Gas turbine engine and a rotor for a gas turbine engine

Abstract

A rotor ( 38 ) for a gas turbine engine ( 10 ) has a low emissivity surface finish, or high emissivity surface finish ( 44 ), on at least a portion of its surface ( 42 ) to reduce temperature differentials between an upper portion and a lower portion of the rotor ( 38 ). This reduces bowing of the rotor ( 38 ) to allow the gas turbine engine ( 10 ) to be started without harmful vibrations of the rotor ( 38 ).

I claim:  
     
         1 . A gas turbine engine comprising at least one rotor and at least one casing arranged coaxially around the at least one rotor, the rotor having an upper portion, a lower portion and a surface, the at least one casing having a surface, at least one of the at least one rotor or the at least one casing having a surface finish on at least a portion of its surface to reduce temperature differentials between the upper portion and the lower portion of the at least one rotor, the surface finish being selected from the group comprising a low emissivity surface finish and a high emissivity surface finish.  
     
     
         2 . A gas turbine engine as claimed in  claim 1  wherein the gas turbine engine comprises a low pressure rotor, a high pressure rotor and at least one casing, the high pressure rotor being arranged coaxially around the low pressure rotor and the at least one casing being arranged coaxially around the high pressure rotor, the high pressure rotor having a radially inner surface and a radially outer surface, the low pressure rotor having a radially inner surface and a radially outer surface.  
     
     
         3 . A gas turbine engine as claimed in  claim 2  wherein the surface is the radially inner surface of the high pressure rotor, the surface finish is arranged on substantially the whole of the radially inner surface of the high pressure rotor and the surface finish is a high emissivity surface finish.  
     
     
         4 . A gas turbine engine as claimed in  claim 3  wherein the surface is the radially inner surface of the low pressure rotor, the surface finish is arranged on substantially the whole of the radially inner surface of the low pressure rotor and the surface finish is a high emissivity surface finish.  
     
     
         5 . A gas turbine engine as claimed in  claim 3  wherein the surface is the radially outer surface of the low pressure rotor, the surface finish is arranged on substantially the whole of the radially outer surface of the low pressure rotor and the surface finish is a high emissivity surface finish.  
     
     
         6 . A gas turbine engine as claimed in  claim 2  wherein a low emissivity surface finish is arranged on at least a portion of the radially outer surface of the high pressure rotor and a low emissivity surface finish is arranged on a portion of the radially inner surface of the high pressure rotor.  
     
     
         7 . A gas turbine engine as claimed in  claim 2  wherein a high emissivity surface finish is arranged on at least a portion of the radially inner surface of the high pressure rotor, a high emissivity surface finish is arranged on at least a portion of the radially outer surface of the high pressure rotor, a low emissivity surface finish is arranged on at least a portion of the radially outer surface of the high pressure rotor and a low emissivity surface finish is arranged on at least a portion of the radially inner surface of the high pressure rotor.  
     
     
         8 . A gas turbine engine as claimed in  claim 2  wherein the surface is the downstream surface of the high pressure rotor, the surface finish is arranged on at least a portion of the downstream surface of the high pressure rotor and the surface finish is a high emissivity surface finish.  
     
     
         9 . A gas turbine engine as claimed in  claim 8  wherein the high emissivity surface finish is arranged on substantially all of the downstream surface of the high pressure rotor.  
     
     
         10 . A gas turbine engine as claimed in  claim 2 , wherein the surface is the downstream surface of the low pressure rotor, the surface finish is arranged on at least a portion of the downstream surface of the low pressure rotor and the surface finish is a high emissivity surface finish.  
     
     
         11 . A gas turbine engine as claimed in  claim 10  wherein the high emissivity surface finish is arranged on substantially all of the downstream surface of the low pressure rotor.  
     
     
         12 . A gas turbine engine as claimed in  claim 2  wherein the high pressure rotor comprises a high pressure compressor and a high pressure turbine and the low pressure rotor comprises a low pressure compressor and a low pressure turbine.  
     
     
         13 . A gas turbine engine as claimed in  claim 12  wherein the high pressure turbine comprises at least one turbine disc and the low pressure turbine comprises at least one turbine disc and each turbine disc has an upstream surface and a downstream surface.  
     
     
         14 . A gas turbine engine as claimed in  claim 13  wherein a high emissivity surface finish is arranged on the upstream surface of each turbine disc on the high pressure rotor and the downstream surface of each turbine disc on the high pressure rotor.  
     
     
         15 . A gas turbine engine as claimed in  claim 13  wherein the high emissivity surface finish is arranged on the upstream surface of each turbine disc on the low pressure rotor and the downstream surface of each turbine disc on the low pressure rotor.  
     
     
         16 . A gas turbine engine as claimed in  claim 12  wherein the at least one casing is arranged around the high pressure turbine and the low pressure turbine, the surface is a radially outer surface of the at least one casing, at least a portion of the at least one casing having a high emissivity surface finish on its radially outer surface to increase the rate of radiation of heat from at least one of the turbines.  
     
