Title of Invention

RECIRCULATION STRUCTURE FOR TURBOCOMPRESSOR

Abstract The invention relates to a recirculation structure for turbo compressor, comprising an annular chamber arranged concentrically with the compressor axis in the area of the free blade ends of a blade ring, the annular chamber radially adjoining the contour of the main flow duct, the annular space, the side of the annular chamber adjoining the contour of the main flow duct being open to the main flow duct over its axial length and over its entire periphery, and a plurality of guide elements, which are arranged in the annular chamber distributed over the periphery thereof, and which are arranged and shaped in a manner favorable to the inlet of the recirculation flow in the axially rear area of the annular chamber and in such a way that the outlet of the recirculation flow in the axially front area of the annular chamber occurs with a defined direction and where appropriate a defined swirl in relation to the downstream blade ring, the guide elements in one of the front area and the rear area of the annular chamber having recesses for the passage of a flow in the peripheral direction, characterized in that the free edges (41 to 44) of the guide elements (37 to 40) over their axial length lie on or close to the contour (11,12) of the main flow duct (9,10), and in that the axial center of the annular chamber (29 to 32) lies upstream of the axial center of the free blade ends (25 to 28).
Full Text Recirculation structure for turbocompressor
The invention relates to a recirculation structure for
turbocompressor, according to the preamble of claim 1,
and to an aero-engine and a static gas turbine.
compressor
Recirculation structures for turbocompressor have been
known for some time and among experts are usually
referred to as "casing treatments". Their primary
function is to increase the aerodynamically stable
operating range of the compressor, the so-called surge
limit being shifted towards higher compressor
pressures, that is towards a higher compressor load.
The disturbances responsible for a local air stream
separation and ultimately for the surging of the
compressor occur, on the casing side, at the ends of
the rotor blades of one or more compressor stages, and
on the hub side at the radially inner guide vane ends,
since the aerodynamic load is greatest in these areas.
Recirculation of the "air particles", circulating at
blade speed between the blade tips and having a reduced
energy, into the main flow, thereby increasing their
energy, stabilizes the flow in the area of the blade
ends once again. Since flow disturbances generally do
not occur uniformly over the stage periphery, it should
also be possible to balance the flow in a peripheral
direction in addition to the substantially axial
recirculation. The main disadvantage of the known
casing treatments is that although they raise the surge
limit they also at the same time reduce the compressor
efficiency.
DE 33 22 295 C3 protects an axial-flow fan having a
casing treatment of the generic type. This discloses
an annular chamber (8) in which guide elements (9) are
fixed. In the downstream area over the rotor blade
ends is a peripherally open area into which the guide
elements do not extend. This type of casing treatment
is characterized by a closed ring (7), which is
approximately flush with the contour of the main flow duct and which separates
the rear inlet area from the front outlet area of the recirculation structure,
forming a smooth, closed surface area.
DE 35 39 604 C1 discloses a quite similar casing treatment, a peripherally open
area here being provided in the front and rear area of the annular chamber (7).
The radially inner ring 6 will also be noted here.
US 5,282,718 A discloses a more recent casing treatment. This improves on the
fluid mechanics of the annular chambers (18,28) and the guide elements (24). In
this case, too, the inlet and outlet for the recirculation flow are separated by a
solid ring presenting a closed, smooth surface to the blades. Such rings in the
blade area must generally be provided with skim or run-in coating in case they
come into contact with the blade tips.
Further casing treatments with axial or axially inclined grooves are disclosed, for
example in US 5,137,419 A. These will not be considered here since in the
absence of any interconnection of the grooves in these versions no peripheral
flow balancing is possible.
US 3620640 discloses an improved propeller shroud comprising a toroidal cavity
formed on its inside surface along its entire periphery level with the blades of
said propeller and along the meridian of the shroud and movable flaps mounted
