Designing of non circular air intakes for subsonic gas-turbine engines

Abstract

The subject matter of the article is the process of subsonic air intake shaping for gas-turbine engines at the airplane preliminarily design stage. The goal is to develop a mathematical model for non-circular air intake shaping for gas-turbine engines on the base of V. I. Polikovskii method of subsonic air intake shaping for high-bypass ratio turbofan. The tasks to be solved are: to consider the possibility of non-circular shape of the external outline of the engine nacelle; to take into account the possibility of non-circular shape of the internal air intake duct (in the first approximation, the shape of internal air intake duct cross-section is defined in the form of a rectangular with possible four different radiuses in its corners); to consider the engine inlet spinner presence. The methods used are: analytical and digital mathematical methods, implemented in MathCAD and Microsoft Visual Studio systems. The following results were obtained: On the base of the proposed method, new calculation module for the Power Unit software version 11.8 has been developed (С-language Win32 UNICODE application) having a friendly user interface. Conclusions. The scientific novelty of the results obtained is as follows: 1) mathematical model (algorithm and its program implementation) for non-circular air intake shaping for gas-turbine engines has been developed considering non-circular shape of the external outline of the engine nacelle, non-circular shape of the air intake duct internal outline, presence of engine inlet spinner, and zero expansion angle in the diffuser outlet cross-section; 2) adequacy of calculation results by the developed mathematical model is shown by means of comparison with the shape of real air intake, developed by the Antonov Company. For the following improvement of the mathematical model, it is desirable to add the possibility of considering S‑shape of the air intake duct, defining its length from designer’s considerations, defining a bigger radius of curvature of the air intake lip, and considering the presence of boundary layer bleeding devices in front of the air intake.