A BLADE TIP CLEARANCE CONTROL ARRANGEMENT FOR A GAS TURBINE ENGINE

Abstract: A blade tip clearance control arrangement (25B) for a compressor (16) of a gas turbine engine (10) comprises a first annular control member (56) which defines a portion of the gas flowpath through the compressor and which is spaced from the tips of the rotor blades (32) by a clearance. The first annular control member (56) is positioned coaxially inwardly of a pair of second annular control members (48,50) and is secured thereto by a radially resilient annular support member (52). The first annular control member (56) is formed from a relatively low expansion material and the second annular control members are formed from a relatively high expansion material. Initially the first annular control member (56) expands rapidly in accordance with its own rate of thermal expansion against the resilience of the resilient annular support member (52), and the first annular control member (56) is caused to expand beyond its fully thermally expanded state by the second annular control members (48,50) and the resilient annular support member (52) in accordance with the rate of thermal expansion of the second annular control members.

Description: The present invention relates to a blade tip clearance control arrangement for a gas turbine engine. In a typical gas turbine engine component efficiencies depend increasingly on the clearance between the rotating rotor blades and the annular member, or members, defining the outer gas flowpath. The casing arrangements which form the annular member or members, must ideally have a thermal responsive characteristic matching the growth of the rotor. The rotor growth is characterised by an initial fast centrifugal growth element superimposing on a slower thermal rotor growth element. Furthermore the thermal rotor growth element at the rim of the rotor is a resultant thermal strain between principally the rotor rim and the rotor cob. Due to its direct contact with the main gas stream, the rotor rim has a fast thermal growth rate, the rotor cob however is much slower in its thermal growth rate. Hence the rotor radial displacement profile can be regarded as a multi-rate responsive system to changes in the gas turbine engine conditions. Many blade tip clearance control arrangements have attempted to match the rotor growth by using several design principles. A first arrangement has used a fast response casing arrangement in which a high thermal expansion material gives a large range of radial displacements. A second arrangement has a slow response casing arrangement in which a low thermal expansion material gives a small range of radial displacements. A third arrangement uses a combination of the first and second arrangements and our UK patents GB1484288, GB1484936 and GB2087979B are examples. A fourth arrangement, is disclosed in our French patent application 2228967A. This discloses the use of a first annular control member and a second annular control member arranged radially outwardly of the first annular control member. The second annular control member has a greater mass than the first annular control member such that the first annular control member expands or contracts at a greater rate than the second annular control member. A number of resilient members are positioned radially between the first and second annular control members to support the first annular control member and to damp vibrations. A prior art blade tip clearance control arrangement for a gas turbine engine comprises a rotor and a stator, the rotor having at least one stage of circumferentially arranged radially extending rotor blades, the stator comprising a first annular control member having a relatively rapid response rate such that it expands or contracts quickly in accordance with a temperature variation, at least one second annular control member having a relatively slow response rate such that it expands or contracts slowly in accordance with a temperature variation, the first annular control member is spaced radially from the blade tips by a clearance and defines a portion of the flowpath through the gas turbine engine, the first annular control member is supported coaxially from and radially inwardly of the second annular control member by a resilient support member whereby the first annular control member initially expands relatively rapidly in a first phase of thermal expansion in accordance with the rate of expansion of the first annular control member against the resilience of the resilient support member, the first annular control member is caused to expand relatively slowly in a second phase of thermal expansion in accordance with the rate of expansion of the second annular control member. Unfortunately these blade tip clearance control arrangements have failed to produce the ideal solution, as they are essentially single rate thermal systems because small blade tip clearances are achieved at certain engine operating conditions at the expense of other engine operating conditions. The present invention seeks to provide an improved blade tip clearance control arrangement for a gas turbine engine. The invention is characterised in that the first annular control member is, formed from a relatively low expansion material, the second annular control member is formed from a relatively high expansion material, the resilient support member is annular and is radially resilient, the radially resilient annular support member is secured to both the first annular control member and the second annular control member whereby the first annular control member expands relatively rapidly in the first phase of thermal expansion against the combined resilience of the resilient annular support member and the second annular control member until the first annular control member is fully thermally expanded, the first annular control member is caused to expand relatively slowly in the second phase of thermal expansion by the resilience of the resilient annular support member, the first annular control member initially contracts relatively rapidly in a first phase of thermal contraction in accordance with the