The study of flight conditions impact on high-pressure turbine disk damaging of the highly maneuverable aircraft

Аuthors

Gogaev G. P.^*, Nemtsev D. V.^**

Lyulka Experimental Design Bureau, branch of the United Engine Corporation – Ufa Engine Industrial Association, 13, Kasatkina str., Moscow, 129301, Russia

*e-mail: gogaevgeorge@rambler.ru
**e-mail: dmitrij_n@inbox.ru

Abstract

The increase in the GTE life cycle cost brings to the forefront the problem of the full safe use of the aviation engines lifetime, which can be achieved by the transition to operation on a technical condition. This transition is possible with the sufficient product testability ensuring obtaining the objective information required for the reliable technical condition estimating.

The crucial problem herewith consists in methods and algorithms developing for estimation the lifetime depletion, accounting for loading specifics of each engine.

Excessive conservatism is inherent to the currently employed methods for lifetime cycle depreciation control due to the lack of actual operation conditions record keeping. Premature engines exclusion fr om operation occurs thereby, which is unfavorable and has an adverse effect on supporting the required combat readiness level of the aircraft fleet.

Thus, the trend of control techniques improvement, analysis of loading and GTE lifetime deprecation control, fully accounting for the operation specifics of each engine is relevant enough.

The purpose of this work consists in studying the impact of flight conditions on the high-pressure turbine (HPT) disc damaging of highly maneuverable aircrafts.

The main contribution to the parts damage accumulation of the highly maneuverable aircraft engine is made by the damages, caused by intermittent operation modes (the low-cyclic fatigue mechanism), and operation at the maximum set modes (the mechanism of long-term strength depletion).

As the service experience of the 4th generation engines being a part of highly maneuverable aircraft of the task aircraft fleet shows, the contribution of a static component to the overall damage of the basic engine parts is significantly less than the cyclic one. Thus, the estimation of the residual engine life is made, as a rule, based only on accounting for the cyclic damages of its basic parts.

The main idea of the 4th generation engine life deprecation accounting for consists in comparing the actual value of the technical condition parameter (the accumulated damage) of the engine basic parts during the operation with its maximum permissible value, accumulated while the endurance tests, with subsequent determination of the residual resource of the engine basic parts according to this comparison.

Currently the number of cycles before the failure (N_pi) and the single damage (П_i) for each cycle type are is detemined at the extreme loads (engine power rating, speed, and flight altitude) for the given GTE operation range.

However, the performed analysis of the highly maneuverable aircraft operation belonged to the task aircraft fleet, revealed that about 80% of the operation was performed at subsonic speeds and heights up to 10 km (without participation in combat operations), at which the basic part load was much lower than its maximum value. Thus, the existing methodology application leads to the excessive conservatism of the accumulated damage calculation.

To assess the effect of flight conditions on the single damage of the main parts, a complex of calculations for HPT disk of the 4th generation engine were performed. The obtained results demonstrated that the single damage of all cycle types of the HPT disk significantly depends on the flight conditions. Thus, the single damage of the loading cycles in the zone, wh ere 80% of operation time is performed in default of combat operations participation, is on average 25% below the values at the maximum loads for all cycle types.

In the context of the HPT disk of the 4th generation engine, the article shows that the existing technique for the lifetime deprecation monitoring by low-cycle fatigue of the 4th generation GTE basic parts includes assumptions leading to the accuracy reduction of determining the accumulated damage and the residual life of the engine and its main parts. This, in turn, leads to an early removal of a serviceable engine, and the life cycle cost increasing.

To avoid the excessive conservatism of the currently used technique, it is necessary to accumulate the cyclic damage of the engine basic parts with account for real flight conditions.

Keywords:

gas-turbine engine, low cycle fatigue, basic parts, damageability, flight conditions

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