Swept gradient boundary layer diverter

A swept gradient air boundary layer diverter for an aircraft. The aircraft includes a fuselage and an air inlet for an engine of the aircraft, where the air inlet includes a cowl at a leading edge of the inlet. The diverter includes a V-shaped ramp portion formed in the fuselage in an area proximate to and in front of the cowl where the ramp portion extends downward away from an outer surface of the fuselage towards an inside of the aircraft. The diverter also includes a V-shaped trough portion formed into the fuselage and being positioned adjacent to and integral with the ramp portion between the ramp portion and the air inlet. Air flowing over the fuselage towards the cowl is expanded and compressed by the ramp portion and the trough portion so as to create pressure gradients that generate vortices to redirect boundary layer airflow around the air inlet.

BACKGROUND

Field

This invention relates generally to an air boundary layer diverter for an aircraft and, more particularly, to a swept gradient air boundary layer diverter for a supersonic aircraft that includes a V-shaped swept expansion and compression ramp and diverter trough positioned in front of an engine inlet of the aircraft.

Discussion

Some modern aircraft must have the capability to operate at supersonic speeds, i.e., above Mach 1, which requires the aircraft to be highly aerodynamic and relatively low weight. In order to operate at supersonic speeds, the engines of such aircraft require a relatively large air inlet, where a typical air inlet for a supersonic aircraft will include a specially shaped leading edge, sometimes referred to as a cowl, and/or compression ramps that reduce the speed of the airflow into the engine to be suitable for proper operation of the engine. The design of these types of air inlets is challenging for aerodynamic operation.

For an aircraft in free flight, a low velocity, low pressure boundary layer of air builds up on the fuselage of the aircraft. The air boundary layer is generated as a result of friction forces on the aircraft fuselage, where air immediately adjacent to the fuselage has a zero velocity and as the distance from the fuselage increases, the velocity of the air also increases as determined by the speed of the aircraft. As the distance from the fuselage increases, the pressure forces of the airflow overcome the friction effect of the fuselage, where at some distance from the aircraft, the airflow becomes a free stream. If this low speed air boundary layer is ingested into the engine air inlet, the engine can encounter operability issues, such as a surge or stall, due to distortion levels beyond the engine's limitations, or rotating machinery high cycle fatigue issues due to increased distortion levels. Ingested boundary layer airflow also reduces the engine thrust and efficiency, which results in a reduced speed of aircraft operation.

In order to overcome these issues caused by the air boundary layer, it is known in the art to design supersonic aircraft with an air boundary layer diverter that prevents the boundary layer air from entering the engine air inlet. A traditional air boundary layer diverter on a supersonic aircraft includes a slot formed between the aircraft fuselage and the air inlet through which the boundary layer air flows, instead of flowing into the inlet. The width of the slot is selectively designed so that the inside edge of the cowl is at a location where only the free air steam is occurring. Such air boundary layer diverters have been shown to be effective in preventing the boundary layer air from entering the air inlet, but they reduce aircraft performance as a result of having a larger aircraft cross-sectional area that increases aircraft drag. Further, the airflow of the boundary layer is directed around the cowl, which often causes this air to impact various structures that are required to incorporate the slot diverter, which also increases drag.

