3D Flow Simulation of a Spiral-Grooved Turbo-Molecular Pump

Abstract. A spiral-grooved turbo-molecular pump is widely used in vacuum technology. Available rota-tional speed of a rotor becomes larger and larger, and reaches 18,000 to 50,000 rpm. The clearance effect between a rotor and its casing is one of the important problems for the performance prediction of turbo-molecular pump which operates under very high speed of revolution. Now the pumping performance can be predicted from the computation of the three-dimensional flows. In the present paper, a flow in a spiral groove of turbo-molecular pump is simulated on the basis of the NS equations to cover a wide range of pressure ratio and mass flow rate. A fully three-dimensional analysis is made to take account of the effect of a gap between a rotor and its casing as well as the centrifugal and Coriolis forces. The pumping performance is shown in comparison with that of the no-gap flow and the channel flow approximations