Fluctuating pressure profile and sensor design for a vortex flowmeter

The fluctuating pressure amplitude profile about a T-cross section vortex shedding cylinder has been experimentally determined. The fluctuating pressure amplitude at a particular point on the cylinder was found to be proportional to the product of the average fluid velocity squared and the fluid density. The proportionality constant was essentially independent of pipe Reynolds number over the range 11,500 to 230,000. The Strouhal number for the test device was constant to within + or - 0.55% over the 40:1 average velocity range of 0.155 to 6.365 m/sec. The pressure profile and shedding frequency data was used to design the lead zirconate titinate piezoelectric bimorph differential pressure sensor used in the commercial version of the flowmeter. Design of the sensor and the associated electronics used to convert the sensed vortex shedding frequency to a 4 to 20 mA signal compatible with process controllers is described.