on downstream of same cooperating with a cavity bottom comprising a
retractable wall with or without streamlined partition walls adapted within said
toroidal cavity and along substantially meridian planes of said shroud.
US 5474417 discloses a tip shroud assembly comprising a segmented annular
shroud, each segment comprising first, second and third arcuate members and a
plurality of vane walls integral with the first second and third members, and each
arcuate member has a radially inner surface, and the third arcuate member is in
spaced relation to the first and second members, and each vane wall spans
between the radially inner surface of the third arcuate member and the radially
inner surfaces of the first and second members.
In view of the disadvantages of the solutions according to the prior art, the
object of the invention is to provide a recirculation structure for turbo
compressor which will permit a clear increase in the surge limit and hence a
distinct enlargement of the stable operating range without any significant
deterioration in compressor efficiency.
This object is achieved by the features of the invention .
According to the invention, there is provided a recirculation structure for turbo
compressors, comprising an annular chamber arranged concentrically with the
compressor axis in the area of the free blade ends of a blade ring, the annular
chamber radially adjoining the contour of the main flow duct, the annular space,
the side of the annular chamber adjoining the contour of the main flow duct
being open to the main flow duct over its axial length and over its entire
periphery, and a plurality of guide elements, which are arranged in the annular
chamber distributed over the periphery thereof, and which are arranged and
shaped in a manner favorable to the inlet of the recirculation flow in the axially
rear area of the annular chamber and in such a way that the outlet of the
recirculation flow in the axially front area of the annular chamber occurs with a
defined direction and where appropriate a defined swirl in relation to the
downstream blade ring, the guide elements in one of the front area and the rear
area of the annular chamber having recesses for the passage of a flow in the
peripheral direction, characterized in that the free edges of the guide elements
over their axial length lie on or close to the contour of the main flow duct and in
that the axial center of the annular chamber lies upstream of the axial center of
the free blade ends .
The essence of the invention resides in the fact that the annular chamber with
the guide elements is fully open towards the main flow duct and over its axial
length and its periphery. There is no need for annular elements with skim
coatings etc. The patent specifications cited above show that experts have
hitherto endeavored to make recirculation structures smooth, virtually gap-free
and closed in relation to the main flow duct, that is to the so-called annular
space, over as large an axial area as possible, in order to produce an extension
to the contour of the main flow duct that is as favorable to the flow and as loss-
free as possible. The invention, by contrast, leads to gaps, fissured surfaces etc.
and consequently seems to be disadvantageous and inappropriate. Experiments
have shown, however, that the recirculation structure according to the invention
is superior to known solutions both with regard to a raising of the surge limit and
in terms of efficiency. The aerodynamic explanation for this is that the free,
unforced development of the recirculation flow in the open annular chamber with
free guide elements and flow connections in a peripheral direction is more
important than having the smoothest possible extension of the main flow duct
contour. The absence of a closed ring has the further advantage that the guide
elements do not require any skim or run-in coating and the savings in overall
radial space and weight bring advantages in terms of structural mechanics.
The invention will be further explained below with reference to the accompanying drawings
which provide a simplified representation that is not to scale. In the accompanying drawings:
Fig. 1 shows a partial longitudinal section through an
axial-flow compressor in the area of a casing-side
recirculation structure,
Fig. 2 shows a comparable partial longitudinal section
in the area of a hub-side recirculation structure,
Fig. 3 shows a partial cross section through the
recirculation structure according to Fig. 1, and
Fig. 4 shows a partial view of the recirculation
structure according to Fig. 1 and 3 radially from
