Patent Description:
A gas turbine engine typically includes at least a compressor section, a combustor section and a turbine section. The compressor section pressurizes air into the combustion section where the air is mixed with fuel and ignited to generate an exhaust gas flow. The exhaust gas flow expands through the turbine section to drive the compressor section and, if the engine is designed for propulsion, a fan section.

The compressor and turbine sections may include multiple stages of rotatable blades and static vanes. Each section may define one or more passages for communicating airflow to cool portions of the engine. Acoustic waves may be introduced into air in the passages from vibrations caused by operation of the engine.

<CIT>, which is prior art according to Art <NUM>(<NUM>) EPC only, discloses a gas turbine engine component for acoustic attenuation.

<CIT> discloses a prior art gas turbine combustion acoustic damping system.

According to a first aspect of the present invention, there is provided a section for a gas turbine engine as set forth in claim <NUM>.

In an embodiment of the above, the rotating structure includes a hub carrying a plurality of blades.

In an embodiment of any of the above, the hub is a hub of a high pressure compressor in the gas turbine engine.

In an embodiment of any of the above, at least one of the plurality of apertures is defined by an offset of the flow guide assembly from a baseline geometry of the flow guide assembly.

In an embodiment of any of the above, a point P is defined along a length of the flow guide assembly. The plurality of apertures are arranged between the point P and an outlet portion of the flow guide assembly.

In an embodiment of any of the above, the plurality of apertures are arranged in a spiral pattern.

In an embodiment of any of the above, the point P is a distance from an outlet portion of the flow guide assembly that is approximately equal to an acoustic wavelength associated with an acoustic-structural coincidence frequency in the flow path.

In an embodiment of any of the above, a percent open area (POA) of the plurality of apertures increases from the point P to the outlet portion of the flow guide assembly.

In an embodiment of any of the above, the POA of the plurality of apertures increases from about <NUM>% at point P to less than about <NUM>% near the outlet portion of the flow guide assembly.

In an embodiment of any of the above, the POA of the plurality of apertures increases from about <NUM>% at point P to about <NUM>% near the outlet portion of the flow guide assembly.

In an embodiment of any of the above, one or more circumferential rows includes three rows.

In an embodiment of any of the above, a circumferential row of apertures are adjacent the inlet portion.

In an embodiment of any of the above, the diameter of the plurality of apertures in the one or more circumferential rows increases from the inlet portion to the outlet portion.

According to a further aspect of the present invention, there is provided a gas turbine engine as set forth in claim <NUM>.

In an embodiment of the above, at least some of the acoustic waves are generated by vibration of the seal.

In an embodiment of any of the above, point P is defined along a length of the flow guide assembly, and the plurality of apertures are arranged between the point P and an outlet portion of the flow guide assembly.

In an embodiment of any of the above, the flow guide assembly is a structure that comprises a single-layered wall.

According to a further aspect of the present invention, there is provided a method of disrupting acoustic waves in a flow path of a gas turbine engine as set forth in claim <NUM>.

<FIG> schematically illustrates an example gas turbine engine <NUM>. However, it should be understood the disclosure herein is applicable to other engine architectures as well.

In the example engine <NUM>, the fan section <NUM> drives air along a bypass flow path B in a bypass duct defined within a nacelle <NUM>, and also drives air along a core flow path C for compression and communication into the combustor section <NUM> then expansion through the turbine section <NUM>.

The fan section <NUM> of the engine <NUM> is designed for a particular flight condition-typically cruise at about <NUM> Mach and about <NUM>,<NUM> feet (<NUM>,<NUM> meters).

