# US 11,028,707 B2 · Zoned surface roughness > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,028,707 B2 - Document ID: US11028707B2 - Status: Granted - Kind: B2 - Application number: 16/470,284 - Filed: 2018-01-19 - Published: 2020-01-09 - Granted: 2021-06-08 - Earliest claimed: 2017-01-19 - Assignees: GKN Aerospace Sweden AB - Applicants: GKN Aerospace Sweden AB - Inventors: Peter Johansson - Web page: https://patentgrep.com/patent/US11028707B2 ## CPC - F01D 9/04: forming ring or sector - F04D 19/028: {Layout of fluid flow through the stages} - F01D 9/06: Fluid supply conduits to nozzles or the like - F04D 29/023: {especially adapted for elastic fluid pumps} - F04D 29/545: {Ducts} - F04D 29/547: {having a special shape in order to influence fluid flow} - F04D 29/681: {especially adapted for elastic fluid pumps} - F04D 29/667: {by influencing the flow pattern, e.g. suppression of turbulence} - F05D 2240/12: Fluid guiding means, e.g. vanes - F05D 2250/60: Structure; Surface texture - F05D 2250/62: smooth or fine - F05D 2250/621: polished - F05D 2250/63: coarse - F05D 2300/516: Surface roughness - F01D: NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES (machines or engines for liquids F03; non-positive displacement pumps F04D) - F04D: NON-POSITIVE-DISPLACEMENT PUMPS (engine fuel-injection pumps F02M; ion pumps H01J41/12; electrodynamic pumps H02K44/02) - F05D: INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS ## Abstract The invention concerns a transition duct for a multi-stage compressor of a gas turbine engine. Regions of the inner surface of the duct are provided with a predetermined and dissimilar surface roughness to optimise gas flow efficiency within the duct. ## Claims ### Claim 1 An apparatus comprising a multi-stage compressor, comprising: a first and second compressor coaxially located with respect to a central axis of a gas turbine engine, wherein an outlet of the first compressor is in fluid communication with an inlet of the second compressor through a duct, the duct defining a channel for gas flow and comprising an inner gas facing wall and an opposing outer gas facing wall defining the inner surfaces of the channel, and wherein regions of the inner surfaces of the channel have a predetermined and dissimilar surface roughness, and wherein at least one region of the inner surface of the channel against which flowing gas impinges is provided with a surface roughness which is lower than regions of the inner surfaces against which flow gas does not impinge. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein regions of the inner surfaces which in use experience lower gas static pressure are provided with a surface roughness which is higher than the remaining inner surfaces of the channel. ### Claim 3 (depends on 1) The apparatus of claim 1, wherein the duct is in the form of a ring coaxially located with respect to a central axis of the compressor which tapers from a first maximum radius measured from the central axis of the compressor to a second smaller radius measured from the central axis of the compressor. ### Claim 4 (depends on 1) The apparatus of claim 1, wherein the duct is in the form of a ring or annulus coaxial with the central axis of the compressor, the circumferential perimeter of the ring or annulus having a generally tapered S or sinusoidal shape in cross-section, wherein the maximum radius of the duct measured from the central axis of the turbine tapers along the length of the duct between the first compressor and the second compressor. ### Claim 5 (depends on 1) The apparatus of claim 1, wherein the inner gas facing wall is the outer surface of a hub of the multi-stage compressor and the opposing outer gas facing wall is the inner surface of the shroud of the multi-stage compressor. ### Claim 6 (depends on 1) The apparatus of claim 1, wherein the regions of the inner surfaces of the channel with a higher surface roughness have an average roughness of 3 microns Ra or greater. ### Claim 7 (depends on 1) The apparatus of claim 1, wherein the regions of the inner surfaces of the channel with a lower surface roughness have an average roughness of between 0.5 and 1.6 microns Ra. ### Claim 8 (depends on 1) The apparatus of claim 1, wherein the regions of the inner surfaces of the channel with a higher surface roughness are provided with protuberances extending from the surface and into the channel. ### Claim 9 (depends on 8) The apparatus of claim 8, wherein the protuberances are in the form of chevrons distributed across the region of the channel. ### Claim 10 (depends on 1) The apparatus of claim 1, further comprising a multi-stage gas turbine engine in which the multi-stage compressor is included. ### Claim 11 A transition duct for a multi-stage compressor of a gas turbine engine, said duct arranged in use to communicate gas between a first and second compressor coaxially located with respect to a central axis of a gas turbine engine, wherein the duct defines a channel for gas flow and comprises an inner gas facing wall and an opposing outer gas facing wall defining the inner surfaces of the channel, and wherein regions of the inner surfaces of the channel have a predetermined and dissimilar surface roughness, and wherein at least one region of the inner surface of the channel against which flowing gas impinges is provided with a surface roughness which is lower than regions of the inner surfaces against which flow gas does not impinge. ### Claim 12 (depends on 11) The transition duct of claim 11, wherein there are at least two regions provided with a modified surface roughness on the outer gas facing wall, and at least two regions provided with a modified surface roughness on the inner gas facing wall. ### Claim 13 (depends on 12) The transition duct of claim 12, wherein measured from an inlet to an outlet of the duct, the first of said at least 2 regions on the outer gas facing wall has a lower surface roughness than the second region. ### Claim 14 (depends on 12) The transition duct of claim 12, wherein measured from an inlet to an outlet of the duct, the first of said at least two regions on the inner gas facing wall has a higher surface roughness than the second region.