Patent Description:
Aircraft propulsion systems that employ gas turbine engines for thrust typically include a thrust reverser configured to regulate a bypass flow stream within a bypass duct of the gas turbine engine. The thrust reverser defines a forward-thrust configuration, in which the bypass flow stream is employed to generate thrust in a forward direction, and a reverse-thrust configuration, in which the bypass flow stream is employed to generate thrust in a reverse direction that is opposite the forward direction.

Placing the thrust reverser in the reverse-thrust configuration generally redirects the bypass flow stream through a thrust reverser duct located radially outward of the bypass duct. The redirection typically includes a significant change in the direction of flow of the bypass flow stream. In order to control the change in direction of the flow, a bullnose ramp or fairing may be utilized to define an inner curvature of the directional change.

In order to provide a desired level of performance of the thrust reverser (or a desired magnitude of the reverse-thrust) it may be desirable to design the thrust reverser such that a boundary layer fluid flow within a boundary layer that is adjacent to the bullnose fairing does not separate from the bullnose fairing. Thus, the inner curvature that is defined by the bullnose ramp or fairing may be dictated by a desired mass flow rate of the bypass flow stream through the reverser duct, a desired average velocity of the bypass flow stream through the reverser duct or the desired magnitude of the reverse-thrust.

<CIT> and <CIT> disclosed prior art assemblies.

In a first aspect, a bullnose ramp for use in a thrust reverser is provided as set forth in claim <NUM>.

In various embodiments, the change in slope between the forward portion and the aft portion is represented by a discontinuity. In various embodiments, the discontinuity extends between the forward portion and the aft portion at an essentially constant axial position with respect to an axial direction. In various embodiments, the forward portion is configured to induce separation of a bypass flow stream from a surface of the bullnose ramp and the aft portion is configured to induce reattachment of the bypass flow stream to the surface of the bullnose ramp.

In various embodiments, the first profile is a first sinuous profile with respect to an axial direction. In various embodiments, the second profile is a second sinuous profile with respect to the axial direction. In various embodiments, the first sinuous profile is characterized by a first curvature profile, the first curvature profile extending from a forward axial position of the bullnose ramp to the transition portion. In various embodiments, the second sinuous profile is characterized by a second curvature profile, the second curvature profile extending from the transition portion to an aft axial position of the bullnose ramp. In various embodiments, the first curvature profile is characterized by a first set of curvature values, the second curvature profile is characterized by a second set of curvature values, and the second set of curvature values is lesser in magnitude than the first set of curvature values.

In another aspect, a thrust reverser is provided according to claim <NUM>.

In various embodiments, the change in slope between the forward portion and the aft portion is represented by a discontinuity in at least one of the change in slope or a rate of change in the change in slope. In various embodiments, the discontinuity extends between the forward portion and the aft portion at an essentially constant axial position with respect to the axial direction.

In another aspect, an assembly for an aircraft propulsion system is provided according to claim <NUM>.

In various embodiments, the change in slope between the forward portion and the aft portion is represented by a discontinuity in at least one of the change in slope or a rate of change in the change in slope. In various embodiments, the change in slope extends between the forward portion and the aft portion at an essentially constant axial position with respect to the axial direction.

Referring now to the drawings, <FIG> provide schematic illustrations of an aircraft propulsion system <NUM> with a thrust reverser <NUM> in a stowed position and a deployed position, respectively. The aircraft propulsion system <NUM> includes a nacelle <NUM> and a gas turbine engine housed within the nacelle <NUM>. Without loss of generality, the gas turbine engine may be configured as a high-bypass turbofan engine or, alternatively, the gas turbine engine may be configured as any other type of gas turbine engine capable of propelling an aircraft during flight. The nacelle <NUM> is configured to house and provide an aerodynamic cover for the gas turbine engine. An outer structure of the nacelle <NUM> extends along an axial centerline A (or an axial direction) between a nacelle forward end <NUM> and a nacelle aft end <NUM>. The nacelle <NUM> includes an inlet structure <NUM>, one or more fan cowls <NUM> (e.g., a left-side fan cowl and a right-side fan cowl) and a nacelle aft structure <NUM>, which is configured as part of or may include the thrust reverser <NUM>. The inlet structure <NUM> is disposed at the nacelle forward end <NUM>. The inlet structure <NUM> is configured to direct a stream of air through an inlet opening <NUM> at the nacelle forward end <NUM> and into a fan section of the gas turbine engine.

