Cavity Acoustic Tone Suppression

Abstract

A cavity system (300-600) is provided. The cavity system comprises a cavity (2) and a spoiler (304-604). The spoiler (304-604) comprises at least one plate (4) having a leading face and a trailing face, and a wavy edge. The spoiler (304-604) is positioned proximate a leading edge (14) of the cavity (2), the leading edge (14) being relative to an actual or intended flow direction (3) of a fluid across the cavity (2), and the spoiler (304-604) is oriented with a longitudinal axis (1) of the spoiler perpendicular or oblique to the actual or intended flow direction (3) such that the leading face faces toward the flow direction (3).

Description

[Technical Field]

[0001] The present invention relates to methods and systems for suppressing acoustic tones and / or resonances and / or noise and / or other acoustic tonal effects in a cavity when the cavity is moving relative to an ambient fluid such as air. The present invention relates particularly, but not exclusively, to such methods and systems for vehicle cavities. Example vehicles include aircraft, and thus example cavities include bays such as weapon bays and landing gear bays. [Background technology]

[0002] When a cavity moves through an ambient fluid, for example, an aircraft bay moving through the air, a shear layer forms between the moving ambient air (from a reference point on the aircraft) and the quiescent air within the cavity. Vortices shed from the leading edge of the cavity, grow as they travel down the shear layer, and strike the aft wall of the bay, causing noise radiation. Sound waves also travel upstream back inside the bay. The fluctuating pressure of the sound waves can cause vortices to shed from the leading edge cavity lip or increase their growth rate, resulting in a series of vortices forming below the shear layer at a selective velocity related to the frequency of the upstream sound wave. The vortices grow into large-scale structures as they propagate downstream through the shear layer and then strike the aft wall of the bay at a characteristic velocity. This results in the generation of acoustic noise at a characteristic velocity, sometimes referred to as an acoustic tone at a characteristic frequency.

[0003] The frequency of the tone can be formulated using Rossiter's equation: It can be seen that there is a feedback loop formed by the passing vortex and the sound wave propagating upstream.

[0004] Similar problems exist in other types of vehicles, such as high performance cars with open roofs or windows, or marine vessels with open hatches that are subject to high impinging wind speeds.

[0005] Therefore, there is a need for a lightweight dampening mechanism to reduce the acoustic noise within the cavity that travels through the fluid.

[0006] In aircraft, it is known to employ spoiler arrangements to divert airflow above and beyond the cavity, i.e., above and beyond any boundary layer or expected shear layer, so that the above-mentioned effects do not occur.

[0007] In other words, existing standard mitigators aim to provide some form of noise suppression by diverting the shear layer away from the cavity, thickening (diverging) the shear layer, or generating small-scale turbulence that creates small vortices within the shear layer. In this way, the large-scale vortices that are part of the tone generation process are prevented from forming in the shear layer. A way to prevent small-scale vortices from becoming larger vortices is to increase the thickness of the shear layer, because the small vortices will move at different speeds, which in turn reduces temporal coherence and prevents larger vortices from forming. Various mitigator / spoiler options have different mechanisms that help reduce noise and tone resonance.

[0008] The inventors have realised how such spoilers can be improved to further reduce acoustic noise within the cavity. Summary of the Invention

[0009] According to a first aspect of the present invention, there is provided a cavity system comprising a cavity and a spoiler, the spoiler comprising at least one plate having a leading face and a trailing face and a wavy edge in longitudinal cross section, the spoiler being positioned proximate to a leading edge of the cavity, the leading edge being relative to an actual or intended flow direction of a fluid across the cavity, the spoiler being oriented with its longitudinal axis perpendicular or at an oblique angle to the actual or intended flow direction, with its leading face facing towards the flow direction.

[0010] Advantageously, having a wavy spoiler surface facing the cavity tends to increase the likelihood of a change in or an increase in the number of fine-scale turbulence sources, with a corresponding increase in the number of small vortices and / or thicker shear layers and / or an increase in the disruption of the temporal coherence of the small vortices. Any such effect can further improve the suppression performance of the suppression system.

[0011] The spoiler may be arranged to rotate or slide relative to the leading edge.

[0012] The wavy edge may be integrally formed on the edge of the or each plate opposite the edge of the or each plate adjacent the cavity. Alternatively, the wavy edge may be attached to the edge of the or each plate. The wavy edge may be offset from the edge of the or each plate opposite the edge of the or each plate adjacent the cavity. The wavy edge may protrude from the surface of the or each plate.

[0013] The cavity system may include a connecting structure for coupling the wavy edge to the or each plate, the connecting structure having a first end attached to the front face or rear face of the or each plate and a second end including the wavy edge.

[0014] The connecting structure may comprise a horizontal member having a first end and extending substantially horizontally from the front or rear face of the or each plate, and a vertical member joined substantially perpendicular to the horizontal member and having a second end.

[0015] The cavity system may include a first connecting structure and a second connecting structure for coupling the first wavy edge and the second wavy edge to the plate or each plate, the first connecting structure having a first end attached to the front surface of the plate or each plate and a second end having the first wavy edge, and the second connecting structure having a first end attached to the rear surface of the plate or each plate and a second end having the second wavy edge.

