Method and apparatus for use in control of clearances in a gas turbine engine

A method for determining the clearance between the rotor blades of a rotor assembly and a shroud disposed radially outside the rotor assembly within a gas turbine engine, wherein the rotor blades of the rotor assembly are attached to a rotor disk, said method comprising the steps of:

• determine one or more steady-state operating conditions using a given temperature value, a given altitude value, and a given mach number value;
• determine a steady-state clearance value for a predetermined power rating of the engine using said one or more steady-state operating conditions;
• determine an instantaneous thermal condition (TR) for the rotor disk, an instantaneous thermal condition (TB) for the rotor blades, and an instantaneous thermal condition (TS) for the shroud;
• provide a transfer function (GROWTHR) representative of the thermal expansion of the rotor disk, a transfer function (GROWTHB) representative of the thermal expansion of the rotor blades, and a transfer function (GROWTHS) representative of the thermal expansion of the shroud, using said instantaneous thermal conditions;
• determine an instantaneous clearance transient overshoot value (CTO), using said transfer functions;
• determine a clearance value using said steady-state clearance value and said instantaneous clearance transient overshoot value.

An apparatus for determining the clearance between the rotor blades of a rotor assembly and a shroud disposed radially outside the rotor assembly within a gas turbine engine, wherein the rotor blades of the rotor assembly are attached to a rotor disk, said apparatus comprising:

• a processing means for determining one or more steady-state operating conditions for a given steady-state power setting using a given temperature value, a given altitude value, and a given mach number value;
• a processing means for determining a steady-state clearance value for a predetermined power rating of the engine using said one or more steady-state operating conditions;
• a processing means for determining an instantaneous thermal condition (TR) for the rotor disk, an instantaneous thermal condition (TB) for the rotor blades, and an instantaneous thermal condition (TS) for the shroud;
• a processing means for determining a value (GAINR) representative of the thermal expansion of the rotor disk, a value (GAINB) representative of the thermal expansion of the rotor blades, a value (GAINS) representative of the thermal expansion of the shroud, using said instantaneous thermal conditions;
• a processing means for determining an instantaneous clearance transient overshoot value (CTO) which utilizes said values representative of the thermal expansion of the rotor disk, rotor blades, and shroud;
• a processing means for determining a clearance value using said steady-state clearance value and said instantaneous clearance transient overshoot value.

An apparatus for determining the clearance between the rotor blades of a rotor assembly and a shroud disposed radially outside the rotor assembly within a gas turbine engine, wherein the rotor blades of the rotor assembly are attached to a rotor disk, said apparatus comprising:

• a processing means for determining one or more steady-state operating conditions for a given steady-state power setting using a given temperature value, a given altitude value, and a given mach number value;
• a processing means for determining a steady-state clearance value for a predetermined power rating of the engine using said one or more steady-state operating conditions;
• a processing means for determining an instantaneous thermal condition (TR) for the rotor disk, an instantaneous thermal condition (TB) for the rotor blades, and an instantaneous thermal condition (TS) for the shroud;
• a processing means that includes a transfer function (GROWTHR) representative of the thermal expansion of the rotor disk, a transfer function (GROWTHB) representative of the thermal expansion of the rotor blades, and a transfer function (GROWTHS) representative of the thermal expansion of the shroud, using said instantaneous thermal conditions;
• a processing means for determining an instantaneous clearance transient overshoot value (CTO) which utilizes said transfer functions;
• a processing means for determining a clearance value using said steady-state clearance value and said instantaneous clearance transient overshoot value.