Gaseous fluid flow meter utilizing karman vortex street

Abstract

A gaseous fluid flow meter utilizing a Karman vortex street has a conduit having opposed flat walls and through which a gaseous fluid to be measured flows, a vortex generating member disposed perpendicularly to the direction of flow of the fluid to generate the Karman vortex street downstream thereof, a vortex detector disposed on the conduit and having a transmitter in one flat wall for transmitting a continuous ultrasonic wave across the Karman vortex street and a receiver in the other flat wall positioned opposite the ultrasonic wave transmitter in a direction perpendicular to the direction of the flow of the gaseous fluid through the conduit for receiving the continuous ultrasonic wave to detect the changes in phase of the ultrasonic wave indicating the number of vortices of the Karman vortex street generated in a unit time, and a sound absorbing material on only the portion of the inner surfaces of the flat walls of the conduit around the transmitter and around the receiver and extending sufficiently far along the walls from the transmitter and receiver for preventing the generation of standing waves in front of the walls due to the reflection of the ultrasonic wave.