[0016] The first wavy edge may include a first set of teeth and the second wavy edge may include a second set of teeth, the first set of teeth being offset from the second set of teeth along the longitudinal axis of the spoiler.

[0017] The wavy edge may include a plurality of teeth. A first tooth of the plurality of teeth may be disposed closer to the leading edge than a second tooth of the plurality of teeth. At least one of the teeth may be oriented such that the plane of its front surface is twisted relative to the adjacent front surface of the plate. A first tooth of the plurality of teeth may be longer than a second tooth of the plurality of teeth. Alternatively, the teeth may all be of uniform height. The teeth may be generally triangular in longitudinal cross section. Alternatively, the teeth may have a generally square, rectangular, or curved shape in longitudinal cross section.

[0018] The percentage of the spoiler area that is occupied by teeth may be 75% or less.

[0019] The spoiler may comprise a plurality of plates, the free edge of each of which is connected to the free edge of an adjacent plate, wherein an angle of 10 to 170 degrees is formed between two adjacent plates such that the plates form a zigzag in cross section. In other words, in cross section, the spoiler has a zigzag shape. Preferably, an angle of 70 to 110 degrees is formed between two adjacent plates.

[0020] The first plate may comprise a first portion of one of the teeth and the second plate comprises a second portion of one of the teeth.

[0021] The front and / or rear surface of the or each plate may be non-planar in transverse cross-section. In transverse cross-section, the front surface of the spoiler may comprise a plurality of peaks and valleys. The front and / or rear surface of the or each plate may be sinusoidal in transverse cross-section.

[0022] The rear face of the spoiler may match the contour of the front face of the spoiler. Alternatively, the rear face of the spoiler may be flat.

[0023] According to a second aspect of the present invention, there is provided an aircraft comprising the cavity system according to the first aspect, wherein the cavity is a weapons bay. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a schematic illustration (not to scale) of a perspective view of a cavity acoustic tone suppression system. [Figure 2] 1 is a schematic illustration (not to scale) of a perspective view of a cavity acoustic tone suppression system. [Figure 3] 1 is a schematic illustration (not to scale) of a perspective view of a spoiler for use in a cavity tone suppression system. [Figure 4] 1 is a schematic illustration (not to scale) of a perspective view of a spoiler for use in a cavity tone suppression system. [Figure 5a] 1 is a schematic illustration (not to scale) of a perspective view of a spoiler for use in a cavity tone suppression system. [Figure 5b] FIG. 5b is a schematic front view (not to scale) of the spoiler of FIG. 5a. [Figure 6] 1 is a schematic illustration (not to scale) of a perspective view of a cavity acoustic tone suppression system. DETAILED DESCRIPTION OF THE INVENTION

[0025] It will be understood that relative terms such as horizontal and vertical, top and bottom, above and below, forward and aft, etc. are used above merely for ease of reference to the figures, and that these terms are not so limiting, and that rather than truly horizontal and vertical, top and bottom, etc., any two different orientations or positions, etc., can be realized. In particular, for convenience, the cavities are shown in the figures as opening at the top of the page, and therefore, for convenience, the term "top" is used to refer to the opening of the cavity, and the term "above" refers to being further away from the cavity. However, while the present disclosure also refers to cavities positioned, for example, below an aircraft wing or fuselage, i.e., upside down from what is shown in the figures, it will be understood that the descriptive use of the term "top" still refers to the open portion of the cavity, and the descriptive use of the word "above" still refers to being further away from the cavity.

[0026] The following concepts are modifications of existing mitigators. The described shapes help reduce undesirable acoustic effects. By changing the geometry of the mitigator (i.e., spoiler) to include a lateral component, it is possible to add a lateral component to the airflow over the mitigator, which reduces the energy of the airflow in the cavity to some extent. Adding an additional sharp edge to the top of the mitigator increases the amount of vortex shedding and reduces the compactness of the shear layer, both of which should reduce undesirable acoustics and noise. Therefore, the modifications of existing spoilers described below improve their mitigating effect in the cavity.

[0027] 1 is a schematic illustration (not to scale) of a perspective view of a first embodiment of a cavity acoustic tone suppression system 100 (hereinafter referred to as suppression system 100). Suppression system 100 comprises a cavity 2 and a substantially plate-shaped member (hereinafter referred to as a spoiler) 104 that, in use, extends from cavity 2 into the ambient airflow.

[0028] In this embodiment, the spoiler 104 has curved (i.e. non-planar wavy) leading and trailing surfaces. The leading surface of the spoiler 104 is the surface facing the incident flow 3.

[0029] In the illustrated embodiment, the spoiler 104 is sinusoidal or corrugated in cross section, i.e., when the spoiler 104 is viewed from above (i.e., in a plan view). In other words, the spoiler 104, or at least its front surface, comprises an arrangement of adjacent convex and concave surface areas. The spoiler 104 being sinusoidal, i.e., having a transverse component, at least across its front surface removes energy from the incident flow 3. In this context, sinusoidal means that the front surface of the spoiler 104 has peaks and valleys, with the peaks being closer to the front wall (front wall 8) of the cavity 2 than the valleys. In the illustrated embodiment, the aft surface of the spoiler 104 matches the contour of the front surface.

