DIFFUSER VANE CUSP BLEED APERTURE WITH AUTOMATIC EJECTOR CONTROL DEVICE

ORIFICE D'EXTRACTION DE PURGE SUR DIFFUSEUR D'AIR, AVEC DISPOSITIF AUTOMATIQUE D'EJECTION

English Abstract

DIFFUSER VANE CUSP BLEED APERTURE
WITH AUTOMATIC EJECTOR CONTROL DEVICE
Abstract of Disclosure
In a gas turbine engine an auxiliary airflow is provided
to power accessories. This auxiliary airflow is obtained from
a bleed aperture which is constructed immediately downstream
of a diffuser vane in a cusp which is formed in the trailing
edge of the vane to provide inertial separation. This high
energy air from the diffuser is used as the primary airflow
in an ejector to draw ambient air into the auxiliary airflow
to lower the temperature of the bleed air. The ejector is con-
structed to automatically adjust the amount of ambient air
according to the energy of the bleed airflow by means of a
piston actuated spike mounted for sliding movement in the
primary nozzle. The spike varies the volume of flow through
the primary nozzle according to the pressure exerted by the
airflow on the piston.

Claims

1. In a gas turbine engine having a compressor stage
which drives high energy airflow through a diffuser, means to
bleed air from the diffuser comprising:
a plurality of diffuser vanes mounted in the diffuser
and having a curved cusp-like surface formed in the trailing
edge thereof;
a connecting duct constructed in the diffuser and com-
municating with the region within the cusp formed in the
downstream end of the diffuser vane; and
a bleed air manifold constructed to receive bleed air
from the connecting duct.
2. In a gas turbine engine means to bleed air from the
diffuser as described in claim 1, further comprising an ejec-
tor assembly having a primary and a secondary nozzle, said
assembly being connected to the bleed air manifold so that
the bleed air flows through the primary nozzle, said nozzle
being constructed with means to automatically adjust the
volumn of airflow in the primary nozzle inversely proportional
to the energy of the airflow in the diffuser, said ejector
assembly connected to draw cooling air through the secondary
nozzle to combine with the bleed airflow.
3. In a gas turbine engine means to obtain bleed air from
the diffuser as described in claim 2 wherein the means to vary
the airflow in the primary nozzle of the ejector comprises:
an elongated spike mounted for axial sliding motion
within the primary nozzle and shaped so that this motion
tends to vary the amount of airflow in the primary nozzle;
a sealed chamber constructed within the ejector;

a piston fixed to the nozzle spike for movement
therewith and extending into the sealed chamber;
a biasing spring operatively associated with the piston
to bias the piston and spike in a position for maximum primary
airflow; and
means to expose one side of the piston to a force
proportional to the pressure of the bleed air in the bleed
manifold so that increased pressure will cause movement of the
piston and spike to reduce the primary airflow.

Description

Backaround o the Invention
.
In some instances it is necessary in a gas turbine engine
to have a source of airflow to perform auxiliaxy functions and
drive accessory devices, Eor example, to generate electricity,
drive air conditioning, and to pressurize passenger areas. In
general, this air10w must be free oE contamination and is
supplied from bleed air obtained at various locations in the
engine. Depending on the skage ak which the b:Leed air is
` obtained, various problems occur; n~nely, contamination,
insuficient energy, excessive energy loss within the engine
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itself or excessive temperature of the bleed air. It is,
therefore, the object of this invention to obtain high energy
auxiliary airflow while minimizing contamination and control-
ling the temperature of the auxiliary airflow without serious
loss of engine power.
Another object is to provide an ejector ass~mbly con-
structed to provide a secondary airflow which varies inversely
proportional to the pressure in the primary nozzle.
Summary of the Invention
In a gas turbine engine, having an ann~lar diffuser con-
nected to a centrifugal compressor stage, radially extending
vanes are constructed having a curved cusp formed in the trail-
ing edge of this vane. A bleed air aperture is located within
the cusp to supply high energy air to an auxiliary system. The
cusp is formed to create inertial separation of contaminants
from the bleed air. This auxiliary airflow forms the primary
airflow of an ejector nozzle having a resiliently biased
nozzle spike which is movable to vary the amount of primary
airflow. Adjustment of the spike is caused by changes in
pressure within the bleed air duct. The cooler ambient air
forms the secondary airflow of the ejector and combines with
the primary airflow to lower the temperature thereof. In this
manner, a high energy, temperature contolled, auxiliary air-
flo~ is provided. The spike is connected to a piston which
slides in a chamber which is subject to the pressure in the
primary nozzle. The piston is spring biase~ to provide
maximum primary airflow.

