Experience With Large Heavy-Duty Gas Turbine Rotors

The peripheral speeds of the rotors of large heavy-duty gas turbines have reached levels which place extremely high demands on material strength properties. The particular requirements of gas turbine rotors, as a result of the cycle, operating conditions and the ensuing overall concepts, have led different gas turbine manufacturers to produce special structural designs to resolve these problems. In this connection, a report is given here on a gas turbine rotor consisting of separate discs which are held together by a center bolt and mutually centered by radial serrations in a manner permitting expansion and contraction in response to temperature changges. In particular, the experience gained in the manufacture, operation and servicing are discussed.

Unbalance Response of a Two Spool Gas Turbine Engine With Squeeze Film Bearings

This paper presents a dynamic analysis of a two-spool gas turbine helicopter engine incorporating intershaft rolling element bearings between the gas generator and power turbine rotors. The analysis includes the nonlinear effects of a squeeze film bearing incorporated on the gas generator rotor. The analysis includes critical speeds and forced response of the system and indicates that substantial dynamic loads may be imposed on the intershaft bearings and main bearing supports with an improperly designed squeeze film bearing. A comparison of theoretical and experimental gas generator rotor response is presented illustrating the nonlinear characteristics of the squeeze film bearing. It was found that large intershaft bearing forces may occur even though the engine is not operating at a resonant condition.

Strengthening Mechanisms and Process Controls for Super Waspaloy

Super Waspaloy is an empirically derived thermomechanically processed version of Waspaloy. Microstructures were evaluated at steps in the hammer forge and heat treat sequence to study how the initial structure is derived. Foils taken from hot tensile, stress rupture, and elevated temperature low cycle fatigue bars were examined by transmission electron microscopy after exposure to temperature and stress. The purpose was to discover the microstructural features resistant to dislocation movement and to seek clues for further improvement of the alloy.

A System to Measure the Response of a High-Speed Rotor to a Sudden Imbalance

A unique rotor dynamic data acquisition system is described to control the gathering and display of rotor displacement data measured at rotor speeds up to 70 000 r/min. The first published results measured with this system are demonstrated with plots of measured transient shaft motion after a sudden increase in shaft imbalance at speeds up to 44 500 r/min. The displacements of the rotor in the forms of Lissajous plots with and without a squeeze film damper are presented at four axial shaft locations below and above the shafts critical speeds. The blade-loss, dynamic test rig is also described.

Refrigerating Gas Turbine Compressor Air Intake

Gas turbines power output is adversely influenced by increasing ambient temperatures. This is mainly caused by the reduction both in the air mass flow rate through the compressor and the developed compression ratio. It is claimed that refrigerating the compressor air intake down to 0 C, will generate enough power to cope with refrigerating system power requirements as well as leaving ample surplus power.

Sintering Microstructure and Properties of Si3N4 and SiC Based Structural Ceramics

The observed properties of typical sintered ceramic alloys based on Si3N4 and SiC are discussed. Properties result from interaction between various components of the phase assemblage. The pure single phase components are inherently strong because of their covalent bonding but they are unsinterable without densification aids. These aids change composition and microstructure, thus can strongly influence some properties. The effect of composition and microstructure on properties of sintered Si3N4 and SiC based ceramics is described.

Using Microprocessors in Fault Monitoring of Aircraft Electronics

This paper discusses the Ultra Electronic Controls Fault Identification Moduel (F.I.M.) as used in the Electronic Engine Control Unit (E.C.U.) for the Olympus 593 engines of the Concorde Supersonic Transport Aircraft. This is based on a C.M.O.S. Microprocessor for low power consumption and enables the Module to be applied to existing units without redesign of power supplies. The Module examines the outputs of existing fault monitoring circuits and compares these with software defined reference levels. It then determines from this and other signals taken from the E.C.U. safety consolidation circuits, the Engine Control Sub-System which is at fault. This Module has been in service with British Airways and Air France for close to one year now and the impact on rapid and accurate fault diagnosis, elimination of premature E.C.U. removals and thus reduction of cost ownership of the E.C.U. is discussed.

The Evaluation of Fuel Property Effects on Air Force Gas Turbine Engines Program Genesis

The Air Force has conducted a series of investigations to quantify the effects of certain fuel properties on the operability and durability of its aircraft gas turbine engines. Initially these efforts were conducted on a small number of engines intended to be representative of the majority of gas turbine engines in the Air Force inventory. The testing was conducted exclusively in rigs representing the combustor and fuel nozzle components of these engines of interest. Test fuels for these programs were primarily blends of hydrocarbons. These test fuels exhibited significant variations in several major fuel properties. Based on results of these evaluations a second generation of test activity in fuel effects area was formulated. Engine system selection was broadened to include more considerations. Test fuels were reduced in number and priorities for modification of certain fuel properties were adjusted. This paper presents dominant test results of early fuel effects programs and supplemental background which dictated the structure of the second, more comprehensive program.

Development of the Self-Temperature Compensated Resistance Strain Gage Used up to 700 C

This paper represents a self-temperature compensated resistance strain gage which is of combined type and developed recently. Because the scatter of the thermal output and the drift of the strain gage are smaller in all heat cycles, they could be compensated by bridge circuit or by dummy gage and better accuracy can be obtained. The gage enables engineers to measure the hot-end parts of aeroengines.

NASA Gas Turbine Stator Vane Ring

AiResearch Casting Company has produced four monolithic stator vane rings from reaction-bonded silicon nitride. This paper describes the various steps involved: wax injection of stator vane patterns, precise fixturing of patterns, mold fabrication, slip preparation, casting, prenitriding, nitriding, and ceramic machining. Each process step is discussed and illustrated, and tables of property measurements are included.