Patent Description:
A nacelle is the housing for a turbofan gas turbine engine used to power, for example, a commercial airliner. The nacelle and the engine together are referred to as the propulsion system or power plant of the aircraft. The nacelle forms the external aerodynamic surfaces of the propulsion system, and also helps form the duct for the bypass air from the fan, as well as encloses all the components and auxiliary devices surrounding and attached to the engine. The nacelle may also optionally provide a reverse thrust means to generate reverse thrust to slow the aircraft, for example during landing. <CIT>, <CIT>, <CIT> and <CIT> disclose panel arrangements of the prior art.

In one aspect a panel for an active laminar flow control arrangement is provided according to claim <NUM>.

In various embodiments, the panel further comprises a flange extending from the sidewall and extending around a perimeter of the panel.

In various embodiments, the ridge comprises a narrow raised band extending from the longitudinal wall.

In various embodiments, the ridge intersects the sidewall at a first end of the panel and intersects the sidewall at a second end of the panel.

In various embodiments, the first end is opposite the panel from the second end.

In various embodiments, the ridge is oriented parallel with the division wall.

In various embodiments, the panel is made from at least one of a metal, a metal alloy, and a composite material.

In various embodiments, the longitudinal wall, the sidewall, the ridge, and the division wall comprise a single, monolithic piece.

In another aspect an active laminar flow control arrangement is provided according to claim <NUM>.

In various embodiments, the inner surface is in fluid communication with the outer surface via the perforated area.

In various embodiments, the cavity is in fluid communication with the outer surface via the perforated area.

In various embodiments, the active laminar flow control arrangement further comprises a sealant disposed on an end of the division wall and the inner surface.

In various embodiments, the longitudinal wall is oriented substantially parallel with the outer skin.

In various embodiments, the panel is coupled to the outer skin at the flange, the ridge, and the division wall.

In another aspect a method of installing a laminar flow control arrangement onto a nacelle inlet is provided according to claim <NUM>.

In various embodiments, the method further comprises compressing the sealant between the outer skin and the division wall.

In various embodiments, the flange extends around a perimeter of the panel.

The foregoing features, elements, steps, or methods as well as the operation of the disclosed embodiments will become more apparent in light of the following description and accompanying drawings.

The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the inventions, it should be understood that other embodiments may be realized and that logical changes and adaptations in design and construction may be made in accordance with this invention and the teachings herein. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option. Surface shading and/or crosshatching lines may be used throughout the figures to denote different parts, but not necessarily to denote the same or different materials.

As used herein, "aft" refers to the direction associated with the tail (e.g., the back end) of an aircraft, or generally, to the direction of exhaust of the gas turbine. As used herein, "forward" refers to the direction associated with the nose (e.g., the front end) of an aircraft, or generally, to the direction of flight or motion.

An active laminar flow control arrangement is disclosed herein, comprising a panel for an inlet outer skin. The panel may define a plurality of plenums for active laminar flow control. The panel may be a one-piece panel, thereby increasing ease of installation and decreasing the number of parts in the arrangement. Furthermore, the panel may provide structural support for the outer skin. In this regard, the outer skin may be devoid of structural stiffeners (e.g., hollow hat stiffeners and/or stringers) at the location of the active laminar flow control ducting. Stated differently, the panel may be installed over a generally smooth inner surface of the outer skin.

The panel may be coupled to the outer skin via a plurality of fasteners (also referred to herein as adhesive fasteners) that are bonded to the inner surface of the outer skin. In this regard, a single nacelle inlet design may be used for nacelles having active laminar flow control or without active laminar flow control since installation of the panel is independent from the nacelle inlet design.

Xyz-axes are provided in certain figures described herein for ease of illustration.

With reference to <FIG> and <FIG>, a turbofan propulsion system for a commercial jetliner may include an engine <NUM>, a pylon <NUM>, and a nacelle package (also referred to herein as a nacelle) <NUM>. The typical nacelle package, or more simply a nacelle, may comprise an inlet <NUM>, a fan cowl <NUM>, a thrust reverser <NUM>, and an exhaust system including an exhaust cone <NUM>, and exhaust nozzle <NUM>. The nacelle <NUM> surrounds the engine providing smooth aerodynamic surfaces for airflow around and into the engine. The nacelle also helps define a bypass air duct through the propulsion system.

