Labyrinth seals flow field evaluation with optical methods

Abstract

This work aims to perform the detailed experimental investigation of the flow field in labyrinth seal specimen using optical methods: LDA (Laser Doppler Anemometry) and schlieren visualization. Preliminary tests were performed on a stationary (rotor model with labyrinth does not move), linear – where the curvature of the specimen is omitted – measuring stand supplied by a vacuum pump. The installation makes it possible to achieve critical pressure ratios, up to two. This investigation was also supported by CFD (Computational Fluid Dynamics) calculations performed using the Ansys CFX v.17 commercial code with a flow model based on the RANS equations. Prediction scheme simulated the experimental campaign parameters. In CFD study, different types of mesh resolution were tested, with variable volume discretization in the area of labyrinth fin tip. Presented study shows challenges as well as the possibilities of flow field visualization including three-dimensional vortexes and strong jets occurring downstream the fin tips. Some limitations of LDA method application were pointed out, especially in areas of rapid fluid expansion. Moreover paper presented that schlieren method is a very efficient way of giving the turbulence structures in linear labyrinth seal fins. In the end, experimental results were compared with CFD study, which reviled the best method for labyrinth seal structures flow field simulation. Comparison of experimental and computed results showed some agreement between those two approaches. Flow visualization also allowed to understand better the flow behavior in cavities, which is crucial for design tools development.