inside,
Fig. 5 shows a partial longitudinal section in the area
of a casing-side recirculation structure that has been
modified compared to that in Fig. 1, and
Fig. 6 shows a partial longitudinal section in the
area of a casing-side recirculation structure that has
been modified compared to those in Fig. 1 and Fig. 5.
The recirculation structure 1 according to Fig. 1 is
incorporated into the casing 5 of a turbocompressor and
can therefore be referred to as a "casing treatment".
The direction of flow in the bladed main flow duct 9 is
indicated on the left by an arrow, that is to say it
runs from left to right. In the area shown the flow is
first incident upon a guide vane ring 13, then on a
rotor blade ring 20 and finally on a guide vane ring 14
again. The radially outer contour 11 of the main flown
duct 9 conforms to the inner contour of the casing 5
and to show this clearly is extended by a dash-dot line
to left and right of the actual representation. The
static recirculation structure 1 interacts with the
rotor blade ring 20 and for the most part is situated
axially in front, that is to say upstream, of the
latter. The annular chamber 29, which together with
the guide elements 37 forms the recirculation structure
1, is situated radially outside and adjacent to the
main flow duct 9 and is open to the latter. The free
edges 41 of the guide elements 37 lie on or close to
the contour 11 of the main flow duct 9, that is to say
they are at least approximately flush with the inner
contour of the casing. The guide elements 37 may be
composed of a metal, such as a nickel-based alloy, or a
light-weight metal, such as aluminum, or a plastic
material, such as thermoplastics, thermoset plastics or
elastomers. From their radially inner edges 35, 36,
the front wall 33 and the rear wall 34 of the annular
chamber 29 are inclined forwards, in order to promote
the recirculation flow indicated by a small arrow.
The angle of inclination of the front wall is denoted
by a and may be identical to or different from the
angle of the rear wall 34. Between the front wall 33,
the guide elements 37 and the rear wall 34 are recesses
45, 46, which permit the flow processes inside the
annular chamber in a peripheral direction, in addition
to the predominantly axial recirculation. 25 denotes
the free blade ends of the rotor blade ring 20 in the
area of which flow disturbances most commonly occur.
In contrast to Fig. 1, Fig. 2 shows a recirculation
structure 2 incorporated into a rotating hub 8. A
rotor blade ring 21, a guide vane ring 15 with radially
inner free blade ends 26 and a rotor blade ring 22 can
be seen from left to right in the main flow duct 10.
Such a new arrangement of a recirculation structure
could quite logically be termed a "hub treatment". The
recirculation structure 2, comprising annular chamber
30 and guide elements 38, with front and rear recesses
47, 48 interacts with a guide vane ring 15 in the main
situated downstream. Since in this case it is the hub
treatment that rotates and the guide vane ring 15 is
stationary, the rotor speed acts fully as differential
speed. The operating principle does not differ
fundamentally from that of a casing treatment. Casing
treatment and hub treatment can even be combined in one
, turbocharger and may be used in multiple stages. The
radially inner contour 12 of the main flow duct here
conforms to the outer contour of the hub 8.
Fig. 3 shows a cross-section through a detail from Fig.
1. The guide elements 37 are inclined at an angle (3 to
the radial, so that the blade ends 25 of the rotor
blade ring 20 promote the recirculation flow into the
annular chamber 29 without major losses; note the
direction of rotation (see arrow). The angle of
inclination (3 may diminish radially outwards to a value
"zero" with correspondingly curved guide elements.
A radial arrangement of the guide elements, that is to
say (3 = 0°, is possible but would probably be less
favorable to the flow.
The view of Fig. 3 according to Fig. 4 shows the blade
profiling of the rotor blade ring 20 in relation to its
direction of rotation (arrow) and gives a good idea of
the flow-promoting profiling and curvature of the guide
elements 37. The person skilled in the art will
recognize that the recirculation outlet in the area of
the upstream edge 35 of the annular chamber 2 9 is here
intended to occur with counter-swirling in relation to
the rotor blade ring 20. 36 denotes the downstream
edge of the annular chamber. It should be remembered
that in their simplest design forms the guide elements
37 may also consist of plane or curved "plates".
The recirculation structure 3 according to Fig. 5 is a
