Multidimensional flow modeling of the compression test of a Gaede pump stage in the viscous regime

Abstract

Two-dimensional and three-dimensional models for a Gaede pump, based on the Navier–Stokes equations, are developed and a commercial Computational Fluid Dynamics code is used to solve them. We simulate a compression test in an outlet pressure range (30–2500 Pa) corresponding to the viscous laminar regime for an experimental pump. Experimental data are collected in order to validate the developed model. The pump tested is the high pressure stage of a commercial hybrid turbomolecular vacuum pump and can work in both transition and viscous regime, according to the operating pressure. The data show that the standard Couette–Poiseuille one-dimensional analytic model, developed by Helmer and Levi to describe the Gaede pump behavior and operating principle, has a limited accuracy when it is used as a design tool and not just as a physical model. The two-dimensional and the three-dimensional model results are compared with the experimental data showing an increasing level of agreement, with only a 10% maximum difference for the three-dimensional model in terms of compression ratio. The different flow structures shown by the models are critically analyzed to explain the different level of agreement.