OPTIMUM ATTENUATION OF GAS-TURBINE NOISE BY ACOUSTICAL CORNER TREATMENT

In this paper two materials, placed over the corner walls surrounding a gas turbine unit in five different geometric configurations, are tested to establish their effectiveness on the noise field of a 45 k W gas turbine unit. The measured noise without wall treatment reveals that about 46% of the noise radiated acoustic power of the unit is in the 1/3 octave band of 12 500 Hz central frequency. The results of this research show that the sound absorber comprised of plastic sponges of irregular shapes of an average linear dimension of 7 cm formed in strings 2 m high and suspended 15 cm from the solid walls is considerably more effective than the traditionally used fiber glass panels also suspended 15 cm from the solid walls. The optimum configuration of the plastic sponges attenuated the dominant pure tone band by about 78% of its original power. Similar reductions took place in the other twenty 1/3 octave bands. The overall broadband attenuation of the measured noise amounts to 71% of the original acoustic power of the noise field of the unit.