The aerodynamic effects of a probe in a high-speed axial compressor are investigated. Regarding probe measurement accuracy and its aerodynamic effects, probe upstream/downstream effects and probe insertion effects are studied by unsteady CFD and high-speed axial compressor measurements in two types of multistage compressors. Probe measurements were planned upstream and downstream of the stator in each case to quantitatively evaluate row performance and its flow field. 
The simple approximation method considering only the interference of the probe effect on the compressor performance was carried out, but it did not agree well with the measured value. Therefore, the unsteady calculation including the probe geometry was carried out. 
Unsteady calculations are performed with a probe inserted completely between the rotor and stator of a 4-stage axial compressor. Since the probe blockage and potential flow field change the operating point of the upstream rotor and increase the work of the rotor, the measured total pressure increase is shown around 2000 [Pa] at the probe head. This value agreed well with the difference between the measured values of the 5-hole pressure probe and the stator leading edge probe because of the probe potential and its blockage. In addition, the developed probe wake interferes with the downstream stator row and locally changes the static pressure at the stator exit. 
To evaluate the probe insertion effect, unsteady calculations with probes at three different immersion heights downstream of the stator in an 8-stage axial compressor are performed. The static pressure value of the probe tip increased about 2000 [Pa] when the probe was immersed from the hub to the tip, corresponding to the measurement trend, but the measured wall static pressure showed no drastic change in the radial direction. When the probe is inserted from the hub to the tip, the probe and blockage increase, and the operating point of the stator locally changes, and the static pressure rise of the stator increases because stator incidence is changed. 
These examples show that unsteady simulations including probe geometry can accurately evaluate the aerodynamic effects of probes in high-speed axial compressors. As for the probe measurement, it is important to pay attention to the probe diameter (= blockage effect), the distance from the blade row (= potential effect), and its relative position to the downstream stator (= clocking effect between the probe and the downstream stator), because the probe locally affects all upstream rotor passages and the downstream stator. 
From the above, the new approximation method including the potential effect is proposed, and it is verified in the 4-stage compressor case. In this method, the distance between the rotor T.E. and the probe is considered by the probe potential effect, which is reflected to the probe blockage. The probe blockage decreases the mass flow rate and changes the operating point of the compressor. It seems that correct blockage approximation enables designer to estimate aerodynamic effects of the probe correctly.

Evaluation of a Flow Measurement Probe Influence on the Flow Field in High Speed Axial Compressors

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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