Each of the one or more fan cowls <NUM> is typically disposed axially between the inlet structure <NUM> and the nacelle aft structure <NUM>. Each of the one or more fan cowls <NUM> is disposed at (e.g., on, adjacent or proximate) an aft end <NUM> of a stationary portion of the nacelle <NUM>, and extends forward to the inlet structure <NUM>. Each of the one or more fan cowls <NUM> is also generally axially aligned with a fan section of the gas turbine engine. The one or more fan cowls <NUM> are configured to provide an aerodynamic covering for a fan case <NUM>, which circumscribes the fan section and partially forms a forward outer peripheral boundary of a bypass flow stream of the aircraft propulsion system <NUM>. The term "stationary portion" is used above to describe a portion of the nacelle <NUM> that is stationary during operation of the aircraft propulsion system <NUM> (e.g., during takeoff, aircraft flight and landing). However, the stationary portion may be otherwise movable, for example, to provide access for inspection or maintenance of the various components that comprise the aircraft propulsion system <NUM>.

The nacelle aft structure <NUM> includes a translating sleeve <NUM>. The translating sleeve <NUM> is disposed at the nacelle aft end <NUM>. The translating sleeve <NUM> extends axially along the axial centerline A (or an axial direction) between a forward end <NUM> thereof and the nacelle aft end <NUM>. The translating sleeve <NUM> is configured to partially form an aft outer peripheral boundary of the bypass flow stream. The translating sleeve <NUM> may also be configured to form a bypass nozzle <NUM> for the bypass flow stream with an inner fixed structure of the nacelle <NUM>, which nacelle inner fixed structure houses a core of the gas turbine engine. The translating sleeve <NUM> includes a pair of sleeve segments (e.g., a first translating sleeve segment and a second translating sleeve segment) arranged on opposing sides of the aircraft propulsion system <NUM> (one such sleeve segment visible in <FIG>). The present disclosure, however, is not limited to such an exemplary translating sleeve configuration. For example, the translating sleeve <NUM> may alternatively have a substantially tubular body. For example, in various embodiments, the translating sleeve <NUM> may extend up to or more than three-hundred and thirty degrees (<NUM>°) about the axial centerline A.

Still referring to <FIG>, the translating sleeve <NUM> is an axially translatable structure. Each translating sleeve segment, for example, may be slidably connected to one or more stationary structures (e.g., a pylon and a lower bifurcation) through one or more respective track assemblies. Each track assembly may include a rail mated with a track beam; however, the present disclosure is not limited to the foregoing exemplary sliding connection configuration. With the foregoing configuration, the translating sleeve <NUM> may translate axially along the axial centerline A and relative to the stationary portion. The translating sleeve <NUM> may thereby move axially between a forward or stowed position (see <FIG>) and an aft or deployed position (see <FIG>). In the forward or stowed position, the translating sleeve <NUM> provides the functionality described above. In the aft or deployed position, the translating sleeve <NUM> at least partially (or substantially completely) uncovers at least one or more other components of the thrust reverser <NUM> such as, but not limited to, a cascade structure <NUM>. In addition, as the translating sleeve <NUM> moves from the stowed position to the deployed position, one or more blocker doors (see, e.g., the thrust reverser blocker door assembly <NUM> illustrated in <FIG>) arranged with the translating sleeve <NUM> may be deployed to divert bypass air from the bypass flow stream through the cascade structure <NUM> to provide reverse thrust.

Referring now to <FIG>, a partial side-sectional illustration of a thrust reverser <NUM>, similar to the thrust reverser <NUM> described above with reference to <FIG>, is provided, in both a stowed position (see <FIG>) and a deployed position (see <FIG>). Without loss of generality, the thrust reverser <NUM> includes a nacelle fixed structure <NUM>, a nacelle translating structure <NUM> and a thrust reverser blocker door assembly <NUM>. The nacelle fixed structure <NUM> is located at an aft end <NUM> of a stationary portion of a nacelle, such as, for example, the aft end <NUM> of the stationary portion of the nacelle <NUM> described above with reference to <FIG>. Note that while the following disclosure is described in part with reference to the thrust reverser <NUM> and the thrust reverser blocker door assembly <NUM>, the disclosure contemplates applicability to other types of thrust reversers and blocker door assemblies, including, for example, traditional drag-link style blocker doors mounted on an inner fixed structure. Accordingly, the disclosure should not be construed as limited to the thrust reverser and the related components illustrated at <FIG>.

