Digital PIV Measurements of Flow in a Centrifugal Compressor

A report describes experiments in which digital particle-image velocimetry (digital PIV) was used to measure the flow field in the diffuser of a high-speed centrifugal compressor. In digital PIV, a sheet of pulsed laser light illuminates a flow field seeded with small tracer particles, the positions of the particles are recorded on a digital charge-coupled-device (CCD) camera at each pulse time, and the digitized image data are processed to extract velocities from the displacements of particles between pulses. In the experiments, a special periscope probe was used to introduce the light sheet into the flow plane of interest inside the compressor. Measurements were obtained while the compressor ran at design speed, yielding highly accurate time-averaged velocity-vector maps in much less time than is needed to generate comparable maps by use of laser Doppler velocimetry (LDV).