DE102014206216B4 - Compaction grating for an axial compressor - Google Patents

Abstract

Compaction grating (1) for an axial compressor with a ring of blades (10a, 10b), each having a leading edge (12a, 12b), a trailing edge (13a, 13b), a pressure side (14) and a suction side (15) and with a compressor axis (16) defining an axial direction, wherein the blades (10a, 10b) are arranged in double rows and form front blades (10a) and rear blades (10b), each with a rear blade (10b) offset axially relative to the front blade (10b); 10 a) and on the pressure side (14) of the front blade (10 a) in the circumferential direction offset to the front blade (10 a) is arranged, wherein between the front and the rear blade (10 a, 10 b) a cover region (18) is formed, and wherein the blades (10a, 10b) are arranged at a pitch t on the rim, which indicates the distance of the trailing edges (13b) of adjacent rear blades (10b) in the circumferential direction, characterized in that for the ratio of the over Covering length Δx in the axial direction to the total length lx of the front and rear blades (10a, 10b) is: 0.01 ≤ Δx / lx ≤ 0.02.

Description

The present invention relates to a compaction grate for an axial compressor with a ring of blades, each having a leading edge, a trailing edge, a pressure side and a suction side, and with a compressor axis defining the axial direction, wherein the blades are arranged in double rows.

In the design of powerful and efficient axial compressors, especially for aircraft engines, it is known to provide double-row blade arrangements, so-called tandem blades. These offer the possibility of achieving a maximum deflection with the highest aerodynamic load in the case of subsonic currents, as a result of which improved tuning to a subsequent compressor stage can be achieved. In this case, very high deflections with relatively low loss can be realized without it comes to flow separation in the blade row.

Out EP 2 626 515 A1 . EP 2 409 002 B1 . DE 27 48 597 A1 . US 3,442,441 A and WO 2010/105 597 A2 For example, a blade of blades is known in which the double-row blade assembly has front blades and rear blades. The respective rear blade is offset in the axial direction to the front blade. Further, the rear blade on the pressure side of the front blade is circumferentially offset from the front blade. Between the front and rear blades, a cover area is formed, creating a nozzle between the blades. DE 697 30 663 T2 discloses a double row blade arrangement in which the front and rear blades do not form a covering area.

The resulting nozzle flow interacts with the wake of the first blade and causes an acceleration of the flow in the front suction-side region of the second blade. Through these mechanisms, a large part of the flow deflection can be realized.

In the design of such a compressor is due to the double-row blade arrangement a variety of design parameters changeable, so that in the optimization of such a compaction grating an enormous amount of effort is necessary.

It is therefore the object of the present invention to provide a compression grille for an axial compressor with a double-row blade arrangement, which has an improved deflection or pressure conversion and reduced aerodynamic losses. It is also the object of the present invention to provide an axial compressor which can be used as a basic design for further adaptations.

The invention is defined by the features of claim 1.

The compaction grate according to the invention has a ring of blades, each having a leading edge, a trailing edge, a pressure side and a suction side. The axial compressor has a compressor axis which defines an axial direction. The blades are arranged in double rows and form front blades and rear blades. In each case a rear blade is arranged offset in the axial direction to the front blade. Further, the rear blade on the pressure side of the front blade is circumferentially offset from the front blade. Between the front and the rear blade, a covering area is formed. The blades are arranged at a pitch t on the rim, which indicates the distance of the trailing edges of adjacent rear blades in the circumferential direction.

The invention is characterized in that the ratio of the overlap length Δx in the axial direction to the total length l _{x of} the front and rear blades is: 0.01 ≦ Δx / l _x ≦ 0.02.

The total length l _x indicates the extension from the leading edge of the leading blade to the trailing edge of the rear blade in the axial direction.

It has been found that such a formation of the overlap region advantageously forms the nozzle formed by the overlap region, so that the nozzle flow formed in the overlap region interacts particularly advantageously with the wake of the first blade and thus the flow in the front suction-side region of the second blade is accelerated.

