Centrifugal Compressor and Bell mouth Air Intake Preliminary Design for Micro Turbojet Engine

Abstract

This paper presents a design of centrifugal compressor and air intake for micro turbojet engine of 200 N thrust. Because of the small size of the micro turbine engines the air intake is designed in the form of bellmouth air intake in order to capture the needed amount of mass flow rate (0.45 kg/s). The function of the air intake is to deliver the air to the entry of the centrifugal compressor. The air intake has been drawn with start-up motor to take in the consideration the effect. The centrifugal compressor was designed to deliver 3.8 pressure ratio with efficiency about 77%.  The compressor impeller was built with 7 main blades and 7 splitters in order to reduce the effect of slip at the exit of the impeller due to pressure difference between pressure and suction side of the main blade.  Diffuser of 13 vanes also was designed to increase the static pressure, direct the flow to the combustion chamber and decrease the flow velocity before to enhance the combustion process.  The structural integrity for impeller was validated using ANSYS software for aluminum alloy 7075-T6; 7075651. In addition, the aerodynamic analysis was investigated using NUMECA software. The most important findings of the extensive analysis were; the impact of air intake on compressor performance is very crucial. It add an increment in efficiency and pressure ratio, it should be taken in consideration in early design stage of the compressor. The highest performance characteristics of compressor were achieved by accurate design optimization of impeller-diffuser interaction.