EP0056233B1 - Diffusor with boundary layer suction - Google Patents

Diffusor with boundary layer suction Download PDF

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Publication number
EP0056233B1
EP0056233B1 EP82100019A EP82100019A EP0056233B1 EP 0056233 B1 EP0056233 B1 EP 0056233B1 EP 82100019 A EP82100019 A EP 82100019A EP 82100019 A EP82100019 A EP 82100019A EP 0056233 B1 EP0056233 B1 EP 0056233B1
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EP
European Patent Office
Prior art keywords
slot
wall
inlet
diffusor
upstream
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP82100019A
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German (de)
French (fr)
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EP0056233A1 (en
Inventor
Michel Vincent De Paul
Gilbert Riollet
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Alsthom Atlantique SA
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Alsthom Atlantique SA
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Priority to AT82100019T priority Critical patent/ATE9832T1/en
Publication of EP0056233A1 publication Critical patent/EP0056233A1/en
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Classifications

    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D29/00—Details, component parts, or accessories
    • F04D29/66—Combating cavitation, whirls, noise, vibration or the like; Balancing
    • F04D29/68—Combating cavitation, whirls, noise, vibration or the like; Balancing by influencing boundary layers
    • F04D29/681—Combating cavitation, whirls, noise, vibration or the like; Balancing by influencing boundary layers especially adapted for elastic fluid pumps
    • F04D29/682—Combating cavitation, whirls, noise, vibration or the like; Balancing by influencing boundary layers especially adapted for elastic fluid pumps by fluid extraction
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D29/00—Details, component parts, or accessories
    • F04D29/40—Casings; Connections of working fluid
    • F04D29/42—Casings; Connections of working fluid for radial or helico-centrifugal pumps
    • F04D29/44—Fluid-guiding means, e.g. diffusers
    • F04D29/441—Fluid-guiding means, e.g. diffusers especially adapted for elastic fluid pumps
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2250/00—Geometry
    • F05D2250/70—Shape
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S415/00—Rotary kinetic fluid motors or pumps
    • Y10S415/914—Device to control boundary layer

