Use of CFD to predict trapped gas excitation as source of vibration and noise in screw compressors

10th International Conference on Compressors and their Systems

Willie, James^1

Gardner Denver Schopfheim GmbH, Johann-Sutter-Straße 6+8, Schopfheim

79650, Germany^1

关键词: Low frequency range;    Noise and vibration;    Oil free screw compressor;    Shock wave generation;    Torsional frequency;    Torsional resonance modes;    Torsional resonances;    Transmission systems;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/232/1/012021/pdf
DOI  :  10.1088/1757-899X/232/1/012021

来源: IOP

【 摘 要 】

This paper investigates the source of noise in oil free screw compressors mounted on highway trucks and driven by a power take-off (PTO) transmission system. Trapped gas at the discharge side is suggested as possible source of the excitation of low frequency torsional resonance in these compressors that can lead to noise and vibration. Measurements and lumped mass torsional models have shown low frequency torsional resonance in the drive train of these compressors when they are mounted on trucks. This results in high torque peak at the compressor input shaft and in part to pulsating noise inside the machine. The severity of the torque peak depends on the amplitude of the input torque fluctuation from the drive (electric motor or truck engine). This in turn depends on the prop-shaft angle. However, the source of the excitation of this low torsional resonance inside the machine is unknown. Using CFD with mesh motion at every 1°rotation of the rotors, it is shown that the absence of a pressure equalizing chamber at the discharge can lead to trapped gas creation, which can lead to over-compression, over-heating of the rotors, and to high pressure pulsations at the discharge. Over-compression can lead to shock wave generation at the discharge plenum and the pulsation in pressure can lead to noise generation. In addition, if the frequency of the pressure pulsation in the low frequency range coincides with the first torsional frequency of the drive train the first torsional resonance mode can be excited.