Analysis of Control Laws for Efficiency Decline Compensation of the Supersonic Passenger Liner Bypass Turbofan Subassemblies

Аuthors

Ezrokhi Y. A.^*, Kalenskii S. M.^**

Central Institute of Aviation Motors named after P.I. Baranov, CIAM, 2, Aviamotornaya str., Moscow, 111116, Russia

*e-mail: yaezrokhi@ciam.ru
**e-mail: 30105@ciam.ru

Abstract

The article being presented considers the basic operational factors, which may lead to the subassemblies essential wearing of a of the supersonic passenger liner turbofan engine. It was demonstrated that the most telling effect on the engine parameters was exerted by the of blade machines, such as compressors and turbines, characteristics degradation.
Among the works on the aviation engines wearing being considered, the complex studies on the compressors and turbines characteristics degradation of the JT9D Pratt & Whitney turbofan engine were highlighted. Dimensionality of the gas generator selected as the subject of research of the supersonic passenger liner turbofan engine is close to the JT9D Pratt & Whitney gas generator dimensionality (Ggg JT9D ~ 7/8 kg/s). Thus, with some approximation for the considered engine, the data on the turbofan engine JT9D Pratt & Whitney subassemblies efficiency degradation while operation process, though with correction corresponding to its resource, was employed.
On the assumption of the published data, the resource of supersonic passenger liner turbofan engine may be of 2000 flight cycles under condition of supersonic flight modes duration 4–5 hours. Thus, assuming the total resource of the prospective engine of the supersonic passenger liner may be of 10000 hours, the resource until the major maintenance would be presumably no more than 5000 hours (the half of the total resource).
Computational esteems of the considered engine parameters were performed with the turbofan bypass engine model with the flows mixing and common nozzle.
The engine operation modes at the flight conditions characteristic of the number of foreign projects of the supersonic passenger liners were selected as the modes at which the subassemblies parameters degradation was being considered. These are the takeoff mode, subsonic cruising mode, supersonic cruising mode and the transonic climbing mode. The thrust value obtained at the takeoff mode was assumed as the basic one, relative to which the required thrust values at the supersonic cruising mode and transonic climbing mode were determined. The subsonic cruising engine operation mode was being determined from the condition of the reduced fan rotational frequency maximum value (nfr = 1).
As computational esteems revealed, parameters efficiency degradation of the selected engine subassemblies (while level maintaining of the gas temperature prior to the turbine at the initial level for each mode) may lead to the thrust reduction (R) to δR ~9%. With this, the gas temperature rise prior to the turbine up to ΔTg* = 50K is necessary for the thrust complete recovery up to the initial level at the mode.
Several control laws of fuel feeding to the combustion chamber for the selected controlling parameters sustaining at every mode were considered to assess the possibilities for the possible thrust decay compensation of the selected engine due to its subassemblies efficiency degradation while in service.
The obtained computational data revealed that of initial rotational speed maintaining of the fan rotor (n1), of the high-pressure compressor (n2), or a total compressor pressure ratio π*к turns out not to be the most effective option. Particularly, at the supersonic cruiser flight mode with n1 = const, the temperature increase was of Т*g ~70К, at n2 = const – Т*г ~90К, and at π*к= const – Т*г~62К.
Sustaining the engine pressure ratio π*дв = const and fan pressure ratio *f = const leads to close results. The engine thrust at the subsonic modes is being preserved at the initial level, while it rises (up to ~2 %) at the supersonic ones. It corresponds to gas temperature “overshoot” Т*г prior to the turbine of 10К compared to its value necessary for the thrust sustaining.
As computational studies revealed, temperature T*k sustaining behind the high-pressure compressor, is capable of ensuring the least error while the required thrust maintenance for the majority of the considered flight modes, compared to the initial one. However, this control law corresponds to the thrust underrun at all considered modes of a flight cycle and is difficult in practical realization, which makes its unacceptable.
Thus, analysis of the possible ways of control for the indirect thrust sustaining by the measured parameters at the bypass turbofan engine parameters degradation of a supersonic passenger liner revealed the preferability of the π*дв=const и *в=const laws. For the subassemblies efficiency decline compensation and maintaining the required thrust ensuring at the basic flight modes while these control laws application, the temperature margin of Т*г  > 55К may be required.

Keywords:

bypass turbofan engine, trust decline during operation, subassemblies efficiency decline, temperature margin at the turbine inlet, engine control laws

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