casing treatment having an annular chamber 31
incorporated into a casing 6. The guide elements 39
here extend to the front wall of the annular chamber 31
and recesses 49 are provided in the rear area, in
direct proximity to the blade ends 27 of the rotor
blade ring 23. The free edges 43 of the guide elements
39 do not extend into the area of rotation of the blade
ends 27. 16 and 17 denote guide vane rings.
The recirculation structure 4 in Fig. 6, with annular
chamber 32 and guide elements 40, is likewise a casing
treatment, which is incorporated into a casing 7 and
interacts with a rotor blade ring 24. In contrast to
Fig. 5, the guide elements 40 here extend to the rear
wall of the annular chamber 32. Recesses 50 are here
provided in the front area. Since the free edges 44 of
the guide elements 40 extend into the area of rotation
of the blade ends 28, in the rear area they are
radially offset outwards in order to reliably prevent
contact with the blades. The edges may naturally also
be correspondingly offset in their entirety.
In all developments of the recirculation structure the
free edges 41 to 44 of the guide elements 37 to 40 do
not have to be offset radially outwards if the guide
elements are made from a soft lightweight metal or a
plastic material, because any contact with the blade
ends 25 to 28 can be permitted without the blades being
damaged.
We Claim:
1. A compressor comprising:
a casing (10, 110, 210) which defines a generally cylindrical flow
passage (42,142);
a rotor carrying at least one set of rotor blades (12);
at least one set of stator blades (14,16); and
a casing treatment (18, 118, 218) including a recirculation passage in
the casing (10, 110, 210) for removing low momentum flow adjacent the
tips of the rotor blades (12), in use, and returning the flow to the
generally cylindrical flow passage (42, 142) upstream of the point of
removal and a plurality of curved guide vanes (22, 122, 222) located
within the recirculation passage, characterized in that the recirculation
passage is formed as a radially inwardly open annular recess (20, 120,
220), and the curved guide vanes (22,122, 222) within the annular recess
(20, 120, 220) define an annular inlet (34, 134) downstream of the vanes
(22, 122) and/or an annular outlet (36, 236) upstream of the vanes (22,
222), each guide vane (22,122, 222) projecting radially inwardly from the
casing (10,110, 210) towards a free end (38,138) which is exposed at or
near the inward mouth (30, 130) of the annular recess (20, 120, 220) to
define a series of radially inwardly open curved channels (40, 140) within
the recess (20, 120, 220) adjacent the annular inlet (34, 134) and/or the
annular outlet (36, 236).
2. A compressor comprising:
a casing which defines a generally cylindrical flow passage;
a rotor carrying at least one set of rotor blades;
at least one set of stator blades; and
a hub treatment having a recirculation passage in the hub of the rotor
adjacent the stator blades and a plurality of curved guide vanes located
within the recirculation passage, characterised in that the recirculation
passage is formed as a radially outwardly open annular recess and the
curved guide vanes within the annular recess define an annular inlet
downstream of the vanes and/or an annular outlet upstream of the vanes,
each guide vane projecting radially outwardly from the rotor hub towards
a free end which is exposed at or near the outward mouth of the annular
recess to define a series of radially outwardly open curved channels within
the recess adjacent the annular inlet and/or the annular outlet.
3. A compressor as claimed in claims 1 or 2, wherein a rear wall (26) of the
annular recess (20, 120, 220) and a front wall (28) of this recess (20, 120, 220)
are inclined at an angle relative to the longitudinal axis of the casing(10, 110,
210).
4. A compressor as claimed in claim 3, wherein the angle of inclination of the
rear wall (26) and the front wall (28) relative to the longitudinal axis of the
casing (10,110, 210) is between 30° and 90°.
5. A compressor as claimed in claim 3 or claim 4, wherein the inclination of the
rear wall (26) relative to the casing longitudinal axis differs from the inclination
of the front wall (28) relative to the casing longitudinal axis.
6. A compressor as claimed in any one of the preceding claims, wherein the
guide vanes (22, 122, 222) are inclined in the radial direction at an angle
between 10° and 90°.
7. A compressor as claimed in claim 6. wherein the inclination of the guide
vanes (22, 122, 222) relative to the radial direction varies along the height
and/or the length of these vanes (22,122, 222).