SUMMARY

The present disclosure describes a swept gradient air boundary layer diverter for an aircraft. The aircraft includes a fuselage and an air inlet for an engine of the aircraft, where the air inlet includes a cowl at a leading edge of the inlet. The diverter includes a V-shaped ramp portion formed in the fuselage in an area proximate to and in front of the cowl, where the ramp portion extends downward away from an outer surface of the fuselage towards an inside surface of the aircraft. The diverter also includes a V-shaped trough portion formed into the fuselage and being positioned adjacent to and integral with the ramp portion between the ramp portion and the air inlet. Air flowing over the fuselage towards the cowl is expanded and compressed by the ramp portion and the trough portion so as to create pressure gradients that generate vortices that redirect boundary layer airflow away from and around the air inlet. In alternate embodiments, the swept gradient diverter can redirect airflow around other aircraft or vehicle systems requiring boundary layer flow control for performance and efficiency purposes, such as visual devices and auxiliary air intakes.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following discussion of the embodiments of the invention directed to a swept gradient air boundary layer diverter for a supersonic aircraft is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. For example, the discussion herein of the swept gradient air boundary layer diverter includes reference to specific aircraft and reference to an engine air inlet. However, as will be appreciated by those skilled in the art, the swept gradient air boundary layer diverter of the invention will have application to many other types of subsonic, supersonic and hypersonic aircraft, and for other applications other than engine inlet applications.

FIG. 1is an isometric view of a Concorde supersonic aircraft10including a fuselage12and aircraft delta wings14. The aircraft10includes four engines two on each side of the fuselage12, and thus also includes a pair of engine air inlets18on each side of the fuselage12. Each air inlet18includes a forward facing cowl20having a particular configuration and shape for providing air compression to reduce the speed of the air as it enters the inlet18. Particularly, side walls of the cowl20are canted to create oblique flow shock waves to provide air compression and decelerate the airflow in a manner well understood by those skilled in the art. The air inlet18is positioned some distance from the wing14to create a slot22that acts as an air boundary layer diverter, where the air boundary layer traveling at the slower speeds proximate the wing14is directed through the slot22and not into the inlet18in a manner well understood by those skilled in the art.

Future supersonic aircraft will be required to operate at increased supersonic speeds, while still providing reduced aircraft drag, reduced weight, reduced complexity, etc. Such aircraft will likely require an improved air boundary layer diverter to provide the desired performance at speeds up to and greater than Mach 2.0. As will be discussed in detail below, the present invention proposes such an air boundary layer diverter that employs a swept gradient design to meet these requirements, and has been shown to be effective for high supersonic speeds up to and above Mach 2.0. However, it is noted that the swept gradient boundary layer diverter discussed herein will also have application for aircraft flying at sub-sonic speeds and hypersonic speeds, i.e., above Mach 4.

FIG. 2is an isometric view of a conceptual supersonic aircraft50that is one possible design that performs at higher supersonic speeds than Mach 1.6. The aircraft50includes a fuselage52and wings54. An air inlet56is provided on both sides of the fuselage52one for each engine66of the aircraft50, and includes a specially configured inlet cowl58, where the cowl58forms or integrates to the fuselage52at points62and64. As will be discussed in detail below, the aircraft50includes a swept gradient air boundary layer diverter60positioned in front of the cowl58, where the diverter60is a specially shaped indentation in the fuselage52of the aircraft50to provide boundary layer air diversion at very high aircraft speeds. Because the diverter60is slightly indented into the aircraft fuselage outer mold line (OML), it enables a lower profile primary inlet that reduces the inlet's contribution to the aircraft's total drag. The cowl58has a general semi-circular shape in this non-limiting design. However, it is noted that although the diverter60is described with reference to the aircraft50including the air inlet56, the diverter60of the invention is applicable to be used on other types of aircraft having other shaped air inlets and cowls including above wing air inlets.

FIG. 3is a front view,FIG. 4is an isometric view andFIG. 5is a plan view showing a section70of the fuselage52of the aircraft50illustrating the swept gradient air boundary layer diverter60. The section70includes a semi-circular compression surface76that slopes upwards at its sides and is provided directly in front of the cowl58. The swept gradient diverter60is a general V-shaped indentation formed in the fuselage52and positioned in front of and around the compression surface76, as shown. The diverter60includes an outer V-shaped swept expansion and compression ramp portion72and a V-shaped diverter trough portion74. A compression surface leading edge78couples to the compression surface76at an end of the trough portion74opposite to the ramp portion72. The ramp portion72is a narrow downwardly sloping surface extending from an outer surface of the fuselage52inward towards the inside of the aircraft50. The trough portion74is an indentation in the fuselage52that is even with the lowest level of the ramp portion72and the compression surface76. In this non-limiting design, side legs82and84of the ramp portion72are swept upward towards outer edges of the diverter60, where the legs82and84end outside, but even with the cowl58at edges90and92, respectively. Side portions86and88of the trough portion74are also flared upward towards outer edges of the diverter60to points94and96, respectively.

