Conventional 3-hole wedge probes fail to measure the correct static pressure when operating in close proximity to a wall or boundary through which the probe is inserted. The free stream pressure near the outer wall of a turbomachine annulus may be over indicated by upto 20% of the dynamic head.

This paper reports a factorial experiment in which the effects of probe wedge angle, stem length, stem shape, flow yaw and pitch angles on this so-called ‘wall proximity effect’ are quantified at representative flow Mach numbers and turbulence intensities. For a given wedge angle, the probe stem length and Mach number are shown to be statistically the most significant of the tested variables. Wall proximity effect is also shown to be influenced by the probe pitch angle, but is largely independent of yaw angle and free stream turbulence intensity.

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