<FIG> shows selected portions of a section <NUM> of a gas turbine engine <NUM>. Section <NUM> can be incorporated into compressor section <NUM> or turbine section <NUM> of engine <NUM>, for example. In a particular example, section <NUM> is incorporated into the high pressure compressor <NUM>. Each airfoil <NUM> includes a platform <NUM> and an airfoil section <NUM> extending in a radial direction R from the platform <NUM> to a tip <NUM>. The airfoil section <NUM> generally extends in a chordwise or axial direction X between a leading edge <NUM> and a trailing edge <NUM>. A root section <NUM> of the airfoil <NUM> is mounted to, or integrally formed with, the rotor <NUM>. A blade outer air seal (BOAS) <NUM> is spaced radially outward from the tip <NUM> of the airfoil section <NUM>. The tips <NUM> of each of the airfoil sections <NUM> and adjacent BOAS <NUM> are in close radial proximity to reduce the amount of gas flow that escapes around the tips <NUM> through a corresponding clearance gap.

A vane <NUM> is positioned along the engine axis A and adjacent to the airfoil <NUM>. The vane <NUM> includes an airfoil section <NUM> extending between an inner platform <NUM> and an outer platform <NUM> to define a portion of the core flow path C. The turbine section <NUM> includes an array of airfoils <NUM>, vanes <NUM>, and BOAS (blade outer air seal) <NUM> arranged circumferentially about the engine axis A. An array of the BOAS <NUM> are distributed about an array of the airfoils <NUM> to bound the core flow path C. The BOAS <NUM> and vanes <NUM> can be secured to the engine case <NUM>, for example. The engine case <NUM> provides a portion of the engine static structure <NUM> (<FIG>) and extends along the engine axis A.

Turning now to <FIG> illustrates a detail view of the section <NUM>. The section <NUM> generally includes a rotating portion and a stationary portion. In this example, the rotating portion is a rotor <NUM> and the stationary portion is part of the engine static structure <NUM>, such as an inner engine case <NUM>. However, other locations of the engine <NUM> with adjacent rotating and static structures can benefit from the teachings herein, such as the low pressure compressor <NUM> or one of the turbines <NUM>, <NUM> (<FIG>). Furthermore, systems other than gas turbine engines can also benefit from the teachings disclosed herein, including ground-based power generation systems.

In the example of <FIG>, the rotor <NUM> has a hub <NUM> that carries a plurality of blades or airfoils <NUM>. In this example, the hub <NUM> is a compressor hub <NUM>. More particularly, the hub <NUM> is a rear hub of the high pressure compressor <NUM>. The airfoils <NUM> can be arranged in one or more stages (an aftmost stage shown for illustrative purposes). The hub <NUM> and airfoils <NUM> are rotatable about longitudinal axis A. The rotor <NUM> can be mechanically coupled to a turbine, such as high pressure turbine <NUM> (<FIG>).

A rotating seal <NUM> extends outwardly from the hub <NUM> to establish a sealing relationship with a row of stationary vanes <NUM> (one shown for illustrative purposes) distributed about the longitudinal axis A and a seal land <NUM> on associated supporting structure. In one example, the seal <NUM> includes one or more knife edge seals. Each seal <NUM> can include one or more segments arranged about the longitudinal axis A to define a substantially hoop-shaped or annular geometry.

The section <NUM> includes a flow guide assembly <NUM> that is dimensioned to guide flow F along a flow path <NUM>. The flow F can be leaked air from the core flow path C, for example. The flow guide assembly <NUM> is generally between the rotating structure (here, the rotor <NUM>/hub <NUM>) and the stationary structure (here, the inner engine case <NUM>) in the section <NUM>. In this example, the flow guide assembly <NUM> comprises a single-layered wall. In a further example, the flow guide assembly <NUM> comprises a metallic material, such as a high temperature metal or alloy.

In the example of <FIG>, the flow guide assembly geometrically tracks at least a portion the rotating structure, the hub <NUM>, and defines a flow path <NUM> between the flow guide assembly <NUM> and the hub <NUM>. In particular, the flow guide assembly <NUM> has a straight portion <NUM> that curves away from the hub <NUM> at the outlet portion 80c of the flow path <NUM>. In particular, at least the intermediate portion 80b of the flow path <NUM> slopes radially inward from the inlet portion 80a to the outlet portion 80c with respect to the longitudinal axis A, with the inlet portion 80a radially outward of the outlet portion 80c. Walls of the hub <NUM> that define the flow path <NUM> slope radially inward from the inlet portion 80a toward the engine longitudinal axis A such that the walls more gradually taper towards the outlet portion 80c.