It is preferably provided that the ratio of the distance θ of the trailing edge of the front blade from the leading edge of the rear blade in the circumferential direction to the pitch t is 0.1 ≦ θ / t ≦ 0.2, preferably 0.13 ≦ θ / t ≤ 0.16.

It has also been found that, for an incoming number of, for example, Ma = 0.5 and various axial contraction ratios in the range between 1 and 1.5 used in the overlap region, an embodiment of the overlap region according to the inventive ratios between overlap length Δx and overall length l _x or between the distance θ and the pitch t are always the most efficient blade arrangements.

It is preferably provided that Δx / l _x = 0.018 and θ / t = 0.14.

This finding is also advantageous in the design of axial compressors with compaction grids with a double-row blade arrangement, since the ratios or ratio ranges according to the invention can be assumed to be predetermined and thus the design process can be simplified.

It is preferably provided that for the ratio of the chord length l _{s1 of} the profile of the front blade to the chord length l _{s2 of} the profile of the rear blade: 1.2 ≦ l _s1 / l _s2 ≦ 1.3.

The chord length is the length of the leading edge and trailing edge of a blade connecting tendon.

It has been found that in addition to the maximum deflection determined by the overlap area, the maximum load of the individual blades in the design of the axial compressor according to the invention has a significant influence. The load distribution of the individual blades is determined inter alia by the chord length of a blade, so that the load distribution on the two blades is improved by the inventive ratio of the chord lengths l _s1 to l _s2 .

It is further preferable that the ratio of the front blade leading edge _clearance l _s1x to the front blade _trailing edge in the axial direction to the rear blade leading edge clearance l _s2x to the rear blade _trailing edge in the axial direction is 0, 92 ≤ l _s1x / l _s2x ≤ 0.96.

The distance l _s1x or l _s2x thus indicates the axial extent of the chord length. In a compacting _grid in which the front and rear blades are arranged such that the ratio of the distance l _s1x to the distance l _{s2x is} in the range specified in the present invention, the load distribution on the two blades is further improved over blades having a different ratio.

_With regard to the specified ratios of the chord length l _s1 to the chord length l _s2 and the _setting off of the l _s1x to the distance l _{s2x, it} has been found that these parameters are always a very efficient arrangement for a Zuse number of Ma = 0.5 and different axial contraction ratios ,

Thus, these parameters can serve as specifications for a design of a compaction grid.

It is preferably provided that the ratio of the pitch t to the total length l _x is 0.88 ≦ t / l _x ≦ 0.92.

With a compression grating according to the invention an improved blade load distribution with optimized deflection is achieved with the lowest possible resistance. Furthermore, simple geometric conditions are predetermined by the ratio specifications according to the invention, so that a design process for a compaction grid, depending on the application, only has to relate to specific profile shapes of the blades. This can save a huge amount of time and money.

It is preferably provided that the ratio of the chord lengths l _s1 to l _s2 is: l _s1 / l _s2 = 1.25.

Furthermore, it can preferably be provided that for the ratio of the distances l _s1x and l _s2x : l _s1x / l _s2x = 0.94.

For the so-called axial division ratio t / l _x, preferably: t / l _x = 0.9.

In a preferred embodiment of the invention, it is provided that for the ratio of the angle β _S1 between the chord of the profile of the front blade and the circumferential direction to the angle β _S2 between the chord of the profile of the rear blade and the circumferential direction: 1.3 ≤ β _S1 / β _S2 ≤ 1.4. It is preferably provided that β _S1 / β _S2 = 1.33.

This so-called Stafflungswinkelverhältnis allows an advantageous adaptation of the arrangement of the blades at the predetermined inflow, so that the design of a compaction grating is simplified.

It is further preferably provided that the blades have a subsonic profile. In other words: In normal operation, the compression grid is exposed to an inflow having a Mach number between 0.4 and 0.9.

In the case of the compacting grid according to the invention, it has been found that the geometric conditions according to the invention have improved total pressure losses at the design point of the grid as well as in the working area limits, the so-called blocking limit and the tear-off limit.

It can thus be provided an aerodynamically significantly improved compaction grid.