     
         17 . A gas turbine engine as claimed in  claim 1  wherein the surface is a radially outer surface of the at least one casing, the surface finish is arranged on at least a portion of the radially outer surface of the at least one casing, the surface finish is a high emissivity surface finish.  
     
     
         18 . A gas turbine engine as claimed in  claim 17  wherein the at least one casing has a radially inner surface, at least a portion of the at least one casing having a high emissivity surface finish or a low emissivity finish on its inner surface.  
     
     
         19 . A gas turbine engine as claimed in  claim 1  wherein the high emissivity surface finish is selected from the group comprising a coating applied to the surface of the at least one rotor or the at least one casing and a coating formed on the surface of the at least one rotor or the at least one casing.  
     
     
         20 . A gas turbine engine as claimed in  claim 19  wherein the coating is selected from the group comprising a high emissivity metal oxide, a metal oxide formed on the at least one rotor or the at least one casing due to oxidation of the at least one rotor or the at least one casing, carbon, black paint and other suitable colour paint.  
     
     
         21 . A gas turbine engine as claimed in  claim 1  wherein the low emissivity surface finish is selected from the group comprising a polished portion of the surface of the at least one rotor, a machined portion of the surface of the at least one rotor and the at least one casing or a coating applied to the surface of the at least one rotor or the at least one casing.  
     
     
         22 . A gas turbine engine as claimed in  claim 21  wherein the coating is selected from the group comprising a polished metal coating, a polished silver coating, a polished gold coating, and a low emissivity metal oxide.  
     
     
         23 . A rotor for a gas turbine engine having an upper portion, a lower portion and a surface, the surface having a surface finish on at least a portion of its surface to reduce temperature differentials between the upper portion and the lower portion of the rotor, the surface finish being selected from the group comprising a low emissivity surface finish and a high emissivity surface finish.  
     
     
         24 . A rotor for a gas turbine engine as claimed in  claim 23  wherein the surface is a radially inner surface of the rotor, a high emissivity surface finish is arranged on at least a portion of the radially inner surface of the rotor.  
     
     
         25 . A rotor for a gas turbine engine as claimed in  claim 24  wherein the high emissivity surface finish is arranged on substantially the whole of the radially inner surface of the rotor.  
     
     
         26 . A rotor for a gas turbine engine as claimed in  claim 23  wherein the surface is a radially outer surface of the rotor, a high emissivity surface finish is arranged on at least a portion of the radially outer surface of the rotor.  
     
     
         27 . A rotor for a gas turbine engine as claimed in  claim 26  wherein the high emissivity surface finish is arranged on substantially the whole of the radially outer surface of the rotor.  
     
     
         28 . A rotor for a gas turbine engine as claimed in  claim 23  wherein the surface is a radially outer surface of the rotor, a low emissivity surface is arranged on at least a portion of the radially outer surface of the rotor.  
     
     
         29 . A rotor for a gas turbine engine as claimed in  claim 28  wherein the low emissivity surface finish is arranged on substantially the whole of the radially outer surface of the rotor.  
     
     
         30 . A rotor for a gas turbine engine as claimed in  claim 23  wherein the rotor has a radially inner surface and a radially outer surface, a high emissivity surface finish is arranged on at least a portion of the radially inner surface of the rotor, a high emissivity surface finish is arranged on at least a portion of the radially outer surface of the rotor, a low emissivity surface finish is arranged on at least a portion of the radially outer surface of the rotor and a low emissivity surface finish is arranged on at least a portion of the radially inner surface of the rotor.  
     
     
         31 . A rotor for a gas turbine engine as claimed in  claim 23  wherein the surface is a downstream surface of the rotor a high emissivity surface finish is arranged on at least a portion of the downstream surface of the rotor.  
     
     
         32 . A rotor for a gas turbine engine as claimed in  claim 31  wherein the high emissivity surface finish is arranged on substantially all of the downstream surface of the rotor.  
     
     
         33 . A rotor for a gas turbine engine as claimed in  claim 23  wherein the rotor is selected from the group comprising a high pressure rotor, an intermediate pressure rotor and a low pressure rotor.  
     
     
         34 . A rotor for a gas turbine engine as claimed in  claims 23  to  37  wherein the high emissivity surface finish is selected from the group comprising a coating applied to the surface of the rotor and a coating formed on the surface of the rotor.  
     
     
         35 . A rotor for a gas turbine engine as claimed in  claim 34  wherein the coating is selected from the group comprising a high emissivity metal oxide, a metal oxide formed on the rotor due to oxidation of the rotor, carbon, black paint and other suitable colour paint.  
     
     
         36 . A rotor for a gas turbine engine as claimed in  claim 23  wherein the low emissivity surface finish is selected from the group comprising a polished portion of the surface of the rotor, a machined portion of the surface of the rotor and a coating applied to the surface of the rotor.  
     
     
         37 . A rotor for a gas turbine engine as claimed in  claim 36  wherein the coating is selected from the group comprising a polished metal coating, a polished silver coating, a polished gold coating, and a low emissivity metal oxide.