Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
1999-09-07
2001-08-28
Thorpe, Timothy S. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
Reexamination Certificate
active
06279322
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the components of a gas turbine engine that receive radial high-velocity airflow from a centrifugal compressor, and then deliver the air to an annular-shaped combustor of the engine. More particularly, this invention relates to a compact deswirler system closely coupled to a diffuser and composed of deswirler vanes located within a bend that redirects the airflow from a radially outward direction to a generally axial direction.
BACKGROUND OF THE INVENTION
Shown in
FIG. 1
are portions of a centrifugal compressor
10
and annular-shaped combustor
12
of a gas turbine engine. The compressor
10
generally includes a rotating impeller
14
configured to accelerate and thereby increase the kinetic energy of the gas flowing therethrough. A stationary annular-shaped diffuser
16
circumscribes the impeller
14
, and serves to decrease the velocity of fluid flow leaving the impeller
14
and thereby increase its static pressure. Diffusers are typically composed of either vanes or pipes that define a plurality of circumferentially-spaced passages
18
. The cross-sectional area of each passage
18
typically increases downstream of the impeller
14
in order to diffuse the flow exiting the impeller
14
.
Both vane and pipe-type diffusers generally include a transition region
20
downstream of the diffuser passages
18
to match the diffuser flowpath to the geometry of the combustor
12
. As shown in
FIG. 1
, the transition region
20
includes an annular manifold
22
that receives the radially-outward air flow from the diffuser
16
, and redirects this airflow aft and often radially inward (as shown) toward the annular-shaped entrance of the combustor
12
. The manifold
22
terminates with a generally straight section
24
in which a number of deswirler vanes
26
are positioned immediately upstream of the entrance to the combustor
12
. The vanes
26
serve to remove the residual circumferential swirl from the flow exiting the diffuser
16
by converting the high tangential velocity component of the flow exiting the diffuser passages
18
to a more useful static pressure. As a result, the flow exiting the deswirler vanes
26
and directed into the combustor
12
is characterized by relatively low swirl and Mach number and a particular meridional (“spouting”) angle that together achieve more stable and efficient combustor performance. In a multistage centrifugal compressor, a diffuser and transition region may be used between each consecutive pair of stages to decelerate and deswirl the air flow exiting the leading stage to a level appropriate for the trailing stage.
The manifold
22
shown in
FIG. 1
generally defines an axi-symmetric free bend that is bounded by one (outer) surface, though bends bounded by two (inner and outer) surfaces are also known. The deswirler vanes
26
within the straight section
24
that follows the bend within the manifold
22
are generally arranged on a conical axi-symmetric flow path. Though a single row of vanes
26
is shown, double-row configurations are known. As a rule, the vanes
26
have been placed downstream of the bend and immediately upstream or at the entrance of the combustor
12
.
While diffuser and deswirler systems of the type shown in
FIG. 1
perform well in a number of successful gas turbine engines, further improvements in the performance are continuously being sought. Of primary interest is achieving reductions in pressure losses that reduce engine performance.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a deswirler system for a centrifugal compressor of a gas turbine engine that improves overall engine performance as a result of exhibiting significantly reduced diffusion (secondary flow) and friction losses. According to this invention, the deswirler system generally entails an annular-shaped manifold having an inlet configured to receive radially-outward flowing gas from a diffuser, an outlet configured to discharge the gas in an axial downstream direction, and an arcuate passage therebetween. In contrast to prior art practices, the deswirler system of this invention provides a plurality of deswirler vanes directly within the arcuate passage and closely coupled to the diffuser, instead of being limited to being within a straight section downstream of the arcuate passage.
A significant advantage of the deswirler system of this invention is the reduction in pressure losses that reduce engine performance. Though not wishing to be held to any particular theory, it is believed that placing the deswirler vanes within the bend that turns the air/gas flow from the radial flow direction of the diffuser to the generally axial flow direction required by the compressor, reduces the amplification of the secondary flow as the air/gas leaves the diffuser. Consequently, the deswirler system of this invention is believed to eliminate bend losses and reduces secondary flow losses attributable to a tangentially unguided bend.
Another significant advantage of this invention is that the total length over which the air/gas travels from the diffuser exit to the combustor plenum is reduced, resulting in less total surface area wetted by the air/gas and, therefore, reduced skin friction losses. The diffuser/deswirler system is also more compact than prior art systems, and enables the weight of the engine to be significantly reduced.
Yet another important aspect of this invention is the determination that placement of the deswirler vanes within the arcuate passage immediately adjacent the diffuser allows for aerodynamic advantages through close coupling the deswirler vanes to the diffuser. For example, improved efficiencies can be realized through appropriate relative circumferential positioning of the deswirler vanes relative to the diffuser passages. As a result, the invention provides greater design flexibility in terms of optimizing the diffuser-deswirler system match to further minimize losses attributable to the diffuser-deswirler interface.
Other objects and advantages of this invention will be better appreciated from the following detailed description.
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Nippert, {umlaut over (U )}ber den Ströungsverlust in gekrëmmten Kanälen, Forschungsarbeiten auf dem Gebiete des Ingenieurwesens, Herausgegeben vom Verein Deutscher Ingenieure (1929).
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General Electric Company
Herkamp Nathan D.
Hess Andrew C.
Rodriguez W.
Thorpe Timothy S.
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