In other examples, the flow path <NUM> can be defined between the flow guide assembly <NUM> and a stationary structure, for instance. Furthermore, in the example of <FIG>, the flow guide assembly <NUM> is mounted or otherwise secured to the stationary structure, e.g., the inner case <NUM> or another portion of the engine static structure <NUM> such that the flow path <NUM> is defined between surfaces of the hub <NUM> and the flow guide assembly <NUM>. It should be understood that in other examples, the flow guide assembly <NUM> can be mounted or otherwise secured to a rotating structure, e.g., the rotor <NUM>/hub <NUM>. Moreover, the teachings herein can benefit other engine arrangements, such as adjacent components that are both stationary or that are both rotating.

The flow guide assembly <NUM> can be circumferentially swept about the longitudinal axis A such that the flow path <NUM> is an annular flow path. The flow guide assembly <NUM> can be contoured to reduce windage, control temperature and/or pressure of flow F through the flow path <NUM>, and manage loads on various bearings in the section <NUM>. In this embodiment, the flow guide assembly <NUM> and flow path <NUM> allows for cooling the hub <NUM>, although other flow guides with other features or functions are contemplated.

The flow path <NUM> includes an inlet portion 80a, an intermediate portion 80b, and an outlet portion 80c that are established along the flow guide assembly <NUM>. The intermediate portion 80b interconnects the inlet and outlet portions 80a, 80c. In the example of <FIG>, an end of the inlet portion 80a is adjacent the seal <NUM>.

The flow path <NUM> has a length L and a height h. In the example of <FIG>, the length L is an order of magnitude or more than height h for the long, thin flow path <NUM>. In one example, the ratio of h/L for is less than about <NUM>. More particularly, the ratio is between about <NUM> and <NUM>. Communication of flow F through the flow path <NUM> may cause an acoustic or unsteady flow field due to the geometry of the flow path <NUM>. The unsteady flow fields may be caused by pressure pulses in the flow path <NUM> during operation of the engine <NUM>, for example.

The acoustic or unsteady flow field alone or coupled with structural resonance modes may cause vibratory loads in components adjacent to the flow path <NUM>, such as the hub <NUM>. The vibratory loads may be communicated to other portions of the rotor <NUM>. For example, vibratory loads communicated to a neck portion <NUM> of the hub <NUM> adjacent the seal <NUM> may cause the neck portion <NUM> to pivot or rock back and forth during operation. The motion of this rocking may be amplified at seal locations <NUM> and may serve to either maintain or amplify the acoustic or unsteady flow field experienced in flow path <NUM>.

Furthermore, in some engine <NUM> operating conditions, natural structural frequencies of the seal <NUM> are near the acoustic resonance frequencies of the flow path <NUM> ("acoustic-structural coincidence"). This reduces aerodynamic damping of the seal <NUM>, which can result in the seal <NUM> fluttering if other sources of damping are insufficient to stabilize the system. In some examples, small values of h/L can destabilize the system near conditions of acoustic-structural coincidence.

The flow guide assembly <NUM> includes one or more acoustic attenuation features for reducing vibratory loads in adjacent components of a gas turbine engine. The acoustic attenuation features are apertures or holes <NUM> in the flow guide assembly <NUM> which can have various sizes, arrangements, orientations, and geometries, as will become apparent from the below description. In general, the holes <NUM> include a plurality of holes <NUM> that have a combined total open area that is selected to improve the aeromechanical stability of the flow guide assembly <NUM> by attenuating the acoustic or unsteady flow field while maintaining desired flow F pressure in the flow path <NUM> and structural viability of the flow guide assembly <NUM>. Accordingly, the holes <NUM> mitigate the destabilizing effects of damping reduction, thereby reducing the likelihood of flutter at the seal <NUM>, and improve the durability of the system without compromising the thermal and mechanical benefits of the flow guide assembly <NUM> and flow path <NUM>.

