AERODYNAMIC COUPLING BETWEEN TWO ANNULAR ROWS OF
STATIONARY, VANES IN A TURBINE ENGINE
The present invention relates to a turbine engine
such as an airplane turboprop or turbojet, which engine
5 has at least two successive annular rows of stationary
vanes, e.g. formed by the vanes of a nozzle stage
arranged at the outlet from a compression stage and by an
annular row of casing arms arranged downstream from the
nozzle.
10 In a turbine engine,;, the nozzle arranged at the
outlet from a compressor has an annular row of stationary
vanes that, in the prior art, are regularly distributed
around the longitudinal axis of the turbine engine.
An annular row of casing arms is arranged downstream
15 from the nozzle, where the casing arms serve to transmit
forces between internal and external casings to which
they are connected and they extend through the stream of
gas flowing from the compressor.
In the prior art, the angular positions of the
20 casing arms relative to the nozzle vanes are not
optimized. The wakes formed at the trailing edges of the
nozzle vanes interact with the casing arms and generate
significant head losses, thereby decreasing the
performance of the turbine engine. Furthermore, it is
25 possible to observe pumping phenomena that are initiated
at the nozzle.
In order to improve the performance of a turbine
engine, it is known to implement aerodynamic coupling
between two stator elements or two rotor elements.
30 Application EP-A-2 071 127 in the name of the Applicant'
describes a method of designing a multistage turbine
engine turbine that makes it possible to achieve
aerodynamic coupling over all of the sets of rotor vanes
or of stator vanes of the turbine.
35 An object of the invention is to improve the
performance of a turbine engine of the above-specified
type by achieving aerodynamic coupling between the
2
stationary vanes of the nozzle and the casing arms
situated downstream, or more generally, between two
successive annular rows of stationary vanes of the
turbine engine.
5 To this end, the invention provides a turbine engine
comprising at least first and second successive annular
rows of stationary vanes, such as for example an annular
row of stationary vanes of a nozzle stage and an annular
row of casing arms arranged downstream from the nozzle,
10 the turbine engine being characterized in that each vane
of the second row extends in a radial plane lying between
the trailing edges of two consecutive vanes of the first
row, and in that the pitch between these two vanes of the
first row is greater than the pitch between the other
15 vanes of the first row.
.According to the invention, the pitch of the
stationary vanes of the first row has a value that is
greater between the vanes that are situated on either
side of the radial plane.passing via the vanes of the
20 second row and a value that is smaller between the vanes
situated between those two radial planes, such that the
wakes formed at the trailing edges of the vanes of the
first row pass respectively on either side of the vanes
of the second row, thereby limiting head losses and
25 aerodynamic interactions between the two rows of vanes.
According to a characteristic of the invention, the
pitch between the two'vanes of the first row that lie on
either side of the radial plane passing via a vane of a
,second row is'equal to 360°(1+m/n)/N, n being the number
30'' of vanes of the second row, N being equal to 360°/P2, and
P2 being the pitch between the vanes of the first row
that lie between two radial planes passing via two
consecutive vanes of the second row, the number of vanes
of the first row being an integer multiple of the number
35 n of vanes of the second row, and m being an integer less
than (n-1) and greater than or equal to zero and such
that N=kn+m, where k is an integer.
3
In an embodiment, the pitch between to vanes of the
first row situated on either side of the radial plane
passing via"a vane of the second row is equal to about
1.5 times the pitch between the other vanes of the first
5 row.
When the vanes of the first row are vanes of a
nozzle stage and the vanes of the second row are formed
by casing arms, the pitch between two vanes of the first
row situated on either side of the radial plane passing
10 via a vane of the second row is equal to about 5.4° and
the pitch between the other vanes of the second row is
equal to about 3.6°.
The radial plane passing via a vane of the second
row may pass between the pressure side of a first vane
15 and the suction side of a consecutive second vane of the
first row. The circumferential distance between said
plane and the pressure side of said first vane may be
less than the circumferential distance between the plane
and the suction side of said second vane.
20 The invention can be better understood and other
details, characteristics, and advantages thereof appear
more clearly on reading the following description made by
way of non-limiting example and with reference to the
accompanying drawings, in which:
25 • Figure 1 is a
view of a nozzle and
turbine engine;
Figure 2 is a
view of a nozzle and
30'' the invention; and
• Figure 3 is a
showing the paths of
highly diagrammatic fragmentary plan
of a casing arm in a prior art
highly diagrammatic fragmentary plan
a casing arm in a turbine engine of
view corresponding to Figure 2 and
the wakes formed at the trailing
edges of the stationary vanes of the nozzle and of the
casing arm.
35 The description below relates to the situation in
which the first row of stationary vanes is that of a
nozzle stage 10 arranged at the outlet from a compression
4
stage in a turbine engine such as an airplane turboprop
or turbojet, and the second row of vanes is formed by an
annular row of casing arms 20 arranged downstream from
the nozzle.
5 The vanes 12 of the nozzle extend substantially
radially through the stream of air flowing out from the
compressor and they are attached to internal and/or
external casings of the turbine engine by appropriate
means.
10 The casing arms 20 located downstream from the
nozzle 10, in particular at the outlet from the low
pressure compressor, serve to connect the internal and
external casings of the compressor together in order to
transmit forces. Each of these casing arms 20 has an
15 upstream leading edge 22 and a downstream trailing edge
24 for air coming from the nozzle 10.
The number of casing arms 20 is less than the number
of stationary vanes 12 of the nozzle 10 and the casing
arms are regularly distributed around the longitudinal
20 axis of the turbine engine.
In the prior art, the stationary vanes 12 of the
nozzle are regularly distributed around the longitudinal
axis of the turbine engine. In other words, the
circumferential pitch P of the vanes 12 is constant.
