Improving Methods for Experimental Stability Margin Determining of Operation and Contraction of the Axial Compressor First Stage as a Part of the Gas Generator

Аuthors

Klinskii B. M.

Central Institute of Aviation Motors named after P.I. Baranov, Moscow, Russia

e-mail: bmklinskiy@ciam.ru

Abstract

With experimental method of studying compressor characteristics, the stable operation margin of high-pressure axial compressor is being determined on special nodal compressor test-benches, or while compressor tests directly as a part of aviation gas-turbine engine, including the case of its being a part of the experimental gas generator.
To determine the of stable operation margin of the compressor as a part of the gas generator, the following may be applied in particular:
- corresponding reduction of the technological jet nozzle critical section area, and reduction of the minimum area of the gas generator high-pressure turbine nozzle block flow section;
- as well as fuel stepped injection into the gas generation combustion chamber and many others.
A number of these methods are being applied with operational limitations, caused primarily by the possibility of the gas temperature prior to the high-pressure turbine reaching the limit value etc. With this regard, the present work considers the method of blowing compressed air into the combustion chamber of an experimental gas generator to determine the value of the stable operation margin of a high-pressure compressor, which allows eliminating a number of disadvantages inherent to the other methods.
The studied high-pressure compressor with the adjustable inlet guide device and guide devices of the two stages with a constant value of relative air intake from the intermediate stage was a part of an experimental gas generator, which was installed in a thermal chamber of a high-altitude stand according to a scheme with an attached inlet pipeline. Two branch pipes were fixed on the case of the gas generator combustion chamber to ensure the possibility of the compressed air blowing from the bench source into the combustion chamber.
Application of the compressed air injection method into the combustion chamber of the experimental gas generator allowed:
- ensuring determination of the high-pressure compressor stable operation margin up to the limit of stable operation in the operating range of the compressor operating modes at steady-state operation of the gas generator while maintaining the stable operation of the combustion chamber without disruption and vibration combustion with a “poor” fuel-air mixture in the combustion chamber by the air flow coefficient  by 30-35 and more percent at the boundary of the gas dynamic stability of the compressor;
- increasing safety of the tests and material part of the gas generator by significantly lowering the gas temperature in the high-pressure turbine and behind the turbine to (100-120)°C at the boundary of the compressor gas dynamic stability compared to the values measured on the nominal line of operating modes without blowing compressed air into the combustion chamber, and also due to the use of a antisurge system for the immediate shutdown of the gas generator after the compressor is surged by stopping the fuel supply to the combustion chamber and cutting off the supply of compressed air to the combustion chamber of the gas generator.
The results of the experimental gas generator test confirmed that the compressed air injection into the combustion chamber, while checking the absence of a “stall” type flutter in the working blades of the high-pressure compressor first stage, can ensure obtaining a normalized reserve value of the mode coefficient in the compressor first stage δKP1 = +(2–4)% [6] above the limit line of operating modes, with account for the production spread of the position of the line of operating modes related to the features and stability of engine production, as well as the operating conditions and operating time during the life of the fleet of turbofan engines in operation without restriction on the maximum permissible gas temperature in the high-pressure turbine of the gas generator.

Keywords:

experimental gas generator, axial multistage compressor, turbojet dual-circuit engine, thermal vacuum chamber, connected inlet pipeline, compressor surge, compressor stable operation margin

References