In general, the flow path <NUM> height h is small compared to the acoustic wavelength of the flow path <NUM>, which results in acoustic waves that extend longitudinally along the flow path <NUM>. For example, vibration of seal <NUM> generates primary acoustic waves adjacent the inlet portion 80a of the flow path <NUM> which propagate longitudinally through the flow path <NUM> towards the outlet portion 80c. The acoustic waves are then reflected back through the flow path <NUM> at the outlet portion 80c of the flow path <NUM>. For certain frequencies, the primary and reflected acoustic waves combine constructively, resulting in acoustic resonance. At or near acoustic resonance, there is a reduction in damping of the system, as discussed above. The holes <NUM> facilitate dissolution of the acoustic waves due to interaction of the flow F with individual holes <NUM> (a grazing flow effect) as well as from jetting of leakage flow F out of the flow path <NUM> and into the surrounding environment. As a result, the primary acoustic waves are attenuated before reaching the reflection point at the outlet portion 80c of the flow path <NUM>, and the resulting reflection wave is weaker or smaller. The reflection/feedback mechanism that generates acoustic resonance is thereby disrupted.

The flow guide assembly <NUM> has a point P that is a distance along length L (<FIG>) from the outlet portion 80c of the flow path <NUM> that is approximately equal to the acoustic wavelength associated with the acoustic-structural coincidence frequency in the flow path <NUM>. In one example, the holes <NUM> are arranged between the point P and the outlet portion 80c. In this example, the loss of pressure in the flow F is minimized near the inlet portion 80a of the flow path. In other examples, however, holes <NUM> can additionally or alternatively be located upstream from point P.

The holes <NUM> can be circular in shape, or can have other geometries. For instance, the holes can be made by laser drilling into the flow guide assembly <NUM>. The holes <NUM> have a total open area which is the sum of the area of the opening or footprint defined by all of the holes <NUM> in the flow guide assembly <NUM>. In some examples, the total open area can be expressed as a percentage of the sum of the area of the opening or footprint defined by all of the holes <NUM> as compared to the total inner surface area of the flow guide assembly <NUM> (e.g., the surface of the flow guide assembly <NUM> adjacent to the flow path <NUM>).

<FIG> shows a detail view of the holes <NUM>. In the example of <FIG>, the holes <NUM> are oriented normal to a surface of the flow guide assembly <NUM>. That is, the holes <NUM> are arranged about an axis D that is oriented <NUM> degrees from the surface of the flow guide assembly <NUM>. In other examples, the axis D of the holes <NUM> is oriented at greater or less than <NUM> degrees from the surface of the flow guide assembly <NUM>.

In some examples, the holes <NUM> are slots defined by a radially inward or radially outward projection. <FIG> shows a radially outward slot projection, in which the flow guide assembly <NUM> includes a baseline geometry 78a (shown in phantom), and the hole <NUM> is defined projection d formed by an offset 78b of the flow guide assembly from the baseline geometry 78a. The offset 78b projects outward away from the baseline geometry 78a and away from the flow path <NUM>. <FIG> shows a radially inward slot projection, in which the flow guide assembly <NUM> includes a baseline geometry 78a (shown in phantom), and the hole <NUM> is defined by projection d formed by an offset 78b which projects inward from the baseline geometry 78a into the flow path <NUM>. In both examples, the offset 78b is spaced from the baseline geometry 78a to form the projection d. Furthermore, in both examples, the offset 78b is oriented such that it faces towards the swirl direction of flow F in the flow path <NUM>. This causes flow to be entrained from the surrounding environment (e.g., outside of the flow path <NUM>), thereby providing acoustic dissipation while eliminating or reducing net leakage from the flow path <NUM>. In some examples, a ratio of a height of the projection d to the height of the flow path h (d/h) is between about <NUM> and <NUM>.

