# Patent

## Title
Method for designing flowfield molded hypersonic inlet for integrated turbojet and ram-scramjet applications

## Abstract

A diverterless hypersonic inlet (DHI) for a high speed, air-breathing propulsion system reduces the ingested boundary layer flow, drag, and weight, and maintains a high capture area for hypersonic applications. The design enables high vehicle fineness ratios, low-observable features, and enhances ramjet operability limits. The DHI is optimized for a particular design flight Mach number. A forebody segment generates and focuses a system of multiple upstream shock waves at desired strengths and angles to facilitate required inlet and engine airflow conditions. The forebody contour diverts boundary layer flow to the inlet sides, effectively reducing the thickness of the boundary layer that is ingested by the inlet, while maintaining the capture area required by the hypersonic propulsion system. The cowl assembly is shaped to integrate with the forebody shock system and the thinned boundary layer region.

## Background
This patent application is subject to U.S. Air Force contract No. F33615-00-D-3053. The Government has certain rights in this invention.


BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates in general to air craft engines and, in particular, to an improved system, method, and apparatus for a diverterless hypersonic inlet for integrated turbojet and ram-scramjet aircraft jet engine applications.
2. Description of the Related Art
Boundary layer diverters using splitter plate and wedge geometries are traditionally employed to reduce or eliminate boundary layer thickness upstream from the inlets of airbreathing propulsion systems at Mach 1 to Mach 2+. The high drag and weight of such devices has been overcome in the past with more thrust (which required bigger engines), more engines, or the additional use of afterburners. These designs result in yet more weight, less vehicle payload capacity, higher fuel consumption, and/or other aircraft design penalties. Higher Mach number, multi-engine aircraft (Mach 2 to 3+) have employed efficient, axisymmetric spike inlets or underwing-mounted nacelles. However, these designs require large amounts of internal boundary layer bleed, add significant drag, and are structurally inefficient.
The development of the ramjet or scramjet powered hypersonic aircraft has been historically thwarted by inefficient inlet and forebody designs. An inefficient hypersonic forebody and inlet design can have poor transonic performance characteristics, which compromises the ability of an on-board gas turbine propulsion system to accelerate to ramjet transition speed without running out of fuel. An inefficient design can also allow ramjet ingestion of a thick boundary layer which delays ramjet startup until the vehicle achieves at least Mach 3.5. Gas turbine propulsion systems are historically inefficient beyond Mach 2.5, so afterburning, base burning, rocket assistance, releasing the vehicle from an aircraft at altitude, and combinations thereof are generally considered to fill the gap between Mach 2.5 and 3.5, and thereby achieve required ramjet start-up conditions. As such, the problems associated with hypersonic inlets (boundary layer flow, high transonic drag, etc.) have not been resolved to facilitate the practical use of efficient, self-powered, hypersonic airbreathing vehicles. An improved solution that addresses these limitations would be desirable.
SUMMARY OF THE INVENTION
One embodiment of a system, method, and apparatus for diverterless hypersonic inlets (DHI) offers solutions that incorporate favorable air flow characteristics for high speed (e.g., Mach 3+) air-breathing propulsion systems. The DHI shape thins the boundary layer for engines that traditionally operate above Mach 3, thereby allowing them to work at lower Mach numbers. The long and narrow shape of DHI designs also improves transonic drag, which is a common issue with traditionally-shaped (i.e., wide and flat) hypersonic vehicles. The DHI reduces the penalties associated with traditional boundary layer diversion techniques and enables vehicle operability well into the hypersonic flight regime.
