Investigation of the Transient Closing Behavior of a Radially Adaptive Seal

Abstract

New radial adaptive sealing concepts in the secondary air system have the potential to increase the partial load efficiency of turbomachinery and accelerate load ramps. These seals are pressure activated, adjusting to engine conditions in order to maintain a minimum gap width during the entire load cycle, defined as the seal’s operating gap width. In this context a hydrostatic advanced low-leakage (HALO) seal was experimentally investigated in the adaptive seals test rig at the Institute for Thermal Turbomachinery (ITS), with a focus on the transient behavior of the seal closing to its’ operating gap width. For this measurement campaign, the pressure ratio, pressure difference, pressure ramp speed and swirl were varied over a series of closing-hold-opening pressure cycle test runs. All measurements were performed without rotation of the test rig rotor. In this paper, the results of these experimental investigations are presented and analysed. From these results, the relative influence of the pressure difference and the pressure ratio across the seal on the transient seal behavior is compared. Of particular interest is the effect of changing the pressure ramp gradient on the operating gap width. Additionally, the results are compared against previous published HALO-seal investigations. The results presented in this study give detailed insight into the transient movement of a HALO seal under various engine-similar influencing parameters. This is crucial to understanding how the seal behavior and performance will be affected when operating under different conditions and in different applications.