[0030] Instead of the spoiler 104 being sinusoidal (ie, having a plurality of adjacent convex and concave regions), the spoiler 104 may be fully convex or fully concave along its length.

[0031] The spoiler 104 may be made from any material strong enough to withstand high freestream speeds and high noise levels. For example, the spoiler 104 may be made from a composite material such as titanium or carbon fiber. Alternatively, the spoiler 104 may be made from plastic or aluminum. The spoiler 104 may be made from the same material as the outer skin of the vehicle to which it is attached. The spoiler 104 may be made from gauze or mesh.

[0032] In this embodiment, cavity 2 is rectangular and has a planar base. Cavity 2 further comprises a front wall 8, a rear wall 10, and two side walls 12, which are defined relative to the actual or intended flow direction 3. In this embodiment, these walls are all perpendicular to the planar base. At the top of cavity 2, cavity 2 comprises a leading edge 14, a rear edge 16, and two side edges 18, respectively, for each of these walls.

[0033] Also shown in FIG. 1 is a plane of a surface 19, for example the skin of a vehicle such as an aircraft, that surrounds cavity 2 (i.e., the surface 19 where a gap or large change in orientation in that surface 19 creates the opening of cavity 2).

[0034] The spoiler 104 may be rotatably mounted to the side wall 12, front wall 8, or rear wall 10 of the cavity 2, or may otherwise be rotatably mounted to a surface 19 surrounding the exterior of the cavity. In other words, the suppression system 100 may include a hinge coupled to the spoiler 104 to allow the spoiler 104 to rotate relative to the cavity 2. Examples of such hinges include an offset hinge or a leaf hinge, thereby positioning the spoiler 104 to rotate into the airflow away from the body of the vehicle during use. For example, the cavity 2 may be an aircraft weapons bay, and when the weapons bay door is open, the spoiler 104 may translate from a first, stowed position, in which its front surface is parallel to the bottom of the cavity 2, to a second, deployed position, in which its front surface is perpendicular to the airflow direction 3.

[0035] Alternatively, the spoiler 104 may be slidably mounted to the front wall 8, rear wall 10, or side wall 12 so that it can slide from a stowed position into the airflow in a deployed position in use without rotating. In yet a further embodiment, the spoiler 104 may be arranged to both slide and rotate in order to move into position in the airflow when the cavity 2 is open (i.e., in use).

[0036] The hinge or sliding mechanism may be motorized, may be mechanically actuated by the movement of a door covering the cavity 2, or may be spring loaded.

[0037] In the illustrated embodiment, the spoiler 104 is a convoluted path, but is positioned with its surface extending across the width of the cavity 2, i.e., transverse to the flow direction 3; that is, in this embodiment, the longitudinal axis 1 of the spoiler 104, rather than the entire front surface of the spoiler 104, is parallel to the leading and trailing edges 14 and 16 and the walls 8, 10, so that the flow direction 3 impinges on the wavy front surface of the spoiler 104. The longitudinal axis 1 of the spoiler 104 is a straight line passing through both ends of the spoiler 104. Thus, in this embodiment, the spoiler 104 is positioned perpendicular to the flow direction 3.

[0038] In this embodiment, the spoiler 104 is positioned downstream of the leading edge 14 (i.e., above the cavity 2), with the spoiler 104 positioned closer to the leading edge 14 than to the aft edge 16. More specifically, in this embodiment, the spoiler 104 is positioned such that the distance of the spoiler 104 from the leading edge 14 is equal to 0.02 to 0.07 times the total distance between the leading edge 14 and the aft edge 16. Preferably, this distance is 0.05 times the total distance between the leading edge 14 and the aft edge 16. In an alternative embodiment, the spoiler 104 is positioned in front of the cavity 2 relative to the flow direction 3. The spoiler 104 may be positioned in front of the cavity 2 by a distance equal to 0.01 to 0.06 (preferably 0.02) multiplied by the total distance between the leading edge 14 and the aft (trailing) edge 16 .

[0039] In this embodiment, the spoiler 104 is positioned so that its lowest end (when viewed on the page) is approximately level with the top (opening) of the cavity 2, i.e., approximately level with the leading edge 14. In other words, in this embodiment, the spoiler 104 does not extend into the cavity 2. However, this does not necessarily have to be the case, and in other embodiments, a portion of the spoiler 104 may extend into the cavity 2.

[0040] In this embodiment, the spoiler 104 extends completely across the width of the cavity 2. However, this does not necessarily have to be the case, and in other embodiments the spoiler 104 may extend across only a portion of the width of the cavity 2, which is preferably at least half the width of the cavity 2, and even more preferably at least three-quarters (¾) or more of the width of the cavity 2.

[0041] The spoiler 104 serves to increase the thickness of the shear layer, which is the region between a line representing the top of the spoiler 104 (i.e., furthest from cavity 2) and a line representing the bottom of the spoiler 104 (i.e., closest to cavity 2). Correspondingly, the thickness of the shear layer at any point along cavity 2 is the distance between the top of the shear layer and the bottom of the shear layer.

