The basic principle of vortex street

When the fluid flows through the barrier or the special element, the flow oscillation is generated, and the oscillation frequency is measured to reflect the flow through.

Vortex street generation principle

A vortex generator is set in the fluid to alternately generate regular vortices from both sides of the vortex generator. This vortex is called Karman vortex street. The vortex rows are arranged asymmetrically in the downstream of the vortex generator body.

The vortex generator is the main component of the detector, which is closely related to the flow characteristics of the instrument (instrument coefficient, linearity, range, etc.) and the resistance characteristics (pressure loss), and the requirements for it are as follows.

(1) It can control the synchronous separation of the vortex in the direction of the axis of the vortex generator;

(2) In a wide range of Reynolds numbers, there are stable vortex separation points, maintaining a constant Strouhal number;

(3) Strong vortices can be generated, and the signal-to-noise ratio of the signal is high;

(4) Simple shape and structure, easy to process, install and combine;

⑤ The material should meet the requirements of fluid properties, corrosion resistance, abrasion resistance, temperature change;

⑥ The natural frequency is outside the frequency band of the vortex signal.

A variety of vortex generators have been developed, which can be divided into two types: single vortex generators and multi-vortex generators. The basic shapes of single vortex generators are cylinder, rectangular column and triangular column, and other shapes are the deformation of these basic shapes.

There are generally 5 ways for the flow meter to detect vortex signals

1) The differential pressure on both sides of the generator is directly detected by the detection element set in the vortex generator body;

2) A pressure guide hole is set up on the vortex generator, and a detection element is installed in the pressure guide hole to detect the differential pressure on both sides of the generator;

3) Detect the alternating circulation around the vortex generator;

4) Detect alternating differential pressure on the back of the vortex generator;

5) Detect vortex columns in the wake.

According to these five detection methods, different detection technologies (thermal, ultrasonic, stress, strain, capacitance, electromagnetic, photoelectric, optical fiber, etc.) can constitute different types of VSF.