抄録
In this study, the flow rate characteristics of ultrasonic flowmeters with variously shaped measurement sections or ducts and the flow characteristics in each measurement section were investigated experimentally and numerically. Also, the feasibility of flow rate measurements over a wide range, including the flow transition region, was investigated.
The experimental results reveal that the flow rate characteristics of the flowmeter were almost constant in regions of both laminar and turbulent flows in the case of a narrow rectangular duct connecting to a straight duct in the upstream side. Furthermore, the difference between the above case and the case of a narrow rectangular duct connecting to a bend in the upstream side was less than 1% in kh or the flow characteristics. Therefore, these results suggest that a narrow rectangular duct is highly suitable for an ultrasonic flowmeter.
The results of numerical simulation by an ultrasonic plane source verified that the flow rate characteristics of the ultrasonic flowmeter with a narrow rectangular duct were not influenced by the change in the velocity profile. That is, the flow rate characteristics of the ultrasonic flowmeter with a narrow rectangular duct were explained from the physical point of view not by an ultrasonic point source which considers the ultrasonic path between sensors to be as a single path or a line but by an ultrasonic plane source which considers the ultrasonic path to be as multipaths or a plane.
The linearity was within ±1.5% over a wide range of measurements. Thus, it is feasible that an ultrasonic flowmeter with a narrow rectangular measurement section can be put to practical use with such a high degree of accuracy.