The geometry (including size), orientation, and arrangement of the holes <NUM> on the flow guide assembly <NUM> is selected to provide a desired total open area. In one example the holes <NUM> all have uniform geometries, and are arranged close together in areas (e.g., a high density of holes) where higher percent open area ("POA") is desired, and further apart (e.g., a lower density of holes) where lower POA is desired. "POA" as used herein is generally a measure of the area of voids or empty space due to holes <NUM> in a localized area of the flow guide assembly <NUM> as compared to an area of a flow guide assembly with the same geometry as the flow guide assembly <NUM> but without any holes <NUM>.

In another example, the holes <NUM> are arranged in a uniform density across the flow guide assembly, but are larger where higher POA is desired and smaller where lower POA is desired. In yet another example, the holes <NUM> have uniform size and hole <NUM> density, but are simply arranged along the flow guide assembly <NUM> to provide the desired POA in a given section of the flow guide assembly <NUM>. Any combination of hole <NUM> geometry, orientation, size, and arrangement is contemplated by this disclosure. Moreover, this description of holes <NUM> includes various geometries, sizes, and orientations. It should be understood that the plurality of holes <NUM> can have uniform geometries, sizes, and orientations, or the plurality of holes <NUM> can have mixtures of the various geometries, sizes, and orientations discussed above.

Turning now to <FIG>, an example flow guide assembly <NUM> with holes <NUM> is shown. In this disclosure, like reference numerals designate like elements where appropriate and reference numerals with the addition of one-hundred or multiples thereof designate modified elements that are understood to incorporate the same features and benefits of the corresponding original elements. The flow guide assembly <NUM> has an inlet portion 178a adjacent the inlet portion 80a of the flow path <NUM> and an outlet portion 178c adjacent the outlet portion 80c of the flow path <NUM> (see <FIG>) and downstream from the straight portion <NUM>. In the example of <FIG>, holes <NUM> are generally concentrated at the outlet portion 178c of the flow guide assembly <NUM>. More particularly, moving from the inlet portion 178a to the outlet portion 178c, the arrangement of holes begins at point P (<FIG> and <FIG>) on the flow guide assembly <NUM>, and the POA of holes <NUM> gradually increases moving from P along straight portion <NUM> and to the outlet portion 178c. The gradual increase in POA of holes <NUM> prevents a significant impedance discontinuity in the flow guide assembly <NUM> wall that bounds the flow F in the flow path <NUM>. A solid wall (e.g., one with no holes) has a high impedance whereas a wall with a high POA of holes has a low impedance. An abrupt change in the impedance of the flow guide assembly <NUM> (e.g., the sudden introduction of many holes with high POA) might cause acoustic waves to reflect, similar to the reflection of waves due to the impedance discontinuity at the outlet 80c of the flow path <NUM> discussed above. Accordingly, the holes <NUM> have a size, geometry, orientation, and arrangement selected so that the POA of the holes <NUM> gradually increases from the point P to the outlet portion 178c. In the example of <FIG>, the holes <NUM> are circular and are arranged in a spiral pattern. In a particular example, the holes have a diameter of about <NUM> inches (about <NUM> millimeter).

In one example, the size and density of the holes <NUM> is selected so that the POA of the holes <NUM> increases from about <NUM>% at point P to less than <NUM>% at the outlet portion 178c. In a more particular example, the size and density of the holes is selected so that the POA of the holes <NUM> increases from about <NUM>% at point P to about <NUM>% at the outlet portion 178c.

