Sound Radiation from a Reciprocating Compressor Orifice without Valve

Abstract

As a first step toward the acoustic radiation modeling of a reciprocating air compressor, the suction and exhaust valves were removed and the compressor was made to cycle air through a single circular orifice. The theoretical model incorporates the aharmonic and large piston motion by thermodynamically modeling the flow in the cylinder. The flow through the orifice was modeled as compressible. Contraction coefficients on an ON-OFF basis were used to account for streamline effects in the orifice section. The farfield acoustic spectrum was predicted by treating the orifice as a monopole source radiating into an infinite half-space. Agreement between theoretical prediction and experimental measurements was encouraging. A small rise in both the predicted and measured frequency spectra was hypothesized to be a Helmholtz resonator effect since it occurred in the expected frequency band. The theoretical calculations were carried out using both a conservation of mass and momentum approach and a conservation of mass and energy approach. Small differences in the results of these two approaches were observed. Finally, because of our desire to simplify future models, influences of individual terms in the derived equations on instantaneous mass flow rates were evaluated.