A fluidic proximity sensor particularly adapted to sense clearance between gas turbine engine compressor blade tips and adjacent wall of compressor housing. In one embodiment, there is provided an air flow passage having a chamber with an inlet and a restricted outlet in series flow relationship. The inlet receives compressor pressurized air and is arranged in a predetermined relatively close spaced-apart relationship with a compressor blade tip which sweeps the inlet to vary the effective flow area thereof. The resulting pressure pulses are integrated in the chamber and the resulting pressure compared to a regulated reference fluid pressure by means of a pressure differential responsive device, the output of which represents the radial clearance between the compressor blade tips and adjacent housing wall. In another embodiment, a second air flow passage connected in parallel flow with the above-mentioned air flow passage is provided with a pair of series flow restrictions between which a reference pressure is generated. The inlet to the second passage is not affected by the compressor blade tips. The reference pressure is compared to the chamber pressure representing the radial clearance between the compressor blade tips and adjacent wall. Detailed application- gas turbine engines particularly for use in high performance aircraft where engine efficiency is of utmost importance are well known. Such engines utilize axial flow air compressors characterized by high air compression ratios to produce the desired operational engine power. The rising air pressure generated as air flow progresses through the various stages of the axial compressor is adversely affected as clearance between the compressor blade tips and adjacent compressor housing wall increases from a predetermined minimum by virtue of inherent manufacturing tolerances and resulting mismatch of compressor and housing, inability to measure accurately the clearance existing between blade tips and housing wall in the assembled condition, as well as the influence of high pressure, high temperature air and resulting differential radial expansion between the compressor blades and housing surrounding the same.
Since the gas turbine engine compressor operates under high temperature, high pressure and high frequency vibration conditions and space allocation as well as weight are extremely limited; very little effort has been expended in attempting to devise a practical proximity sensor for use in such an environment by virtue of the undesirable limitations of mechanical and electrical devices. Various prior art fluidic or pneumatic proximity sensors for sensing dimensional characteristics of piece parts and the like are known but such sensors are impractical for use for obvious reasons in the above-mentioned compressor environment wherein the clearance to be measured is between a continuously rotating compressor and a stationary housing surrounding the same.
