Vortex Shedding Frequency; Vortex Frequency Sensing - GE PanaFlow MV80 User Manual

Chapter 1. Introduction

1.3.1 Vortex Shedding Frequency

Von Karman vortices form downstream of a shedder bar into two distinct wakes. The vortices of one wake rotate
clockwise while those of the other wake rotate counterclockwise. Vortices generate one at a time, alternating from the
left side to the right side of the shedder bar. Vortices interact with their surrounding space by over-powering every other
nearby swirl on the verge of development. Close to the shedder bar, the distance (or wave length) between vortices is
always constant and measurable. Therefore, the volume encompassed by each vortex remains constant, as shown in
Figure 2 below. By sensing the number of vortices passing by the velocity sensor, the PanaFlow™ Flowmeter
computes the total fluid volume.
Velocity Sensor
Vortex Shedder Bar
Vortices
Flow
Constant Wave Length
Figure 2: Measurement Principle of Vortex Flowmeters

1.3.2 Vortex Frequency Sensing

The velocity sensor incorporates a piezoelectric element that senses the vortex frequency. This element detects the
alternating lift forces produced by the Von Karman vortices flowing downstream of the vortex shedder bar. The
alternating electric charge generated by the piezoelectric element is processed by the transmitter's electronic circuit to
obtain the vortex shedding frequency. The piezoelectric element is highly sensitive and operates over a wide range of
flows, pressures and temperatures.
PanaFlow™ MV80 & MV82 User's Manual 3