Vortex flowmeter is to set a stagnant flow part in the pipeline of flowmeter. When the fluid flows through the stagnation part, two rows of asymmetric vortices will be generated downstream of the stagnation part due to the stagnation effect on the surface of the stagnation part and other reasons. These vortices are separated at the side and back of the stagnation part to form the so-called Karman vortex row, and the two rows of vortices rotate in opposite directions. Karman proved theoretically that when H/L = 0.28 1, L is the distance between two adjacent vortices), the vortex array is stable. In this case, the relationship between the frequency f generated by eddy current and the fluid velocity υ in the flowmeter pipeline is as follows:

f

=sv/d

V = direction finding/second

formula

d

—— Diameter of cylindrical stagnation piece;

S- dimensionless constant, called Strouhal number, is related to Reynolds number Re of fluid flow state.

Reynolds number Re of circular cross-section pipeline of flowmeter is:

formula

υ —— flow velocity of fluid, m/s;

Rho-density of fluid, kg/m3;

μ —— Dynamic viscosity of fluid, (kg? m- 1)/s .

And the flow of fluids:

q=a

* V

As can be seen from the above formula, the vortex flowmeter has been selected and designed, and the flow rate Q is not only related to F, but also to Reynolds number Re. Reynolds number Re is a dimensionless number representing the flow characteristics of viscous fluid, and its physical meaning is the ratio of inertial force to viscous force of fluid flow. Therefore, the flow state of fluid also has a certain influence on the use of vortex flowmeter. If environmental parameters affect the fluid flow state, it will also affect the performance of vortex flowmeter.

When the vortex precession flowmeter flow enters the product along the axial fluid flow sensor, it is forced to rotate around the center line under the action of the vortex generator, resulting in vortex, which precesses in the Venturi tube and accelerates after reaching the contraction section. When passing through the diffusion section, the vortex center precesses along the conical spiral line. At this time, the precession frequency of the vortex center passing through the detection point is directly proportional to the flow rate of the fluid. The dynamic frequency signal of vortex flow detected by piezoelectric sensor is converted into flow value after amplification, filtering and shaping for local display or signal selection.