Definitions

  • the present invention relates to a symmetrical parietal suction diffuser of revolution autor of an axis AA 'and with a substantially axial inlet, used for example in a turbine or in a wind tunnel, comprising an outer wall surrounding the fluid flowing at the interior of the diffuser from the inlet to the outlet, said wall being provided with a circular slot evacuating one of the incoming flow and having a pattern such that the pressure gradient measured at its surface in the direction of flow is negative in upstream of said slot.
  • the object of the invention is to avoid any separation.
  • This object is achieved by a diffuser as defined above which is characterized in that said wall, downstream of said slot, has a layout such that the direction of flow all along said wall downstream of said slot either in the direction of entry towards exit and that the pressure gradient measured on its surface in the direction of flow is positive.
  • Diffusers are also known in which the pressure gradient upstream and downstream of the slot is zero.
  • the diffuser according to the invention making it possible to use a lower suction rate on an outer wall having a pattern such that the pressure gradient measured on its surface in the direction of flow is negative upstream of said slot and positive downstream, which prevents any separation of the boundary layer upstream of the slit as downstream.
  • the angle of entry of the fluid into the slot is between 100 ° and 120 °.
  • the optimal width of the slit is close to this value. Indeed, if the slit has a small width, on the one hand, this reduces the possibilities of picking up any detached areas occurring upstream of the slit and, on the other hand, it increases the losses in the slit, the speed penetration into the slot then being too high (at constant suction rate). On the other hand, if the width of the slit is too large, the speed of penetration into the slit is too low (at constant suction rate) and the detachments upstream of the slit are facilitated, and moreover there will be a overspeed on the leading edge downstream of the slit causing a thickening of the boundary layer which can go as far as detachment.
  • the offset between the plane perpendicular to the axis and tangent to the convex wall upstream of the slot and the plane perpendicular to the axis and passing through the center of the osculating circle at the edge of the wall downstream of the slit is equal to or slightly greater than with X, So, r, V1, R1 being defined as above.
  • Figure 1 shows a first type of flow in a diffuser with axial inlet and wall suction.
  • FIG. 2 represents a second type of flow in a diffuser with axial inlet and wall suction.
  • FIG. 3 represents a diffuser according to the invention.
  • FIG. 4 represents an enlargement of the inlet of the suction slot of the diffuser according to the invention, marked IV in FIG. 3.
  • Figures 5 to 8 show the variation curves of the suction rate as a function of the width of the slot.
  • FIG. 9 represents the variation of the speed of the fluid along the external wall of the diffuser.
  • FIGS 1 and 2 there is shown an axial inlet diffuser having an outer wall and a slot 1 separating said wall into an upstream part 2 and a downstream part 3.
  • the diffuser also has an internal wall 4.
  • the diffuser is symmetrical with revolution around an axis and the outer wall 2, 3 has a pattern such that the pressure gradient upstream and downstream of the slot is zero.
  • Figure 1 there is shown a normal flow which is sought.
  • the boundary layer located upstream of the slot 1 along the outer wall 2 is sucked in through the slot 1.
  • a represents the variation in the suction rate X as a function of the width of the width b of the slot 1.
  • a first curve (1) in dashed line represents the minimum values of X as a function of b for which the flow regime of FIG. 1 is established
  • a second curve (II) in solid line represents the maximum values of X as a function of b where it is established, for sure, the flow regime of figure 2.
  • b bo we obtain a value of X, X i on the curve 1 and X 2 on curve II. For the values of X less than or equal to X 2 , only the flow regime of FIG. 2 is established.
  • the two flow regimes can be established and for the values of X greater than or equal to X 1 , only the regime of FIG. 1 can be established.
  • suction rate X a value equal to or greater than that defined by curve 1.
  • FIG 3 there is shown the diffuser according to the invention also symmetrical with respect to an axis of revolution AA '.
  • the outer wall is interrupted by a slot 1 which separates it from the upstream wall 2 and the downstream wall 3.
  • the outer wall has a pattern such that the pressure gradient measured at its surface in the direction of flow is negative upstream of the said wall. slit and positive downstream.
  • the inlet section of the diffuser is So and the average speed in this section is Vo.
  • the circular slot 1 is also symmetrical in revolution about the axis AA 'and has a width b at its inlet BC and the speed of the fluid on the wall 2 at the inlet of the slot 1 at point C is V 1 . Slot 1 widens slightly after entering.
  • R 1 the radius of curvature of the upstream wall 2 at the entrance to the slot 1 and by r the radius measured with respect to the axis AA 'of the entrance to the slot.
  • the angle of the slot with respect to the axis AA ' is ⁇ .
  • FIG. 6 shows the curves I and II for a diffuser according to the invention, in which the outer wall has a line such that the pressure gradient measured at its surface in the direction of flow is negative upstream of the slot and positive downstream.
  • Curves 1 and II are lowered and it is therefore possible to obtain, with the same slot width (if we compare with FIG. 5), correct operation by using a suction rate X which is significantly lower.
  • the pressure on the wall 2 will gradually decrease from the inlet of the diffuser to the inlet of the slot 1, so that the fluid will be accelerated and the state of the boundary layer will be further from the separation.
  • We will generally take a speed of 15% to 40% higher than the speed of entry into the diffuser, depending on the layout possibilities available.
  • the layout of the wall 3 will reduce the risks of formation of the flow of FIG. 2.
  • the slit width is an important parameter so much. In fact, if it is too low, the possibilities of capturing any detached areas occurring on the wall 2 are reduced. In addition, this increases losses in the slit (at constant suction rate). If the width is too large, the detachment on the wall 2 is facilitated and in addition the stopping point S (where the speed is zero) may be slightly inside the slot, hence a significant overspeed of the flow around the leading edge following S on the wall 3, which will cause a thickening of the boundary layer on the wall 3 which can go as far as detachment, therefore greater losses for this diffuser.
  • the optimal width b oP t will be close to With l
  • the ratio V1 Vo can easily be measured by placing a static pressure tap at the inlet of the slot (p 1 ) and another in the inlet plane of the diffuser (in), then by measuring the stop pressure ( pô) in said entry plane using a pitot probe
  • FIG. 9 shows the variation of the ratio V Vo (V being the speed at point M taken on the wall 2 or 3) as a function of the curvilinear abscissa OM, 0 being the point of the wall 2 at the entry of the diffuser.
  • the wall 3 downstream of the slot is offset in the flow (see FIG. 4); this offset ⁇ is measured by the distance of two planes perpendicular to the axis AA ', one tangent to the upstream convex wall 2, the other passing through the center of the osculating circle at the leading edge of the downstream wall 3
  • This offset 0 is preferably equal to or slightly greater than the value b o p t previously indicated.

Abstract

The diffuser is symmetrical about an axis AA' and has a flared outer wall (2,3) going from an axial inlet to an outlet. The outer wall is divided into an upstream portion (2) and a downstream portion (3) by a circular bleed slot (1) disposed symmetrically about the axis. The profile of the outer wall is such that, in operation, the direction of fluid flow along the outer wall is from the inlet towards the outlet, both over the upstream portion, and over the downstream portion. Further, it is so arranged that the pressure gradient measured at the surface of the wall and along the direction of fluid flow is negative upstream from the bleed slot and positive downstream therefrom. This ensures that only a small percentage of the fluid flow needs to be bled off to achieve desirable flow conditions, thereby providing good diffuser efficiency.