A fan draws and directs a flow of air into and through the propulsion system. After the fan, the air is divided into two principal flowpaths, one flowpath through the engine core, and another flowpath through a bypass air duct. The engine core flowpath is directed into the engine core and initially passes through a compressor that increases the air flow pressure, and then through a combustor where the air is mixed with fuel and ignited. The combustion of the fuel and air mixture causes a series of turbine blades at the rear of the engine core to rotate, and to drive the engine's rotor and fan. The high-pressure exhaust gases from the combustion of the fuel and air mixture are thereafter directed through an exhaust nozzle at the rear of the engine for thrust.

The bypass air flowpath includes air that is directed around the engine core in a duct or ducts defined by the nacelle. The bypass air exits the duct at a nozzle at the aft end of the nacelle for thrust. In turbofan engines, the bypass flow typically provides a large percentage of the thrust for an aircraft. The bypass air ducts in the nacelle may be C-shaped, and may be principally defined by the exterior surface of the inner fixed structure (IFS) <NUM> and the inside surface of the outer sleeve <NUM>. If the nacelle includes a typical thrust reverser, the thrust reverser blocks bypass air in the bypass air duct from reaching the nozzle, and instead redirects the bypass air to exit the duct in a forward direction of the aircraft to generate reverse thrust.

The engine <NUM> may be mounted to pylon <NUM> in two places. One of these at the aft end of the pylon <NUM>, over the engine turbine case, and in one of two places at the forward end of pylon <NUM>: the engine core (core mount) or the engine fan case (fan mount). Pylon <NUM> transmits structural loads (including thrust) between engine <NUM> and a wing.

The thrust reverser <NUM> may comprise two halves generally configured to surround the engine core. The thrust reverser <NUM> may be hinged to the pylon <NUM> via one or more hinges. The thrust reverser <NUM> comprises an IFS <NUM> and an outer sleeve <NUM>. The IFS generally surrounds the engine core. As used herein, the outer sleeve <NUM>, though it may have any shape, may generally be a C shaped structure. An exterior surface of the outer sleeve is external to the nacelle. An interior surface of the outer sleeve <NUM>, along with the IFS <NUM>, partially defines a cold flow path of the propulsion system of the aircraft. The IFS <NUM> and the outer sleeve <NUM> are typically coupled together and attached to the pylon <NUM> via a hinge beam <NUM>. As used herein, the IFS <NUM> is generally referred to as an IFS; however it should be appreciated that a first IFS half may be configured to partially surround an engine core and a second IFS half may be configured to substantially partially surround the remaining engine core.

In operation, an ambient air flow <NUM> on the exterior of the nacelle <NUM> generates drag. The drag force tends to increase fuel consumption. Accordingly, it is desirable to minimize the drag.

If the flow around the nacelle <NUM> is laminar the drag force will be reduced compared to a turbulent flow. Aircraft and nacelle designers have utilized nacelle external aerodynamic shapes that maintain a natural laminar flow over a portion of the nacelle <NUM>. By carefully selecting the aerodynamic profile, natural laminar flow can be achieved. The portion where it is desired to achieve laminar flow should be clean of debris and aerodynamically smooth (e.g., fastener heads should be flush and parallel with the surrounding surface). Steps and gaps can cause the laminar flow to trip and transition to turbulent flow. Other active or hybrid natural/active techniques have been proposed for achieving and maintaining laminar flow on an aircraft nacelle and other aircraft surfaces. One such technique is through boundary layer ingestion or suction where the boundary layer next to the aircraft surface is pulled through small holes in the surface to remove the low energy boundary layer and regenerate it or maintain it at a minimum or near minimum energy level. Active or hybrid laminar flow techniques may achieve and maintain laminar flow more consistently than natural means alone, and may be able to extend further aft the region of nacelle <NUM> which has laminar flow.