Turning now to <FIG>, another example flow guide assembly <NUM> is shown. In the example of <FIG>, the flow guide assembly <NUM> includes a row of circumferentially spaced holes <NUM> at each of points P1, P2, and P3 along the flow guide assembly <NUM> (as discussed above, the flow guide assembly <NUM> is annular since it is arranged about the longitudinal axis A of the engine <NUM>). <FIG> schematically shows a graph of the points P1, P2, and P3 and holes <NUM> where the point (<NUM>,<NUM>) represents the longitudinal axis A of the engine <NUM>, the x-dimension represents a distance from the longitudinal axis A of the engine <NUM> in a first direction, e.g., a horizontal direction, and the y-dimension represents a distance from the longitudinal axis A of the engine <NUM> in one another direction orthogonal to the first direction, e.g., a vertical direction.

In this example, each of points P1, P2, and P3 are in an intermediate portion 278b of the flow guide assembly <NUM> which corresponds to intermediate portion 80b of the flow path <NUM>. In a particular example, the point P1 is located at R=<NUM> inches (<NUM> millimeters), the point P2 is located at R=<NUM> inches (<NUM> millimeters), and the point P3 located at R= <NUM> inches (<NUM> millimeters) where R represents a radial distance from the longitudinal axis A of the engine <NUM>. In other examples, the points P1, P2, and P3 can be in different portions of the flow guide <NUM>.

In this example, each row of holes <NUM> includes <NUM> circular holes that are evenly circumferentially spaced around the flow guide assembly <NUM>. The holes <NUM> in each row have a common diameter. The holes <NUM> have an increasing diameter moving from the inlet portion 80a of the flow path <NUM> to the outlet portion 80c of the flow path <NUM>. That is, the holes <NUM> in the P1 row have the smallest diameter, the holes <NUM> in the P2 row have a diameter larger than the holes <NUM> in the P1 row, and the holes <NUM> in the P3 row have the largest diameter which is larger than the diameter of the holes <NUM> in the P1 and P2 rows. In a particular example, the holes <NUM> in the P1 row have a diameter of about <NUM> inches (about <NUM> millimeters), the holes <NUM> in the P2 row have a diameter of <NUM> inches (about <NUM> millimeters), and the holes <NUM> in the P3 row have a diameter of <NUM> inches (about <NUM> millimeters). However, it should be understood that the arrangement of holes <NUM> in each row (e.g., the spacing between holes <NUM>), the number of holes <NUM> in each row and the size of the holes <NUM> can be different than in the aforementioned example. That is, the hole <NUM> size, geometry, arrangement, and/or orientation can be selected according to the options discussed above.

Turning now to <FIG>, another example flow guide assembly <NUM> is shown. In the example of <FIG>, the flow guide assembly <NUM> includes a row of circumferentially spaced holes <NUM> at each of points P1, P2, P3, and P4 along the flow guide assembly <NUM> (as discussed above, the flow guide assembly <NUM> is annular since it is arranged about the longitudinal axis A of the engine <NUM>). <FIG> schematically shows a graph of the points P1, P2, P3, and P4 and holes <NUM> where the point (<NUM>,<NUM>) represents the longitudinal axis A of the engine <NUM>, the x-dimension represents a distance from the longitudinal axis A of the engine <NUM> in a first direction, e.g., a horizontal direction, and the y-dimension represents a distance from the longitudinal axis A of the engine <NUM> in one another direction orthogonal to the first direction, e.g., a vertical direction.

In this example, point P1 is in an inlet portion 378a of the flow guide assembly <NUM> that corresponds to the inlet portion 80a of the flow path and each of points P2, P3, and P4 are in an intermediate portion 378b of the flow guide assembly <NUM> which corresponds to intermediate portion 80b of the flow path <NUM>. In a particular example, the point P1 is located at R=<NUM> inches (<NUM> millimeters), the point P2 is located at R=<NUM> inches (<NUM> millimeters), the point P3 located at R= <NUM> inches (<NUM> millimeters), and the point P4 is located at R=<NUM> inches (<NUM> millimeters) where R represents a radial distance from the longitudinal axis A of the engine <NUM>. In other examples, the points P1, P2, P3, and P4 can be in different portions of the flow guide <NUM>.