Description

La présente invention a trait à un diffuseur à aspiration pariétale symétrique de révolution autor d'un axe AA' et à entrée sensiblement axiale, utilisé par exemple dans une turbine ou dans une soufflerie, comportant une paroi extérieure entourant le fluide s'écoulant à l'intérieur du diffuseur de l'entrée vers la sortie, ladite paroi étant munie d'une fente circulaire évacuant une du débit entrant et ayant un tracé tel que le gradient de pression mesuré à sa surface dans le sens de l'écoulement soit négatif en amont de ladite fente.The present invention relates to a symmetrical parietal suction diffuser of revolution autor of an axis AA 'and with a substantially axial inlet, used for example in a turbine or in a wind tunnel, comprising an outer wall surrounding the fluid flowing at the interior of the diffuser from the inlet to the outlet, said wall being provided with a circular slot evacuating one of the incoming flow and having a pattern such that the pressure gradient measured at its surface in the direction of flow is negative in upstream of said slot.

Un tel diffuseur est décrit dans le brevet britannique n° 1 024 328.Such a diffuser is described in British Patent No. 1,024,328.

Dans le diffuseur connu, l'écoulement du fluide le long de la paroi en aval de la fente se fait dans le sens inverse de l'écoulement général, c'est-à-dire dans le sens sortie vers entrée.In the known diffuser, the flow of the fluid along the wall downstream of the slot takes place in the opposite direction to the general flow, that is to say in the outlet to inlet direction.

Il se produit un décollement en aval de la fente.There is a detachment downstream of the slit.

L'invention a pour but d'éviter tout décoll- ment. Ce but est atteint par un diffuseur tel que défini ci-dessus qui est caractérisé en ce que ladite paroi, en aval de ladite fente, a un tracé tel que le sens de l'écoulement tout le long de ladite paroi en aval de ladite fente soit dans le sens de l'entrée vers la sorti et que le gradient de pression mesuré à sa surface dans le sens de l'écoulement soit positif.The object of the invention is to avoid any separation. This object is achieved by a diffuser as defined above which is characterized in that said wall, downstream of said slot, has a layout such that the direction of flow all along said wall downstream of said slot either in the direction of entry towards exit and that the pressure gradient measured on its surface in the direction of flow is positive.

L'existence d'une recompression en aval de la fente s'oppose à l'établissement d'une écoulement à contre courant le long de la paroi.The existence of a recompression downstream of the slit is opposed to the establishment of a countercurrent flow along the wall.

On connaît également des diffuseurs dans lesquels le gradient de pression en amont et en aval de la fente est nul.Diffusers are also known in which the pressure gradient upstream and downstream of the slot is zero.

De tels diffuseurs sont décrits par exemple dans le brevet britannique n° 1 000 767.Such diffusers are described for example in British Patent No. 1,000,767.

Dans de tels diffuseurs, les décollements de la couche limite peuvent, en grande partie, être évités grâce à l'aspiration de celle-ci par la fente circulaire. Toutefois, des essais ont montré qu'il existe un large domaine de taux d'aspiration (quantité de fluide aspirée par la fente divisée par la quantité de fluide entrant dans le diffuseur) pour lequel le fonctionnement n'est pas stable.In such diffusers, detachments of the boundary layer can, to a large extent, be avoided by virtue of the suction of the latter by the circular slot. However, tests have shown that there is a wide range of suction rates (amount of fluid drawn in through the slit divided by the amount of fluid entering the diffuser) for which the operation is not stable.

C'est pourquoi il est nécessaire d'utiliser des taux d'aspiration assez élevés (10% ou plus), ce qui limite considérablement l'intérêt industriel de tels diffuseurs.This is why it is necessary to use fairly high suction rates (10% or more), which considerably limits the industrial interest of such diffusers.

Le diffuseur selon l'invention permettant d'utiliser un taux d'aspiration plus faible a une paroi extérieure ayant un tracé tel que le gradient de pression mesuré à sa surface dans le sens de l'écoulement soit négatif en amont de ladite fente et positif en aval, ce qui évite tout décollement de la couche limite en amont de la fente comme en aval.The diffuser according to the invention making it possible to use a lower suction rate on an outer wall having a pattern such that the pressure gradient measured on its surface in the direction of flow is negative upstream of said slot and positive downstream, which prevents any separation of the boundary layer upstream of the slit as downstream.

Selon un premier perfectionnement de l'invention, l'angle d'entrée du fluide dans la fente, mesuré à partir de l'axe de révolution orienté dans le sens d'entrée du fluide dans le diffuseur, est compris entre 100° et 120°.According to a first improvement of the invention, the angle of entry of the fluid into the slot, measured from the axis of revolution oriented in the direction of entry of the fluid into the diffuser, is between 100 ° and 120 °.

Ainsi le taux d'aspiration pour lequel les décollements sont en grande partie évités peut être diminué.Thus the suction rate for which detachments are largely avoided can be reduced.