[0042] With reference to FIG. 1 , the spoiler 104 is defined as being sinusoidal across its longitudinal axis 1 (i.e., the spoiler 104 has a leading edge and a trailing edge, both of which are sinusoidal), although one skilled in the art will appreciate that other spoiler 104 designs will provide the same or similar effect. For example, in one embodiment, the trailing edge of the spoiler 104 is planar, and the leading edge of the spoiler 104 is sinusoidal. Instead of being sinusoidal, the leading edge or the leading and trailing edges may follow a cosine wave. Also alternatively, the leading edge or the leading and trailing edges of the spoiler 104 may be stepped at right angles in cross-section, i.e., when the spoiler 104 is viewed from above and below (i.e., a square wave pattern with peaks and valleys having right-angle corners). In other words, some areas (peaks) on the front face of the spoiler 104 are closer to the front wall 8 of the cavity 2 than other areas (valleys), but the longitudinal axis 1 of the spoiler 104 is parallel to the leading edge 14.

[0043] An alternative spoiler 204 configuration that provides an effect similar to that of spoiler 104 of Figure 1 is illustrated as part of suppression system 200 in Figure 2. Figure 2 is a view of the same suppression system 100 as shown in Figure 1, and the same reference numbers are used for the same features as used in the previous figure.

[0044] 2, the spoiler 204 has a zigzag shape. In other words, when a cross section of the spoiler 204 is viewed from top to bottom (i.e., in a plan view), the leading and trailing faces of the spoiler 204 form a series of connected angles (i.e., triangles with no base, or in other words, two straight lines connected at an acute, right, or obtuse angle) projecting in the direction of flow 3.

[0045] In one embodiment, the spoiler 204 is formed from a single sheet of material. In another embodiment, the spoiler 204 comprises a series of planar plates 4 (panels, sheets), with adjacent plates 4 joined at acute, obtuse, or right angles to each other. Thus, the spoiler 204 is formed with a series of sharp peaks and valleys along its path in the flow direction 3. Preferably, when viewed from above, adjacent plates 4 are arranged such that an angle between 10 degrees and 170 degrees is formed between them. Even more preferably, when viewed from above, adjacent plates 4 are arranged such that an angle of approximately 90 degrees is formed between them.

[0046] The number of plates 4 forming the spoiler 204 is two or more. In other words, the spoiler 204 includes at least one chevron. The depth of the chevron may be about 10 centimeters.

[0047] In one embodiment, there may be a flat portion (i.e., a gap or space) between each chevron. In other words, a portion of the front face of the spoiler 204 may be parallel to the leading edge 14.

[0048] The chevrons described above may have sides of equal length, with the axis of symmetry of each chevron (the axis passing through the apex) positioned perpendicular to the leading edge 14 .

[0049] Alternatively, the spoiler 204 may have a sawtooth cross section, where the two sides of the angle are not of equal length. For example, the plane of one plate 4 forming the spoiler 204 may be oriented perpendicular to the axis of the leading edge 14, while the connecting plates 4 may be arranged so that their planes are oblique to the leading edge 14, with the two free ends of each plate being equidistant from the leading edge 14.

[0050] As illustrated in Figures 3-6, spoilers 304-604 may include teeth 5 (ie, a series of protrusions). Figures 3-5b illustrate perspective cutaway views of various spoiler designs.

[0051] FIG. 3 illustrates a perspective view of a spoiler 304, the concept of which may be incorporated into the suppression system 100 / 200 described with reference to FIGS. 1 and 2. Here, the spoiler 304 is formed from two parts. The spoiler 304 comprises a plate 4 and one or more teeth 5. In the embodiment illustrated in FIG. 3, the teeth 5 and the plate 4 are integrally formed, i.e., the teeth 5 are formed on the upper surface (i.e., upper edge) of the plate 4. The plate 4 has the same general form as the spoiler 104 / 204 described with reference to FIGS. 1 and 2. In an alternative embodiment, the plate 4 is planar, i.e., flat over the majority of its front surface.

[0052] 3, all of the teeth 5 are shown as occupying the entire width of the top edge of the spoiler 304, but this need not be the case. The first tooth may be located closer to the front of the spoiler 304 than the second tooth, where both teeth are located on the top edge of the spoiler 304. In this way, air striking the spoiler 304 from flow direction 3 will tend to hit the first tooth before the second tooth, thereby introducing a change in vortex shedding.

[0053] In the illustrated embodiment, the teeth 5 all have the same longitudinal cross-sectional shape (a triangle with substantially equilateral sides when viewed along the flow direction 3 or from an elevational view) and are all the same size as one another. Instead of being triangular, the teeth 5 may be rectangular, rounded, semicircular, irregular, or square in longitudinal cross-section (i.e., when viewed along the flow direction 3 or from an elevational view). In other words, the teeth 5 may be more curved or rounded or flatter than the pointed teeth 5 illustrated. The teeth 5 may be much wider (i.e., longer in the direction of the longitudinal axis 1 of the spoiler 304) than illustrated. The teeth 5 may be wide and rounded so that the upper edge of the plate 4 appears to have a wave-like or sinusoidal wave shape in longitudinal cross-section.