The nacelle fixed structure <NUM> includes a bullnose ramp <NUM> (or a bullnose) and an internal nacelle support structure <NUM>. Note the term "bullnose" originates from the rounded nose of a bull and typically refers to a smooth, rounded structure or a rounded edge on a surface or object having a smooth, rounded or finished appearance. The bullnose ramp <NUM> is configured to provide a smooth aerodynamic transition from a bypass flow stream B to a thrust reverser duct <NUM>, which extends axially between the internal nacelle support structure <NUM> and the nacelle translating structure <NUM>. In various embodiments, the internal nacelle support structure <NUM> circumscribes and supports the bullnose ramp <NUM>. The internal nacelle support structure <NUM> also provides a base to which a cascade structure <NUM>, similar to the cascade structure <NUM> described above with reference to <FIG>, may be mounted. The cascade structure <NUM> may thereby project axially aft from the internal nacelle support structure <NUM> and downstream of the bullnose ramp <NUM>. With such a configuration, when the nacelle translating structure <NUM> is in the stowed position (see <FIG>), the cascade structure <NUM> is located within an internal cavity <NUM> of the nacelle translating structure <NUM>. When the nacelle translating structure <NUM> is in the deployed position (see <FIG>), the cascade structure <NUM> is uncovered and located within the thrust reverser duct <NUM>.

Referring now to <FIG>, a schematic side-sectional view of a thrust reverser <NUM>, similar to the thrust reverser <NUM> described above with reference to <FIG>, is provided and illustrated in a deployed position. Similar to the description above, the thrust reverser <NUM> includes a nacelle fixed structure <NUM>, a nacelle translating structure <NUM> and a thrust reverser blocker door assembly <NUM>. The nacelle fixed structure <NUM> includes a bullnose ramp <NUM> (or a bullnose) and an internal nacelle support structure <NUM>. The bullnose ramp <NUM> is configured to provide a smooth aerodynamic transition from a bypass flow stream B to a thrust reverser duct <NUM>, which extends axially between the internal nacelle support structure <NUM> and the nacelle translating structure <NUM>. In various embodiments, the internal nacelle support structure <NUM> circumscribes and supports the bullnose ramp <NUM>. The internal nacelle support structure <NUM> also provides a base to which a cascade structure <NUM>, similar to the cascade structure <NUM> described above with reference to <FIG>, may be mounted. The cascade structure <NUM> may thereby project axially aft from the internal nacelle support structure <NUM> and downstream of the bullnose ramp <NUM>.

When the nacelle translating structure <NUM> is in the deployed position, the cascade structure <NUM> is uncovered and located within the thrust reverser duct <NUM>. At the same time, a blocker door <NUM> of the thrust reverser blocker door assembly <NUM> is deployed, thereby blocking the bypass flow stream B from exiting the bypass flow stream exhaust and forcing the bypass flow stream to turn radially outward and exit the cascade structure <NUM> as a reverse thrust flow stream T. As described above, the bullnose ramp <NUM> provides an aerodynamic surface that functions to smoothly turn the bypass flow stream B toward the cascade structure <NUM>. As described in further detail below, the bullnose ramp <NUM> may be characterized by a bullnose profile (or a ramp profile) that extends from a forward axial position <NUM> (or an axial ramp start) to an aft axial position <NUM> (or an axial ramp end). The bullnose profile may be characterized as a functional relationship between a radius R as a function of axial length X between the forward axial position <NUM> and the aft axial position <NUM>. Additional parameters that may be used to characterize the bullnose profile and the radial position of the cascade structure <NUM> include the radius R of the forward axial position <NUM>, RSTART, the radial position at the aft axial position <NUM>, REND, and the radius of the cascade structure <NUM>, RCASCADE.

