Investigations into the thermodynamic processes in labyrinth seal flow fields have been carried out using the nonintrusive optical technique of holographic interferometry. Labyrinth seals in the form of two-dimensional actual size models were used. The types of seal geometry tested reflected those in current use in aerogas turbines, their sizes being typically 10 mm × 20 mm in section with sealing constrictions as small as 0.25 mm. The tests provided a great deal of information that had not previously been available and confirmed several experimental and theoretical results that were not fully understood. The data were obtained in the form of isodensity contour maps. These full field density measurements of the test section flow were analyzed in several ways to provide an insight into the processes occurring within the labyrinth seal. The effects of kinetic energy carry-over upon seal stage performance were dramatically demonstrated in both straight-through and stepped seals. Useful qualitative, as well as quantitative, information regarding the flow field structure could be obtained from the isodensity maps. An indication of particular flow features was obtained at a glance. The optical technique was found to be ideally suited to the investigations and the expected difficulties associated with working in the very small test sections did not arise. The configuration of the optical system ensured that image aberrations were minimized and temporal flow instabilities did not adversely affect the isodensity contour maps. The paper reviews the optical technique and presents a selection of the holographic results along with their interpretation.

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