As discussed above, in this non-limiting design, the side legs82and84of the ramp portion72and the side portions86and88of the trough portion74flare upwards. This is because of the shape of the fuselage52of the aircraft50. However, the side legs82and84and the side portions86and88as discussed herein can be, for example, flat across their top surface for operation of the diverter.

When the boundary layer air flows along the fuselage52and encounters the swept gradient diverter60it will first turn and flow downward along the expansion and compression ramp portion72, which will cause the airflow to expand and speed up. Once the airflow reaches the bottom edge of the ramp portion72and flows onto the trough portion74it is compressed, which acts to slow the airflow down and create oblique shock waves. This creates an expansion and compression wave creating a pressure gradient that generates vortices to redirect the airflow away from the cowl58of the inlet56along the legs82and84of the ramp portion72and the side portions86and88of the trough portion74. Thus, the expansion and compression of the airflow created by the combination of the ramp portion72and the trough portion74operates to redirect the boundary layer air away from the inlet56by creating a pressure gradient in a diagonal direction relative to the original airflow that generates vortices to direct the boundary layer air away from the inlet56.

The flow of boundary layer air around the inlet56as described above caused by the swept gradient diverter60can be illustrated byFIGS. 6 and 7.FIG. 6shows a plan view of the section70that does not include the diverter60, where lines100represent the flow of air particles in front of and around the inlet56. Area102represents the inlet56, line104represents the cowl58and area106represents the compression surface76. As is apparent inFIG. 7, there is some diversion of the airflow shown by flow lines100away from the inlet56, but it is not significant.

FIG. 7is a plan view of the section70including the swept gradient diverter60, where area110represents the trough portion74and area112represents the ramp portion72. As is apparent, the diverter60causes the airflow particle lines100to be directed away from and around the inlet56as a result of the V-shape of the depression created by the ramp portion72and the trough portion74. The pressure gradients caused by the expansion and compression waves create air vortices represented by lines114. The swept gradient diverter60creates pressure gradients that are strong enough to manipulate the low energy boundary layer flow close to the fuselage52, but the higher energy flow at the very top of the boundary layer and in the free stream overcome these gradients and continue to move forward to be captured by the inlet56.

The discussion above describes using the swept gradient diverter60to redirect boundary layer air around an engine air inlet on an aircraft. However, the swept gradient diverter60of the invention will have other applications. For example, aircraft and other vehicles may include an auxiliary air intake that provides secondary air for other aircraft systems, such as compartment cooling, component cooling, etc. Such aircraft systems may benefit from preventing boundary layer air from entering the auxiliary air intake, such as the ability to eliminate the need for a pump. The aircraft50inFIG. 2shows an auxiliary air intake120positioned in the fuselage52as an example of the location where the auxiliary air intake could be. A swept gradient boundary air diverter122of the type discussed above is provided in front of the auxiliary air intake120to divert the boundary air layer around the intake120.

Aircraft and other vehicles may also include various visual devices, such as a landing camera mounted, extending from the aircraft skin. Turbulent air around these devices may affect their visual requirements and performance. By providing a swept gradient air boundary layer diverter as discussed herein, the airflow may be redirected around the device, thus improving its performance. To illustrate this, the aircraft50includes a turret130that extends from the fuselage52and houses a visual device132, such as a landing camera. A swept gradient boundary air diverter134of the type discussed above is provided in front of the turret130to divert the boundary air layer around the turret130.