The present invention is well suited for ramjet and/or scramjet engines. The DHI reduces the ingested boundary layer flow, reduces drag and weight associated with traditional boundary layer diverter configurations, maintains a high capture area for hypersonic applications, enables high vehicle fineness ratios (which lowers transonic drag), provides a practical basis for low-observable features, and enhances ramjet operability limits.
In one embodiment, the DHI comprises a cowl assembly mounted to a segmented, contoured forebody. The DHI is designed to fit vehicle size constraints and is optimized for specific flight Mach numbers. The forebody includes segments that generate and focus a system of multiple upstream shock waves at desired strengths and angles to facilitate required inlet and engine airflow conditions. The forebody contour diverts boundary layer flow to either side of the inlet, effectively reducing the thickness of the boundary layer that is ingested by the inlet, while maintaining the capture area required by a hypersonic propulsion system. The cowl assembly is shaped to integrate with the forebody shock system and the thinned boundary layer region. The outer mold line of the DHI enables the vehicle to maintain a high fineness ratio which is beneficial for transonic acceleration.
The DHI has been computationally proven for at least Mach 3 to Mach 10 applications, which is well above the nominal operating envelope of traditional boundary layer diverting systems. The DHI is highly effective in boundary layer reduction above Mach 3, which is important for ramjet and scramjet applications. The present invention facilitates successful engine start-up and enhanced operability and performance at much lower Mach numbers than those demonstrated in the prior art. A lower Mach number start speed for a ramjet system closes the gap between the maximum speed of a gas turbine accelerator and the minimum speed at which a ramjet can take over. This design enables a dual mode, air breathing vehicle to propel itself to hypersonic speeds from a standing start on the ground. The DHI utilizes an elegant design method that converges on an optimized solution with few iterations, minimizing computer time, and requiring relatively few man hours. It provides a uniform flowfield at the cowl plane and can be modified to include low-observable features.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the features and advantages of the invention, as well as others which will become apparent are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only an embodiment of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.
FIG. 1 is a plot of engine performance versus speed for turbojet, ramjet, and scramjet engines;
FIG. 2 is an isometric view of one embodiment of an aircraft having a diverterless hypersonic inlet (DHI) constructed in accordance with the present invention;
FIG. 3 is a front isometric view rendering comparing a DHI design augmented with and without boundary layer control;
FIG. 4 is a side view rendering comparing boundary layer thickness for the DHI and a two-dimensional wedge-shaped inlet;
FIG. 5 is a side view rendering of the shock system for one embodiment of a DHI design constructed in accordance with the present invention;
FIG. 6 illustrates isometric view renderings of a flowfield generator (FFG) spanwise contour for one embodiment of a DHI design constructed in accordance with the present invention;
FIG. 7 illustrates isometric view renderings of the FFG of FIG. 6 with streamline seeds and planes for one embodiment of a DHI design constructed in accordance with the present invention; and
FIG. 8 is a high level flow diagram of one embodiment of a method constructed in accordance with the present invention.



