Particle Image Velocimetry in a High-Speed Short-Duration Turbine Rig

Abstract

This article presents the implementation of a particle image velocimetry (PIV) into the high-speed short-duration rotating turbine facility of the von Karman Institute. The advantage of PIV as a whole-field measurement is emphasized in such circumstances for which the use of optical technique can drastically reduce the number of tests and the need for multiple intrusive expensive probes, ultimately lowering the testing cost. Practical solutions were demonstrated that address various challenges for the effective application of PIV. An endoscope delivered the laser sheet to the region of interest and a plano-concave window provided optical access for the measurement in the annular test section. Sub-micron scale oil droplets were seeded into the main flow through custom-made probes located upstream of the nozzle guide vane and into a pipeline supplying rim seal purge flow. A high-speed laser system and a high-speed camera were synchronized at 1 kHz sampling rate. Complementary measurements and dedicated image processing were performed to ensure the synchronization of the PIV images with the rotor position that was monitored through an encoder. The region of interest was the blade-to-blade plane at the 58% span turbine exit on a rectangular field of view covering approximately one rotor pitch and 0.15 rotor axial chord from the rotor trailing edge. Phase-locked-average velocity fields are obtained from PIV and compared against steady-state Reynolds-averaged Navier–Stokes (RANS) simulations along with four-hole probe measurement results. Together with uncertainty analysis, the results demonstrate the promising robustness and accuracy of PIV. A practical guideline for PIV application in such kinds of turbine test rigs is provided as a conclusion of the paper.