[0054] In alternative embodiments, some teeth 5, or even one tooth of a set of teeth 5, may have a different cross-sectional shape or surface area than the other teeth 5. For example, a first tooth may be semicircular in cross section, while a second adjacent tooth may be rectangular in cross section.

[0055] In this embodiment, the teeth 5 are arranged on the plate 4 so that the face of each tooth 5 is parallel to the portion of the plate 4 to which it is attached, i.e., so that the front plane of each tooth 5 is generally perpendicular to the flow direction 3.

[0056] In this embodiment, the teeth 5 are all arranged in a symmetrical, evenly spaced arrangement, i.e., the teeth 5 are evenly distributed across the plate 4. One tooth is shown directly bonded to an adjacent tooth. Alternatively, there may be regular gaps between each tooth.

[0057] The teeth 5 are illustrated as forming approximately 10% of the total surface area of ​​the spoiler 304. This is for illustrative purposes only. The teeth 5 may be smaller or larger than illustrated, such that between 1% and 75% of the surface area of ​​the spoiler 304 is formed by the teeth 5. Preferably, between 5% and 15% of the surface area of ​​the spoiler 304 is formed by the teeth 5.

[0058] In operation, one effect of the spoiler 104 with multiple teeth 5 is to help increase the thickness of the shear layer compared to when the spoiler 304 with teeth 5 is not present, or even when the plate 4 is present but without the teeth 5. This is at least in part due to the teeth 5 disrupting or changing the air flow direction to deflect the flow both into and out of the cavity 2 (the latter nevertheless being near the top of the cavity 2).

[0059] The teeth 5 can increase the deflection of vortices into and / or out of the cavity 2, thereby further enhancing the thickening of the shear layer. Additionally or alternatively, the teeth 5 can act as an additional source of fine-scale turbulence that induces even smaller vortices, thus helping to provide even further loss of temporal coherence.

[0060] The teeth 5 may extend to different heights relative to one another. For example, a first tooth may be at height x, an adjacent second tooth may be at a different height y, and another tooth adjacent to the second tooth may be at height x. This is shown in Figure 6.

[0061] When the teeth 5 are arranged on a plate 4 having the shape described with reference to the spoiler 104 / 204 of Figures 1 and 2, the number of teeth 5 on the spoiler 104 / 204 is adjusted by varying the frequency and amplitude of the waves or the number of panels that make up the zigzag, as well as the width of each tooth.

[0062] In FIG. 4 , the teeth 5 are offset from the spoiler 404 along the axis of the flow direction 3. In other words, a connecting structure can be used to attach the teeth 5 to the plate 4 so that the teeth 5 protrude from the top of the spoiler 104 / 204. Here, the teeth 5 are connected to protrude upward from the rear surface of the plate 4. In an alternative embodiment, the teeth 5 protrude upward from the front surface of the plate 4. Also in an alternative embodiment, the teeth 5 protrude upward from both the front and rear surfaces of the plate 4, as illustrated in FIG. 5 a.

[0063] In the illustrated embodiment, the connecting structure comprises a horizontal member 7 and a vertical member 6. Those skilled in the art will appreciate that the horizontal member 7 need not be exactly horizontal, and the vertical member 6 need not be exactly vertical. One end of the horizontal member 7 is connected to the rear-facing surface of the plate 4. The vertical member 6 is attached to the free end of the horizontal member 7 at a substantially right angle (i.e., between 75 degrees and 105 degrees). Teeth 5 are located along the top edge of the vertical member 6, similar to that described above with reference to FIG. 3.

[0064] In alternative embodiments, the connecting structure may be a single member, such as a diagonal member that projects upwardly away from the face of the plate 4. Alternatively, the connecting structure may comprise only a vertical member 6 joined by its surface to the rear face of the plate 4.

[0065] 3, the teeth 5 are illustrated as extending along the entire length of the vertical member 6, and the vertical member 6 is illustrated as extending along the entire length of the plate 4. However, in other embodiments, there may be gaps between the teeth 5, the teeth 5 may extend only partially along the vertical member 6, or the vertical member 6 may extend only partially along the length of the plate 4.

[0066] By having teeth 5 offset from plate 4, vortex shedding tends to occur at different times, i.e., at different stages of shear layer formation (by providing sources of fine-scale turbulence at different times along the flow), thus tending to further increase the degree of disruption of temporal coherence between different vortices shed by different teeth 5, thus reducing noise and acoustic tones within cavity 2.

[0067] In Figure 5a, a first set of teeth 5a projects upward from the front face of the plate, and a second set of teeth 5b projects upward from the rear face of the plate 4. The first set of teeth 5a and the second set of teeth 5b (collectively 5) are attached to the plate 4 by the same connecting structure as described with reference to Figure 4.

