Measurement and simulation of the dynamic characteristics of plain and profiled annular seals

Abstract

The performance and reliability of turbomachinery is often limited by shaft vibrations induced by fluid forces of (i) plain or profiled annular seals, (ii) pistons and (iii) journal bearings. The rotordynamic coefficients namely, stiffness, damping and inertia of plain annular seals are in general calculated using the bulk-flow approach developed by Childs. However, when applying the calculation method to profiled gaps, especially those with non-symmetrical profiles, large differences between simulation and experimental data are reported. Furthermore, reliable experimental data as well as large databases including experimental and simulation results from a single author are limited. To overcome this, the paper introduces a unique active magnetic bearing test rig, built and operated at the Technische Universität Darmstadt as well as the corresponding simulation method to determine the rotordynamic influence of annular seals. An extensive experimental study is carried out investigating plain, symmetrically profiled and non-symmetrically profiled annular seals within the relevant parameter range for turbulent flow in pumps. The results are compared to the simulation results showing a significant influence of profiled gaps on the dynamic characteristics in comparison to plain annular seals. Furthermore, it is shown that symmetric and non-symmetric profiles have a different influence on the dynamic quantities inertia, damping and stiffness.