The main goal of these investigations was the refined measurement of unsteady high-speed flow in a centrifugal compressor by using the advanced FRAP® fast-response aerodynamic probe system. The present contribution focusses on the impeller exit region and shows critical comparisons between fast-response (time-resolving) and conventional pneumatic probe measurement results.

Three probes of identical external geometry (1 fast and 2 pneumatic) were used to perform wall-to-wall traverses close to the impeller exit. The data shown refer to a single running condition near the best point of the stage.

The mass flow obtained from different probe measurements and from the standard orifice measurement were compared. Stage work obtained from temperature rise measured with a FRAP® probe and from impeller outlet velocity vectors fields by using Euler’s turbine equation are presented.

The comparison in terms of velocity magnitude and angle distribution is quite satifactory, indicating the superior DC measurement capabilities of the fast-response probe system.

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