In this example, each row of holes <NUM> includes circular holes that are evenly circumferentially spaced around the flow guide assembly <NUM>. The holes <NUM> in each row have a common diameter. The holes <NUM> have an increasing diameter moving from the inlet portion 80a of the flow path <NUM> to the outlet portion 80c of the flow path <NUM>. That is, the holes <NUM> in the P1 row have the smallest diameter, the holes <NUM> in the P2 row have a larger diameter than the holes <NUM> in the P1 row, and so forth.

In a particular example, there are <NUM> evenly circumferentially spaced holes <NUM> in the P1 row, <NUM> evenly circumferentially spaced holes <NUM> in the P2 row, <NUM> evenly circumferentially spaced holes <NUM> in the P3, and <NUM> evenly circumferentially spaced holes <NUM> in the P4 row. In this example, holes <NUM> in the P1 row have a diameter of about <NUM> inches (about <NUM> millimeters), the holes <NUM> in the P2 row have a diameter of <NUM> inches (about <NUM> millimeters), the holes <NUM> in the P3 row have a diameter of <NUM> inches (about <NUM> millimeters), and the holes <NUM> in the P4 row have a diameter of <NUM> inches (about <NUM> millimeters). However, it should be understood that the arrangement of holes <NUM> in each row (e.g., the spacing between holes <NUM>), the number of holes <NUM> in each row and the size of the holes <NUM> can be different than in the aforementioned example. That is, the hole <NUM> size, geometry, arrangement, and/or orientation can be selected according to the options discussed above.

In another particular example, there are <NUM> evenly circumferentially spaced holes <NUM> in each of the rows at P1, P2, P3, and P4. In this example, holes <NUM> in the P1 row have a diameter of about <NUM> inches (about <NUM> millimeters), the holes <NUM> in the P2 row have a diameter of <NUM> inches (about <NUM> millimeters), the holes <NUM> in the P3 row have a diameter of <NUM> inches (about <NUM> millimeters), and the holes <NUM> in the P4 row have a diameter of <NUM> inches (about <NUM> millimeters). However, it should be understood that the arrangement of holes <NUM> in each row (e.g., the spacing between holes <NUM>), the number of holes <NUM> in each row and the size of the holes <NUM> can be different than in the aforementioned example. That is, the hole <NUM> size, geometry, arrangement, and/or orientation can be selected according to the options discussed above.

Claim 1:
A section (<NUM>) for a gas turbine engine (<NUM>) comprising:
a rotating structure;
a stationary structure (<NUM>);
a flow guide assembly (<NUM>, <NUM>, <NUM>, <NUM>) arranged generally between the rotating structure and the stationary structure (<NUM>) such that a flow path (<NUM>) is defined between the flow guide assembly (<NUM>, <NUM>, <NUM>, <NUM>) and one of the rotating structure and the stationary structure (<NUM>), the flow guide assembly (<NUM>, <NUM>, <NUM>, <NUM>) including a plurality of apertures (<NUM>, <NUM>, <NUM>, <NUM>) configured to disrupt acoustic waves of air in the flow path (<NUM>); and
a seal (<NUM>) configured to establish a sealing relationship between the rotating structure and the stationary structure (<NUM>), wherein an inlet (80a) to the flow path (<NUM>) is adjacent the seal (<NUM>), wherein the flow guide assembly (<NUM>, <NUM>, <NUM>, <NUM>) includes an inlet portion (178a, 378a) adjacent an inlet (80a) to the flow path (<NUM>), an outlet portion (178c) adjacent an outlet (80c) to the flow path (<NUM>), and an intermediate portion (278b, 378b) between the inlet portion (178a, 378a) and the outlet portion (178c), the plurality of apertures (<NUM>, <NUM>, <NUM>, <NUM>) are arranged in one or more circumferential rows in the intermediate portion (278b, 378b), the plurality of apertures (<NUM>, <NUM>, <NUM>, <NUM>) evenly circumferentially spaced in the row.