8. A compressor as claimed in any one of the preceding claims, wherein the ratio
between the guide vane radial projection height and the radial depth of the
annular recess (20,120, 220) is less than 1.0.
9. A compressor as claimed in claim 8, wherein the ratio between the guide vane
radial projection height and the radial depth of the annular recess (20,120, 220)
varies along the axial length of the guide vanes (22,122, 222).
10. A compressor as claimed in any one of the preceding claims, wherein the
ratio between the volume of the guide vanes (22,122, 222) and the total volume
of the annular recess (20,120, 220) is greater than 0.5.
11. A compressor as claimed in any one of the preceding claims, wherein the
ratio between the cross-sectional width of the channel (40, 140) between
adjacent guide vanes (22, 122, 222) and the cross-sectional pitch of the guide
vanes (22,122, 222) is between 0.3 and 1.0.
12. A compressor as claimed in claim 11, wherein the ratio between the cross-
sectional width of the channel (40,140) between adjacent guide vanes (22,122,
222) and the cross-sectional pitch of the guide vanes (22,122, 222) varies along
the radial projection height and/or the axial length of the guide vanes (22,122,
222).
13. A compressor as claimed in any one of the preceding claims, wherein the
ratio between the vane radial projection height and the overall axial width of the
annular recess (20,120, 220) is between 0.2 and 1.0.
14. A compressor as claimed in claim 1, wherein the axial midpoint of the
annular recess (20, 120, 220) lies upstream of the rotor blade axial chord
midpoint in the blade tip region.
15. A compressor as claimed in claim 1, wherein the ratio between the axial
width of the annular recess (20, 120, 220) and the rotor blade axial chord is
between 0.4 and 1.0.
16. A compressor as claimed in any one of claims 1 to 15, which comprises a
single-stage compressor.
17. A compressor as claimed in any one of claims 1 to 15, which comprises a
multi-stage compressor.
18. A compressor as claimed in claim 16 or claim 17, which is designed for axial
flow.
19. A compressor as claimed in claim 16 or claim 17, which is designed for
diagonal flow.
20. A compressor as claimed in claim 16 or claim 17, which is designed for radial
flow.
21. A compressor as claimed in claim 1, wherein the casing comprises a casing
insert being connectable to the compressor casing adjacent the rotor blades and
defining the casing treatment.
22. A compressor as claimed in claim 21, wherein a rear wall of the annular
recess and a front wall of this recess are inclined at an angle relative to the
longitudinal axis of the casing.
23. A compressor as claimed in claim 22, wherein the angle of inclination of the
rear wall and the front wall relative to the longitudinal axis of the casing is
between 30° and 90°.
24. A compressor as claimed in claim 22 or claim 23, wherein the inclination of
the rear wall relative to the casing longitudinal axis differs from the inclination of
the front wall relative to the casing longitudinal axis.
25. A compressor as claimed in any one of claims 21 to 24, wherein the guide
vanes are inclined in the radial direction at an angle between 10° and 90°.
26. A compressor as claimed in claim 25, wherein the inclination of the guide
vanes relative to the radial direction varies along the height and/or the length of
these vanes.
27. A compressor as claimed in any one of claims 21 to 26, wherein the ratio
between the guide vane radial projection height and the radial depth of the
annular recess is less than 1.0.
28. A compressor as claimed in claim 27, wherein the ratio between the guide
vane radial projection height and the radial depth of the annular recess varies
along the axial length of the guide vanes.
29. A compressor as claimed in any one of claims 21 to 28, wherein the ratio
between the volume of the guide vanes and the total volume of the annular
recess is greater than 0.5.
30. A compressor as claimed in any one of claims 21 to 29, wherein the ratio
between the cross-sectional width of the channel between adjacent guide vanes
and the cross-sectional pitch of the guide vanes is between 0.3 and 1.0.
31. A compressor as claimed in claim 30, wherein the ratio between the cross-
sectional width of the channel between adjacent guide vanes and the cross-
sectional pitch of the guide vanes varies along the radial projection height and/or
the axial length of the guide vanes.
32. A compressor as claimed in any one of claims 21 to 31, wherein the ratio
between the vane radial projection height and the overall axial width of the
annular recess is between 0.2 and 1.0.