Selon un deuxième perfectionnement de l'invention, on choisit une largeur de fente à l'entrée voisine de

Figure imgb0001
avec
Figure imgb0002

  • X étant le taux d'aspiration, rapport du débit aspiré au débit total entrant dans le diffuseur
  • So étant la section d'entrée du diffuseur
  • Vo la vitesse moyenne dans la section d'entrée du diffuseur
  • r le rayon à partir de l'axe de l'entrée de la fente
  • V1 étant la vitesse du fluide sur la paroi à l'entrée de la fente en amont de cette dernière.
  • R1 étant le rayon de courbure de la paroi à l'entrée de la fente et en amont.
According to a second improvement of the invention, a slot width is chosen at the entrance close to
Figure imgb0001
 with
Figure imgb0002
  • X being the suction rate, ratio of the aspirated flow to the total flow entering the diffuser
  • So being the inlet section of the diffuser
  • Vo the average speed in the inlet section of the diffuser
  • r the radius from the axis of the slot entry
  • V1 being the speed of the fluid on the wall at the entrance to the slot upstream of the latter.
  • R1 being the radius of curvature of the wall at the entrance to the slot and upstream.

La largeur optimale de la fente est voisine de cette valeur. En effet, si la fente a une largeur faible, d'une part, cela réduit les possibilités de captation des zones décollées éventuelles se produisant en amont de la fente et, d'autre part, cela augmente les pertes dans la fente, la vitesse de pénétration dans la fente étant alors trop élevée (à taux d'aspiration constant). Par contre, si la largeur de la fente est trop importante, la vitesse de pénétration dans la fente est trop faible (à taux d'aspiration constant) et les décollements en amont de la fente se trouvent facilités, et de plus il se produira une survitesse sur le bord d'attaque en aval de la fente entraînant un épaississement de la couche limite pouvant aller jusqu'au décollement.The optimal width of the slit is close to this value. Indeed, if the slit has a small width, on the one hand, this reduces the possibilities of picking up any detached areas occurring upstream of the slit and, on the other hand, it increases the losses in the slit, the speed penetration into the slot then being too high (at constant suction rate). On the other hand, if the width of the slit is too large, the speed of penetration into the slit is too low (at constant suction rate) and the detachments upstream of the slit are facilitated, and moreover there will be a overspeed on the leading edge downstream of the slit causing a thickening of the boundary layer which can go as far as detachment.

Selon un troisième perfectionnement de l'invention, le décalage d'entre le plan perpendiculaire à l'axe et tangent à la paroi convexe en amont de la fente et le plan perpendiculaire à l'axe et passant par le centre du cercle osculateur au bord d'attaque de la paroi en aval de la fente est égal ou légèrement supérieur à

Figure imgb0003
avec
Figure imgb0004
X, So, r, V1, R1 étant définis comme ci-dessus.According to a third improvement of the invention, the offset between the plane perpendicular to the axis and tangent to the convex wall upstream of the slot and the plane perpendicular to the axis and passing through the center of the osculating circle at the edge of the wall downstream of the slit is equal to or slightly greater than
Figure imgb0003
 with
Figure imgb0004
 X, So, r, V1, R1 being defined as above.

Les avantages apportés par l'invention sont particulièrement intéressants dans le cas où l'angle de sortie du fluide est égal ou voisin de 90°, c'est-à-dire où le diffuseur est à sortie sensiblement radiale.The advantages provided by the invention are particularly advantageous in the case where the outlet angle of the fluid is equal to or close to 90 °, that is to say where the diffuser has a sensitive outlet radial.

En effet, en raison de la déviation du fluide qui s'ajoute à la recompression du fluide, la tendance aux décollements des couches limites est très importante.Indeed, due to the deflection of the fluid which is added to the recompression of the fluid, the tendency for detachments of the boundary layers is very significant.

La présente invention va maintenant être décrite plus en détail en se référant à un mode de réalisation particulier cité à titre d'exemple non limitatif et représenté par des dessins annexés.The present invention will now be described in more detail with reference to a particular embodiment cited by way of non-limiting example and shown in the accompanying drawings.

La figure 1 représente un premier type d'écoulement dans un diffuseur à entrée axiale et à aspiration pariétale.Figure 1 shows a first type of flow in a diffuser with axial inlet and wall suction.

La figure 2 représente un second type d'écoulement dans un diffuseur à entrée axiale et à aspiration pariétale.FIG. 2 represents a second type of flow in a diffuser with axial inlet and wall suction.

La figure 3 représente un diffiseur selon l'invention.FIG. 3 represents a diffuser according to the invention.

Le figure 4 représente un agrandissement de l'entrée de la fente d'aspiration du diffuseur selon l'invention repérée IV sur la figure 3.FIG. 4 represents an enlargement of the inlet of the suction slot of the diffuser according to the invention, marked IV in FIG. 3.

Les figures 5 à 8 représentent les courbes de variation du taux d'aspiration en fonction de la largeur de la fente.Figures 5 to 8 show the variation curves of the suction rate as a function of the width of the slot.