Referring now to <FIG>, graphs illustrating various ramp profiles and curvature profiles for a bullnose ramp are illustrated. Note the term curvature profile is used to enable the curvature to vary along an axial extent of the ramp profile, rather than be constant along the ramp profile. Referring to <FIG>, three mathematical profiles - sinuous, elliptical and circular - are provided. The axial position along the X-axis is normalized to run from zero to unity, with zero corresponding to a forward axial position (e.g., the forward axial position <NUM>) and unity corresponding to an aft axial position (e.g., the aft axial position <NUM>) of a bullnose ramp (e.g., the bullnose ramp <NUM>). Similarly, the radial position along the Y-axis is normalized to run from zero to unity, with zero corresponding to RSTART and unity corresponding to REND of the bullnose ramp. Referring to <FIG>, normalized values of curvature for the three mathematical profiles - sinuous, elliptical and circular - are provided. The axial position along the X-axis is normalized in the same fashion as for <FIG>, while the curvature along the Y-axis is suitably normalized to run from zero to unity. An important distinction to recognize from the profiles presented in <FIG> is the relative degree of curvature for each of the profiles. For example, the curvature of the sinuous profile starts at a start value (Y ≈ <NUM>) at the forward axial position, which is relatively high with respect to an end value (Y ≈ <NUM>) at the aft axial position, where Y indicates the value of curvature on the Y-axis as a function of the axial distance X on the X-axis (or axial extent along the X-axis). Conversely, the curvature of the elliptical profile starts at a start value (Y ≈ <NUM>) at the forward axial position, which is relatively low with respect to an end value (Y ≈ <NUM>) at the aft axial position. As expected, the curvature for the circular arc is constant along the axial extent of the profile. Note the foregoing values of Y refer to the local values of curvature illustrated at <FIG>, with the local values of curvature along the X-axis generally understood to mean a reciprocal of the local radii of curvature along the X-axis.

The foregoing profiles may be considered in the design of a bullnose ramp for various thrust reverser configurations. However, current research suggests the profiles are not optimal for maximizing mass flow through a cascade, which, if successful, may result in an engine design configured to experience less drag during flight via shortening the thrust reverser portion of the engine. More specifically, maximizing the mass flow through the cascade enables the use of shorter cascades where flow separation along the bullnose ramp is reduced. Reducing the amount of flow separation along the bullnose ramp, particularly at the forward region of the cascade, enables an increase in the mass flow through the cascade and a more uniform reverse thrust flow stream T (see <FIG>). Conversely, where substantial flow separation develops along the bullnose ramp and in the region radially inward of the forward region of the cascade, the velocity vectors through the cascade at the forward region of the cascade may be reduced in magnitude, thereby reducing the mass flow through the cascade and thereby reducing the magnitude of the reverse thrust.

Referring now to <FIG>, a compound profile for a bullnose ramp, such as, for example, the bullnose ramp <NUM> described above with reference to <FIG> and the bullnose ramp <NUM> described above with reference to <FIG>, is illustrated. In various embodiments, solutions to the drawbacks described above, including reducing flow separation along the bullnose ramp, particularly in the region radially inward of the forward region of the cascade are accomplished by introducing a transition portion, which, in various embodiments, may be represented by a discontinuity <NUM>, in the profile of the bullnose ramp, with the discontinuity <NUM> separating a first profile <NUM> (or a first axial profile) from a second profile <NUM> (or a second axial profile), where the two profiles exhibit different degrees of curvature along their axial extent. For example, as illustrated at <FIG>, the first profile <NUM> ("Profile <NUM>") exhibits a larger or greater degree of curvature along the length of the profile (or a smaller or lesser radius of curvature) than does the second profile <NUM> ("Profile <NUM>"). Thus, the first profile <NUM> may be characterized by a first curvature profile or a first set of curvature values that extend along the axial length of Profile <NUM>, while the second profile <NUM> may be characterized by a second curvature profile or a second set of curvature values that extend along the axial length of Profile <NUM>. A compound profile <NUM> is constructed by employing the first profile <NUM> from a forward axial position (X ≈ <NUM>) (e.g., the forward axial position <NUM> described above with reference to <FIG>) to an intermediate axial position (X ≈ <NUM>) where the discontinuity is positioned. The compound profile <NUM> then continues from the discontinuity <NUM> by incorporating the second profile <NUM> to an aft axial position (X ≈ <NUM>) (e.g., the aft axial position <NUM> described above with reference to <FIG>). In various embodiments, the second profile <NUM> is incorporated into the compound profile <NUM> by translating the second profile <NUM> in a forward direction F, from an axial position (X ≈ <NUM>), where the radial value <NUM> of the second profile <NUM> is equal to the radial value of the first profile <NUM> at the discontinuity <NUM>, to the end of the second profile (X ≈ <NUM>), with the shift, ΔX, being approximately equal to ΔX ≈ <NUM>, as illustrated. Note each of Profile <NUM> and Profile <NUM> is also, according to the claimed invention, characterized by a slope (e.g., the first derivative of the ramp profile) or may also, in examples not forming part of the claimed invention, be characterized by a rate of change in slope (e.g., the second derivative of the ramp profile) along the axial extent. Note also the ramp profile extending along the transition portion and, in particular, the discontinuity <NUM>, may be characterized as being C<NUM>, C<NUM> or C<NUM> continuous.

