A Theoretical and Experimental Analysis of the Sealing Capability of a Membrane Seal

Improvements in turbine performance are increasingly being driven by the need to control leakage both in the main gas path as well as secondary air flow systems. Membrane seals have long been established as a method of sealing in some of the harshest of environments found in gas turbines. The membrane seal has a wide usage in gas turbines for stationary component interface sealing. The geometry is of plate construction with bulbous ends, the seals are assembled vertically and are retained by the component grooves. The grooves allow relative sliding and rotation against their surfaces a necessary feature, since during operation the seal needs to withstand relative movements due to thermal growth, vibratory forces, excitation and assembly loads. However, more accurate leakage estimates are required. Thus, in order to evaluate the complete performance characteristics of the seal for a wide range of working conditions, a theoretical and experimental campaign was undertaken.The membrane seal performance curves were created based on a series of tests performed in a specially designed rig. The rig utilised an actuation system that allowed for the precise adjustment of the seal’s relative position in two directions while performing the tests at a given working condition. It was noted that not only the movement and deformation of the membrane but also, assembly clearances and surface condition of the components have an impact on the seal’s performance. To assist in the understanding of the influence of the changing parameters on the performance of the seal an FEA study was undertaken employing known data to aid the understanding and improve the knowledge of how the seal behaves under specific engine conditions. The evaluation gives confidence in the experimental test results.Copyright © 2014 by Alstom Technologie AG