rate of contraction of the first annular control member against the combined resilience of the resilient annular support member and second annular control member, the first annular control member is caused to contract relatively slowly in a second phase of thermal contraction in accordance with the rate of contraction of the second annular control member by the resilience of the resilient annular support member. Preferably two second annular control members are axially spaced, the first annular control member is supported coaxially from and radially inwardly of second annular control members by the radially resilient annular support member, the axial ends of the resilient annular support member are secured to the second annular control members, the first annular control member is connected to the resilient annular support member by connection means substantially at the mid portion of the resilient annular support member. The first annular control member, the resilient annular support member and the connection means may be formed integrally. The rotor may comprise a plurality of axially spaced stages of rotor blades, the stator comprises a plurality of first annular control members each one of which is spaced radially from the blade tips of a respective one of the stages of rotor blades by a clearance, a plurality of second annular control members, each first annular control member is supported coaxially from and radially inwardly of a pair of second annular control members by a respective resilient annular support member, the axial ends of each resilient annular support member are secured to the respective pair of second annular control members, each first annular control member is connected to the respective resilient annular support member by connection means substantially at the mid portion of the resilient annular support member. The axially upstream second annular control member of at least one pair of second annular control members may be secured to the axially downstream second annular control member of the pair of second annular control members axially adjacent in an upstream direction by an annular casing member such that the second annular control members, the resilient annular members and the annular casing member define a stator casing. A stage of stator vanes may be positioned axially between adjacent stages of rotor blades, each stage of stator vanes being secured at their upstream end and downstream end to first annular control members. The second control member may be insulated. The rotor may be a turbine rotor. The rotor may be a compressor rotor. The axially upstream second annular control member of at least one pair of second annular control members, the axially downstream second annular control member of the pair of second annular control members axially adjacent in an upstream direction and the annular casing member may be formed integrally. The rotor and rotor blades may be formed from titanium. The ratio of the thermal expansion coefficient of the at least one second annular control member to the thermal expansion coefficient of the first annular control member may be between 1 and 2 preferably between 1.3 and 1.4. The first annular control member may be formed from a high temperature resistant steel, the second annular control member is formed from a nickel alloy. The first and second annular control members may be formed from a high temperature resistant steel. The first annular control member may comprise a plurality of circumferentially arranged segments. The present invention will be mote fully described by way of example with reference to the accompanying drawings in which:- Figure 1 is a partially cut away view of a gas turbine engine showing the present invention. Figure 2 shows an enlarged cross-sectional view in greater detail of the embodiment shown in Figure 1. Figure 3 shows a further enlarged cross-sectional view of part of the embodiment in Figure 2. Figure 4 shows a graph of radial displacement against time for the present invention. Figure 5 shows an enlarged cross-sectional view to the same scale as Figure 3 of a further embodiment of the present invention. A turbofan gas turbine engine 10 is shown in Figure 1 and comprises in axial flow series an intake 12, a fan 14, a compressor section 16, a combustion section 18, a turbine section 20 and an exhaust nozzle 22. The gas turbine engine 10 operates quite conventionally and its operation will not be discussed herein. A part of the compressor section 16 is shown more clearly with reference also to Figures 2 and 3, and comprises an outer stator casing 24 and an inner stator casing 26 which is positioned coaxially within the outer stator casing 24. The inner casing 26 carries a plurality of stages of stator vanes 28, the stages of stator vanes 28 are spaced axially. A compressor rotor 30 is rotatably mounted coaxially within the inner casing 24 by bearings (not shown), and the compressor rotor 30 has a plurality of stages of circumferentially arranged radially outwardly extending rotor blades 32. The stages of rotor blades are spaced axially and are arranged axially alternately with the stator vanes 28. A number of blade tip clearance control arrangements 25A, 25B and 25C are shown in Figures 2 and 3. The intermediate blade tip clearance control arrangement 25B comprises a first annular control member 56 which is spaced radially from the tips of one of the stages of rotor blades 32 by a relatively small clearance, the first annular control member 56 defines a portion of the flowpath of the gas, air, through the compressor section 16. The first annular control member 56 is formed from a material having a relatively low expansion coefficient. The first annular control member 56 is positioned coaxially with and radially inwardly of a pair of second annular control members 48,50, and the first annular control member 56 is supported by the second annular control members 48,50 by a radially resilient annular support member 52. The ends of the resilient annular support member 52 have radially extending flanges by means of which the resilient annular support member is secured to the second