Arrangement of a gas temperature sensing device in a gas turbine vane

Abstract: A gas turbine engine gas temperature sensing device comprises an aerofoil vane (23) having a chamber (24) adjacent its leading edge (19). The chamber (24) contains a thermocouple (25) and a nozzle (29) which directs gases from the exterior of the vane (23) on to the thermocouple (25). The nozzle (29) has an inlet (26) which is positioned on the suction surface (22) of the vane (23) adjacent the leading edge (19). A chamber outlet (31) is positioned on a portion of the aerofoil suction surface (22) where the gas pressure is lower than that where the inlet (26) is positioned, thereby ensuring a gas flow through the chamber (24) over the thermocouple (25).

Description: This invention relates to a gas turbine engine gas temperature sensing device and in particular to a sensing device for use in determining the temperature of gases flowing through the turbine of such an engine. It is necessary to determine the temperature of gases passing through the turbine of a gas turbine engine in order to provide necessary data for the engine's fuel control system. Gas temperature data is also necessary for cockpit display if the gas turbine engine in question powers an aircraft. One way of monitoring turbine gas temperatures is to place a suitable thermocouple in the gas stream of interest. However, this can lead to undesirable aerodynamic losses in that gas stream. Additionally, the thermocouple is prone to damage by foreign objects that may pass through the turbine. If the turbine contains hollow aerofoil vanes, aerodynamic losses can be avoided by placing a thermocouple inside one of the vanes. Suitably dimensioned orifices are provided in the suction and pressure flanks of the vane so that turbine gases flow through the vane from the pressure flank to the suction flank and hence over the thermocouple. It is also known, for instance from US-A-4605315, GB-734702A, US-A-2946221 and US-A-3348414 to provide an orifice on the leading edge of the vane to direct turbine gases over the thermocouple. While such arrangements can be effective in providing a reliable indication of turbine gas temperature under most operating conditions, difficulties can still arise during extremes of engine operation. For instance, during engine start-up, which can be either on the ground or in flight, there can be insufficient difference in pressure between the vane flanks to provide a gas flow through the vane and over the thermocouple. Consequently, the gas temperature signal provided by the thermocouple is not necessarily truly indicative of the temperature of the gases flowing through the turbine. This, of course, could have a detrimental effect upon the efficient operation of the engine. It is an object of the present invention to provide a gas turbine engine gas temperature sensing device that is capable of providing an accurate indication of the temperature of gases passing through the turbine of such an engine under a wider range of engine operating conditions than has heretofore been the case. According to the present invention, a gas turbine engine gas temperature sensing device comprises an aerofoil cross-section vane for location in a gas stream, said vane having a leading edge, a trailing edge, pressure and suction flanks interconnecting those leading and trailing edges, and a chamber therein, which chamber in turn contains a gas temperature sensor, said gas outlet being in communication with a region of gas at a pressure lower than that of gas adjacent said gas inlet to facilitate the flow of gas from said inlet to said outlet through said chamber, said gas inlet being adapted to direct gas on to said gas temperature sensor prior to its exhaustion through said gas outlet, said gas inlet being in communication with a region of the exterior of said suction flank adjacent said leading edge to direct gas from that region on to said gas temperature sensor. The present invention ensures that turbine gases flow over the gas temperature sensor under a wide range of operating conditions. Said gas inlet is preferably positioned between the stagnation streamline of said gas flow incident upon said vane under engine starting conditions and the stagnation streamline of said gas flow incident upon said vane under other engine operating conditions. Said gas outlet may be positioned on said suction surface of said vane at a position downstream of said gas inlet. Said inlet may be constituted by one end of a nozzle which extends into said chamber, the other end of which is positioned adjacent said sensor to direct said gas on to said gas temperature sensor. Said nozzle is preferably of progressively decreasing cross-sectional area in the direction of gas flow towards said temperature sensor. Preferably said inlet is defined by longitudinally extending edges which are of curved cross-sectional configuration so as to facilitate the smooth flow of gases into said nozzle. Said nozzle may progressively change from a generally square cross-sectional shape at said inlet to a generally circular cross-sectional shape at its outlet. Said nozzle may have a longitudinal axis which is so aligned with respect to the remainder of said vane that the degree of turning of said gas flow to enter said nozzle is minimised. Said chamber is preferably located adjacent the leading edge region of said vane. The present invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic sectioned side view of a ducted fan gas turbine engine having a gas temperature sensing device in accordance with the present invention. Figure 2 is a partially exploded view of some of the turbine stator vanes of the gas turbine engine shown in Figure 1, one of which additionally functions as a gas temperature sensing device in accordance with the present invention. Figure 3 is a sectioned plan view of the front portion of the turbine stator vane shown in Figure 2 that additionally functions as a gas temperature sensing device in accordance with the present