[0068] Figure 5b shows the teeth 5 when viewed straight on from the front of the spoiler 504. The teeth 5a on one side of the spoiler 504 are offset along the longitudinal axis 1 of the spoiler 504 from the corresponding teeth 5b on the opposite side of the spoiler 504. In Figure 5b, the teeth 5 are viewed from the front, i.e., as they are seen when viewed along the flow direction 3. In other words, when the spoiler 504 is viewed from the front, all of the teeth 5 on both sides of the spoiler 504 are visible. This provides a similar effect to the spoilers 104 / 204 of Figures 1 and 2, in that the airflow strikes different parts of the spoiler 504 at different times.

[0069] The concepts outlined in Figures 3-5b can be combined. For example, in a set of teeth 5, the first tooth may be integrally formed with the top edge of the spoiler (as in Figure 3), while the second immediately adjacent tooth may be offset from the top edge of the spoiler (as in Figure 4), and the third immediately adjacent tooth is also integrally formed with the top of the spoiler.

[0070] 6 illustrates a further embodiment of a suppression system 600, similar to the suppression system 200 of FIG. 2, having a spoiler 604 with teeth 5 arranged on its upper surface, where adjacent teeth 5 are arranged at different heights. Each plate 4 is provided with half a tooth, such that two adjacent plates 4 form a single tooth.

[0071] In operation, the effect of the multiple teeth 5 spread at different heights across the span of the plate 4 is to help provide multiple sources of fine-scale turbulence that induce multiple small vortices at different heights. Due at least in part to the thicker shear layer and, in particular, the multiple heights at which vortices are shed due to the different heights of the different teeth 5, the vortices tend not to combine into larger vortices. By providing a thicker shear layer and the multiple heights at which vortices are shed due to the different heights of the different teeth 5, vortices 30 closer to the top of the shear layer (i.e., closer to the ambient fluid flow) propagate downstream faster than vortices closer to the bottom of the shear layer (i.e., closer to the quiescent air within the cavity 2). Thus, the vortices arrive at a given point downstream at different times, i.e., there is a loss of temporal coherence, thereby disrupting the traditional tendency to form large-scale turbulent structures that would otherwise play a significant role in generating undesirable acoustic tones. Furthermore, due to the additional height achieved overall by using the full height of the spoiler 604, different boundary layer thicknesses tend to be easily accommodated (without the need for position adjustments).

[0072] By providing teeth 5 of different heights relative to the top of wavy spoiler 604, different tooth 5 heights are located at different distances along the streamwise direction 3 from the leading edge 14. This helps to encourage vortex shedding to occur at different times, i.e., at different stages of shear layer development (by providing sources of fine-scale turbulence at different points along the streamwise direction), thus further increasing the degree of disruption of temporal coherence between different vortices shed by different teeth 5. A similar benefit, although less effective, is achieved if all teeth 5 are of uniform height along the wavy spoiler 104 / 204 shown in Figures 1 and 2.

[0073] In general, it will be appreciated that any non-uniformity introduced into the configuration of one or more individual teeth 5, and / or between one or more different teeth 5, and / or their relative placement / location, etc., may serve to provide a potential change or increase in the number of sources of fine-scale turbulence, with a corresponding increase in the number of small vortices and / or thicker shear layers and / or increased disruption of the temporal coherence of the small vortices. Any such effect may further improve the suppression performance of the suppression system 100 / 200.

[0074] In the above embodiment, the teeth 5 are all spaced apart in a symmetrical, evenly spaced arrangement, i.e., the teeth 5 are evenly distributed across the top surface of the plate 4. However, this need not be the case, and in other embodiments, some or all of the teeth 5 are unevenly distributed across the top surface of the plate 4 (i.e., the spacing between adjacent teeth 5 may not be uniform). There may also be irregular gaps between the teeth 5. An uneven distribution, particularly an uneven height distribution, serves to further disrupt the temporal coherence of small vortices. Furthermore, the teeth 5 may extend only partway along the length of the plate 4. For example, the teeth 5 may be centered at the midpoint of the plate 4 and extend only 50% along the plate 4. Preferably, the teeth 5 extend between 50% and 100% along the length of the plate 4.

[0075] In the above embodiment, the plane of each tooth is arranged parallel to the plane of plate 4 at the point where the tooth is connected to plate 4. In other words, if plate 4 is parallel to leading edge 14, then the leading plane of tooth 5 is parallel to leading edge 14. However, this does not necessarily have to be the case, and in other embodiments, one or more of teeth 5 may be twisted relative to plate 4, i.e., the plane of the tooth may not be parallel to the plane of plate 4.

[0076] Instead of being disposed perpendicular to the flow direction 3, the spoilers 104-604 may be angled relative to the flow direction 3 (in a vertical plane as viewed in the figures). In this embodiment, the front faces of the spoilers 104-604 form an acute angle with the impinging flow direction 3. In other words, a first region of the front face of the spoiler 104-604 is located closer to the front of the cavity 2 than a second region of the front face of the spoiler 104-604. In particular, if the spoiler 104 has a wavy front face, as in FIG. 1, a longitudinal axis passing through each end of the spoiler 104 may form an obtuse angle with the impinging flow direction 3.

