Study on noise reduction of jet noise from microgasturbine

Gas turbine is widely used as a power source of airplanes and generators and has characteristics that is high power, less vibration and easy to handle because of the simple structure. Therefore, the gas turbine is expected to apply for small aircrafts such as unmanned vehicles and emergency generators as well as conventional large aircrafts. It is so called the micro gas turbine. One of demerits of the gas turbine is the exhaust noise, which acoustic energy is proportional to the sixth to eighth power of the flow speed. So the establishment of technology for lowering noise is indispensable. As the traditional methodology for reduction of the jet noise from gas turbine for aircrafts, it is well known that the modification of the shape of the nozzle such as the “Chevron type”, which can improve the flow corresponding to the aerodynamic source is effective, however it is not still unclear the relationships between the flow structure and the noise and the effectiveness on the micro gas turbine. In order to reduce aerodynamic noise radiated from subsonic jet such as an exhaust flow of micro gas turbine, the effect of shapes of exhaust nozzles on jet noise was investigated experimentally by using the low noise wind tunnel with cold air and numerically by using the commercial CFD software. Also, the effect was examined by applying the nozzle to the micro gas turbine for model aircrafts. As the first step, the nozzles of various shapes such as annular type, Chevron type and so on were prototyped by ABS plastics and the test with cold air flow in low-noise wind tunnel were conducted. The Mach number of the jet core was set by 0.20, 0.27 and 0.34 and the maximum effect of the noise reduction by 3.6 dB was obtained. Secondly, several nozzles that have significant effect or not to noise reduction were picked and the CFD simulations were conducted. As a result, it was found that the Chevron nozzle could extend the length of the jet core and reduce the contribution of the shear layer as the sound source by comparing with the circular nozzle. Finally, in order to examine the noise reduction effect, the improved nozzle for the actual micro gas turbine was manufactured and tested with hot gas.修士(工学)法政大学 (Hosei University