Considerations for Use of Three-Hole Probes for Turbomachinery Applications

Abstract

Three-hole probes are frequently employed to characterize the flow field upstream, within, and downstream of turbomachines. From three pressure measurements, the static pressure, total pressure, Mach number, and a single axis flow angle can be resolved. Despite this utility, there are induced errors related to the use of these probes that are particularly pertinent to use in turbomachines. Small passages cause end-wall proximity effects, the rotor induces flow unsteadiness, and complex flow three-dimensional flow structures are developed. These effects are considered in this effort by contrasting experimental inlet distortion data from an auxiliary power unit inlet of a centrifugal compressor with computational inlet-only models. The aerodynamic interface plane was measured using a rotatable rake assembly with trapezoidal three-hole probes and fast response pressure transducers. Two computational models are presented, one with and one without the aerodynamic interface plane instrumentation used in the experiment. The measurements from the simulated traverse are compared to the inlet-only computational model and experimental results. End-wall effects were the dominant error driver for the static pressure measurements. Swirl was predominantly altered by perpendicular flow angle magnitudes above 10 deg. Indicated total pressure was impacted by radial flow angle and unsteadiness that were highly coupled.