invention. Figure 4 is a view on arrow A of Figure 3. Figure 5 is a view on section line B-B of Figure 3. With reference to Figure 1, a ducted fan gas turbine engine generally indicated at 10 is of conventional general configuration comprising a propulsive fan 11, intermediate and high pressure air compressors 12 and 13 respectively, combustion equipment 14 and high, intermediate and low pressure turbines 15, 16 and 17 respectively. The present invention is particularly concerned with the low pressure turbine 17 that powers the fan 11. The structure and operation of the remaining portions of the engine 10 are well known to those skilled in the art and will not, therefore, be described in further detail. The low pressure turbine 17 comprises, in the conventional manner, axially alternate annular arrays of rotor blades and stator vanes. Part of one of those arrays of stator vanes 18 can be seen if reference is now made to Figures 2 and 3. The stator vanes in the array 18 are all the same conventional aerofoil cross-section external configuration. Thus each vane has a leading edge 19, a trailing edge 20, and pressure and suction flanks 21 and 22 respectively. One of the stator vane array 18, designated 23 in Figure 2, is provided with a chamber 24 internally of the region adjacent its leading edge 19 as can be seen in Figure 3. The chamber 24 contains a thermocouple 25 that is of a type suitable for measuring the temperature of gases flowing through the low pressure turbine 17. The thermocouple 25 is of conventional construction and will not, therefore, described in any further detail. In order to provide the thermocouple 25 with communication with those gases, a gas inlet 26 is provided in the suction flank 22 of the vane 23 adjacent its leading edge 19. The gas inlet 26 is, as can be seen in Figure 4, of generally square cross-sectional configuration at the external surface of the stator vane 23. However, the longitudinally extending edges 27 and 28 of the gas inlet 26 are, as can be seen in Figure 3, of curved cross-sectional shape so as to facilitate the smooth flow of turbine gases into the inlet 26 as will be described later. The inlet 26 constitutes the upstream end of a nozzle 29 that extends into the chamber 24 and is aligned with the thermocouple 25. The nozzle 29 changes progressively from the generally square cross-sectional configuration of its inlet 26 to a circular cross-sectional configuration of smaller cross-sectional area at its outlet 30. This combination of change in cross-sectional shape and reduction in cross-sectional area of the nozzle 29 has the effect of accelerating the gas flow through the nozzle 29 and suppressing any regions of turbulent flow that may have formed in the gas entering the nozzle 29. However, the dimensions of the nozzle 29 are selected such that they do not provide significant constriction of that gas flow. The nozzle 29 is so disposed that the turbine gases exhausted from it are directed on to the thermocouple 25, thereby enabling the thermocouple 25 to provide an output signal that is representative of the temperature of the gases. The gases then flow towards a chamber outlet 31 that is positioned in the suction flank of the vane 23. The chamber outlet 31 is located on a portion of the vane suction flank 22 where the overall turbine gas pressure is lower than it is in the vicinity of the nozzle inlet 26. It is this turbine gas pressure gradient between the inlet 26 and outlet 31 which ensures that there is a constant flow of turbine gases through the nozzle 29 which flow over the thermocouple 25 before being exhausted through the outlet 31 to rejoin the turbine gas flow over the exterior surfaces of the vane 23. The turbine gases which are incident upon the leading edge 19 of the vane 23 divide and flow in opposite directions to pass over the pressure and suction flanks 21 and 22 respectively of the vane 23. The mean position 33 at which the gases divide under normal operating conditions to flow over the pressure and suction flanks 21 and 22 is defined by a stagnation streamline 32 that extends normal to the vane 23 external surface. Thus, some of the turbine gases flowing over the suction flank 22 from the stagnation streamline 32 are diverted into the inlet 26 and nozzle 29. The curvature of the inlet edge 28 is so arranged that the energy losses in that flow are as small as possible. During gas turbine engine start-up, which is an extreme engine operating condition, the stagnation streamline 34 is located at a mean position 35 that is on, and normal to, the suction flank 22. It is also on the opposite side of the inlet 26 to the vane leading edge 19. Under these conditions, the turbine gases that flow over the pressure flank 21 must first flow across a small portion of the suction flank 22 before reaching the leading edge 19 and subsequently the pressure flank 21. This takes the flow across the nozzle inlet 26 and so, in view of the pressure gradient between the inlet 26 and outlet 31, some of the turbine gases flow into the inlet 26. The curved cross-sectional configuration of the gas inlet edge 27 ensures that such a flow is as non-turbulent as possible. It will be seen, therefore, that at any one point during a normal operating cycle of the engine 10, turbine gases will flow across the nozzle inlet 26 in one of two opposite directions. Those directions will depend upon whether the engine is starting, or operating under steady state or changing conditions. Consequently, during engine operation, some of that flow always passes through the nozzle 29 and on to the thermocouple 25. The axis 32 of the nozzle 29 is so orientated with respect to the vane 23 outer surface local thereto that the flow of turbine gases into the nozzle 29 is as smooth as possible. As a result of this, the thermocouple 25 provides an accurate indication of turbine gas temperature under a very wide range of engine operating conditions. Consequently, effective engine control and operation over that range of conditions are ensured.