The invention further relates to an axial compressor with a compacting grid according to the invention.

In the following, the invention will be explained in more detail with reference to the following figures.

In the single figure is the inventive compaction grid 1 shown schematically.

The compaction grid 1 has a wreath of shovels 10a . 10b on. The blades are arranged in double rows, so that front blades 10a and rear shovels 10b are formed. The blades each have a pressure side 14 and a suction side 15 on. Furthermore, the front blade has 10a a leading edge 12a and a trailing edge 13a on and the rear shovel 10b has a leading edge 12b and a trailing edge 13b on.

The rear scoop 10b is offset axially of the front blade 10a arranged. The axial direction is through the compressor axis 16 specified.

Further, the rear blade is 10b on the print side 14 the front bucket 10a and the circumferential direction offset to the front blade 10a arranged. The circumferential direction is indicated in the figure by a double arrow and is orthogonal to that through the compressor axis 16 predetermined axial direction.

Between the front and rear shovels 10a . 10b is a coverage area 18 formed so that between the pressure side 14 the front bucket 12a and the suction side 15 the rear shovel 12a in the coverage area 18 a nozzle is formed.

In the nozzle, a nozzle flow can arise, which with the of the trailing edge 13a the front bucket 10a extending wake stream can interact. There is an acceleration of the flow on the suction side 15 the second blade 10b , As a result, an advantageous flow deflection can be realized.

The blades have in the circumferential direction at a distance which is predetermined by a pitch t. The pitch t thus describes the distance of the trailing edges 13b two adjacent rear blades 10b ,

The arrangement of the blades 10a . 10b on the wreath of the compaction grid 1 can be described with different, simple geometric parameters.

The front scoop 10a has a profile with a tendon 20a up, extending from the leading edge 12a to the trailing edge 13a the front bucket 10a extends. The chord length l _s1 describes the length of the tendon 20a ,

Accordingly, the rear blade 10b a tendon 20b up, extending from the leading edge 12b to the trailing edge 13b the rear shovel 10b extends. The chord length l _s2 describes the length of the chord 20b ,

The distance l _s1x describes the distance between the leading edge 12a the front bucket 10a to the trailing edge 13a the front bucket 10a in the axial direction. The distance l _s1x thus describes the extent of the tendon 20a in the axial direction.

The distance l _s2x describes the distance of the leading edge 12b the rear shovel 10b to the trailing edge 13b the rear shovel 10b in the axial direction. The distance l _s2x thus also describes the extension of the tendon 20b in the axial direction.

The extension of the coverage area 18 in the axial direction is indicated by the overlap length Δx. The overlap length Δx thus gives the distance in the axial direction between the leading edge 12b the rear shovel 10b and the trailing edge 13a the front bucket 10a at.

The design of the coverage area 18 in the circumferential direction is described by the distance θ, which is the distance of the trailing edge 13a the front bucket 10a and the leading edge 12b the rear shovel 10b in the circumferential direction describes.

Furthermore, the angle β _{S1 describes} the position of the tendon 20a the front bucket 10a to the circumferential direction. In other words, the angle β _S1 indicates at what angle the blade 10a is arranged and thus, how this is employed to the flow.

The angle β _S2 indicates the angle at which the tendon 20b the rear shovel 10b extends to the circumferential direction.

It has been found that different geometrical conditions can be achieved with a subsonic flow, for example with an inflow of Ma = 0.5, an improved deflection with reduced aerodynamic losses. For the overlap length Δx and the total length l _{x the following} applies: Δx / l _x = 0,018. Further, for the ratio of the distance θ to the pitch t, θ / t = 0.14.

It has been found that an embodiment of the coverage area 18 with these geometrical conditions, even at different axial contraction ratios of 1-1.5 represents a very efficient blade assembly.

Thus, the coverage area 18 , Which represents a central mechanism of action of the blade assembly, designed by means of these geometric specifications in a particularly advantageous manner.

Furthermore, for the chord length l_s1 and l_s2: l_s1/ l_s2 = 1.25. For the axial distances l_s1x and l_s2x applies: l_s1x/ l_s2x  = 0.94.