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Brief Description o-f the Drawing
This invention is described in more detail below with
reference to the appended drawing in which:
Figure 1 is a sectional view of a gas turbine engine
incorporating the subject invention;
Figures 2 and 2a are partial side views of the diffuser
showing the diffuser vanes of this invention and the cusp and
bleed aperture magnified, respectively; and
Figure 3 is a sectional view of the ejector nozzle
associated with this invention.
Detailed Description of the Invention
In a gas turbine engine an annular diffuser 1 r as shown
in Figures 1 and 2, receives high energy airflow from a
centrifugal compressor impeller 2. The diffuser 1 is constructed
with radially extending vanes 3 constructed across the diffuser
channel. The vanes 3 gradually expand in width from their orward
edge 4 to the downstream edge 5. A curved cusp 6 is machined
into the trailing edge 5 of the diffuser vane 3 in order to
minimize the wa]ce caused by the vane 3 and to induc~ a vortex at
the trailing edge 5. A bleed aperture 7 is constructed in the
wall of diffuser 1 within the cusp in the trailing edge 5 of the
diffuser vane 3. The bleed aperture 7 connects to a bleed flow
manifold 8 and is designed to allow high energy air within the
cusp region of the diffuser vane 3 to flow into the bleed
manifold ~.
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An auxiliary airflow duct 9 communicates directly with
the bleed manifold 8. An ejector nozzle assembly 10, as shown
in Figure 3, is constructed in the auxiliary duct 9 so that
the bleed air forms the primary flow through the primary nozzle
11 o~ the ejector 10. Cooler ambient air is obtained from
outside of the engine through the secondary nozzle 12 of the
ejector 10. The primary nozzle 11 is controlled by a spike 13
which is axially movable within the nozzle 10. The rearward
portion 14 o* the spike 13 is formed as a piston which trans-
lates within a closed chamber 15. The piston 14 is biased by
spring 16 to provide maximum primary airflow. The pressure
in the bleed manifold 8 forces air through opening 17 into
well 1~ of chamber 15 and exerts a force on one side of the
piston 14 against the biasing spring 16 to cause movement of
the spike 13 to reduce the primary airflow, thereby controlling
the ratio of the primary to the secondary air.
In opexation high energy air exits through the bleed
aperture 7 at the trailing edge 5 of the di~user vane 3 and
enters the bleed manifold 8 which supplies the auxiliary duct
9. At low engine speeds the bleed air is at relatively low
energy and the ejector nozzle 10 is set for maximum primary
flow essentially eliminating the introduction of ambient air.
As engine speeds increase, the higher energy bleed air exerts
a ~orce on the spike 13 against its biased spring 16 to trans-
late the spike 13 in a direction which reduces the amount of
primary air flowing in the primary nozzle 11. As this happens
secondary airflow increases causing an auxiliary airflow of
reduced temperature suitahle to driving accessory devices.

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The curved surface of the cusp 6 constructed in the trail-
ing edge 5 of the diffuser vane 3 requires the bleed airflo~
to turn sharply in order to exit through the aperture 7. This
creates a centrifugal inertial separation effect which sub-
stantially eliminates contaminants in the bleed air stream,
thereby eliminating the need for further separation or filter- :
ing of the auxiliary airfl.ow.
According to the above description, the following invention
is claLmed as novel and is desired to be secured by Letters
Patent.
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