Claims: A gas turbine engine gas temperature sensing device comprising an aerofoil cross-section vane (23) for location in a gas stream, said vane (23) having a leading edge (19), a trailing edge (20), pressure and suction flanks (21,22) interconnecting those leading and trailing edges, and a chamber therein, said chamber (24) in turn containing a gas temperature sensor (24), said chamber (24) having a gas inlet (26) and a gas outlet (31), said gas outlet (31) being in communication with a region of gas at a pressure lower than that of gas adjacent said gas inlet (26) to facilitate the flow of gas from said inlet (26) to said outlet (31) through said chamber (24), said gas inlet (26) being adapted to direct gas on to said gas temperature sensor (25) prior to its exhaustion through said gas outlet (31), characterised in that said gas inlet (26) is in communication with a region of the exterior of said suction flank (22) adjacent said leading edge (19) to direct gas from that region on to said gas temperature sensor (25). A gas turbine engine gas temperature sensing device as claimed in claim 1 characterised in that said gas inlet (26) is positioned between the stagnation streamline (34) of said gas flow incident upon said vane under engine starting conditions and the stagnation streamline (32) of said gas flow incident upon said vane (23) under other engine operating conditions. A gas turbine engine gas temperature sensing device as claimed in claim one or claim 2 characterised in that said gas outlet (31) is positioned on said suction surface (22) of said vane (23) at a position downstream of said gas inlet (26). A gas turbine engine gas temperature sensing device as claimed in any one preceding claim characterised in that said inlet (26) is constituted by one end of a nozzle (29) which extends into said chamber (24), the other end of which is positioned adjacent said sensor (25) to direct said gas on to said gas temperature sensor (25). A gas turbine engine gas temperature sensing device as claimed in any one preceding claim characterised in that said nozzle (29) is of progressively decreasing cross-sectional area in the direction of gas flow towards said temperature sensor (25). A gas turbine engine temperature sensing device as claimed in any one preceding claim characterised in that said inlet (26) is defined by longitudinally extending edges which are of curved cross-sectional so as to facilitate the smooth flow of gas into said nozzle (29). A gas turbine engine temperature sensing device as claimed in any one preceding claim characterised in that said nozzle (29) progressively changes from a generally square cross-sectional shape at its inlet (26) to a generally circular cross-sectional shape at its outlet (30). A gas turbine engine temperature sensing device as claimed in any one preceding claim characterised in that said nozzle (29) has a longitudinal axis (32) which is so aligned with respect to the remainder of said vane (23) that the degree of turning of said gas flow to enter said nozzle (29) is minimised. A gas turbine engine temperature sensing device as claimed in any one preceding claim characterised in that said chamber (24) is located adjacent the leading edge region of said vane (23). A gas turbine engine temperature sensing device as claimed in any one preceding claim characterised in that said vane (23) is so configured as to be a turbine vane. A gas turbine engine temperature sensing device as claimed in any one preceding claim characterised in that said temperature sensor (25) is a thermocouple.

Inventors: CONNELLY JEFFREY ARTHUR, HAARMEYER JOERG, NEGULESCU DIMITRIE, WHITE ADRIAN JAMES, CONNELLY, JEFFREY ARTHUR, HAARMEYER, JOERG, NEGULESCU, DIMITRIE, WHITE, ADRIAN JAMES, Haarmeyer, Jörg
Applicants: ROLLS ROYCE DEUTSCHLAND, ROLLS ROYCE PLC, ROLLS-ROYCE DEUTSCHLAND LTD & CO KG, ROLLS-ROYCE PLC
Application year: 1998
Main classification: F01D5
IPC codes: F01D5