Method and apparatus for modulating flow separation

[00002] The present invention relates generally to the field of modulating flow separation and more specifically to the use of a pulse detonation actuator (PDA) for injecting fluid into a boundary layer of an aerodynamic surface.

[00003] In a wide variety of applications, aerodynamic surfaces are used to manipulate the speed and pressure of moving fluids. Examples of aerodynamic surfaces include, but are not limited to, airfoils and channel surfaces. Examples of airfoils include, without limitation: aircraft wings; rotor blades for propellers, fans, compressors, turbines, helicopters, and other rotorcraft; and stator vanes for compressors and turbines. Examples of channel surfaces include, without limitation, diffusers for gas turbine engines.

[00004] Many aerodynamic surfaces are designed to create an adverse pressure gradient, i.e., a region wherein pressure increases along the direction of flow. Such an adverse pressure gradient may cause the fluid boundary layer to separate from the aerodynamic surface thereby reducing the efficacy of the design.

[00005] One strategy for reducing the tendency toward boundary layer separation is to inject fluid into the boundary layer through jets in the aerodynamic surface. Typically, the effectiveness of this strategy increases as the velocity of the injected fluid approaches the velocity of the bulk fluid flow. Conversely, applicability of the strategy is conventionally limited by the pressure rise and velocity increase for fluid injection producible by conventional means.

[00006] A pulse detonation actuator (PDA) provides a means for creating a pressure rise and velocity increase greater, in some applications, than the pressure rise and velocity increase available for boundary layer fluid injection by conventional means. Opportunities exist, therefore, to broaden the applicability of boundary layer fluid injection through the use of PDAs.

[00007] The opportunities described above are addressed in one embodiment of the present invention by an apparatus comprising: an aerodynamic surface adapted for producing an adverse pressure gradient in a fluid flow; and a first pulse detonation actuator disposed adjacent the aerodynamic surface and adapted for impulsively detonating a fuel/air mixture to produce a pressure rise and velocity increase of combustion products therein, the aerodynamic surface having a plurality of separation control holes adapted for communicating combustion product flows from the first pulse detonation actuator to the aerodynamic surface for modulating separation of the fluid flow from the aerodynamic surface.

[00010] In accordance with one embodiment of the present invention, the FIGURE illustrates an orthographic projection of an apparatus 100 that includes an aerodynamic surface 110 and a first pulse detonation actuator 120. In operation, aerodynamic surface 110 produces an adverse pressure gradient in a fluid flow. First pulse detonation actuator 120 extends along aerodynamic surface 110 and impulsively detonates a fuel/air mixture to produce a pressure rise and velocity increase of combustion products therein. For modulating separation of the fluid flow, aerodynamic surface 110 has a number of separation control holes 130 for communicating combustion product flows from first pulse detonation actuator 120 to aerodynamic surface 110.

[00011] As used herein, a “pulse detonation actuator” is understood to mean any device or system which produces both a pressure rise and velocity increase from a series of repeating detonations or quasi-detonations within the device. A “quasi-detonation” is a combustion process which produces a pressure rise and velocity increase higher than the pressure rise and velocity increase produced by a deflagration wave. Typical embodiments of PDAs comprise a means of igniting a fuel/air mixture, and a detonation chamber in which pressure wave fronts initiated by the ignition process coalesce to produce a detonation wave. The geometry of the detonation chamber is such that the pressure rise of the detonation wave expels combustion products out the PDA exhaust. As used herein, “impulsively detonating” refers to a process of repeating detonations or quasi-detonations wherein each detonation or quasi-detonation is initiated either by external ignition (for example, without limitation, spark discharge or laser pulse) or by gas dynamic processes (for example, without limitation, shock initiation or autoignition).

[00012] In a more detailed embodiment in accordance with the embodiment of the FIGURE, separation control holes 130 are shaped to promote attachment of the boundary layer to airfoil surface 140 so that separation is a decreasing function of the combustion product flows. Decreasing the tendency toward separation is useful in increasing the lift of airfoil surfaces and in decreasing the wake produced by some surfaces.

[00013] In an alternative embodiment, lift control holes 130 are shaped to promote separation of the boundary layer from airfoil surface 140 so that separation is an increasing function of the combustion product flows. Increasing the tendency toward separation is useful in some nozzle applications wherein a smaller effective nozzle area is realized by increasing the combustion product flows.

[00014] In another more detailed embodiment in accordance with the embodiment of the FIGURE, apparatus 100 further comprises a second PDA 125 disposed adjacent aerodynamic surface 110 with a portion of separation control holes 130 communicating combustion product flows from second PDA 125 to aerodynamic surface 110 for modulating the separation. In some embodiments, combustion product flows from second PDA 125 serve to decrease the separation; in alternative embodiments, combustion product flows from second PDA 125 serve to increase the separation. For some applications, having both separation decreasing and separation increasing PDAs extends the range of operation of apparatus 100.

[00015] In another more detailed embodiment in accordance with the embodiment of the FIGURE, second PDA 125 operates out of phase with first PDA 120. Out of phase operation raises the frequency with which combustion product pulses are delivered to the boundary layer and, in some applications, produces a temporally more uniform boundary layer compared to operation with a single PDA.

[00016] In another more detailed embodiment in accordance with the embodiment of the FIGURE, apparatus 100 further includes a diffuser 140 for generating an adverse pressure gradient in a fluid flow. First pulse detonation actuator 120 extends along diffuser 140 and impulsively detonates a fuel/air mixture to produce a pressure rise and velocity increase of combustion products therein. For modulating separation of the fluid flow from aerodynamic surface 110, diffuser 140 has a number of separation control holes 130 for communicating combustion product flows from first PDA 120 to aerodynamic surface 110 of diffuser 140. Typical applications of diffuser 140 include, without limitation, gas turbine engines.

[00017] While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.