Investigation of Rotordynamic Coefficients of Gas Labyrinth Seals Using a Steady State CFD Approach

Abstract

Abstract Labyrinth seals were one of the first seal configurations used in modern turbomachinery and continue to be one of the most frequently used clearance seal configurations today. Their primary purpose is to control internal leakage between the rotating and stationary components of centrifugal compressors. However, when fulfilling this objective, labyrinth seals have been shown to be a potential source of instability within the rotor-stator system. Driving forces inside the leakage flow path of the cavities often induce destabilizing vibrations on the rotor. The forces are characterized by stiffness and damping coefficients which describe the stability behavior of the seal. Therefore, accurately predicting these rotordynamic coefficients remains an important area of interest in gas compressor design. This paper reviews the status of current methods of obtaining rotordynamic coefficients. The objective of this work is to verify the accuracy of current steady state CFD models used to predict rotordynamic coefficients in dry gas labyrinth seals. For this purpose, a full 3D eccentric CFD model is conducted for three different labyrinth seal geometries. In this approach, the rotordynamic coefficients are predicted from the regression of the radial and tangential impedances as a function of whirl frequencies. For comparison, two seals are compared with experimental data available in literature, and a third seal is compared to bulk flow and numerical CFD results also found in the literature. Furthermore, the influence of pre-swirl entering the labyrinth seal and turbulence modeling are also considered in this work.