Low-Frequency Oscillations Behavior of a Radially Adaptive Seal

Abstract New radial shaft sealing concepts have the potential to increase turbomachinery efficiency, especially under partial load conditions. Hydrostatic advanced low-leakage (HALO) seals are radially adaptive, noncontacting shaft seals with a large installation clearance that reduces to an optimized minimum operating clearance under pressurized conditions. A HALO seal configuration was experimentally investigated in the adaptive seals test rig at the Institute for Thermal Turbomachinery, with a focus on the response to relative oscillation between rotor and stator. This was enacted by moving the stator casing vertically with sinusoidal motion while the rotor axis remained fixed. The influence of oscillation amplitude and frequency, up to 2 s−1, was investigated under varying shaft rotation speeds and upstream swirl conditions. In this paper, the results of these experimental investigations are presented. Increasing oscillation amplitude drastically reduced the minimum clearance, even resulting in contact under axial flow, and reduced the average leakage of the sealing interface, up to 11.9%, whereas varying the frequency had no identifiable influence. The rotation speed and swirl altered the specific trends of how the clearances and leakage changed with increasing amplitude. The results presented in this study give a first insight into how a radially adaptive seal can respond to conditions where the relative movement between rotor and stator meets and exceeds the operating clearance and the impact on sealing performance.