With reference to <FIG>, a schematic view of an active laminar flow control arrangement <NUM> is illustrated, in accordance with various embodiments. In various embodiments, active laminar flow control arrangement <NUM> includes a nacelle inlet <NUM>. Nacelle inlet <NUM> may be similar to nacelle inlet <NUM> of <FIG>. A laminar flow control duct arrangement <NUM> may be coupled to nacelle inlet <NUM>. Laminar flow control duct arrangement <NUM> may be in fluid communication with a plurality of orifices (i.e., perforations) <NUM> disposed in the outer skin <NUM> of nacelle inlet <NUM>. In various embodiments, outer skin <NUM> defines an outer aerodynamic surface of nacelle inlet <NUM>. Laminar flow control duct arrangement <NUM> may be in fluid communication with a pump <NUM> whereby an ambient airflow <NUM> is drawn into laminar flow control duct arrangement <NUM> from outside of nacelle inlet <NUM> through orifices <NUM>. Pump <NUM> may be a fluid (e.g., air) pump. Pump <NUM> may be mounted to a fan case. It is appreciated that the location of pump <NUM> is not particularly limited. In this manner, a laminar or near laminar flow may be maintained over nacelle inlet <NUM>, thereby increasing the aerodynamic performance of the nacelle inlet <NUM>. It is appreciated that the present disclosure may be useful for an active laminar flow control system for any desirable aerodynamic surface of an aircraft or any suitable portion of a nacelle, such as the fan cowl for example.

In various embodiments, nacelle inlet <NUM> comprises an inner barrel <NUM>. Nacelle inlet <NUM> may comprise a nose lip <NUM>. Inner barrel <NUM> may be coupled to outer skin <NUM> via nose lip <NUM>. In various embodiments, inner barrel <NUM> may be acoustically treated. In various embodiments, nacelle inlet <NUM> includes an acoustic liner <NUM> coupled to inner barrel <NUM>. Nacelle inlet <NUM> may include an attachment ring <NUM>. Nacelle inlet <NUM> may be configured to be coupled to an adjacent fan case via attachment ring <NUM>. Nacelle inlet <NUM> may include an aft bulkhead <NUM> extending between attachment ring <NUM> and outer skin <NUM>.

With combined reference to <FIG>, a section view of an active laminar flow control arrangement <NUM> is illustrated, in accordance with various embodiments. In various embodiments, active laminar flow control arrangement <NUM> includes a nacelle inlet <NUM>. Nacelle inlet <NUM> may be similar to nacelle inlet <NUM> of <FIG>. Nacelle inlet <NUM> may be coupled to a fan case <NUM>. A laminar flow control duct arrangement <NUM> may be coupled to nacelle inlet <NUM>. An outer skin <NUM> of nacelle inlet <NUM> may comprise a perforated area <NUM>. Laminar flow control duct arrangement <NUM> may receive a flow of air through the perforated area <NUM> of outer skin <NUM>. Outer skin <NUM> may comprise an outer surface <NUM> and an inner surface <NUM>. Perforated area <NUM> may comprise a plurality of perforations placing outer surface <NUM> in fluid communication with inner surface <NUM>.

Active laminar flow control arrangement <NUM> may comprise a panel <NUM> coupled to inner surface <NUM> and defining one or more cavities (e.g., cavity <NUM> and cavity <NUM>) disposed between panel <NUM> and inner surface <NUM> of outer skin <NUM>. In various embodiments, panel <NUM> may comprise a ridge <NUM> disposed between cavity <NUM> and cavity <NUM>. Stated differently, cavity <NUM> may be separated from cavity <NUM> by ridge <NUM>.

With particular focus on <FIG>, panel <NUM> may be coupled to outer skin <NUM> via ridge <NUM>. A plurality of fasteners <NUM> may be coupled between outer skin <NUM> and panel <NUM> at ridge <NUM>. In various embodiments, fasteners <NUM> are rivets or the like. Ridge <NUM> may comprise a plurality of orifices for receiving fasteners <NUM>. In various embodiments, fasteners <NUM> are countersunk into outer skin <NUM> such that fasteners <NUM> are flush with outer skin <NUM>. In this regard, ridge <NUM> may be in direct contact with outer skin <NUM> in the installed position. Sheer forces may be transferred between panel <NUM> and outer skin <NUM> via fasteners <NUM>.

Panel <NUM> comprises a longitudinal wall <NUM> extending substantially parallel with respect to outer skin <NUM>. Ridge <NUM> may comprise a narrow raised band extending from longitudinal wall <NUM>.