DETAILED DESCRIPTION OF THE INVENTION
Referring to FIGS. 1-8, various embodiments of a system, method, and apparatus for a diverterless hypersonic inlet (DHI) constructed in accordance with the present invention are shown. As shown in FIG. 1, the performance 11 of aircraft with conventional turbojet engines deteriorates quickly as flight speed approaches Mach 3. Similarly, the performance 13 of conventionally configured ramjets and scramjets is also weak at flight speeds in the vicinity of Mach 3. However, a high speed aircraft configured with a DHI constructed in accordance with the present invention has a performance 15 with a significantly enhanced region of improvement 17 over conventional inlet designs. The turbojet, ramjet, and scramjet engine applications for the DHI of the present invention include flight speeds of approximately Mach 2.5 to 10.
FIG. 2 illustrates an aircraft 21 with one embodiment of a DHI design 23 for processing hypersonic airflow. The DHI 23 extends along the forebody and incorporates the cowl 27 to define an intake manifold for the aircraft's engine. The forebody has a longitudinal axis 31 extending along a length of the aircraft 21, a lateral axis 33 orthogonal to the longitudinal axis 31, and a transverse axis 35 orthogonal to both the longitudinal and lateral axes 31, 33. In one embodiment, the DHI 23 also configures the forebody with a high outwash angle 37 (e.g., at least 3.9°) with respect to the longitudinal axis 31 for spilling the boundary layer airflow.
As best shown in FIG. 5, the DHI 23 includes a plurality of ramp segments 41, 43, 45 (three shown) that are formed in a profile of the forebody extending along the longitudinal axis 31. Although the illustrated embodiment depicts three ramp segments 41, 43, 45, more or fewer segments may be utilized. Each of the ramp segments 41, 43, 45 are formed at angles with respect to the longitudinal and transverse axes 31, 35, such that the ramp segments 41, 43, 45 form a series of angles that sequentially increase in a downstream direction toward the cowl 27. As a result, the forebody of DHI 23 has significantly greater length 61 (lower half of FIG. 4) than the length 63 of a conventionally equipped inlet (upper half of FIG. 4). Even though the DHI is longer than conventionally equipped inlets, the boundary layer is proportionally thinner, as explained below.
The DHI 23 also comprises spanwise contours 47 that are formed on the forebody adjacent each lateral side of the cowl 27. The spanwise contours 47 extend along both the longitudinal and lateral axes 31, 33. As best shown in FIG. 6, the spanwise contours 47 are designed to effectively divert and thin the boundary layer airflow for turbojet, ramjet, and scramjet engine applications. In contrast, an aircraft 51 with a conventional inlet 53 (top of FIG. 4) develops excessive boundary layer conditions 55 that degrade the performance 13 (see FIG. 1) of high speed aircraft engines. In one embodiment, the spanwise contours 47 are super elliptical as defined by the equation: (x/a)n+(y/b)n=1, where n>2 and a and b are the ellipse radii.
In addition, the DHI 23 enables the aircraft 21 to have a fineness ratio in excess of six (6). For purposes of the present invention, fineness ratio is defined as the length of the aircraft divided by the equivalent circular diameter of the maximum frontal cross-sectional area of the aircraft.
Referring now to FIG. 8, the present invention also comprises a method of designing a hypersonic inlet for an aircraft. In one embodiment, the method begins as indicated at step 81, and comprises establishing a centerline geometry for a flowfield generator (FFG) (step 83); optimizing the FFG and a shock system 121 (FIG. 5) configuration to fit aircraft geometrical constraints and engine airflow requirements (step 85); establishing spanwise contours for the FFG (step 87); gridding and running computation fluid dynamics (CFD) for the FFG (step 89); and iterating steps (a) through (d) until the desired cowl plane Mach number, flowfield uniformity, and geometrical constraints are achieved (step 91).
In one embodiment, the method further comprises streamline tracing 123 (FIG. 7) a diverterless hypersonic inlet (DHI) forebody within a three-dimensional, FFG CFD solution and transferring the streamlines into a computer aided design (CAD) environment (step 93); surfacing streamlines of the DHI forebody in the CAD environment and consolidating them with a cowl assembly (step 95); gridding DHI geometry and running viscous CFD analysis (step 97); modifying the DHI geometry and confirming with follow-on viscous CFD runs (step 99); and then integrating the DHI geometry with geometry of the aircraft for aerodynamic analysis (step 101), before ending as indicated at step 103.
In step 83, the method also may comprise performing a series of inviscid conical and two-dimensional shock calculations to determine viable shock system configurations, including a plurality of shocks and shock angles, to achieve the desired cowl plane Mach number; and designing a segmented, cone-shaped FFG required to generate the desired shock system configuration. In step 85, the method may comprise factoring an intended streamline cut position of approximately 10% to 40% of the cowl height.
In step 87, the method may comprise contouring each spanwise contour individually, wherein each spanwise contour affects a spanwise shape of generated shocks, lateral boundary layer migration, and capture area of the cowl. In step 89, the method may comprise constructing streamline seed planes, superimposing construction planes to represent aircraft constraints and cowl geometry, assessing cowl plane flowfield uniformity and Mach number, assessing shock positions with respect to cowl geometry, and running streamlines forward from the cowl plane to assess a capture area thereof.
In addition, step 97 may comprise reassessing shock positions, cowl plane Mach number, and capture area, and assessing boundary layer thickness and surface pressure gradients; and step 99 may comprise evaluating off-design conditions and augmenting with DHI forebody flow control.
While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.

