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Advances in Gas Turbine Technology Part 16

Tham khảo tài liệu 'advances in gas turbine technology part 16', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 440 Advances in Gas Turbine Technology b Fig. 8. Characteristic forms of failures to gas turbine caused by long-lasting excessive temperature of exhaust gases Reports 2000-2010 a - burn-through of turbine rotor blades b - melting of a nozzle vane a 2.3 Chemical failures a. high-temperature corrosion Fig. 9 a b Fig. 9. Failures to turbine blades operated in the seashore environment caused by chemical impact of exhaust gases Reports 2000-2010 a - on blade surface b - on blade leading edge b. intercrystalline corrosion Fig. 10 . Blade deformations in the form of dents Fig. 2 are caused by a foreign matter ingested by the turbojet engine compressor and by particles of metal and hard carbon deposits from the combustion chamber. Such dents result in stress concentrations in blade material and prove conducive to the initiation of fatigue processes. Scratches on blade surfaces Fig. 3 due to the foreign matter impact are also reasons for local stress concentrations and consequently potential corrosion centers. What results is again material fatigue which together with possible corrosion prove conducive to fatigue fracture. 441 Damageability of Gas Turbine Blades - Evaluation of Exhaust Gas Temperature in Front of the Turbine Using a Non-Linear Observer Fatigue of material of turbine rotor blades is caused by a sum of loads due to non-uniform circumferential distribution of the exhaust gas stream leaving the combustion chamber and its unsteadiness in time non-uniformity of the exhaust gas stream leaving the nozzle and excitations from the structure of e.g. the turbojet engine. The dynamic frequency of free vibration attributable to the rotor blade of variable cross-section depends on the centrifugal force therefore it is a function of rotation speed. It also depends on temperature of the working agent affecting the longitudinal modulus of elasticity Young s modulus of the material. The most hazardous are instances of turbine blade operation at resonance of the 1st form of .