Studying the flow non-uniformity impact at the inlet on the aircraft gas turbine engine basic parameters under the simulated altitude-speed conditions

DOI: 10.34759/vst-2023-1-117-130

Аuthors

Klinskii B. M.

e-mail: bmklinskiy@ciam.ru

Abstract

According to paragraph «33.65 Surge and Stall Characteris-tics» of the Aviation Regulations, part 33 (Aircraft Engine Airworthiness Standards) the fol-lowing is stated. «It is required that while engine operation according to the Op-eration Manual the engine startup, power or thrust changing, power or thrust forcing, limit non-uniformity of the air flow at the engine inlet should not cause surging or flow separation, which might lead to the flame breaking, destruction of the structure, temperature rise or breaking the possibility of recovering power or thrust in any point of the operation modes range». In this regard, the issues of simulating the required type and level of the flow non-uniformity at the inlet prior to the engine while bench testing to confirm sufficient margin of the gas-dynamic stability of the compressor and relatively trifle impact on the basic parameters of the engine vibration-strength characteristics, become up-to-date and of practical meaningfulness.

The field of velocities and pressures at the inlet of the engine as a part of the power plant is being determined by the aircraft flight conditions (altitude and flight Mach number, angles of attack and sideslip, etc.), the engine operation mode and the air intake design. In general, this field is non-uniform, and the flow prior to the engine is non-stationary. Thus, its imitation while bench testing of a gas turbine engine is a difficult technical task.

The following basic requirements are being imposed on the simulators of a non-uniform flow prior to the engine:

the values of the total pressure coefficient s_in, averaged over the channel section prior to the engine and the values of the parameters (criteria) of the non-uniform flow (the circumferential non-uniformity criteria of the total pressure and the total pressure pulsations intensity) behind the power plant air intake and simulator, should be the same;

the simulator should generate a total pressure field prior to the en-gine, similar to the real field of total pressures behind the air intake at equal values of the reduced air mass flow through the engine.

The main reasons causing the uneven flow prior to the engine are associ-ated with the local separation zones occurrence in the air intake duct, accompanied by the total pres-sure loss and an increase in the flow turbulence.

Various methods and technical means are employed in practice to reproduce characteristics of the uneven flow at the engine inlet. However, the main ones in practice are as follows:

hydraulic grids with different density installing in the bench inlet device for the engine testing, which are employed in case of simulating a low level intensity of the pulsations full pressure prior to the engine (less than 2%);

installing interceptors of various configurations in the bench inlet device prior to the engine inlet, which allow simulating a high level of flow non-uniformity, including the of pulsations intensity.

This article presents the main results of simulating the flow non-uniformity basic parameters at the engine inlet by two interceptor-segments with different values of the relative flow shading area depending on the value of the reduced mass flow density q(l).

The article presents also the experimentally obtained correction factors flow non-uniformity impact on the tested engine basic parameters.

Keywords:

gas turbine engine, thermal pressure chamber, attached inlet pipeline, interceptor, flow non-uniformity, circumferential irregularity, pulsation intensity

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