[0077] Returning to a more general description of further embodiments, in the above embodiments, the spoilers 104-604 are positioned downstream of the leading edge, and the spoilers 104-604 are positioned such that the distance of the spoilers 104-604 from the leading edge 14 is equal to 0.05 multiplied by the total distance between the leading edge 14 and the aft edge 16. However, this need not be the case, and in other embodiments, the spoilers 104-604 may be positioned anywhere downstream of the leading edge 14, close to the leading edge 14. This may include, for example, any location downstream of the leading edge 14 closer to the leading edge 14 than the aft edge 16, since some degree of suppression would still tend to occur. Preferably, however, the spoilers 104-604 are positioned closer to the leading edge 14, since in this case a greater degree of suppression would tend to occur. For example, not only is it preferable to position the leading edge 14 downstream at a distance of 0.05 times the total distance between the leading edge 14 and the aft edge (trailing edge) 16, but it is even more preferable to position it at a distance of 0.05 times the total distance or less, more generally it is also preferable to position it at a distance of 0.1 times the total distance or less, and even more generally it is even more preferable to position it at a distance of 0.2 times the total distance or less.

[0078] In the above embodiments, the spoiler 104-604 is positioned downstream of the leading edge 14 (i.e., above the cavity 2). However, this need not be the case, and in other embodiments, the spoiler 104-604 may be positioned upstream of the leading edge 14, i.e., above the surface 19 rather than above the cavity 2. In such embodiments, the spoiler 104-604 may be positioned upstream from the leading edge 14 at any position proximate to the leading edge 14, which may be any distance from the leading edge that is less than or equal to half the distance between the leading edge 14 and the aft edge (trailing edge) 16. However, preferably, the spoiler 104-604 is positioned upstream from the leading edge 14 at a distance from the leading edge that is no greater than 0.2 multiplied by the distance between the leading edge 14 and the aft edge (trailing edge) 16, more preferably no greater than 0.1 multiplied by the distance between the leading edge 14 and the aft edge (trailing edge) 16, and even more preferably no greater than 0.05 multiplied by the distance between the leading edge 14 and the aft edge (trailing edge) 16.

[0079] In still further embodiments, the spoilers 104-604 may be positioned directly above the leading edge 14. It will also be appreciated that in embodiments in which the spoilers 104-604 are disposed at an oblique angle to the flow direction 3, the different heights of each of the spoilers 104-604 may be located at any two or three of the above possibilities, i.e., downstream of the leading edge 14, directly above the leading edge 14, and upstream of the leading edge 14.

[0080] In the above embodiment, cavity 2 is rectangular and has a planar base. Cavity 2 further includes a front wall 8, a rear wall 10, and two side walls 12, all defined relative to actual or intended airflow direction 3, at right angles to the planar base. However, these particular cavity details are not required, and any other cavity shape may be present in other embodiments. For example, there need not be only four walls, the walls need not be upright or perpendicular, the cavity may be defined by one or more walls that form a curved or partially curved perimeter relative to the cavity, the perimeter may be irregularly shaped, one or more walls may be sloped, the base and / or one or more walls may be wavy or sloped, etc. However, the more directly defined or present leading edge 14 (relative to actual or intended airflow direction 3) is, the more throttling tends to occur.

[0081] Additionally, in embodiments having cavity 2 shapes as described above, including irregularly shaped cavities 2, it will be understood that those skilled in the art may modify the directions described above as parallel, transverse, perpendicular, etc., suitable for regularly shaped cavities 2 to provide other directions that achieve, at least to some extent, the functionality corresponding to the directions described above as parallel, transverse, perpendicular, etc. Also, even when cavity 2 has a regular shape, in still further embodiments, directions that include resolved portions of the described parallel, transverse, perpendicular, and similar directions may be implemented instead of entirely parallel, transverse, perpendicular, and similar directions. For example, spoilers 104-604 may traverse rectangular cavity 2 in transverse directions that are oblique to the described directions but include resolved elements of their direction, and therefore their effect, at, for example, 15°, 30°, or 45° relative to a direction parallel to leading edge 14.

