sie ist ins­besondere auch anwendbar bei Dampfturbinen oder den Turbinen von Abgasturboladern, welche beide in der Regel einen so­genannten axial-radialen Austritt aus der Beschaufelung haben. Die Mittel zur Drallwegnahme werden in solchen Maschinen durch den radialen Teil des Austrittsgehäuses selbst repräsentiert.Of course, the invention is not limited to the exemplary embodiment shown and described, which relates to a diffuser with an axial outlet and thus greatly facilitates the arrangement of the flow ribs. It is also particularly applicable to steam turbines or the turbines of exhaust gas turbochargers, both of which generally have a so-called axial-radial exit from the blading. In such machines, the means for swirl removal are represented by the radial part of the outlet housing itself.

Desweiteren sind auch 2 oder mehrere hintereinanderangeordnete Leitgitter denkbar, wenn besonders hohe Ansprüche hinsichtlich Wirkungsgrad im Teillastgebiet bestehen.Furthermore, two or more guide grids arranged one behind the other are also conceivable if particularly high demands are made with regard to efficiency in the partial load area.

Schliesslich kann in Abweichung zum gezeigten und beschriebe­nen Beispiel die Skelettform der Leitschaufeln auch gekrümmt sein, was selbstverständlich zu einer wesentlichen Verteuerung dieser Zusatzmassnahme führen würde.Finally, in deviation from the example shown and described, the skeleton shape of the guide vanes can also be curved, which would of course lead to a significant increase in the cost of this additional measure.

Claims (9)

1. Axialdurchströmte Turbine, an deren Austrittslaufschau­feln (12) sich ein Diffusor (13) anschliesst, wobei innerhalb dessen Verzögerungszone Mittel zur Drallwegnahme (8) der drallbehafteten Strömung vorgesehen sind,
dadurch gekennzeichnet, dass zwischen den Mitteln zur Drall­wegnahme (8) und den Austrittslaufschaufeln (12) mindestens eine Reihe mit verstellbaren Leitschaufeln (11) angeordnet ist.1. Turbine through which there is an axial flow and to whose outlet blades (12) a diffuser (13) is connected, means within the deceleration zone providing means for removing the swirl (8) of the swirling flow,
characterized in that at least one row with adjustable guide vanes (11) is arranged between the means for swirl removal (8) and the outlet rotor blades (12). 2. Axialdurchströmte Turbine nach Anspruch 1, dadurch gekennzeichnet, dass die Leitschaufeln (11) eine gerade Skelettlinie mit symmetrischem Profil aufweisen.2. Axial flow turbine according to claim 1, characterized in that the guide vanes (11) have a straight skeleton line with a symmetrical profile. 3. Axialdurchströmte Turbine nach Anspruch 2, dadurch gekennzeichnet, dass die Leitschaufeln (11) in radialer Richtung konisch verlaufen.3. Axial flow turbine according to claim 2, characterized in that the guide blades (11) are conical in the radial direction. 4. Axialdurchströmte Turbine nach Anspruch 2, dadurch gekennzeichnet, dass die Leitschaufeln (11) verwunden sind.4. Axial flow turbine according to claim 2, characterized in that the guide vanes (11) are twisted. 5. Axialdurchströmte Turbine nach Anspruch 1, dadurch gekennzeichnet, dass das Verhältnis Teilung zu Sehne der Leit­schaufeln (11) im Mittelschnitt des durchströmten Kanales zwischen 0,5 und 1 beträgt.5. Axial flow turbine according to claim 1, characterized in that the ratio of pitch to chord of the guide vanes (11) in the central section of the flow channel is between 0.5 and 1. 6. Axialdurchströmte Turbine nach Anspruch 1, dadurch gekennzeichnet, dass die Mittel ,zur Drallwegnahme innerhalb des Diffusors (13) gleichmässig über dem Umfang angeordnete Strömungsrippen (8) sind mit gerader Skelettlinie und symme­trischem Profil und mit einem Verhältnis Teilung zu Sehne zwischen 0.5 und 1 im Mittelschnitt des durchströmten Kanales.6. Axial flow turbine according to claim 1, characterized in that the means for swirl removal within the diffuser (13) are arranged over the circumference flow ribs (8) with a straight skeleton line and symmetrical profile and with a ratio pitch to chord between 0.5 and 1 in the middle section of the flowed channel. 7. Axialdurchströmte Turbine nach Anspruch 6, dadurch gekennzeichnet, dass die Strömungsrippen (8) in radialer Richtung konisch verlaufen.7. Axial flow turbine according to claim 6, characterized in that the flow ribs (8) are conical in the radial direction. 8. Verfahren zum Betrieb einer axialdurchströmten Turbine nach Anspruch 1, dadurch gekennzeichnet, dass die Leitschau­feln in Funktion von Betriebsparametern derart verstellt werden, dass bei jedem Betriebszustand die Wellenleistung den grösstmöglichen Wert annimmt.8. The method for operating an axially flowed turbine according to claim 1, characterized in that the guide vanes are adjusted in function of operating parameters such that the shaft power assumes the greatest possible value in each operating state. 9. Verfahren zum Betrieb einer axialdurchströmten Turbine nach Anspruch 1, dadurch gekennzeichnet, dass die Leitschau­feln in Funktion von Betriebsparametern derart verstellt werden, dass bei jedem Betriebszustand der Druck zwischen den Austrittslaufschaufeln und den Leitschaufeln den kleinstmögli­chen Wert annimmt.9. The method for operating an axially flowed turbine according to claim 1, characterized in that the guide vanes are adjusted in function of operating parameters such that the pressure between the outlet rotor blades and the guide vanes assumes the smallest possible value in each operating state.
EP90113994A 1989-09-12 1990-07-21 Axial turbine Expired - Lifetime EP0417433B1 (en)

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US5102298A (en) 1992-04-07
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EP0417433B1 (en) 1993-06-09
JP3162363B2 (en) 2001-04-25

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