Title:
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A numerical and experimental investigation of pulsation induced noise in screw compressors
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Intermittent gas flow through the suction and discharge ports of a screw compressor
generates pressure oscillations in the suction and discharge systems. These have been
recognised as the main source of structural vibration and noise within the compressor
system. Parameters proposed in earlier studies did not help in finding a means to reduce
these gas pulsations. This thesis describes a detailed analytical and experimental study
of the screw compressor process, which was therefore carried out to predict the level of
gas pulsations thus generated and how they could be reduced.
Three different simulation models were used to determine the pressure variations within
the discharge chamber. These comprised a thermodynamic model of the screw
compressor discharge process, a 3-D CFD model of flow through the compressor,
originally used to predict pressure variations, and a coupled model which joins the 3-D
model of flow in the discharge chamber with a thermodynamic model of the working
chamber and the discharge system. The last model accounts for the complex geometry
of the discharge chamber and reduces computational time.
It was shown in the simulation results that the shape of the discharge port is an
important parameter which influences the level of gas pulsations in the discharge
chamber. If selected carefully it can reduce gas pulsations without a substantially
adverse effect on the compressor performance.
The analytical procedure used was then validated in a test programme, carried out on a
standard oil injected air compressor to compare predicted and measured pulsations
within it. Test results confirmed the trends shown by the predictions.
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