The invention relates to a recirculation structure for turbo compressor,
comprising an annular chamber arranged concentrically with the compressor axis
in the area of the free blade ends of a blade ring, the annular chamber radially
adjoining the contour of the main flow duct, the annular space, the side of the
annular chamber adjoining the contour of the main flow duct being open to the
main flow duct over its axial length and over its entire periphery, and a plurality
of guide elements, which are arranged in the annular chamber distributed over
the periphery thereof, and which are arranged and shaped in a manner favorable
to the inlet of the recirculation flow in the axially rear area of the annular
chamber and in such a way that the outlet of the recirculation flow in the axially
front area of the annular chamber occurs with a defined direction and where
appropriate a defined swirl in relation to the downstream blade ring, the guide
elements in one of the front area and the rear area of the annular chamber
having recesses for the passage of a flow in the peripheral direction,
characterized in that the free edges (41 to 44) of the guide elements (37 to 40)
over their axial length lie on or close to the contour (11,12) of the main flow duct
(9,10), and in that the axial center of the annular chamber (29 to 32) lies
upstream of the axial center of the free blade ends (25 to 28).

Documents:

1393-kolnp-2004-abstract.pdf

1393-kolnp-2004-claims.pdf

1393-KOLNP-2004-CORRESPONDENCE-1.1.pdf

1393-kolnp-2004-correspondence.pdf

1393-kolnp-2004-description (complete).pdf

1393-kolnp-2004-drawings.pdf

1393-kolnp-2004-examination report.pdf

1393-kolnp-2004-form 1.pdf

1393-KOLNP-2004-FORM 15.pdf

1393-kolnp-2004-form 18.pdf

1393-kolnp-2004-form 2.pdf

1393-kolnp-2004-form 26.pdf

1393-kolnp-2004-form 3.pdf

1393-kolnp-2004-form 5.pdf

1393-KOLNP-2004-FORM-27-1.pdf

1393-KOLNP-2004-FORM-27.pdf

1393-kolnp-2004-granted-abstract.pdf

1393-kolnp-2004-granted-claims.pdf

1393-kolnp-2004-granted-correspondence.pdf

1393-kolnp-2004-granted-description (complete).pdf

1393-kolnp-2004-granted-drawings.pdf

1393-kolnp-2004-granted-examination report.pdf

1393-kolnp-2004-granted-form 1.pdf

1393-kolnp-2004-granted-form 18.pdf

1393-kolnp-2004-granted-form 2.pdf

1393-kolnp-2004-granted-form 26.pdf

1393-kolnp-2004-granted-form 3.pdf

1393-kolnp-2004-granted-form 5.pdf

1393-kolnp-2004-granted-reply to examination report.pdf

1393-kolnp-2004-granted-specification.pdf

1393-kolnp-2004-granted-translated copy of priority document.pdf

1393-KOLNP-2004-PA.pdf

1393-kolnp-2004-reply to examination report.pdf

1393-kolnp-2004-specification.pdf

1393-kolnp-2004-translated copy of priority document.pdf


Patent Number 235854
Indian Patent Application Number 1393/KOLNP/2004
PG Journal Number 36/2009
Publication Date 04-Sep-2009
Grant Date 02-Sep-2009
Date of Filing 21-Sep-2004
Name of Patentee MTU AERO ENGINES GMBH
Applicant Address DACHAUER STRASSE 665, D-80995 MUNCHEN
Inventors:
# Inventor's Name Inventor's Address
1 SEITZ, PETER BULACHSTRASSE 58, 85232 BERGKIRCHEN/GUNDING
PCT International Classification Number F01D 11/08
PCT International Application Number PCT/DE2003/00623
PCT International Filing date 2003-02-26
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 02/1688 2002-02-28 South Africa
2 10238837.7 2002-08-23 South Africa