Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Vane or deflector
Reexamination Certificate
2001-04-04
2003-04-01
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Vane or deflector
C415S211200
Reexamination Certificate
active
06540481
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a diffuser system for centrifugal compressors in which the air that is discharged from the rotating impeller is turned both radially and axially with fewer losses. More particularly, the present invention relates to a diffuser having improved diffuser recovery by minimizing boundary layer build-up that would otherwise partially block the diffuser flow passageway, and also one having reduced total pressure loss.
Centrifugal compressors are often utilized in gas turbine engines to raise the pressure of the incoming air before it enters a combustion chamber, within which the air is mixed with fuel and the fuel-air mixture is ignited to provide output power in the form of jet thrust or shaft horsepower. Such compressors generally include a rotatable, disk-like impeller that has on its upstream face a plurality of substantially radially-extending impeller blades. The impeller is contained within a casing that defines an inlet opening at the hub of the impeller and an outlet opening adjacent the impeller periphery. Between the impeller periphery and the compressor outlet opening there is provided a diffuser for receiving the air that is centrifugally discharged from the rotating impeller at a high velocity, to convert the kinetic energy of the air leaving the impeller into increased static pressure, and simultaneously to turn the airflow from a substantially tangential direction, relative to the impeller, to one that has a major velocity component in the axial direction of the compressor.
It has been found that much of the efficiency losses of centrifugal compressors occur in the diffuser system. Those losses arise as a consequence of the need to reduce the velocity of the air that leaves the rotating impeller, and the need to remove from the flow stream the high degree of swirl by turning the flow stream into a generally axial direction. Simultaneously, the flow is turned from a radially outward direction, at which it leaves the impeller periphery, to a generally inward direction toward the compressor longitudinal axis, so the high pressure air can be introduced at a relatively low velocity into the combustor that is axially downstream of the compressor.
With respect to the velocity reduction, the Mach number of the flow at the impeller exit is generally in the transonic range, from about 0.9 to about 1.2, and that Mach number must be reduced at the combustor inlet to a value typically of about 0.1. Along with the velocity reduction, the swirl from the impeller periphery, which can be an angle of the order of from about 65° to about 76°, is reduced so that it is not greater than about 5° at the combustor inlet. Additionally, the airflow must be turned from a generally radially outward flow direction to a substantially axially and radially inward flow direction, which oftentimes involves turning the airflow through an angle of from about 90° to about 140°.
Those velocity and directional changes are generally accomplished by providing a diffuser in which the air flows through a diverging passageway to reduce the velocity, an axisymmetric bend to turn the flow from radially outward to substantially axial, and also a deswirler cascade of turning vanes to turn the flow into an axial direction. In the course of slowing and redirecting the airflow, the diffuser and deswirler systems contribute losses that are largely inherent in such arrangements, and also additional losses that occur as a result of build-up of a boundary layer within the diffuser, which operates to constrict the flow through the diffuser and thereby reduce its efficiency.
The present invention serves to improve the efficiency of centrifugal compressor diffusers by reducing aerodynamic blockage to improve diffuser recovery, and by reducing the total pressure loss by providing a diffuser expansion area ratio that is substantially an optimum value.
SUMMARY OF THE INVENTION
Briefly stated, in accordance with one aspect of the present invention, a diffuser is provided for a centrifugal compressor that includes an impeller rotatably carried within a casing. The diffuser includes a plurality of diffuser passageways that have their respective longitudinal axes disposed tangentially to an imaginary circle that has its center coincident with the impeller axis. The diffuser passageways include a diffuser inlet region that commences adjacent the impeller periphery, a diffuser throat region that is downstream of the diffuser inlet region, and a diffuser outlet region that is downstream of the diffuser throat region. The diffuser passageways are each bounded by a pair of circumferentially spaced diffuser panels having respective leading edges adjacent the impeller periphery and that lie on a diffuser leading edge circle. The diffuser panels also have trailing edges that are spaced radially outwardly of and circumferentially offset from the leading edges and that lie on a diffuser trailing edge circle. At least one ridge is provided that extends substantially longitudinally relative to and within the diffuser inlet region between the impeller periphery and the diffuser leading edge circle. The at least one ridge also extends inwardly into the diffuser passageway and is positioned between and is spaced from the leading edges of adjacent diffuser panels. The ridges serve to mix air that leaves the impeller and that enters the diffuser passageway to reduce boundary layer build-up upstream of the diffuser throat region.
In accordance with another aspect of the present invention, the diffuser outlet regions include splitter vanes that divide the flow adjacent the exit to the diffuser outlet region. Providing such splitter vanes permits a larger overall expansion ratio in the region in which the splitter vanes are provided. Moreover, the splitter vanes serve as deswirler vanes to reduce the tangential flow component of the air that exits from the diffuser.
In accordance with further aspect of the present invention, deswirler splitter vanes can be provided in the deswirler section of the compressor outlet to aid in efficiently turning the flow into an axial direction.
REFERENCES:
patent: 3184152 (1965-05-01), Bourquard
patent: 3333762 (1967-08-01), Vrana
patent: 3644055 (1972-02-01), Davis
patent: 3765792 (1973-10-01), Exley
patent: 4012166 (1977-03-01), Kaesser et al.
patent: 4027997 (1977-06-01), Bryans
patent: 4354802 (1982-10-01), Nishida et al.
patent: 4395197 (1983-07-01), Yoshinaga et al.
patent: 4431374 (1984-02-01), Benstein et al.
patent: 4576550 (1986-03-01), Bryans
patent: 4696622 (1987-09-01), Traczyk et al.
patent: 4877370 (1989-10-01), Nakagawa et al.
patent: 5310309 (1994-05-01), Terasaki et al.
patent: 5387081 (1995-02-01), LeBlanc
patent: 5709531 (1998-01-01), Nishida et al.
Laidlaw Gilbert John
Moussa Zaher Milad
Tapparo David John
Edgar Richard A.
General Electric Company
Herkemp Nathan D.
Look Edward K.
Mangels Alfred J.
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