Centrifugal air flow control

Details Centrifugal air flow control Centrifugal air flow control

1999-02-25

2001-03-20

Look, Edward K. (Department: 3745)

Rotary kinetic fluid motors or pumps

With passage in blade, vane, shaft or rotary distributor...

C415S119000, C415S914000, C416S091000, C244S207000

Reexamination Certificate

active

06203269

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
Commonly owned copending U.S. patent applications filed contemporaneously herewith, Ser. Nos. 09/257,565, 09/257,563, and 09/257,564), contain subject matter related to that disclosed and claimed herein.
TECHNICAL FIELD
This invention relates to centrifugal pumping of ambient air to drive nozzles directed into the boundary layer on a blade, such as a fan blade or a helicopter rotor blade.
BACKGROUND ART
Gas flow in the shear layer adjacent to a surface exhibits a reduction in velocity due to friction of the molecular viscosity interacting with the surface, which results in a strong velocity gradient as a function of perpendicular distance from the surface: essentially zero at the surface, raising to mainstream velocity at the outer edge of the boundary layer. The reduced velocity results in a lower momentum flux, which is the product of the density of the gas times the square of its velocity. Along a diverging surface (that is, a surface that tails away from the mean flow direction), as is the case on the suction side of an airfoil (such as a fan blade or helicopter blade), the flow along the surface is accompanied by a pressure rise, which is accomplished only by conversion of momentum flux. The momentum and energy of the gas along the surface is consumed in overcoming the pressure rise and friction so that the gas particles are finally brought to rest and the flow begins to break away from the wall, resulting in boundary layer separation, downstream of the separation point. Boundary layer separation typically results in the termination of pressure rise (recovery) and hence loss in performance (e.g., airfoil lift) and dramatic decrease in system efficiency, due to conversion of flow energy into turbulence, and eventually into heat. It is known that boundary layer separation can be deterred or eliminated by increasing the momentum flux of the gas particles flowing near the surface. In the art, the deterrence or elimination of boundary layer separation is typically referred to as “delaying the onset of boundary layer separation”.
One method for overcoming boundary layer separation is simply blowing high energy gas tangentially in the downstream direction through a slot to directly energize the flow adjacent to the surface. This technique, however, requires a source of pressure and internal piping from the source to the orifices at the surface. This greatly increases the cost, weight and complexity of any such system, and have not as yet been found to be sufficiently effective to warrant any practical use.
In the helicopter art, it is known that retreating blade stall establishes limits on rotor load and flight speed. In addition to the loss of capability to generate lift, unsteady blade stall transmits very large impulsive blade pitching moments to the flight control system.
In order to prevent excess control loads, stall boundaries are set as a function of rotor load and flight speed. Stall boundaries define the maximum blade loads, which impact maneuverability and agility as well as speed and payload. Improved payload capability can arise from gains in aerodynamic efficiency in hover via reduction of tip stall and in forward flight via reduction in retreating blade stall. In axial flow, gas turbine engines, such as those used in military aircraft and in commercial transport aircraft, a totally different problem is fan blade wake blockage at the entrance to the core region (low compressor) of the engine. This occurs near the root of the blade.
Yet another problem in any fan is blade tip leakage. To date, no scheme has been found to solve these problems which does not ultimately degrade overall engine performance, due to energy consumed by the compensating apparatus, or parasitic impact on the overall system.
DISCLOSURE OF INVENTION
Objects of the invention include improved boundary layer flow, improved deterrence of boundary separation, increased efficiency of airflow machinery, increased efficiency and lift in helicopter rotor blades, increased efficiency and lift in vertical takeoff and landing aircraft propellers, increased efficiency in gas turbine aircraft engines, reduced fan blade wake blockage in jet engine core inlets, reduced blade tip leakage effects in fans, boundary layer control which is effective, efficient, having low initial cost and zero operating costs, and boundary layer control which is relatively simple and provides low parasitic impact on the host structures and systems.
According to the present invention, a flow of air directed into the gaseous flow (such as air) adjacent to a rotating airfoil or blade is passively powered by centrifugal force, ambient air entering the blade near the hub being forced outwardly to and through one or more slots in the blade's surface, closer to the tip, thereby to control the flow adjacent to the blade. In further accord with the invention, the blade may be a helicopter rotor blade, or a fan blade. In still further accord with the invention, the blade may be in the first stage of a gas turbine engine, or in an air moving machinery fan.
In one application of the invention, the airflow is directed at a low angle of incidence (essentially tangentially) in the vicinity of the boundary layer separation point of a fan blade or an airfoil, thereby to deter or prevent boundary layer separation. The invention provides gas particles into the downstream boundary layer which have higher momentum flux than gas particles of the upstream boundary layer, thereby to deter the onset of boundary layer separation; the gas particles may preferentially be injected essentially tangentially to the boundary layer.
In another application of the invention, the airflow is directed into the flow adjacent the surface of jet engine fan blades, the tips of which are rotating at supersonic speeds, at a point near or aft of mid-chord, where supersonic shock and boundary layer separation occur. This reduces the Mach number gradient to thereby increase efficiency.
According further to the present invention, air passing through the fan of an axial fan gas turbine engine, near the root of the fan, is suctioned off by a slot in the suction side of the blade near the root, to reduce fan blade wake blockage and thereby increase the efficiency of flow into the core engine (low compressor). In accordance with the invention, the suctioned air is pumped centrifugally through the hollow blades and discharged closer to the tip of the blades; in one embodiment, the air is discharged on the suction side, near or aft of mid chord of the blade, thereby to reduce shock and delay the onset of boundary layer separation; in another embodiment, the suctioned air is discharged on the pressure side of the tips of the blade, thereby to reduce blade leakage effects.
Other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing.


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Smith, D., Amitay, M., Kibens, V., Parekh,

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