The quality of the fossil record

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 so as to produce Karman's vortices at a rate proportional to the velocity of the flowing fluid, with means for detecting the rate of production of vortices to give a linearly related measure of fluid velocity. To improve the correspondence of vortex production rate with flow velocity over wide conditions of flow, the element is formed with a rectangular cross-section in which the depth d along the direction of flow and the height h across the direction of flow are arranged in a ratio d/h of between about 0.5 and 0.9 and preferably in a ratio of 2/3. In the vortex generating element, passageway means extend between openings in the two opposed rectangle sides which are aligned with the direction of flow. The passageway means communicate fluid fluctuations past a flow detector to measure the frequency of vortex production and thereby determine the velocity of the fluid stream. Further improvement of the correspondence of vortex production rate with flow velocity is attained by dimensioning the area A of the passageway opening in relation to the area Ao of the rectangle side containing the opening so that 0.3vortex generating element is related to the inside diameter D of the pipe in which the element is placed so that 0.5rectangle height h is related to the inside diameter D of the pipe so that 0.2