# US 8,770,339 B2 · Silencer for an auxiliary power unit of an aircraft > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,770,339 B2 - Document ID: US8770339B2 - Status: Granted - Kind: B2 - Application number: 13/628,181 - Filed: 2012-09-27 - Published: 2013-04-04 - Granted: 2014-07-08 - Earliest claimed: 2011-09-30 - Assignees: Airbus Operations GmbH - Applicants: Airbus Operations GmbH - Inventors: Rudolf Starobinski; Matthias Siercke - Web page: https://patentgrep.com/patent/US8770339B2 ## CPC - B64D 33/06: {Silencing exhaust or propulsion jets} - B64D 41/00: Power installations for auxiliary purposes - F02K 1/827: {Sound absorbing structures or liners} - G10K 11/172: using resonance effects - F05D 2220/50: for auxiliary power units (APU's) - Y02T 50/60: Efficient propulsion technologies, e.g. for aircraft - B64D: EQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENT OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT - F02K: JET-PROPULSION PLANTS (features of jet-propulsion plants common to gas-turbine plants, air intakes or fuel supply control of air-breathing jet-propulsion plants F02C7/00, F02C9/00) - G10K: SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR - F05D: INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS - Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION ## Abstract A silencer for an auxiliary power unit of an aircraft includes an inlet, an outlet, a housing, and a flow channel of a porous material, arranged in the housing. Between the housing and the flow channel an intermediate space is created, which space is divided by at least one outer partition into outer cells arranged around the flow channel. A central body includes a casing that is permeable to gas at least in some regions and that is arranged in the interior of the silencer. The central body includes inner partitions dividing the central body into inner cells. The resonance frequency of the inner cells corresponds to the natural frequency of the first radial mode in a channel formed between the central body and the inner surface of the inlet. In this manner particularly good sound attenuation is achieved with a compact installation space of a silencer. ## Claims ### Claim 1 A silencer for an auxiliary power unit of an aircraft, comprising a longitudinal inlet section; an outlet; a housing downstream of the inlet section; a flow channel, arranged in the housing, comprising a porous wall material; wherein between the housing and the flow channel an intermediate space is created, the intermediate space being divided by at least one outer partition into at least first and second outer cells arranged around the flow channel, and a central body comprising a casing permeable to gas in at least in one region, the central body being arranged in the interior of the inlet section and upstream of the flow channel and the at least first and second outer cells and comprising a plurality of inner partitions dividing the central body into a plurality of inner cells, wherein the resonance frequency of the inner cells corresponds to the natural frequency of the first radial mode in a channel formed between the central body and the inner surface of the inlet. ### Claim 2 (depends on 1) The silencer of claim 1, wherein the casing of the central body comprises a porous material. ### Claim 3 (depends on 1) The silencer of claim 1, wherein the flow resistance R of the material of the casing of the central body corresponds to 1 to 1.5 times the basic resistance calculated by R = 410 · ( 293 T ) 1 ⁢ , 26 ⁢ Pa m s wherein T denotes the temperature in Kelvin (K) of the gas flowing through the silencer. ### Claim 4 (depends on 1) The silencer of claim 1, wherein the casing is cylindrical and is arranged so as to be coaxial to the flow channel. ### Claim 5 (depends on 1) The silencer of claim 1, wherein the central body is at least in part aligned so as to be coaxial to the inlet section. ### Claim 6 (depends on 1) The silencer of claim 1, further comprising a perforated walling enclosing the casing. ### Claim 7 (depends on 1) The silencer of claim 1, further comprising a perforated walling arranged on the inside of the casing. ### Claim 8 (depends on 6) The silencer of claim 6, further comprising an air gap between the casing and the perforated walling. ### Claim 9 (depends on 6) The silencer of claim 6, wherein the degree of perforation of the perforated walling is configured such that the resonance frequency of the inner cells corresponds to 0.95 to 1.05 times the first transversal natural frequency of a standing wave in the space between the inlet section and the central body. ### Claim 10 An aircraft comprising an auxiliary power unit and a silencer, the silencer comprising: a longitudinal inlet section; an outlet; a housing downstream of the inlet section; a flow channel, arranged in the housing, comprising a porous wall material, wherein between the housing and the flow channel an intermediate space is created, the intermediate space being divided by at least one outer partition into at least first and second outer cells arranged around the flow channel, and a central body comprising a casing permeable to gas in at least in one region, the central body being arranged in the interior of the inlet section and upstream of the flow channel and the at least one first and second outer cells and comprising a plurality of inner partitions dividing the central body into a plurality of inner cells, wherein the resonance frequency of the inner cells corresponds to the natural frequency of the first radial mode in a channel formed between the central body and the inner surface of the inlet; and wherein the inlet of the silencer is connected to an exhaust gas outlet of the auxiliary power unit. ### Claim 11 (depends on 10) The aircraft of claim 10, wherein the central body is connected to a turbine stator of the auxiliary power unit.