Steady state flow measurements as obtained by multi hole pneumatic pressure probes are relevant to the current design process. These probes are calibrated in a uniform flow in a wind tunnel prior to their application in the test compressor. It is known that the probes do not behave in the same way in the test compressor as in the wind tunnel, one of the factors is that the flow in the compressor is fluctuating and this is thought to influence the probe’s operation. This two part paper investigates the influence of unsteady effects on probe operation. Part one covers an experimental investigation in which two pneumatic probes were calibrated firstly in a wind tunnel, then in low and high speed compressors. The probe that was used for the low speed compressor was scaled up from its high speed counterpart due to the increased size of the machine. The calibration graphs obtained by yawing the probe in the wind tunnel were reproduced with good accuracy when the same process was performed in the compressors. Whereas for the low speed compressor, the probe Reynolds number was the same as in the wind tunnel, the high speed compressor operated at a much larger Reynolds number.

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