It has been found that the load distribution on the two blades is influenced in particular by the chord lengths or ratio of chord lengths. The predetermined ratios of the chord lengths and the axial distances lead to an improved load distribution on the two blades 10a . 10b , so that an advantageous deflection with the lowest possible resistance and thus low losses is possible.

Furthermore, it has been found that the ratio of the pitch t to the total length l _x is optimal at a value of 0.9. With respect to the angles β _S1 and β _S2 , β _S1 / β _S2 = 1.33.

The inventive arrangement of the compaction grid offers a double-row arrangement of blades 10a . 10b with subsonic profiles, which allows improved deflection or pressure conversion with reduced aerodynamic losses. Furthermore, the compacting grate according to the invention offers a design approach which is optimized with regard to the specified geometric variables and which can be used for optimum tuning of individual subsequent or previous compressor stages. In the optimization of the invention, a compaction grid having axial compressor thus time and effort can be saved, since with respect to the double row arranged blades of the compression grating according to the invention 1 only the concrete profile forms have to be developed and the geometrical arrangements of the blades 10a and 10b are predetermined to each other.

Claims (8)

Compaction grid ( 1 ) for an axial compressor with a ring of blades ( 10a . 10b ), each having a leading edge ( 12a . 12b ), a trailing edge ( 13a . 13b ), a printed page ( 14 ) and a suction side ( 15 ) and with an axial direction of a predetermined compressor axis ( 16 ), the blades ( 10a . 10b ) are arranged in double rows and front blades ( 10a ) and rear blades ( 10b ), wherein in each case a rear blade ( 10b ) offset in the axial direction to the front blade ( 10a ) and on the print side ( 14 ) of the front blade ( 10a ) in the circumferential direction offset to the front blade ( 10a ), wherein between the front and the rear blade ( 10a . 10b ) a coverage area ( 18 ) is formed, and wherein the blades ( 10a . 10b ) are arranged with a pitch t on the rim, the distance of the trailing edges ( 13b ) of adjacent rear blades ( 10b in the circumferential direction, characterized in that for the ratio of the overlap length Δx in the axial direction to the total length l _{x of} the front and rear blades ( 10a . 10b ): 0.01 ≤ Δx / l _x ≤ 0.02. Compaction grating according to claim 1, characterized in that for the ratio of the distance θ of the trailing edge ( 13a ) of the front blade ( 10a ) from the leading edge ( 12b ) of the rear blade ( 10b ) in the circumferential direction to the pitch t: 0.1 ≦ θ / t ≦ 0.2. Compaction grating according to claim 1 or 2, characterized in that for the ratio of the chord length l _{s1 of} the profile of the front blade ( 10a ) to the chord length l _{s2 of} the profile of the rear blade ( 10b ): 1.2 ≤ l _s1 / l _s2 ≤ 1.3. Compaction grating according to one of claims 1 to 3, characterized in that for the ratio of the distance l _s1x the leading edge ( 12a ) of the front blade ( 10a ) to the trailing edge ( 13a ) of the front blade ( 10a ) in the axial direction to the distance l _{s2x of} the leading edge ( 12b ) of the rear blade ( 10b ) to the trailing edge ( 13b ) of the rear blade ( 10b ) in the axial direction: 0.92 _≦ l _s1x / l _{s2x ≦} 0.96. Compaction grating according to one of claims 1 to 4, characterized in that for the ratio of the pitch t to the total length l _x is: 0.88 ≤ t / l _x ≤ 0.92. Compaction grating according to one of claims 1 to 5, characterized in that for the ratio of the angle β _S1 between the chord ( 20a ) of the profile of the front blade ( 10a ) and the circumferential direction to the angle β _S2 between the chord ( 20b ) of the profile of the rear blade ( 10b ) and the circumferential direction: 1.3 ≤ β _S1 / β _S2 ≤ 1.4. Compaction grate according to one of claims 1 to 6, characterized in that the blades ( 10a . 10b ) have a subsonic profile. Axial compressor with a compaction grid according to one of claims 1 to 7.

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