La figure 9 représente la variation de la vitesse du fluide le long de la paroi extérieure du diffuseur.FIG. 9 represents the variation of the speed of the fluid along the external wall of the diffuser.

Sur les figures 1 et 2 on a représenté un diffuseur à entrée axiale comportant une paroi extérieure et une fente 1 séparant ladite paroi en une partie amont 2 et une partie aval 3. Le diffuseur comporte également une paroi interne 4. Le diffuseur est symétrique de révolution autour d'un axe et le paroi extérieur 2, 3 a un tracé tel que le gradient de pression en amont et en aval de la fente soit nul.In Figures 1 and 2 there is shown an axial inlet diffuser having an outer wall and a slot 1 separating said wall into an upstream part 2 and a downstream part 3. The diffuser also has an internal wall 4. The diffuser is symmetrical with revolution around an axis and the outer wall 2, 3 has a pattern such that the pressure gradient upstream and downstream of the slot is zero.

Pour un même taux d'aspiration X (quantité de fluide aspirée par la fente divisée par la quantité de fluide entrant dans le diffuseur) et dans un domaine plus au moins étendu de X, on a pu constater que deux types d'écoulement étaient possibles.For the same suction rate X (quantity of fluid sucked in through the slit divided by the quantity of fluid entering the diffuser) and in a more or less extensive range of X, it has been observed that two types of flow were possible .

Sur la figure 1 on a représenté un écoulement normal qui est recherché. La couche limite située en amont de la fente 1 le long de la paroi extérieure 2 est aspirée par la fente 1.In Figure 1 there is shown a normal flow which is sought. The boundary layer located upstream of the slot 1 along the outer wall 2 is sucked in through the slot 1.

Il s'ensuit que l'écoulement n'est pas décollé en aval de la fente.It follows that the flow is not detached downstream of the slot.

Dans le cas de la figure 2 il se produit un écoulement à contre courant le long de la paroi extérieure 3 en aval de la fente 2. Lorsqu'un tel écoulement s'établit il n'est plus possible de recom- primer le fluide dans le diffuseur.In the case of FIG. 2, there is a countercurrent flow along the outer wall 3 downstream of the slot 2. When such a flow is established it is no longer possible to recompress the fluid in the diffuser.

Sur la figure 5 on a représente la variation du taux d'aspiration X en fonction de la largeur de la largeur b de la fente 1.In FIG. 5, a represents the variation in the suction rate X as a function of the width of the width b of the slot 1.

Une première courbe (1) en trait tireté représente les valeurs de X minimales en fonction de b pour lesquelles il s'établit, à coup sûr, le régime d'écoulement de la figure 1, et une seconde courbe (II) en trait plein représente les valeurs de X maximales en fonction de b où il s'établit, à coup sûr, le régime d'écoulement de la figure 2. Pour une même valeur de b, bo nous obtenons une valeur de X, Xi sur la courbe 1 et X2 sur la courbe Il. Pour les valeurs de X inférieures ou égales à X2, seul le régime d'écoulement de la figure 2 s'établit.A first curve (1) in dashed line represents the minimum values of X as a function of b for which the flow regime of FIG. 1 is established, and a second curve (II) in solid line represents the maximum values of X as a function of b where it is established, for sure, the flow regime of figure 2. For the same value of b, bo we obtain a value of X, X i on the curve 1 and X 2 on curve II. For the values of X less than or equal to X 2 , only the flow regime of FIG. 2 is established.

Pour les valeurs de X comprises entre X2 et Xi, les deux régimes d'écoulement peuvent s'établir et pour les valeurs de X supérieures ou égales à X1, seul le régime de la figure 1 peut s'établir.For the values of X between X 2 and X i , the two flow regimes can be established and for the values of X greater than or equal to X 1 , only the regime of FIG. 1 can be established.

Il s'ensuit qu'il conviendra de prendre pour taux d'aspiration X une valeur égale ou supérieure à celui défini par la courbe 1.It follows that it will be necessary to take as suction rate X a value equal to or greater than that defined by curve 1.

Sur la figure 3 on a représenté le diffuseur selon l'invention également symétrique par rapport à un axe de révolution AA'. La paroi extérieure est interrompue par une fente 1 qui la sépare en paroi amont 2 et paroi aval 3. La paroi extérieure a un tracé tel que le gradient de pression mesuré à sa surface dans le sens de l'écoulement soit négatif en amont de ladite fente et positif en aval.In Figure 3 there is shown the diffuser according to the invention also symmetrical with respect to an axis of revolution AA '. The outer wall is interrupted by a slot 1 which separates it from the upstream wall 2 and the downstream wall 3. The outer wall has a pattern such that the pressure gradient measured at its surface in the direction of flow is negative upstream of the said wall. slit and positive downstream.

La section d'entrée du diffuseur est So et la vitesse moyenne dans cette section est Vo.The inlet section of the diffuser is So and the average speed in this section is Vo.

