Single slot impeller bleed

Details Single slot impeller bleed Single slot impeller bleed

1999-02-04

2001-02-06

Lopez, F. Daniel (Department: 3745)

Rotary kinetic fluid motors or pumps

Working fluid bypass

Selectively adjustable vane or working fluid control for bypass

C415S001000, C415S026000, C415S914000, C415S173200

Reexamination Certificate

active

06183195

ABSTRACT:

TECHNICAL FIELD
This invention relates to compressors for use in gas turbine engines and, more particularly, to centrifugal compressors including air bleed in association therewith for regulating the operating characteristics of the compressor.
BACKGROUND OF THE INVENTION
In gas turbine engines for use in powering aircraft, air is directed through multiple stage compressors as it flows axially or axially and radially through the engine to a burner. As the air passes through each successive compressor stage, the pressure of the air is increased. Under certain conditions, such as when the engine is throttled back or during start-up, the compressor pumping capacity is significantly reduced. In this condition, an engine surge or blow-out may occur, endangering the operation of the engine and the associated aircraft. In the past, it has been recognized that inadequate surge margin in such compressors could be eliminated by bleeding a substantial percentage of the compressor air flow at strategic locations along the gas path.
It has been proposed in U.S. Pat. No. 4,248,566 which is entitled DUAL FUNCTION COMPRESSOR BLEED and issued to Chapman et al. on Feb. 3, 1981, to form an annular control slot in the stationary shroud so as to allow the inflow of air from outside the shroud to the rotor chamber under high r.p.m. conditions of the compressor operations and to allow air flow to bleed from the rotor chamber to the exterior of the shroud when the rotor is operating at a low r.p.m. whereby to stabilise the flow of the rotor at low r.p.m. operation. Nevertheless, the annular slot disclosed in this patent is not circumferentially continuous and the radial air flow is affected by reinforcing bridges on the shroud. The reinforcing bridges connect the two parts of the shroud separated by the slot and serve to carry structural roads.
It is also suggested that separate holes in a circumferential row could replace the annular slot as long as the desired bleed flow area is maintained. The outer tip of the impeller bleed will be effected by the local pressure variation when the outer tip of each blade sweeps from an area having open bleed passages to an area without bleed passages or blocked by the bridges, which is an undesirable dynamic component to the compressor operation.
To increase the engine r.p.m. over which compressors can operate in a stable manner, U.S. Pat. No. 4,743,161 entitled COMPRESSORS which issued to Fisher et al. on May 10, 1998, discloses a compressor having an air bleed passage in communication with the normal intake so that the air is thus not bled to the exterior of the impeller housing, and thus atmosphere, nor drawn in from the exterior atmosphere separately from the normal gas intake to the compressor, as in U.S. Pat. No. 4,248,566, but is bled back to the normal intake or is drawn from the normal intake. In one embodiment illustrated in
FIG. 5
of U.S. Pat. No. 4,743,161, a circumferentially continuous annular slot is provided for communication with the chamber in which the impeller wheel rotates and an annular chamber. The annular chamber also communicates with the intake through a series of holes. However, the gas pressure is released in the intake rather than the annular chamber. The gas bleed passage includes not only the annular slot but also the annular chamber and the series of holes. The bleed gas flow is not circumferentially even because of the holes and the circumferential pressure variation causes the dynamic component and affects the outer tips of the impeller, particularly, in the case where the holes are close to the outer tip of the blade, which is illustrated in the Figure.
Bleed valves are also used for gas turbine engines to provide adjustable bleed passages. U.S. Pat. No. 5,380,151 which issued to Kostka et al. on Jan. 10, 1995 and entitled AXIALLY OPENING CYLINDRICAL BLEED VALVE, is an example. In this patent, Kostka discloses a bleed valve for a gas turbine engine having a housing made of two segments and which forms a gas flow path through the compressor. A first segment is moveable from the second segment thereby creating an opening therebetween. The moveable segment has one or more arms with rollers attached thereto where the stationary segment defines recessed paths in which the rollers travel. The moveable segment is caused to move away from the stationary segment thereby opening the valve. Because the arms extend across the annular opening between the two segments to moveably connect the two segments, the bleed passage provided by the valve is faced with the same problem as discussed in the above prior art, that is, a dynamic component is created to affect the blades when the air passes through the bleed passage. Further, the arms, rollers and the travel path fixed to the bleed valve segments add weight and machining operations to the construction of the valve which translates into additional manufacturing costs.
Therefore, there exists a need for a structure for an impeller bleed passage of a compressor for a gas turbine engine which eliminates the dynamic component that affects the blades of the impeller when air passes through the bleed passage. It is also desirable to provide a structure for an adjustable bleed passage that is relatively simple and inexpensive to manufacture.
SUMMARY OF THE INVENTION
An object of the invention is to provide a structure for an impeller bleed passage of a compressor for a gas turbine engine, to minimise dynamic components which affect the impeller blades when air passes through the bleed passage.
Another object of the invention is to provide a structure for an impeller bleed passage of a compressor for a gas turbine engine, having a minimum width of the bleed passage to decrease operational inefficiency of the compressor caused by the air bleed.
Another object of the invention is to provide a structure for an impeller bleed passage of a compressor for a gas turbine engine, having a width of the bleed passage that is adjustable for different engines depending on the requirements of use of a particular engine.
Yet another object of the invention is to provide a structure for an impeller bleed passage of a compressor for a gas turbine engine, having a width of the bleed passage that is self-regulating in response to changes in the air pressure within the impeller chamber.
A further object of the invention is to provide a structure for impeller bleed passage of a compressor for a gas turbine engine that is relatively simple and inexpensive to manufacture.
In accordance with one aspect of the invention a compressor for a gas turbine engine is provided, which includes an annular shroud having an inlet end, an outlet end and an inner surface; a compressor rotor located within the shroud including a plurality of blades directed radially and outwardly from the rotor. The annular shroud comprising:
an upstream annular segment and a downstream annular segment independently supported and axially spaced apart to form a circumferentially continuous uninterrupted annular slot therebetween, such that the annular slot extends through the shroud.
Preferably, at least one of the segments being elastically deformable so that a width of the slot changes in response to changes in air pressure within the shroud during operation of the compressor. Preferably, the downstream annular segment is elastically deformable.
The slot width is preferably adjustable for different engines depending on requirements of use of a particular engine.
In accordance with another aspect of the invention, a compressor for a gas turbine engine is provided, which includes a stationary annular shroud having an inlet end and an outlet end and an inner surface; a rotor located within the shroud including a plurality of blades directed radially and outwardly from the rotor, each blade having an outer tip that is of similar contour to and located in a close spaced relationship to the inner surface of the shroud; the annular shroud comprising:
an upstream annular segment and a downstream annular segment axially spaced apart to form a circumferentially c

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