With particular focus on <FIG>, panel <NUM> comprises sidewall <NUM> and a flange <NUM> extending from the sidewall <NUM> and extending around the perimeter <NUM> of panel <NUM>. A plurality of fasteners <NUM> may be coupled between outer skin <NUM> and panel <NUM> at flange <NUM>. Flange <NUM> may comprise a plurality of orifices for receiving fasteners <NUM>. In various embodiments, fasteners <NUM> are rivets or the like. In various embodiments, fasteners <NUM> are countersunk into outer skin <NUM> such that fasteners <NUM> are flush with outer skin <NUM>. Flange <NUM> may be in direct contact with outer skin <NUM> in the installed position. Sheer forces may be transferred between panel <NUM> and outer skin <NUM> via fasteners <NUM>.

With continued combined reference to <FIG>, panel <NUM> comprises one or more division walls (e.g., division wall 328a, division wall 328b, division wall 328c, and division wall 328d). The division walls divide cavity <NUM> and/or cavity <NUM> into a plurality of plenums (e.g., plenum 340a, plenum 340b, plenum 340c, plenum 340d, plenum 340e, and plenum 340f). Division wall 328a may divide cavity <NUM> into plenum 340a and plenum 340b. Division wall 328b may divide cavity <NUM> into plenum 340b and plenum 340c. Division wall 328c may divide cavity <NUM> into plenum 340d and plenum 340e. Division wall 328d may divide cavity <NUM> into plenum 340e and plenum 340f.

Laminar flow control duct arrangement <NUM> may receive a flow of air through the perforated area <NUM> of outer skin <NUM> into each plenum (e.g., plenum 340a, plenum 340b, plenum 340c, plenum 340d, plenum 340e, and plenum 340f). In various embodiments, the pressure of air in each plenum varies.

In various embodiments, division wall 328a, division wall 328b, division wall 328c, and/or division wall 328d may extend from longitudinal wall <NUM> towards outer skin <NUM> in the installed position. The division walls and longitudinal wall <NUM> may comprise a single monolithic piece. In various embodiments, the division walls may be cured to longitudinal wall <NUM>, for example during a carbon fiber composite layup process. In various embodiments, the division walls may be bonded to longitudinal wall <NUM>. In various embodiments, the division walls may be welded to longitudinal wall <NUM>, for example where panel <NUM> is made from a metal or metal alloy. It is appreciated that the method of attachment of the division walls to longitudinal wall <NUM> is not particularly limited.

Division wall 328a, division wall 328b, division wall 328c, and/or division wall 328d comprise a T-shaped structure. With particular focus on division wall 328a, the divisional walls may comprise a first wall <NUM> extending substantially orthogonal to longitudinal wall <NUM> and a second wall <NUM> extending substantially orthogonal to first wall <NUM>, thereby forming the T-shaped structure. A sealant <NUM> is disposed on an end <NUM> of the division walls (i.e., division wall 328a, division wall 328b, division wall 328c, and/or division wall 328d). Sealant <NUM> is compressed between the division walls and outer skin <NUM>. In various embodiments, sealant <NUM> is a class-B sealant such as a polysulfide-based sealant for example. Sealant <NUM> may aid in sealing panel <NUM> to outer skin <NUM>. Sealant <NUM> may aid in hermetically sealing panel <NUM> to outer skin <NUM>. Division wall 328a, division wall 328b, division wall 328c, and/or division wall 328d may aid in structurally supporting outer skin <NUM>, particularly against external pressure loading on outer skin <NUM>. Stated differently, division wall 328a, division wall 328b, division wall 328c, and/or division wall 328d may support outer skin <NUM> from deflecting towards panel <NUM>.

Panel <NUM> may provide structural support to outer skin <NUM>. Panel <NUM> may provide torsion rigidity, bending stiffness, and buckling resistance to nacelle inlet <NUM>.

