Fluid handling – Systems – Multiple inlet with single outlet
Reexamination Certificate
2000-08-15
2001-10-30
Chambers, A. Michael (Department: 3753)
Fluid handling
Systems
Multiple inlet with single outlet
C137S896000, C060S247000, C060S248000, C060S249000, C060S226100, C060S262000
Reexamination Certificate
active
06308740
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to the field of ejectors for pumping a fluid flow, and more particularly to an ejector in which the efficiency of mixing the primary high-velocity fluid, or jet, and the secondary low-velocity fluid is improved by pulsating the primary fluid flow into the secondary low-velocity fluid.
BACKGROUND OF THE INVENTION
In an ejector, a primary high-velocity fluid, such as a steam, gas, or vapor jet, is used to entrain and pump a secondary low-velocity fluid while mixing with it. In an ejector, the mixing of the primary high-velocity fluid and the secondary fluid occurs in the mixing section of the diffuser by sheer forces between the high-velocity stream and the secondary low-velocity fluid. Ejectors have a low power conversion efficiency due to the dissipation of energy resulting from friction forces between the primary high-velocity fluid stream and the secondary low-velocity fluid.
Jet engines create thrust by directing a high-energy exhaust stream from an exhaust nozzle. Typically, a jet engine accepts air through an inlet and compresses the air in a compressor section. The compressed air is directed to a combustion chamber, mixed with fuel, and burned. Energy released from the burning fuel creates a high temperature in the combustion chamber. The high-pressure air passes through a turbine section and into an exhaust chamber. The high-pressure air is then forced from the exhaust chamber through a nozzle, where the air exits the engine. Typically, as the air passes through the throat of the nozzle, it expands and accelerates from subsonic to supersonic speeds, essentially translating the energy of the exhaust flow from a pressure into a velocity. The energy level of the air in the exhaust chamber generally relates to the velocity of the air as it exits the nozzle. The greater the velocities of a given mass flow of air exiting the engine, the greater the thrust created by the engine.
High performance aircraft commonly augment the energy level of the air in the exhaust chamber by using an after-burner. After-burners add fuel to the exhaust chamber and ignite the fuel in the exhaust chamber. This increases the temperature of the exhaust flow. Although the energy added by after-burn fuel can greatly increase the thrust of the engine, the reduced density of the hotter air requires a larger nozzle effective throat area. Failure to increase the nozzle effective area during after-burning with a typical jet engine can cause excessive backpressure in the compressor section and turbine section, causing the engine to stall. To alleviate these difficulties, jet engines with after-burners typically use variable geometry nozzles to throttle the exhaust flow from the exhaust chamber. When an after-burn is initiated, the circumference of the nozzle's throat is increased to increase the cross-sectional flow area through the throat. This increased cross-sectional maintains a reasonable pressure in the exhaust while accommodating higher temperatures. Modern after-burning jet engines with variable geometry nozzles can require as much as a two-fold increase in cross-sectional throat area to maintain constant engine flow and back-pressure in response to the extra thermal energy added by the after-burner.
Although variable geometry nozzles allow the use of an after-burner, they also have many inherent disadvantages, which penalize aircraft performance. For instance, a variable geometry nozzle can be a significant component of the weight of an engine. Such nozzles are typically made of large, heavy metal flaps, which mechanically alter nozzle geometry by diverting exhaust flow with a physical blockage and thus have to endure the high temperatures and pressures associated with exhaust gases. In an IRIS type nozzle, typically used on after-burner equipped engines, the actuators used to adjust the nozzle flaps to appropriate positions in the exhaust flow tend to be heavy, expensive and complex because of the forces presented by the exhaust flow which the nozzle must overcome.
Further, the nozzle flaps typically constrict the exhaust flow by closing and overlapping each other, which allows hot air to escape between the flaps. These leaks cause reduction in thrust. Additionally, variable geometry nozzles are also difficult to implement on exotic nozzle aperture shapes typical of an advanced tactical fighter aircraft.
One method of overcoming this weight restriction is the use of a fixed geometry nozzle in a jet engine to inject a secondary flow of high-pressure air across the primary flow as the primary flow passes through this nozzle. The secondary flow can partially block the exhaust exiting the nozzle to increase the pressure within the exhaust chamber. When an over-pressure exists in the exhaust chamber, the secondary flow can be reduced to increase nozzle throat area and reduce the nozzle pressure.
Although the injection of a secondary flow will support a fixed geometry nozzle in an after-burning jet engine, this method also introduces inefficiencies to the operation of the engine. Primarily, the injection of air across the flow of the exhaust tends to use a large amount of high-pressure air to obtain an effective nozzle blockage. Thus, injection can introduce inefficiencies as the total momentum of the exhaust flow is decreased by the decreased flow from the compressor section into the combustion section if compressed air is bled from the compressor section for injection. This inefficiency can result in a reduced range of operations for a given fuel supply and fuel flow.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to decrease the inefficiency associated with the injection of high-pressure compressor air into the primary exhaust flow of a jet engine. This reduced inefficiency can result in a greater range of operations for a given fuel supply and fuel flow by decreasing the secondary flow from the compressor section into the combustion section for injection into the primary flow.
The present invention reveals a method and apparatus for more efficiently injecting a primary fluid flow. In one embodiment, the primary fluid flow is a pulsed or unsteady fluid flow contained within an inner nozzle situated within a secondary flow field. This secondary fluid flow is bounded within the walls of the ejector shroud. The secondary and primary fluid flows meet within a mixer section of the ejector wherein the secondary fluid flow is entrained by the primary fluid flow. The mixer section's geometry is such as to allow the combined injected and entrained fluid flow to mix before exiting the ejector. The mixing section's geometry is determined so as to allow a pressure wave that reflects from the open end of the secondary and moves up stream to treach the primary exit at the beginning of a primary pulse. The acoustic properties, frequency and amplitude, of the pulsed primary fluid flow determine the mixing sections' geometric properties for peak efficiency. Furthermore, the frequency and amplitude of the primary fluid flow may be varied in order to vary the efficiency of the injector.
In accordance with the present invention, a high-velocity unsteady or pulsed flow is injected into the low-velocity fluid contained within an ejector. A further object of this invention is to efficiently accelerate a low-velocity fluid such as low-pressure or ambient air using high-pressure compressor air to obtain fluidic blockage for control of a nozzle throat area. The entrained mass flow increases the total mass flow of the ejector, which is then injected into the nozzle. The pulsed ejector increases the effective blockage created by the injector as compared to injecting the ejector primary directly into the nozzle. Pulsed ejectors are more efficient than steady ejectors for both pumping and compression of a low-velocity flow using a high-pressure flow. Conventional ejectors use an available high-pressure source to pump a lower pressure fluid. For example, a small jet of high-pressure fluid is situated inside a larger shro
Bender Erich E.
Ginn Kerry B.
Miller Daniel N.
Smith Brian R.
Yagle Patrick J.
Chambers A. Michael
Hughes & Luce, L.L.P.
Hulsey III William N.
Lockheed Martin Corporation
McShane Thomas L.
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