Numerical Study of the Single-Shaft Turbojet Characteristics in the Windmilling Modes Area

Aeronautical and Space-Rocket Engineering


Аuthors

Leshchenko I. A.1*, Donskikh V. V.2**, Rozhkova M. V.2***

1. United Engine Corporation “Saturn”, 163, Lenin av., Rybinsk, Yaroslavl region, 152903, Russia
2. Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: igor.leschenko@yandex.ru
**e-mail: vic@mai.ru
***e-mail: rozhkovamv@mai.ru

Abstract

The windmilling relates to the one of the less studied engine operating modes. Aircraft gas turbine engines run at such sub-idle modes during startup (stationary mode), or windmill flight restart (dynamic or transient mode) [5-6] The article studies engine windmilling modes at reduced shaft speeds, such as n ̅cor = 0.1–0.6 (specific speed). At such modes, the engine rotor speeds decelerate rapidly to the rotational speed nwind (windmilling rotation speed), which is being sustained by the incident flow velocity, producing a ram pressure at the engine inlet. The input impulse of the airflow is being transferred to the compressor blades, causing the turbomachine to rotate in a direction that coincides with the direction of rotation during normal operation.
At these sub-idle modes, the compressor may run in three modes, namely compressor (turbine pressure ratio is greater than one), mixer and turbine (turbine pressure ratio is less than one) [1, 6]. It is impossible thereby to apply the traditional compressor characteristics representation through the efficiency. The article presents an alternative form of the compressor and turbine characteristics representation through torque.
The presence of detailed compressor and turbine characteristics is necessary for the engine operation at sub-idle modes computations performing. As of today, interpolation and extrapolation are one of the basic methods for the engine components characteristics obtaining, but they are not accurate enough. Thus, it is necessary to obtain characteristics computationally or experimentally. The article presents the technique for characteristics computing of the compressor and turbine of a single shaft turbojet at sub-idle modes. Numerical simulation was accomplished with the Numeca FineTurbo v.15.1 that allowed obtaining reasonable accurate results with relatively low computing power costs.
The article presents as well computing of these modes with the thermodynamic model of a single-shaft engine in Thermogte. The result of joint application of the obtained compressor and turbine characteristics as a part of the thermodynamic model allowed plotting the working modes line ant the single-shaft turbojet at the windmilling mode. Thus, the issue of obtaining the engine components characteristics in the windmilling modes and these modes computing are both important and up-to-date.

Keywords:

gas turbine engines windmilling, windmilling modes mathematical model, axial-flow compressor, compressor head-capacity characteristic, operating modes line, rotor rotation frequency

References

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