Measuring turbocharger compressor inlet backflow through particle image velocimetry

[Display omitted] •Laser Particle Image Velocimetry (PIV) has been applied to a turbocompressor inlet.•Reversed flows at unstable conditions are entirely confined in a straight inlet pipe.•Data is obtained from both longitudinal and transversal velocity fields.•Extracted velocity profiles are validated against previous temperature results.•Results show that PIV is a suitable tool for measuring unstable, confined backflow. An experimental measurement campaign is presented where particle image velocimetry (PIV) was used in an effort to characterize the velocity field in a turbocharger compressor when unstable operating conditions lead to flow reversing from the diffuser into the inlet pipe. Previous studies have successfully used this and similar techniques, but the most relevant results have been obtained in an open compressor where the backflow can diffuse into the ambient. In this work a glass pipe long enough to confine the full extent of the backflow has been used. Advantage was taken from the fact that this backflow is at higher temperature due to the compression process, enabling a preliminary work where a thermocouple array was used to estimate its maximum length across the compressor map. Using these results as a reference both axial and transversal velocity fields were measured. Issues associated with each one are described, along with relevant results that show how the technique correctly identifies the reversed flow, a conclusion that is supported by the comparison of the velocity average and standard deviation profiles with those of measured temperature.