An Experimental Method of Determining the Mechanism of Aerodynamic Noise Generation

The noisiest equipment in mechanical engineering is of the type that uses aerodynamic processes. Fans, compressors, pneumatic motors, internal combustion engines, gas turbines and other units belong to this group. The design of fundamentally new low-noise power equipment requires knowledge of the causes of noise generation in existing machines. This paper proposes an original experimental method to determine the mechanism of aerodynamic noise generation in different power plants based on a simple physical experiment with a rotary Roots blower manufactured by the Melitopol Compressor Plant. Gas dynamic processes in technical devices are the source of intense acoustic energy, the generation of which can be interpreted by means of ideal mathematical models (monopole, dipole, quadrupole). It is known from theoretical acoustics that the sound energy generated by these three types of audio sources depends on the aerodynamic flow velocity of the 4th, 6th or 8th power, respectively. The experiment allowed the zones of monopole, dipole and quadrupole nature of noise generation to be identified in the frequency range of (125–8 000) Hz at different modes of operation. The sound emission processes were thoroughly investigated through the analysis of aerodynamic noise emission of Roots blowers in octave frequency bands. The analysis has shown that despite the fact that three mechanisms of noise occurrence are possible, for the existing modes of operation of rotary blowers (up to 3 000 min–1) the monopole emission subject to the forth power law is dominant. One should, therefore, use the mathematical apparatus of the monopole emitter for numerical simulation of sound generation in Roots blowers.

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