25 Furthermore, the angular positions of the casing
arms 20 relative to the nozzle vanes 12 are random. That
arrangement gives rise to significant head losses as a
result of the interaction between the wakes formed at the
trailing edges 16 of the vanes 12 with the casing arms
30 20, and also gives rise to risk of pumping being
initiated in the nozzle.
The invention serves to remedy that problem by
optimizing the number of nozzle vanes, the
circumferential pitch between the nozzle vanes, and the
35 angular positions of these vanes relative to the casing
arms, enabling aerodynamic coupling to be achieved
between the nozzle vanes and the casing arms.
5
As shown in Figures 2 and 3, each casing arm 120
extends ina radial plane C lying substantially between
two consecutive vanes 112' of the nozzle 110. The casing
arms 120 are angularly positioned relative to the vanes
5 112, 112' of the nozzle in such a manner that their
radial planes C lie between pairs of consecutive vanes
112', and more particularly between the pressure side of
one of the vanes 112' and the suction side of the other
vane 112'. Advantageously, the circumferential direction
10 D1 between the plane C anel the suction side of the first
vane 112' is less than the circumferential distance D2
between the plane C and the suction side of the other
vane 112'.
The pitch P1 between the vanes 112' situated on
15 either side of the plane C is greater in value than the
pitch P2 between the other vanes 112 of the nozzle.
According to the invention, the pitch P1 may be
defined by the following relationship:
P1 = 360°(1+m/n)/N
20 where:
n is the number of casing arms;
N is equal to 360°/P2;
the number of nozzle vanes being an integer multiple
of the number n of casing arms; and
25 m is an integer less than (n-1) and greater than or
equal to zero such-that:
N = kn + m
where k is an integer.
The above relationship may also be written in the
30` following form:
Pl = P2 + (360° - P2xN')/n
where N' is the number of nozzle vanes.
This relationship may be obtained by starting from a
prior art example in which the nozzle has N stationary
35 vanes distributed uniformly around the axis, at a pitch
P2 equal to 360°/N between the vanes, the number of
casing arms being n. According to the invention, the
6
pitch P2 is conserved between the nozzle vanes that are
situated between the radial planes passing via the casing
arms, and the pitch Pl between the vanes on either side
of these radial planes are determined by the above
5 relationship, the number N' of nozzle vanes now being an
integer multiple of the number of casing arms.
The pitch P2 between the nozzle vanes in the
invention is equal to the mean pitch P of the uniformly
distributed nozzle vanes of the prior art in order to
10 limit any risk of losing pumping margin when pumping is
initiated at the nozzle.
By way of example, the pitch P2 between the vanes
112' is equal to approximately 1.5 times the pitch P2
between the other vanes 112. The pitch P1 may be equal
15 to about 5.4° and the pitch P2 may be equal to about
3.6°, for example. The number of stationary vanes 112,
112' of the nozzle 110 may be equal to 96, for example,
and the number of casing arms 120 may be equal to 8, for
example.
20 As can be seen in Figure 3, the wakes 130 formed
downstream from the trailing edges of the vanes 112' of
the nozzle 110 pass respectively on either side of the
casing arms 120 and follow its profile without generating
head loss, after which they flow on either side of the
25 wake 132 formed by the trailing edge of the arm.
This limits interaction between the casing arms and
the nozzle vanes situated upstream from these arms,
reduces axially symmetrical disturbances at the nozzle,
,,,and limits the risks of loss of pumping margin at the
30 nozzle.
The invention applies to all configurations in which
two annular rows of stationary vanes are consecutive and
downstream one from the other in a turbine engine.
7
CLAIMS
1. A turbine engine comprising at least first and second
successive annular rows of stationary vanes, such as for
example an annular row of stationary vanes (112, 112') of
5 a nozzle stage (110) and an annular row of casing arms
(120) arranged downstream from the nozzle, the turbine
engine being characterized in that each vane (120) of the
second row extends in a radial plane (C) lying between
the trailing edges of two consecutive vanes (112') of the
10 first row, and in that the pitch (P1) between these two
vanes (112') of the first row is greater than the pitch
(P2) between the other vanes (112) of the first row.
2. A turbine engine according to claim 1, characterized
15 in that the pitch (Pl) between the two vanes (112') of
the first row that lie on either side of the radial plane
passing via a vane (120) of a second row is equal to
360°(l+m/n)/N, n being the number of vanes of the second
row, N being equal to 360°/P2, and P2 being the pitch
20 between the vanes of the first row that lie between two
radial planes passing via two consecutive vanes of the
second row,the number of vanes of the first row being an
integer multiple of the number n of vanes of the second
row, and m being an integer less than (n-1) and greater
25 than or equal to zero and such that N=kn+m, where k is an,,
integer.
3. A turbine engine according to claim 1 or claim 2,
characterized in that the pitch (Pl) between two vanes
30' (112') of the first row situated on either side of the
radial plane (P) passing via a vane (120) of the second
row is equal to about 1.5 times the pitch (P2) between
the other vanes (112) of'the first row.
35 4. A turbine engine according to any one of claims 1 to
3, characterized in that the pitch (Pl) between two vanes
(112') of the first row situated on either side of the
8
radial plane (C) passing via a vane (120) of the second
row'is equal to'about 5.4° and the pitch (P2) between the
other vanes'°jof the second row is equal to about 3.6°.
5 5. A turbine engine according to any preceding claim,
characterized in that the radial plane (C) passing via a
vane of the second row passes between the pressure side
of a first vane (112') and the suction side of a
consecutive second vane (112') of the first row, and the.
10 circumferential distance (P1) between said plane and the
pressure side of said first vane is less than the
circumferential distance (D2) between the plane and the
suction side of said second vane.