La fente 1 circulaire est également symétrique de révolution autour de l'axe AA' et a une largeur b à son entrée B C et la vitesse du fluide sur la paroi 2 à l'entrée de la fente 1 au point C est V1. La fente 1 va en s'évasant légèrement après son entrée.The circular slot 1 is also symmetrical in revolution about the axis AA 'and has a width b at its inlet BC and the speed of the fluid on the wall 2 at the inlet of the slot 1 at point C is V 1 . Slot 1 widens slightly after entering.

Nous désignons par R1 le rayon de courbure de la paroi amont 2 à l'entrée de la fente 1 et par r le rayon mesuré par rapport à l'axe AA' de l'entrée de la fente.We denote by R 1 the radius of curvature of the upstream wall 2 at the entrance to the slot 1 and by r the radius measured with respect to the axis AA 'of the entrance to the slot.

L'angle de la fente par rapport à I'axe AA' est β.The angle of the slot with respect to the axis AA 'is β.

Sur la figure 6 on a représenté les courbes I et Il pour un diffuseur selon l'invention, dans lequel la paroi extérieure a un tracé tel que le gradient de pression mesuré à sa surface dans le sens de l'écoulement soit négatif en amont de la fente et positif en aval.FIG. 6 shows the curves I and II for a diffuser according to the invention, in which the outer wall has a line such that the pressure gradient measured at its surface in the direction of flow is negative upstream of the slot and positive downstream.

Les courbes 1 et Il sont abaissées et il est donc possible d'obtenir, avec une même largeur de fente (si nous comparons avec la figure 5), un fonctionnement correct en utilisant un taux d'aspiration X nettement inférieur.Curves 1 and II are lowered and it is therefore possible to obtain, with the same slot width (if we compare with FIG. 5), correct operation by using a suction rate X which is significantly lower.

La pression sur la paroi 2 va diminuer progressivement de l'entrée du diffuseur jusqu' à l'entrée de la fente 1, si bien que le fluide va être accéléré et que l'état de la couche limite sera plus éloigné du décollement. Il faut toutefois éviter d'avoir des vitesses trop élevées à l'entrée de la fente, ce qui conduirait à des pertes très importantes dans cette fente et éventuellement des problème liés à la compressibilité. On prendra en géneral une vitesse de 15% à 40% supérieure à la vitesse d'entrée dans le diffuseur, suivant les possibilités de tracé dont on dispose.The pressure on the wall 2 will gradually decrease from the inlet of the diffuser to the inlet of the slot 1, so that the fluid will be accelerated and the state of the boundary layer will be further from the separation. However, avoid having too high speeds at the entrance to the slot, which would lead to very large losses in this slot and possibly problems related to compressibility. We will generally take a speed of 15% to 40% higher than the speed of entry into the diffuser, depending on the layout possibilities available.

Le tracé de la paroi 3 va diminuer les risques de formation de l'écoulement de la figure 2.The layout of the wall 3 will reduce the risks of formation of the flow of FIG. 2.

Sur la paroi concave interne 4 la loi de pression dépend de la déviation que l'on désire obtenir avec le diffuseur considéré.On the internal concave wall 4 the pressure law depends on the deviation which it is desired to obtain with the diffuser considered.

En choisissant un angle de direction de fente β compté à partir de l'axe de révolution AA', compris entre 100° et 120°, on diminue les taux d'aspiration minimaux de la courbe 1 (voir figure 7).By choosing a slit direction angle β counted from the axis of revolution AA ', between 100 ° and 120 °, the minimum suction rates of curve 1 are reduced (see Figure 7).

La largeur de fente est un paramètre important. En effet, si elle est trop faible, les possibilités de captation des zones décollées éventuelles se produisant sur la paroi 2 sont réduites. De plus cela augmente les pertes dans la fente (à taux d'aspiration constant). Si la largeur est trop grande, le décollement sur la paroi 2 est facilité et en plus le point d'arrêt S (où la vitesse est nulle) pourra se trouver légèrement à l'intérieur de la fente, d'où une survitesse importante de l'écoulement au contournement du bord d'attaque faisant suite à S sur la paroi 3, ce qui entraînera un épaississement de la couche limite sur la paroi 3 pouvant aller jusqu'au décollement, donc des pertes plus importantes pour ce diffuseur.The slit width is an important parameter so much. In fact, if it is too low, the possibilities of capturing any detached areas occurring on the wall 2 are reduced. In addition, this increases losses in the slit (at constant suction rate). If the width is too large, the detachment on the wall 2 is facilitated and in addition the stopping point S (where the speed is zero) may be slightly inside the slot, hence a significant overspeed of the flow around the leading edge following S on the wall 3, which will cause a thickening of the boundary layer on the wall 3 which can go as far as detachment, therefore greater losses for this diffuser.