## Claims

1. A method of designing a hypersonic inlet for an aircraft, the method comprising:
(a) establishing a centerline geometry for a flowfield generator (FFG);
(b) establishing spanwise contours for the FFG;
(c) gridding and running computational fluid dynamics (CFD) for the FFG;
(d) iterating steps (a) through (c) until a desired inlet aperture flow characteristics uniformity, and geometrical constraints are achieved;
(e) streamline tracing a diverterless hypersonic inlet (DHI) forebody within a three-dimensional, FFG CFD solution and transferring the streamlines into a computer aided design (CAD) environment; and
(f) surfacing streamlines of the DHI forebody in the CAD environment and consolidating them with an inlet aperture design.

2. A method according to claim 1, wherein step (a) comprises performing a series of shock calculations to determine viable shock system configurations, including at least one of a shock and a shock angle,  to achieve the desired inlet aperture flow characteristics; and
based on the shock calculations, designing an FFG required to generate a desired shock system configuration.

3. A method according to claim 1, further comprising factoring an intended streamline cut position of approximately 10% to 40% of the inlet aperture.

4. A method according to claim 1, wherein step (b) comprises contouring each spanwise contour individually, wherein each spanwise contour affects a spanwise shape of generated shocks, lateral boundary layer migration, and a capture area of the inlet aperture.

5. A method according to claim 1, wherein step (c) comprises constructing streamline seed planes, applying aircraft constraints and inlet aperture geometry, assessing inlet aperture flowfield characteristics, assessing shock positions, and calculating streamlines forward from the inlet aperture to assess a capture area thereof.

6. A method according to claim 1, further comprising reassessing shock positions, inlet aperture flow characteristics, and capture area, and assessing boundary layer thickness and surface pressure gradients.

7. A method according to claim 1, further comprising evaluating off-design conditions and augmenting with DHI forebody flow control.

8. A method of designing a hypersonic inlet for an aircraft, the method comprising:
(a) establishing a centerline geometry for a flowfield generator (FFG);
(b) optimizing the FFG and a shock system configuration to fit aircraft geometrical constraints and engine airflow requirements;
(c) establishing spanwise contours for the FFG, and contouring each spanwise contour individually, wherein each spanwise contour affects a spanwise shape of generated shocks, lateral boundary layer migration, and a capture area of a cowl;
(d) gridding and running computation fluid dynamics (CFD) for the FFG by constructing streamline seed planes, applying aircraft constraints and inlet aperture geometry, assessing inlet aperture flowfield characteristics, assessing shock positions, and calculating streamlines forward from the inlet aperture to assess a capture area thereof;
(e) iterating steps (a) through (d) until a desired inlet aperture flow characteristics and geometrical constraints are achieved;
(f) streamline tracing a diverterless hypersonic inlet (DHI) forebody within a three-dimensional, FFG CFD solution and transferring the streamlines into a computer aided design (CAD) environment; and
(g) surfacing streamlines of the DHI forebody in the CAD environment and consolidating them with an inlet aperture design

9. A method according to claim 8, wherein step (a) comprises performing a series of shock calculations to determine viable shock system configurations, including a at least one of a shock and shock angle, to achieve the desired inlet aperture flow characteristics; and
designing an FFG based onthe shock calculations required to generate a desired shock system configuration.

10. A method according to claim 8, wherein step (b) comprises factoring an intended streamline cut position of approximately 10% to 40% of the inlet aperture.

11. A method according to claim 8, further comprising reassessing shock positions, inlet flowfield characteristics, and capture area, and assessing boundary layer thickness and surface pressure gradients.

12. The method according to claim 8, further comprising:
gridding DHI geometry and running viscous CFD analysis;
modifying the DHI geometry and confirming with follow-on viscous CFD runs;
evaluating off-design conditions and augmenting with the DHI with forebody flow control; and integrating the DHI geometry with geometry of the aircraft for aerodynamic analysis.