Studying criterion parameters of the total pressure input non-uniformity impact on the thrust of a turbojet engine

Aeronautical and Space-Rocket Engineering

Thermal engines, electric propulsion and power plants for flying vehicles


Аuthors

Ezrokhi Y. A.*, Khoreva E. A.**

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 presence of the total pressure non-uniformity may affect the basic engine parameters, and, in the first place, its gas-dynamic stability margin, as well as thrust-economic characteristics. Circumferential non­uniformity of the total pressure and its non-stationary component greatly affect the engine gas-dynamic stability. As for the engine thrust, the radial and circumferential effects are close enough, and non­stationary component does not affect the engine thrust at all. It allows employ one-dimensional approaches while this phenomenon modelling, and consider the impact of both stationary components of non–uniformity of the total pressure (both circumferential and radial) from the single methodological positions

In case of a non-uniform input flow, the flight-thrust decrease occurs for to the several reasons. Reduction of the general level of the total pressure along the engine passage, which leads to the pressure drop reduction in the jet nozzle pressure difference and, correspondingly, the decrease of the engine specific thrust may be assigned to the first cause. Besides, due to the general level of the input pressure reduction, physical air consumption reduction through the engine occurs as well.

The second reason of flight thrust reduction is associated with additional total pressure losses due to the “wash-out” of areas with various level of the total pressure in compression elements. It leads to the additional losses of the total pressure in compressor stages, which reduces the aircraft engine thrust to an even greater degree.

The authors suggested and justified criterion parameter Er for correct estimation of the thrust- economic parameters of the engine, operating in conditions of non-uniform input field of the total pressure. To the contrary of the W parameter, this parameter reflects additionally the relative values of the area, occupied by the zones with various total pressure values, being conditional indicator of the reduced pressure “concentration” per unit of the input area.

On a calculation example of the one-shaft turbojet with sufficiently conservative level of the design parameters the effect of the total pressure non–uniformity on its key parameters, such as thrust and gas-dynamic stability margin of the compression system was considered. This kind of engine selection is explained by the fact that to the contrary of the bypass jet engine, considered in the previous articles, the non-uniform field at the turbojet compressor inlet is considered as known, and its impact on a single compressor would be determinant for the whole turbo jet engine.

The performed calculation estimations revealed that the decrease in the engine thrust δR due to the non-uniform field of the total pressure at the inlet was completely defined by value of this parameter (dependence between δR and Er is almost linear), and also by the engine operating mode, such its shaft rotation frequency.

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