La largeur boPt optimale sera voisine de

Figure imgb0005
avec L
Figure imgb0006
Le rapport V1 Vo peut facilement être mesuré en plaçant une prise de pression statique à I'entrée de la fente (p1) et une autre dans le plan d'entrée du diffuseur (po), puis en mesurant la pression d'arrêt (pô) dans ledit plan d'entrée à l'aide d'une sonde pitotThe optimal width b oP t will be close to
Figure imgb0005
 With l
Figure imgb0006
 The ratio V1 Vo can easily be measured by placing a static pressure tap at the inlet of the slot (p 1 ) and another in the inlet plane of the diffuser (in), then by measuring the stop pressure ( pô) in said entry plane using a pitot probe

Le rapport

Figure imgb0007
The report
Figure imgb0007

On a représenté sur la figure 9 la variation du rapport V Vo (V étant la vitesse au point M pris sur la paroi 2 ou 3) en fonction de l'abscisse curviligne OM, 0 étant le point de la paroi 2 à l'entrée du diffuseur.FIG. 9 shows the variation of the ratio V Vo (V being the speed at point M taken on the wall 2 or 3) as a function of the curvilinear abscissa OM, 0 being the point of the wall 2 at the entry of the diffuser.

Quand M varie de O à C, le rapport

Figure imgb0008
augmente régulièrement. En S la vitesse V est nulle, puis augmente fortement avant de décroîre vers une limite donnée.When M varies from O to C, the ratio
Figure imgb0008
 increases steadily. In S the speed V is zero, then increases sharply before decreasing towards a given limit.

La paroi 3 à l'aval de la fente est décalée dans I'écoulement (voir figure 4); ce décalage δ est mesuré par la distance de deux plans perpendiculaires à l'axe AA', l'un tangent à la paroi convexe amont 2, l'autre passant par le centre du cercle osculateur au bord d'attaque de la paroi aval 3. Ce décalage 0 est de préférence égal ou légèrement supérieur à la valeur bopt signalée précédemment.The wall 3 downstream of the slot is offset in the flow (see FIG. 4); this offset δ is measured by the distance of two planes perpendicular to the axis AA ', one tangent to the upstream convex wall 2, the other passing through the center of the osculating circle at the leading edge of the downstream wall 3 This offset 0 is preferably equal to or slightly greater than the value b o p t previously indicated.

Lorsque le décalage est choisi égal ou légèrement supérieur à bopt et que les conditions imposées pour les courbes de la figure 7 sont remplies la courbe est pratiquement confondue avec la courbe Il (voir figure 8), le minimum de ces courbes étant obtenu pour une largeur de fente égale ou voisine de bopt.When the offset is chosen equal to or slightly greater than b o p t and the conditions imposed for the curves of figure 7 are fulfilled the curve is practically coincident with the curve II (see figure 8), the minimum of these curves being obtained for a slot width equal to or close to b o p t .

On choisira de préférence le tracé du bord d'attaque de la paroi 3, de façon que le rayon du cercle osculateur soit égal ou
supérieur à bopt 4.We will preferably choose the path of the leading edge of the wall 3, so that the radius of the osculating circle is equal or
greater than b opt 4.

Comme il ressort des graphiques des diverses figures 5 à 8, le choix judicieux de la largeur de la fente, de son orientation et de son décalage permettra de minimiser le taux d'aspiration du diffuseur et donc d'accroître le rendement.As can be seen from the graphs in the various figures 5 to 8, the judicious choice of the width of the slot, of its orientation and of its offset will make it possible to minimize the suction rate of the diffuser and therefore to increase the efficiency.

Dans le cas d'un diffuseur à entrée axiale à sortie axiale utilisé par exemple dans les turbines à gaz, la paroi interne 4 sera, bien entendu, supprimée.In the case of an axial inlet diffuser with an axial outlet used for example in gas turbines, the internal wall 4 will, of course, be eliminated.

Claims (5)

