Application of particle image velocimetry to a transonic centrifugal compressor

Abstract

A variety of measurement techniques have been applied to investigate the flow phenomena occurring in advanced turbomachinery components. In an ongoing research project the performance and internal flow field of a high pressure ratio centrifugal compressor is being investigated. Based on the results obtained the compressor was redesigned and resulted in an improved impeller and diffuser. The stage was designed for a total pressure ratio of 6:1 and a mass flow rate of 2.55 kg/s, the corresponding rotor tip speed was 586 m/s, resulting in transonic flow conditions at the inlet of the diffuser vane passage at a static temperature of 260°C. The improvement of the impeller flow and the broadening of the stable operating range was predicted by CFD and successfully verified by means of laser-2-focus (L2F) measurements.Current activities in the research program involve the use of particle image velocimetry (PIV) to analyze and further improve the understanding of the complex flow phenomena inside the vaned diffuser. The study includes phase-resolved measurements of the flow inside a diffuser vane passage with respect to the impeller blade position. Both, instantaneous and phase-averaged velocity fields will be presented.Optical access is given via a quartz glass window, which was manufactured to match the 3-D contour of the diffuser casing in order to minimize disturbance of the near-wall flow. An adjustable periscope light sheet probe was specifically designed for this application and delivered the laser light sheet (LLS) to the desired vane span positions for the flow field investigation. The periscope probe was purged with compressed air during operation for cooling and to protect the open outlet of the probe from seeding particle deposits.The flow field results obtained with PIV will be used for validation of the CFD calculations. Based on this approach a better understanding of the complex flow characteristics is expected, which will finally result in a further improvement of the compressor performance.

Investigation of New Design Principles for the Centrifugal Compressor Vaned Diffusers

“…H Krain [3] carried out the numerical and experimental researches on the transonic flow fields of the centrifugal compressors, identified areas of large flow loss in centrifugal compressors, and improved compressor performance by modifying the impeller thickness and blade angle. M Voges [4] used PIV to conduct experimental measurement and analysis of the transonic flow field. With the deepening understands of the internal flow field of the compressor, the design method of the impeller blade has been developed from two dimensions to three dimensions.…”

The challenge of stereo PIV measurements in the tip gap of a transonic compressor rotor with casing treatment

“…The particle size distribution was quoted by the manufacturer to be in the order of 300 -800 nm. In comparison to seeding provided by atomizer based systems the particle response time in the strong gradients (shock) of the transonic compressor flow field could be reduced by a factor of 2 -4 (Voges et al 2007).…”

Off-line phase-averaged particle image velocimetry and OH chemiluminescence measurements using acoustic time series

“…The flow was seeded via plenum upstream of the burner with aluminum oxide powder (Al 2 O 3 , 0.3-0.8 μm grain size) by means of an aerated fluidized-bed particle generator. Sonic flow conditions at its exit and the associated strong shear forces helped to separate particle agglomerates into the smaller primary particle sizes [9,10].…”