With reference to <FIG>, a perspective view of a panel <NUM> is illustrated, in accordance with various embodiments. Panel <NUM> may be similar to panel <NUM> of <FIG>. Panel <NUM> may define a cavity <NUM> and a cavity <NUM>. Panel <NUM> may comprise a ridge <NUM> disposed between cavity <NUM> and cavity <NUM>. Stated differently, cavity <NUM> may be separated from cavity <NUM> by ridge <NUM>. Cavity <NUM> and cavity <NUM> may be partially defined by ridge <NUM>. Panel <NUM> may comprise a longitudinal wall <NUM>. Ridge <NUM> may comprise a narrow raised band <NUM> extending from longitudinal wall <NUM>. Ridge <NUM> may extend from a first end <NUM> of panel <NUM> to a second end <NUM> of panel <NUM>. Panel <NUM> may comprise sidewall <NUM> and a flange <NUM> extending from the sidewall <NUM> and extending around the perimeter <NUM> of panel <NUM>. Ridge <NUM> may intersect sidewall <NUM> at first end <NUM>. Ridge <NUM> may intersect sidewall <NUM> at second end <NUM>. In this regard, sidewall <NUM> may extend around the entire perimeter of panel <NUM>.

Panel <NUM> may comprise one or more division walls (e.g., division wall 428a, division wall 428b, division wall 428c, and division wall 428d). The division walls may divide cavity <NUM> and/or cavity <NUM> into a plurality of plenums (e.g., plenum 440a, plenum 440b, plenum 440c, plenum 440d, plenum 440e, and plenum 440f). Division wall 428a may divide cavity <NUM> into plenum 440a and plenum 440b. Division wall 428b may divide cavity <NUM> into plenum 440b and plenum 440c. Division wall 428c may divide cavity <NUM> into plenum 440d and plenum 440e. Division wall 428d may divide cavity <NUM> into plenum 440e and plenum 440f. The division walls are oriented parallel with ridge <NUM>.

A sealant <NUM> is disposed on the division walls (i.e., division wall 428a, division wall 428b, division wall 428c, and/or division wall 428d).

In various embodiments, panel <NUM> may be made of a composite material such as carbon fiber, a glass fiber, and/or an aramid fiber. In this regard, panel <NUM> may be formed during a carbon fiber layup process. In various embodiments, panel <NUM> may be made of a metal or metal alloy, such as aluminum for example. In this regard, panel <NUM> may be formed via a metal stamping process or a hydroforming process, among other processes.

With reference to <FIG>, a panel <NUM> coupled to an outer skin <NUM> is illustrated, in accordance with various embodiments. Having mentioned that an outer skin may be coupled to a panel via a fastener such as a rivet, it is further contemplated herein that an outer skin may be coupled to a panel via an adhesive fastener <NUM>. Examples of a suitable adhesive fastener may include one or more of the fastening products available from Click Bond, Inc. of Carson City, Nev.

In various embodiments, adhesive fastener <NUM> may comprise a baseplate <NUM> and a threaded stud <NUM> extending from the baseplate <NUM>. The baseplate <NUM> may be coupled to outer skin <NUM> via an adhesive <NUM>. A seal <NUM> may be placed around the threaded stud <NUM> and over baseplate <NUM>. Panel <NUM> may be fitted around threaded stud <NUM> and a nut <NUM> may be threadingly coupled to threaded stud <NUM> to compress panel <NUM> between nut <NUM> and seal <NUM>.

In various embodiments, a liner <NUM> may be placed over threaded stud <NUM> an coupled between seal <NUM> and baseplate <NUM>. A bulb portion <NUM> of seal <NUM> may be compressed between liner <NUM> and panel <NUM>. Liner <NUM> may be made from a metal material or a composite material. In various embodiments, fasteners <NUM> and/or fasteners <NUM> (see <FIG>) may be similar to adhesive fastener <NUM>.

With reference to <FIG>, a panel <NUM> coupled to an outer skin <NUM> via an adhesive fastener <NUM> is illustrated, in accordance with various embodiments. In various embodiments, adhesive fastener <NUM> may be similar to adhesive fastener <NUM> of <FIG>, except that the liner <NUM> of adhesive fastener <NUM> is coupled between baseplate <NUM> of threaded stud <NUM> and outer skin <NUM>. Bulb portion <NUM> of seal <NUM> may be compressed between liner <NUM> and panel <NUM>. Liner <NUM> may be made from a metal material or a composite material. Liner <NUM> may be bonded to outer skin <NUM> via an adhesive. The baseplate <NUM> may be bonded to liner <NUM> via an adhesive <NUM>. Panel <NUM> may be fitted around threaded stud <NUM> and a nut <NUM> may be threadingly coupled to threaded stud <NUM> to compress panel <NUM> between nut <NUM> and seal <NUM>. In various embodiments, fasteners <NUM> and/or fasteners <NUM> (see <FIG>) may be similar to adhesive fastener <NUM>.

