Unsteady Flow Field Measurements In An Industrial Centrifugal Compressor

Unsteady flow field measurements of both static and total pressure, and discharge angle have been carried out downstream of an industrial centrifugal impeller. Phase-resolved measurements were performed using a cylindrical single sensor fast response aerodynamic pressure probe (FRAPP) traversing and rotating from the impeller hub up to the shroud. Since FRAPP operates as a virtual three-hole probe, it was possible to obtain a detailed bidimensional reconstruction of the flow field. An experimental campaign was conducted on a closed loop rotating rig, where a multistage compressor was replicated using a pseudostage just upstream of the impeller to be tested, which was purposely designed for oil and gas applications. By varying the flow coefficient along a speed line, flow field modifications with pressure ratio variations were highlighted and analyzed in detail. The results are presented as bidimensional distributions of total and static pressure as well as blade to blade angle (i.e., the angle in the plane normal to the probe axis) and Mach number; hub-to-shroud profiles and mass averaged data of the most significant quantities are also shown. Moreover the typical pulsating behavior of centrifugal impellers, also known as the jet and wake phenomenon, has been captured and verified against standard pneumatic pressure probes (such as multihole probes) that in some cases evidence a lack of reliability. A comparison of these different techniques has been drawn through a commercial five-hole probe that was mounted in the same radial location as the fast response probe.