AIR FLOW MEASUREMENT SYSTEM HAVING REDUCED SENSITIVITY TO FLOW FIELD CHANGES

摘要

A system (100) for measuring air flow rate in a duct (116) includes an air flow sensor (12) and an air flow conditioning device (122) for collecting and accelerating a portion of the total air stream (28) to the sensor, which may be means as known in the art. The conditioning device (122) includes two opposed converging walls (126a, 126b) defining a nozzle, preferably a venturi, the sensor being disposed in the throat (132) of the nozzle. The surfaces of the venturi walls (126a, 126b) are textured to trip the boundary layer (136a, 136b) near the wall surface into turbulence to maintain attachment of flowing air to the walls even when the angle of attack of the air is significantly non-axial. The wall texturing may be random or may be an organized pattern (180, 182, 184, 186, 188, 190, 192, 194, 196, 198). A currently preferred tripping pattern (180) is an array of depressions (170) similar to the surface of a golf ball. The flow profile results in reduced sensitivity to variations in upstream duct configurations.