With reference to <FIG>, a panel <NUM> coupled to an outer skin <NUM> via an adhesive fastener <NUM> is illustrated, in accordance with various embodiments. In various embodiments, adhesive fastener <NUM> may be similar to adhesive fastener <NUM> of <FIG>, except that instead of being compressed between a liner and the panel <NUM>, bulb portion <NUM> of seal <NUM> is compressed between flange <NUM> of panel <NUM> and outer skin <NUM>. The baseplate <NUM> may be bonded to outer skin <NUM> via an adhesive <NUM>. Panel <NUM> may be fitted around threaded stud <NUM>. A nut <NUM> may be threadingly coupled to threaded stud <NUM> to compress panel <NUM> between nut <NUM> and seal <NUM>. In various embodiments, fasteners <NUM> and/or fasteners <NUM> (see <FIG>) may be similar to adhesive fastener <NUM>.

With reference to <FIG>, a method <NUM> for installing an active laminar flow control arrangement onto a nacelle inlet is illustrated, in accordance with various embodiments. Method <NUM> includes disposing a sealant over an end of a division wall of a panel (step <NUM>). Method <NUM> includes disposing the panel over an inner surface of an outer skin (step <NUM>). Method <NUM> includes coupling a flange of the panel to the outer skin (step <NUM>). Method <NUM> includes coupling a ridge of the panel to the outer skin (step <NUM>). Method <NUM> includes compressing the sealant between the outer skin and the division wall (step <NUM>).

With combined reference to <FIG>, and <FIG>, step <NUM> includes disposing sealant <NUM> over end <NUM> of division wall 328a of panel <NUM>. Step <NUM> includes disposing panel <NUM> over inner surface <NUM> of outer skin <NUM>. Step <NUM> includes coupling flange <NUM> of panel <NUM> to outer skin <NUM>. Step <NUM> may include coupling flange <NUM> of panel <NUM> to outer skin <NUM> via fasteners <NUM>. Step <NUM> includes coupling ridge <NUM> of panel <NUM> to outer skin <NUM>. Step <NUM> may include coupling ridge <NUM> of panel <NUM> to outer skin <NUM> via fasteners <NUM>. Step <NUM> may include compressing sealant <NUM> between the outer skin <NUM> and division wall 328a. Sealant <NUM> may be compressed between the outer skin <NUM> and division wall 328a in response to tightening fasteners <NUM> and/or fasteners <NUM>. Sealant <NUM> may be compressed between the outer skin <NUM> and division wall 328a by applying a force, for example by hand or by rollers, to panel <NUM>.

However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the inventions. The scope of the inventions is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more.

Claim 1:
A panel for an active laminar flow control arrangement, comprising:
a longitudinal wall (<NUM>,<NUM>);
a sidewall (<NUM>,<NUM>) extending from the longitudinal wall (<NUM>,<NUM>);
a ridge (<NUM>,<NUM>) intersecting the sidewall (<NUM>,<NUM>);
a cavity (<NUM>,<NUM>,<NUM>,<NUM>) disposed in the panel and at least partially defined by the sidewall (<NUM>,<NUM>) and the longitudinal wall (<NUM>,<NUM>); and
a division wall (<NUM>,<NUM>) disposed in the cavity (<NUM>,<NUM>,<NUM>,<NUM>) and extending from the longitudinal wall (<NUM>,<NUM>), wherein the division wall (<NUM>,<NUM>) divides the cavity (<NUM>,<NUM>,<NUM>,<NUM>) to at least partially define a first plenum (340a,440a) and a second plenum (340b,440b); characterised by
a sealant (<NUM>,<NUM>) disposed on an end (<NUM>) of the division wall (<NUM>,<NUM>) and configured to be compressed between the end of the division wall (<NUM>,<NUM>) and an outer skin (<NUM>);
wherein the division wall (<NUM>,<NUM>) is T-shaped.