The manner of translation described above, where the first profile <NUM> and the second profile <NUM> exhibit differing values of curvature along their lengths, assures the existence of the discontinuity <NUM> in the compound profile <NUM>, with the discontinuity being, for example, in the slope of the compound profile <NUM>. Referring briefly to <FIG>, the discontinuity may be manifest as a crease <NUM> that extends along an intersection of the bullnose ramp <NUM> between a forward portion <NUM> (represented by the first profile <NUM>) and an aft portion <NUM> (represented by the second profile <NUM>). As illustrated, the crease <NUM> extends about the bullnose ramp <NUM> at an essentially constant axial position. In various embodiments, the axial location of the discontinuity <NUM> (or the crease <NUM> illustrated in <FIG>), is determined through experimental or computational analysis of the expected axial location of the onset of flow separation following deployment of the thrust reverser. Positioning the discontinuity <NUM> at an axial location proximate the onset of flow separation allows, or even induces, the flow to separate and then immediately reattach downstream of the discontinuity <NUM> and on the second profile <NUM>, which, as described above, is characterized by a second set of curvature values having a generally smaller curvature (or larger radius of curvature) than that of a first set of curvature values that characterize the first profile <NUM>. The smaller curvature of the second profile <NUM> provides a surface less amenable to flow separation throughout the remainder of the compound profile <NUM>, thereby providing a more uniform flow, particularly at the forward region of the cascade, which thereby enables an increase in the mass flow through the cascade and a more uniform reverse thrust flow stream T (see <FIG>). Note that instead of characterizing the profiles by sets of curvature values, the first and second sets of curvature values might be further characterized by integrating the curvature along the lengths of the first and second profiles (taking care to scale any differences in lengths of the profiles) to obtain scalar results representative of the average curvature of the two profiles.

The foregoing disclosure provides an apparatus and method to improve or increase the mass flow rate through a cascade of a thrust reverser. The bullnose structures disclosed above, which include the surface profiles of the structures generally immediately upstream of the cascade, prevent or impede flow separation in an upstream region of the cascade where a bypass flow stream is being turned or redirected into the bypass duct where the cascade is positioned. The characteristics of the improved flow field (e.g., a flow field exhibiting minimal flow separation from the surface of the bullnose) enables the use of cascades having reduced axial length. A reduction in the axial length of the cascade enables a reduction in the length of the translating sleeve of the thrust reverser, thereby reducing weight of the propulsion system and reducing aerodynamic drag experienced at the outer surface of the nacelle of the propulsion system during flight.

Claim 1:
A bullnose ramp (<NUM>, <NUM>) for use in a thrust reverser, comprising:
a forward portion (<NUM>), the forward portion (<NUM>) characterized by a first profile (<NUM>) having a first slope and extending from a forward axial position (<NUM>) to an intermediate axial position;
an aft portion (<NUM>), the aft portion (<NUM>) characterized by a second profile (<NUM>) having a second slope and extending from the intermediate axial position to an aft axial position (<NUM>); and
a transition portion (<NUM>) positioned at the intermediate axial position between the forward portion (<NUM>) and the aft portion (<NUM>), the transition portion (<NUM>) defining a change in slope from the first slope to the second slope between the first profile (<NUM>) and the second profile (<NUM>).