annular control members 48,50 by bolted joint arrangements, or other suitable joining means. The first annular control member 56 is connected to the resilient annular support member 52 by a radially extending annular connecting member 54, the annular connection member 54 is secured to the mid portion of the resilient annular support member 52. Preferably the first annular control member 56, the annular connecting member 54 and the resilient annular support member 52 are formed integrally. The second annular control members 48,50 are formed from a material having a relatively high expansion coefficient. The upstream blade tip clearance control arrangement 25A comprises a first annular control member 42 which is spaced radially from the tips of an upstream stage of rotor blades 32 by a small clearance, the first annular control member 42 defines a portion of the flowpath of the gas, air, through the compressor section 16. The first annular control member 42 is formed from a material having a relatively low expansion coefficient. The first annular control member 42 is positioned coaxially with and radially inwardly of a pair of second annular control members 34,36 and the first annular control member 42 is supported by the second annular control members 34,36 by a radially resilient annular support member 38. The ends of the resilient annular support member 38 have radially extending flanges by means of which the resilient annular support member is secured to the second annular control members 34,36 by a bolted joint arrangement, or again any other suitable joining means. The first annular control member 42 is connected to the resilient annular support member 38 by a radially extending annular connecting member 40, the annular connecting member 40 is secured to the mid portion of the resilient annular support member 38. The first annular control member 42, the annular connecting member 40 and the resilient annular support member 38 are formed integrally. The second annular control members 34,36 are formed from a material having a relatively high expansion coefficient. Similarly the downstream blade tip clearance control arrangement 25C comprises a first annular control member 70, a pair of second annular control members 62,64, a radially resilient annular support member 66 and a radially extending annular connecting member 68. The first annular control member 70 is formed from a material having a relatively low expansion coefficient, and the second annular control members 62,64 ate formed from a material having a relatively high expansion coefficient. The first annular control member 70, the annular connecting member 68 and the resilient annular support member 66 are also formed integrally. Generally the inner casing 26 comprises the second annular control members 34,36 and resilient annular support member 38 of the upstream blade tip clearance control 25A, the second annular control members 48,50 and resilient annular support member 52 of the intermediate blade tip clearance control 25B and the second annular control members 62,64 and resilient annular support member 66 of the downstream blade tip clearance control 26C. The upstream second annular control member 48 of the pair of second annular control members 48,50 of the intermediate blade tip clearance control 25B is secured to the downstream second annular control member 36 of the pair of second annular control members 34,36 of the upstream blade tip clearance control 25A by an annular casing member 74. Similarly the upstream second annular control member 62 of the pair of second annular control members 62,64 of the downstream blade tip clearance control 25C is secured to the downstream second annular control member 50 of the pair of second annular control members 48,50 of the intermediate blade tip clearance control 25B by a second annular casing member 76. The first annular control members 42,56 and 70 of the blade tip clearance control arrangements 25A,25B and 25C are arranged to carry the stages of stator vanes 28. The first annular control member 42 is provided with annular recesses 44 and 46 on its upstream and downstream faces, similarly first annular control member 56 has annular recesses 58 and 60 on its, upstream and downstream faces and first annular control member 70 has an annular recess 72 on its upstream face. The outer platforms 78 and 84 of the stator vanes 28 have axially extending feet 80,82 and 86,88 which fit into the annular recesses 46,58 and 60,72 to retain the stator vanes 28. An annular chamber 90 is formed radially between the resilient annular support member 38, the second annular control member 36, the annular casing member 74, the second annular control member 48, the resilient annular support member 52 and the first annular control member 42, the platform 78 and the first annular control member 56. Similarly a second annular chamber 92 is formed radially between the resilient annular support member 52, the second annular control member 50, the second annular casing member 76, the second annular control member 62, the resilient annular support member 66 and the first annular control member 56, the platform 84 and the first annular control member 70. The annular chambers 90 and 92 are filled with an insulating material, for example air or other suitable material. The second annular control members may be provided with insulating coatings. Referring to Figure 3, the blade tip clearance control 25B comprises two principally different thermally responsive annular control members 48,50 and 56. The first annular control member 56 comes into direct contact with the main gas stream and is heated almost immediately. The first annular control member 56 is effectively suspended from the two second annular control members 48,50 by the resilient annular support member 52. Heat transfer to the second annular control members 48,50 may be limited to thermal conduction from the resilient annular support member 52 at the face contacts of the flange points. The heat conducted from the first annular control member 56 is choked or restricted by the connecting member 54. In operation, referring to Figure 