Mathematical modelling application for characteristics estimation of bypass turbojet with common afterburner

Aeronautical and Space-Rocket Engineering

Thermal engines, electric propulsion and power plants for flying vehicles


Аuthors

Ezrokhi Y. A.*, Fokin D. B.**, Nyagin P. V.

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

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

Abstract

Turbofan engines (TFE) with common afterburning chamber are the basic ones applied in power plants of maneuverable aircraft both in our and foreign countries. Recently, the TFE with low bypass ratio (no more than 0.3 ... 0.5) that has a certain feature in the scheme of mixing and burning processes in the afterburning chamber are most widely spread.

The absence of special mixing devices at the afterburning chamber inlet in a number of TFEs structures may lead to the situation when a certain air portion of the second duct would not admix to the main flow and participate in combustion process even at the full speed-up.

In this case, rather high values of total excess air factor ( αΣ ≥1,2 ... 1,3) realize at the afterburning chamber outlet, which may eventually reduce the engine speed-up degree at these modes.

With a view to the specifics of TFE interaction units in the engine system, the share of the air not participating in the air burning process at various operating modes may change in a rather wide range.

The estimation inaccuracy of this value can eventually lead to essential errors in determining the main TFE parameters sucha as its thrust and specific fuel consumption.

A specially developed model of the stage-by-stage air of the bypass duct admixing to the main flow at the afterburning chamber inlet was integrated into the general mathematical model of the engine and allowed refine both working process in the TFE and its characteristics at the speed-up modes.

The following scheme of the afterburning chamber of the two-stage successive air admixing of the bypass duct air to the main loop flow is assumed while mixing-afterburning chamber modelling. At the first stage, the entire gas of the internal loop and a fraction of air of the second loop participate in mixing. At the second stage, the remaining airflow, being flown through the subscreen duct, is being admixed to the gas at the afterburning chamber outlet.

Equality of static pressures herewith is assumed in the mixing section, as well as fulfillment of conditions of conservation of mass, energy an impulse for the mixing flows, peculiar to the conditionally full mixing in the conditional cylindrical duct.

Estimation, performed on the example of technical appearance analysis of the fifth generation Pratt & Whitney F119-PW-100 TFE analysis was performed. Its altitude-speed and throttle performances, among all, as a part of the F-22A Raptor aircraft power plant, revealed telling impact of the factor under consideration on both TFE characteristics and the aircraft as a whole.

Keywords:

turbofan engine, mathematical modelling, afterburning chamber, altitude-speed performances, engine trust, aircraft performance

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