Measurement Errors Downstream of a Rotor Due to Probe–Blade Row Interaction

Abstract

Pneumatic probes are widely used to measure flow properties in turbomachinery, including downstream of rotor blade rows. This paper investigates the aerodynamic interaction between a row of compressor blades and a downstream cylindrical probe, using unsteady, three-dimensional simulations. The study demonstrates the probe influence on rotor performance as a function of probe size and rotor proximity, identifies the physical mechanisms driving rotor-probe interactions, and quantifies the resulting probe measurement errors. A probe downstream of a rotor row causes each blade passage to deviate periodically from the steady, axi-symmetric characteristic, as they pass the probe. In this study, the largest rotor disturbance occurs for a probe of diameter 14% blade chord, located 30% axial chord downstream of the rotor trailing edges. The flow coefficient, 𝜙, moving with the rotor passage, varies between −10.4% and +5.5% compared to a case with no downstream probe. The total-to-total pressure rise coefficient, 𝜓𝑡 𝑡 , increases by up to 7.7%. These rotor-probe interaction effects are driven by the unsteady response of the rotor passage to the potential field of the probe. In the stationary frame, measurement error occurs because the probe is exposed to the disturbed flow field and this leads to maximum average errors of Δ𝜙 = −15.1% and Δ𝜓𝑡𝑡 = 8%. The magnitude of the rotor disturbance decreases as the probe is moved away from the trailing edge of the blades and when probe size is reduced. Reducing probe size close to the blade row reduces the rotor disturbance more than moving a large probe downstream. Including a stator blade row downstream of the probe does not have a large impact on the sensitivity to probe size and proximity and the physical mechanisms are unchanged.