Influence of liquid film in star wheel tip clearance on dynamic characteristics of single screw compressor

Abstract

The liquid film in the tooth tip clearance plays a critical role in reducing wear and sealing gas leakage in a single-screw compressor, yet its influence on shaft system dynamics has not been systematically quantified. In this paper, a comprehensive mathematical model of the liquid film in the star wheel tooth tip clearance is established, considering the conjugate geometry, the pressure governing equation, and the gas pressure equation. The finite difference method is employed to solve the pressure field, from which the bearing forces, frictional forces, axial/radial bearing loads, and rotating resistance torques are derived. The effects of the liquid film on the odd-groove and even-groove screw are compared, and a torque fluctuation ratio is introduced to quantify rotational stability. Results show that the liquid film in the odd-groove screw generates a larger frictional resistance torque on the star wheel, but induces smaller fluctuations in the rotating resistance torque on the screw rotor than in the even-groove screw. The axial load on the screw bearing in the even-groove case reaches approximately 154.8 N, which is about 26.2% higher than that in the odd-groove case. The radial load distributions on the bearings exhibit significant differences between the two configurations. The torque fluctuation ratio increases with viscosity and rotating speed, and decreases with suction temperature; with increasing discharge pressure, it decreases for the odd-groove rotor while showing a non-monotonic trend for the even-groove rotor. The even-groove rotor consistently exhibits higher values across all conditions, confirming the superior rotational stability of the odd-groove design. The findings provide quantitative guidance for single screw compressor design and bearing selection.