[0082] While the above-described embodiments of the suppression systems 100-600 are suitable for application to aircraft such as commercial airliners, military fighter jets, or helicopters, they are also suitable for other forms of vehicles. For example, the suppression systems 100-600 are applicable to land vehicles such as trains and high-performance cars, as well as naval vessels such as yachts and submarines. The ambient fluid is described above as an airflow (i.e., air stream), but may also be water. The cavity may be a wheel well, torpedo tube, weapon bay, window, sunroof, open superstructure, or any other cavity through which a fluid may travel. The inventions described in the claims of the present application as originally filed are set forth below. [C1] A cavity and a spoiler are provided, the spoiler comprises at least one plate having a front surface and a rear surface and a wavy edge in longitudinal cross section; the spoiler is positioned proximate a leading edge of the cavity, the leading edge being relative to an actual or intended flow direction of fluid across the cavity; 10. A cavity system wherein the spoiler is oriented with the front surface facing toward the flow direction and the longitudinal axis of the spoiler perpendicular or oblique to the actual or intended flow direction. [C2] A cavity system as described in C1, wherein the wavy edge is integrally formed on an edge of the or each plate opposite an edge of the or each plate adjacent the cavity. [C3] A cavity system as described in C1, wherein the wavy edge is offset from the edge of the or each plate opposite the edge of the or each plate adjacent the cavity. [C4] A cavity system as described in C3, comprising a connection structure for coupling the wavy edge to the or each plate, the connection structure having a first end attached to the front surface of the or each plate or the rear surface of the or each plate, and a second end comprising the wavy edge. [C5] a first connecting structure and a second connecting structure for connecting the first wavy edge and the second wavy edge to the or each plate; the first connecting structure has a first end attached to the front surface of the or each plate and a second end having the first wavy edge; the second connecting structure having a first end attached to the rear surface of the or each plate and a second end having the second wavy edge; Cavity system as described in C4. [C6] 5. The cavity system of claim 4, wherein the first wavy edge comprises a first set of teeth and the second wavy edge comprises a second set of teeth, the first set of teeth being offset from the second set of teeth along the longitudinal axis of the spoiler. [C7] A cavity system according to any one of C1 to C4, wherein the wavy edge comprises a plurality of teeth. [C8] The cavity system of C7, wherein a first tooth of the plurality of teeth is positioned closer to the leading edge than a second tooth of the plurality of teeth. [C9] 9. The cavity system of claim 6, 7, or 8, wherein the teeth are generally triangular in longitudinal cross section. [C10] The cavity system according to any one of C6 to C9, wherein the ratio of the area of ​​the spoiler occupied by the teeth is 75% or less. [C11] 11. A cavity system according to any one of claims 1 to 10, wherein the spoiler comprises a plurality of plates, the free edge of each plate of the plurality of plates being joined to the free edge of an adjacent plate, wherein an angle of 10 degrees to 170 degrees is formed between two adjacent plates such that the plurality of plates form a zigzag in cross section. [C12] The cavity system of claim C11 when dependent on any one of claims C7 to C10, wherein a first plate comprises a first portion of one of the teeth and a second plate comprises a second portion of the one of the teeth. [C13] A cavity system according to any one of C1 to C12, wherein the front and / or rear surface of the or each plate is non-planar in cross-section. [C14] A cavity system as described in C12, wherein the front and / or rear surface of the or each plate is sinusoidal in cross-section. [C15] An aircraft comprising the cavity system according to any one of C1 to C14, wherein the cavity is a weapon bay.

Claims

1. A cavity and a spoiler are provided, the spoiler comprises at least one plate having a front face and a rear face and a wavy edge in longitudinal cross section; the spoiler is positioned proximate a leading edge of the cavity, the leading edge being relative to an actual or intended flow direction of fluid across the cavity; the spoiler is positioned with the front surface facing towards the flow direction and the longitudinal axis of the spoiler perpendicular or oblique to the actual or intended flow direction; a cavity system, wherein the spoiler has the wavy edge at a position offset from an edge of the plate opposite an edge of the plate adjacent to the cavity, or from an edge of each plate opposite an edge of each plate adjacent to the cavity.

2. 2. The cavity system of claim 1, further comprising a connecting structure for coupling the wavy edge to the or each plate, the connecting structure having a first end attached to the front face of the or each plate or the rear face of the or each plate, and a second end comprising the wavy edge.

3. a first connecting structure and a second connecting structure for connecting the first wavy edge and the second wavy edge to the or each plate; the first connecting structure has a first end attached to the front surface of the or each plate and a second end having the first wavy edge; the second connecting structure having a first end attached to the rear surface of the or each plate and a second end having the second wavy edge; The cavity system of claim 2 .

4. 4. The cavity system of claim 3, wherein the first wavy edge comprises a first set of teeth and the second wavy edge comprises a second set of teeth, the first set of teeth being offset from the second set of teeth along the longitudinal axis of the spoiler.

5. The cavity system of claim 1 , wherein the wavy edge comprises a plurality of teeth.

6. The cavity system of claim 5 , wherein a first tooth of the plurality of teeth is located closer to the leading edge than a second tooth of the plurality of teeth.

7. The cavity system of claim 5 , wherein the teeth are generally triangular in longitudinal cross section.

8. The cavity system of claim 5 , wherein the teeth occupy 75% or less of the area of ​​the spoiler.

9. 10. The cavity system of claim 1, wherein the spoiler comprises a plurality of plates, adjacent plates of the plurality of plates joined at an angle, wherein an angle between the adjacent plates is between 10 degrees and 170 degrees such that the plurality of plates form a zigzag.

10. 10. The cavity system of claim 9, wherein the wavy edge comprises a plurality of teeth, a first plate comprising a first portion of one of the teeth, and a second plate comprising a second portion of the one of the teeth.

11. 2. A cavity system according to claim 1, wherein the front and / or rear surface of the or each plate is non-planar in cross-section.

12. 11. A cavity system according to claim 10, wherein the front and / or rear surface of the or each plate is sinusoidal in cross-section.

13. An aircraft comprising a cavity system according to any one of claims 1 to 12, wherein the cavity is a weapons bay.

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