Rotary kinetic fluid motors or pumps – Working fluid bypass
Reexamination Certificate
2000-03-24
2001-12-04
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid bypass
Reexamination Certificate
active
06325595
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to gas turbine engine compressor bleed and, more particularly, to bleed ports in the compressor for extracting two or more portions of compressor air from a single stage of the compressor.
2. Discussion of the Background Art
Gas turbine engines, such as a bypass turbofan engine, bleed or extract air between stages of a multi-stage axial compressor for various purposes. The extracted air is often referred to as secondary air. Secondary air is usually required for turbine cooling, hot cavity purging or turbine clearance control and is often referred to as domestic bleed because it is used for the engine. Secondary air is also often required to pressurize the aircraft cabin and for other aircraft purposes and, is thus, referred to as customer bleed. Domestic bleed flow levels are generally a constant percentage of compressor flow (i.e. 2%), whereas customer bleed requirements typically vary (i.e. 0-10%).
It is frequently desirable to have both customer and domestic bleed extracted from the same stage of the compressor, where the air has the desired pressure and temperature properties. This is, typically, desirable in a gas turbine engine having a low number of stages in the high pressure ratio compressor. The problem that this poses is to design a bleed system that allows the customer bleed to be modulated with minimal impact on the bleed pressure supplied to domestic bleed. If the domestic bleed pressure is allowed to drop below a threshold level, then, insufficient cooling air may be supplied to the hot section of the engine, resulting in decreased life on hot parts.
Conventional engines are designed with the customer and the domestic bleed ports isolated at different stages of the compressor and, thus, the domestic bleed pressure is relatively insensitive to the customer bleed rate. A high recovery bleed slot to supply both the customer and domestic bleeds has been used in engines with a low number of high pressure compressor stages. The problem with two bleed circuits using the same slot and plenum is that the slot recovery and, hence, the plenum pressure is very sensitive to the level of customer bleed.
At high levels of customer bleed, the bleed slot throat and exit Mach numbers become high and large dump losses are realized at the slot exit into the plenum. This significantly reduces the pressure available to the domestic bleed circuit. It is, thus, highly desirable to have a means for bleeding air from a compressor for two or more different air circuits, such as the customer and domestic bleeds, and being able to modulate one of the circuits with minimal impact on the bleed pressure supplied to the bleed for the other circuit or circuits.
SUMMARY OF THE INVENTION
A compressor air bleed assembly for a gas turbine engine includes a compressor casing surrounding a row of circumferentially spaced compressor blades extending from a rotatable shaft and defining a flowpath for receiving compressor airflow compressed by the blades. The casing includes a bleed port disposed downstream of at least a row of the blades for receiving a portion of the compressed air as bleed airflow. A bleed duct, preferably in the form of an annular slot, extends away from the bleed port and duct has a first throat downstream of the port and a second throat downstream of the first throat. A first duct outlet in the duct leads to a first bleed air circuit, receives a first portion of the bleed airflow, and is disposed between the first and second throats. A second duct outlet in the duct leads to a second bleed air circuit, receives a second portion of the bleed airflow, and is disposed downstream of the second throat.
In a preferred embodiment, the second throat is smaller than the first throat and the first throat has a first throat area sized such that at a maximum compressor bleed flow to the first and the second bleed circuits a first Mach number M
1
at the first throat is approximately equal to an average axial Mach number MA at a vane trails edge TE of an airfoil directly upstream of the port. A second throat area of the second throat is sized such that during operation with a maximum amount of the customer bleed flow portion being extracted the diffusion in the domestic bleed flow is not excessive i.e there is no separation along an aft surface of the annular slot.
In one particular embodiment, the first bleed air circuit is a customer bleed air circuit and the second bleed air circuit is a domestic bleed air circuit of the gas turbine engine and a valve is disposed in the customer bleed air circuit downstream of the first throat. The first inlet leads to a first plenum in the first circuit and the second inlet leads to a second plenum in the second circuit. In a yet more particular embodiment, a diffuser is located between the second throat and the second duct outlet. The valve is preferably disposed in piping in the customer bleed air circuit downstream of the first plenum.
REFERENCES:
patent: 3945759 (1976-03-01), Bobo
patent: 4156344 (1979-05-01), Cuthbertson et al.
patent: 4248566 (1981-02-01), Chapman et al.
patent: 5155993 (1992-10-01), Baughman et al.
patent: 5209633 (1993-05-01), McGreehan et al.
patent: 5351478 (1994-10-01), Walker et al.
patent: 5680754 (1997-10-01), Giffin et al.
patent: 6109868 (2000-08-01), Bulman et al.
Breeze-Stringfellow Andrew
Szucs Peter N.
Wood Peter J.
General Electric Company
Herkamp Nathan D.
Hess Andrew C.
Look Edward K.
McAleenan James M
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