Optimization of a bluff body in a vortex shedding flowmeter and new method to estimate its flow measurement uncertainty

摘要

A vortex shedding flowmeter is widely used for measurements of various fluids in many fields of industry because of its numerous advantages, such as wide rangeability, long term reliability and low maintenance cost. Today, vortex flowmeters of various designs are manufactured by many companies in the world although the flowmeter design is not specified in the present industrial standards. The research project presented in this paper consists of a series of experimental studies and its objective is to develop a new design of a vortex shedding flowmeter, which can be used without any calibration using the actual fluid. This paper describes the first result of the project, i.e. optimization of the flowmeter design and determination of the measurement uncertainty. First, four of the bluff body dimensions were selected and optimized through series of systematic experiments so that the Strouhal number was least dependent on the Reynolds number. Next, the optimized design has been applied to flowmeters with inner diameters from 100 mm to 400 mm. These flowmeters were calibrated and the Strouhal number was precisely determined. Finally, a new method to calculate the uncertainty of the Strouhal number from the dimensional deviations of the parts of the flowmeter was developed experimentally and analytically. This project has been carried out by National Research Laboratory of Metrology and 10 collaborating companies in Japan. The results shown in this report are obviously very important for future standardization of a vortex flowmeter and for improvement of the accuracy in flow measurement in the world.