3, when heat is applied, i.e. during an engine acceleration event, the first annular control member 56 initially expands rapidly and the second annular control members 48,50 expand slowly, but the resilient annular support member 52 bends radially outwardly to allow for the difference in thermal expansion rates of the control members. The first annular control member 56 expands in accordance with its own rate of thermal expansion, but expands against the combined resilience of the resilient annular support member 52 and the second annular control members 48,50, which control the rate of expansion of the first annular control member 56. At some point the first annular control member 56 becomes fully thermally expanded, i.e. it reaches its maximum thermal radial displacement, but the second control members 48,50, because of their higher coefficient of expansion and slower response rate, continue to expand thermally. Eventually the second annular control members 48,50 expand radially by more than the maximum thermal radial displacement of the first annular control member 56, and thus the first annular control member 56 is caused to expand further relatively slowly in accordance with the rate of expansion of the second annular control member 48,50 because of the interconnection between the second annular control members 48,50 and the first annular control member 56. During the second phase of thermal expansion the resilient annular support member 52 is caused to become bent radially inwardly due to the resistance to further expansion of the first annular control member 56. At some point the second control members 48,50 become fully thermally expanded, i.e. reach their maximum thermal radial displacement. When heat is reduced i.e. during an engine deceleration event, the first annular control member 56 initially contracts rapidly and the resilient annular support member 52 bends radially inwardly to allow for the difference in thermal expansion rates of the control members. The first annular control member 56 contracts in accordance with its own rate of thermal contraction, but contracts against the combined resillence of the resilient annular support member 52 and the second annular control members 48,50 which control the rate of contraction of the first annular control member 56. The resilience of the resilient annular support member 52 prevents the first annular control member 56 from contracting fully thermally, but as the second control members 48,50 contract the first control member 56 is allowed to contract slowly in accordance with the rate of contraction of the second annular control members 48,50. The radial displacements of the first annular control member 56 and second annular control members 48,50 with time for an acceleration are shown in Figure 4. Curve A shows the free radial displacement of the first annular control member 56 with time during an acceleration, it can be seen that the first annular control member expands initially rapidly and then remains substantially constant when it reaches its maximum thermal radial displacement. Curve B shows the free radial displacement of the second annular control members 48,50 with time during an acceleration, it can be seen that the second annular control members 48,50 expand relatively slowly throughout the time period shown. Curve C shows the effect on the first annular control member 56 on coupling it to the second annular control members 48,50 by the resilient annular support member 52, it can be seen that the first annular control member initially expands relatively quickly and then expands relatively slowly in accordance with the second annular control members. Beyond point D the first annular control member is caused to expand beyond its natural fully thermally expanded condition i.e. beyond its maximum thermal radial displacement. As an example, a fast response casing arrangement of the prior art will, in general, enable a small initial cold build blade tip clearance to be defined at the expense of a transient overshoot, i.e. a large transient blade tip clearance, when heat is applied in operation. On the other hand, with a slow response casing arrangement of the prior art a large initial cold build blade tip clearance is required. This large clearance does not fully reduce until well into the take-off part of the gas turbine engine operating cycle. One of the objectives of the present invention is to attain at least a dual rate radial displacement against time profile in operation. The dual rate radial displacement against time profile comprises a relatively fast rate of expansion in the initial phase and a more gradual but continuous expansion in a final phase of operation. Even though a passive blade tip clearance control is not able to match the almost instantaneous response of the rotor under centrifugal loading, the present invention enables a relatively small initial cold build blade tip clearance to be defined with considerably reduced risk of blade tip contact and no risk of transient overshoot. The present invention therefor provides a significant increase in transient surge margin when it is needed most i.e. for good manoeuverability. The multi-rate response concept ensures a more optimum matching with rotor rim growth producing a small blade tip clearance for increased efficiency at various stabilised operating conditions. The embodiment of a blade tip clearance control arrangement shown in Figure 5 is substantially the same as that shown in Figures 2 and 3. It again comprises two different thermally responsive annular control members 134,136 and 142. The first annular control member 142 comes into direct contact with the main gas stream and is heated almost immediately. The first annular control member 142 is suspended from the two second annular control members 134,136 by a resilient annular support member 138. The major difference between this embodiment and that in Figures 2 and 3 is that the second annular control member 134 is formed integral with an annular casing member 144 and the second annular control member 136 is formed integral with an annular casing member 146. In effect the