1. A diffusor with boundary layer suction of a rotational symmetry around an axis AA', comprising an essentially axial inlet, an outer wall (2,3) surrounding the fluid flowing within the diffusor from the inlet to the outlet, said wall (2, 3) being provided with a circular slot (1) evacuating a fraction of the inlet flow rate and having a profile such that the pressure gradient measured at its surface in the direction of the fluid flow is negative upstream of said slot (1), characterized in that the profile of said wall (3) downstream of said slot (1) is such that the fluid flow direction along said wall (3) downstream of said slot (1) is directed from the inlet to the outlet and that the pressure measured at its surface in the direction of the fluid flow is positive.
2. A diffusor according to claim 1, characterized in that the inlet angle of the fluid (,8) into the slot (1), measured from the revolution axis (AA') and oriented in the direction of the fluid inlet into the diffusor, is comprised between 100 and 120°.
3. A diffusor according to one of the claims 1 and 2, characterized in that the width of the slot (1) at the inlet is near bopt
Figure imgb0017
with
Figure imgb0018
in which
X is the suction rate, i. e. ratio of the sucked-in flow rate to the total flow rate entering the diffusor,
So is the inlet cross section of the diffusor,
Vo is the average speed in the inlet cross section of the diffusor,
r is the slot radius from the inlet axis,
V1 is the speed of the fluid on the wall (2) at the
entry of the slot (1) upstream of the latter,
R1 is the radius of curvature of the wall (2) at the inlet of the slot (1) and upstream therefrom.
4. A diffusor according to one of the preceding claims, in which the shift d between the plane which is perpendicular to the axis and which touches the convex wall (2) upstream of the slot (1), and the plane which is perpendicular to the axis and passes through the centre of the osculating circle at the attacking edge of the wall (3) downstream of the slot is equal to or slightly larger than
Figure imgb0019
with
Figure imgb0020
in which
X is the suction rate, i.e. ratio of the sucked-in flow rate to the total flow rate entering the diffusor,
So is the inlet cross section of the diffusor,
Vo is the average speed in the inlet cross section of the diffusor,
r is the slot radius from the inlet axis,
V1 is the speed of the fluid on the wall (2) at the entry of the slot (1) upstream of the latter,
R1 is the radius of curvature of the wall (2) at the inlet of the slot (1) and upstream therefrom.
5. A diffusor according to one of the preceding claims, characterized in that the outlet angle of the diffusor is about 90°.
EP82100019A 1981-01-08 1982-01-05 Diffusor with boundary layer suction Expired EP0056233B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT82100019T ATE9832T1 (en) 1981-01-08 1982-01-05 DIFFUSER WITH BOUNDARY LAYER EXTRACTION.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8100210A FR2497544A1 (en) 1981-01-08 1981-01-08 PARIETAL SUCTION DIFFUSER
FR8100210 1981-01-08

Publications (2)

Publication Number Publication Date
EP0056233A1 EP0056233A1 (en) 1982-07-21
EP0056233B1 true EP0056233B1 (en) 1984-10-10

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EP (1) EP0056233B1 (en)
JP (1) JPS57146003A (en)
KR (1) KR890000914B1 (en)
AT (1) ATE9832T1 (en)
AU (1) AU547535B2 (en)
BR (1) BR8200051A (en)
CA (1) CA1193513A (en)
DE (1) DE3260910D1 (en)
ES (1) ES8302862A1 (en)
FR (1) FR2497544A1 (en)
RO (1) RO82608A (en)
ZA (1) ZA82121B (en)

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US5059093A (en) * 1990-06-07 1991-10-22 United Technologies Corporation Compressor bleed port
FR2835019B1 (en) * 2002-01-22 2004-12-31 Snecma Moteurs DIFFUSER FOR A LAND OR AERONAUTICAL GAS TURBINE ENGINE
GB0229307D0 (en) * 2002-12-17 2003-01-22 Rolls Royce Plc A diffuser arrangement
US8474266B2 (en) 2009-07-24 2013-07-02 General Electric Company System and method for a gas turbine combustor having a bleed duct from a diffuser to a fuel nozzle
US8381532B2 (en) * 2010-01-27 2013-02-26 General Electric Company Bled diffuser fed secondary combustion system for gas turbines
US20130051974A1 (en) * 2011-08-25 2013-02-28 Honeywell International Inc. Gas turbine engines and methods for cooling components thereof with mid-impeller bleed cooling air
CN103244459B (en) * 2013-04-25 2015-08-05 哈尔滨工业大学 A kind of aerodynamic design method of subsonic adsorption type axial compressor

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FR992353A (en) * 1944-06-22 1951-10-17 Cem Comp Electro Mec Improved diffuser recovery
US3216455A (en) * 1961-12-05 1965-11-09 Gen Electric High performance fluidynamic component
GB1000767A (en) * 1963-05-08 1965-08-11 Int Research & Dev Co Ltd Diffusers for fluids
FR2401311A1 (en) * 1977-08-25 1979-03-23 Europ Turb Vapeur EXHAUST SYSTEM FOR AXIAL CONDENSABLE FLUID TURBINE

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ES508555A0 (en) 1982-12-01
EP0056233A1 (en) 1982-07-21
AU7926482A (en) 1982-07-15
RO82608A (en) 1983-09-26
FR2497544A1 (en) 1982-07-09
US4471910A (en) 1984-09-18
JPS57146003A (en) 1982-09-09
ES8302862A1 (en) 1982-12-01
FR2497544B1 (en) 1985-05-03
DE3260910D1 (en) 1984-11-15
ATE9832T1 (en) 1984-10-15
JPH0259285B2 (en) 1990-12-12
AU547535B2 (en) 1985-10-24
ZA82121B (en) 1982-11-24
KR890000914B1 (en) 1989-04-13
BR8200051A (en) 1982-10-26
KR830009415A (en) 1983-12-21
CA1193513A (en) 1985-09-17

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