Flow velocity measuring device

Abstract

A flow metering apparatus of the type having a vortex generating element with a generally elongate cylindrical shape placed in a stream of flowing fluid in a pipe so as to produce Karman's vortices at a rate proportional to the velocity of the flowing fluid, with ultrasonic means for detecting the rate of production of vortices to give a linearly related measure of fluid velocity. To improve the sensitivity of detection, especially at low velocities, the element is formed with a passageway transverse to the stream to produce therein an alternating fluid flow corresponding to the alternating shedding of vortices, and an ultrasonic generator and an ultrasonic receiver are positioned on opposite sides of the element so that the ultrasonic signal generated will be propagated through the passageway in the element and will be modulated by the alternating fluid flow therein. Further improvement of detection sensitivity is attained by mounting the cases housing the ultrasonic generator and receiver to the pipe carrying the flowing fluid with elastic O-rings, and with a mounting means positioned at the vibratory nodes of the cases, to reduce transmission of sounds to and from the pipe. Flow deflecting projections on the inner wall of the pipe are positioned downstream from the vortex generating element to control vortex generating conditions and improve detection.