flanges of the annular casing members form the second annular control members. The advantage of this arrangement over the embodiment shown in Figures 2 and 3 is that there is a reduction in the number of components forming the casing 26, and there is a weight reduction. However the arrangement is equally effective at controlling the blade tip clearance as the embodiments in Figures 2 and 3. Although the radial displacement of the first annular control member, and hence blade tip clearance, is principally controlled by the interaction of the first and second annular control members, a multi-rate radial time displacement against time profile may be achieved by suitable selection of materials with respect to thermal expansions and thermal diffusivities, thermal inertias and radial structural resilience of the first and second annular control members. The ratio of thermal expansion coefficient of the second annular control member to the thermal expansion coefficient of the first annular control member is selected to be between 1.0 and 2.0, and preferably is selected to be between 1.3 and 1.4. The radially resilient annular support member further controls the interaction between the first and second annular control members by its own thermal inertia and structural resilience. The axial length and the thickness of the resilient annular support member control the stiffness between the first annular control member and the second annular control member. The resilient annular support controls the rate of expansion/contraction of the first annular control member. The material for the resilient annular support member, and the axial length and thickness are selected to give the desired characteristics. For example the axial length of the resilient annular support member is approximately 1 inch = 2.5 cm, and the thickness is 1/10 inch = 0.25 cm. As an example of the invention applied to a titanium high pressure compressor rotor, with titanium rotor blades, the first annular control rings and the resilient annular support ring are manufactured from a steel with high temperature and creep resistant properties sold under the trade name FV535, and the second annular control rings are manufactured from a nickel base alloy sold under the trade name INCO 901. FV535 has a nominal composition of 10% Chromium, 6% Cobalt, 0.8% Molybdenum, and the balance is Iron. INCO 901 has a nominal composition of 35% Iron, 12% Chromium, 6% Molybdenum, 3% Titanium and the balance is Nickel with minor addition of Cobalt. A further example of the invention applied to a titanium high pressure compressor rotor with titanium rotor blades, the first annular control ring, the resilient annular support ring and the second annular control rings are manufactured from the steel sold under the trade name FV535. The advantage of using the all steel arrangement is that of a reduction in manufacturing costs. For lower temperature and lower pressure stages of the high pressure compressor of a low pressure compressor a low temperature steel sold under the trade name Jethete may be used. The optimum blade tip clearance is 0.25 mm for a blade with a 1 inch = 2.5 cm blade true chord, and the invention is capable of controlling the blade tip clearance between the range of 0.15 mm - 0.30 mm at high power conditions. The invention controls the blade tip clearance to improve the efficiency and surge margin of the compressor. The first control member, as described with reference to the embodiments, is a completely annular member, this allows the first control member to expand or contract thermally equally in all radial directions. The first control member may comprise a plurality of circumferentially arranged segments, which together form a complete annulus. However, the use of the segmented first control member is not the preferred solution because in operation the segments of the segmented first control member expand or contract thermally in a circumferential direction in addition to the radial direction. The segmented first control member therefore does not respond as quickly as the fully annular first control member to match fast transient growth of the rotor rim. The segmented first control member will also suffer from leakage of gas between adjacent segments. Although the description and drawings have described the invention with reference to a compressor the invention is equally applicable to a turbine of a gas turbine engine.

Claims: A blade tip clearance control arrangement for a gas turbine engine comprising a rotor (30) and a stator (24,26), the rotor (30) having at least one stage of circumferentially arranged radially extending rotor blades (32), the stator (24,26) comprising a first annular control member (56) having a relatively rapid response rate such that it expands or contracts quickly in accordance with a temperature variation, at least one second annular control member (48,50) having a relatively slow response rate such that it expands or contracts slowly in accordance with a temperature variation, the first annular control member (56) being spaced radially from the blade tips (32) by a clearance and defines a portion of the flowpath through the gas turbine engine (10), the first annular control member (56) is supported coaxially from and radially inwardly of the second annular control member (48,50) by a resilient support member (52) whereby the first annular control member (56) initially expands relatively rapidly in a first phase of thermal expansion in accordance with the rate of expansion of the first annular control member (56) against the resilience of the resilient support member (52), the first annular control member (56) is caused to expand relatively slowly in a second phase of thermal expansion in accordance with the rate of expansion of the second annular control member (48,50), characterised in that the first annular control member (56) is formed from a relatively low expansion material, the second annular control member (48,50) is formed from a relatively high expansion material, the resilient support member (52) is annular and is radially resilient, the radially resilient annular support member (52) is secured to both the first annular control member (56) and the second annular control member (48,50) whereby the first annular control member (56) expands relatively rapidly in the first phase of thermal expansion against the combined resilience of the resilient annular support member (52) and the second annular control member (48,50) until the first annular control member (56) is fully thermally expanded, the first annular control member (56) is caused to expand relatively slowly in the second phase of thermal expansion by the resilience of the resilient annular support member (52), the first annular control member (56) initially contracts relatively rapidly in a first phase of thermal contraction in accordance with the rate of contraction of the first annular control member (56) against the combined resilience of the resilient annular support member (52) and the second annular control member (48,50), the first annular control member (56) is caused to contract relatively slowly in a second phase of thermal contraction in accordance with the rate of contraction of the second annular control member (48,50) by the resilience of the resilient annular support member (52). A blade tip clearance control arrangement as claimed in claim 1 in which two second annular control members (48,50) are axially spaced, the first annular control member (56) is supported coaxially from and radially inwardly of the second annular control members (48,50) by the radially resilient annular support member (52), the axial ends of the resilient annular support member (52A, 52B) are secured to the second annular control members (48,50), the first annular control member (56) is connected to the resilient annular support member by connection means (54) substantially at the mid portion of the resilient annular support member (52). A blade tip clearance control arrangement as claimed in claim 2 in which the first annular control member (56), the resilient annular support member (52) and the connection means (54) are formed integrally. A blade tip clearance control arrangement as claimed in claim 2 or claim 3 in which the rotor comprises a plurality of axially spaced stages of rotor blades (32), the stator comprises a plurality of first annular control members (42,56,70) each one of which is spaced radially from the blade tips of a respective one of the stages of rotor blades (32) by a clearance, a plurality of second annular control members (34,36,48,50,62,64), each first annular control member (42,56,70) is supported coaxially from and radially inwardly of a pair of second annular control members (34,36,48,50,63,64) by a respective resilient annular support member (38,52,66), the axial ends of each resilient annular support member (38,52,66) are secured to the respective pair of second annular control members (34,36,48,50,62,64), each first annular control member (42,56,70) is connected to the respective resilient annular support member (38,52,66) by connection means (40,54,68) substantially at the mid portion of the resilient annular support member (38,52,66). A blade tip clearance control arrangement as claimed in claim 4 in which the axially upstream second annular control member (48) of at least one pair of second annular control members (48,50) is secured to the axially downstream second annular control member (36) of the pair of second annular control members (34,36) axially adjacent in an upstream direction by an annular casing member (74) such that the second annular control members (34,36,48, 50), the resilient annular members (38,52) and the annular casing member (74) define a stator casing (26). A blade tip clearance control arrangement as claimed in claim 5 in which a stage of stator vanes (28) is positioned axially between adjacent stages of rotor blades (30), each stage of stator vanes (28) being secured at their upstream end and downstream end to first annular control members (42,56,70). A blade tip clearance control arrangement as claimed in claim 5 or claim 6 in which the axially upstream second annular control member (136) of at least one pair of second annular control members (134,136), the axially downstream second annular control member of the pair of second annular control members axially adjacent in an upstream direction and the annular casing member (146) are formed integrally. A blade tip clearance control arrangement as claimed in any of claims 1 to 7 in which the ratio of the thermal expansion coefficient of the at least one second annular control member (48,50) to the thermal expansion coefficient of the first annular control member (56) is between 1 and 2. A blade tip clearance control arrangement as claimed in claim 8 in which the ratio of the thermal expansion coefficient of the at least one second annular control member (48,50) to the thermal expansion coefficient of the first annular control member (56) is between 1.3 and 1.4. A blade tip clearance control arrangement as claimed in any of claims 1 to 9 in which the second control member (48,50) is insulated. A blade tip clearance control arrangement as claimed in any of claims 1 to 10 in which the rotor is a turbine rotor. A blade tip clearance control arrangement as claimed in any of claims 1 to 10 in which the rotor (30) is a compressor rotor. A blade tip clearance control arrangement as claimed in claim 12 in which the rotor and rotor blades are formed from titanium. A blade tip clearance control arrangement as claimed in claim 13 in which the first annular control member (56) is formed from a high temperature resistant steel, the second annular control member (48,50) is formed from a nickel alloy. A blade tip clearance control arrangement as claimed in claim 13 in which the first annular control member (56) and second annular control members (48,50) are formed from a high temperature resistant steel. A blade tip clearance control arrangement as claimed in any of claims 1 to 15 in which the first annular control member (56) comprises a plurality of circumferentially arranged segments.

Inventors: LAU, KWOK YAN
Applicants: ROLLS-ROYCE PLC
Application year: 1989
Main classification: F01D11
IPC codes: F01D11