A vortex flowmeter measures fluid flow by detecting the frequency of vortices shed by a bluff body (a solid obstruction) placed in the flow stream. As fluid flows past the bluff body, alternating vortices form on each side in a pattern known as a Kármán vortex street. The frequency at which these vortices are shed is directly proportional to the fluid velocity, according to a fixed Strouhal number relationship. A piezoelectric or capacitive sensor detects the pressure oscillations created by the vortices and converts them to a frequency signal, which the transmitter converts to a flow rate.
Vortex flowmeters can be used for oil measurement under the right conditions. They work well with low-viscosity petroleum products at moderate to high flow velocities. However, vortex meters have a minimum flow rate below which the vortex shedding signal becomes too weak to detect reliably—this is known as the low-flow cutoff. At viscosities above approximately 10 centistokes (cSt), the viscosity dampens the vortex shedding process, reducing accuracy and potentially disabling the measurement altogether. For heavy fuel oil or high-viscosity crude oil, vortex meters are generally not recommended.
The main advantages of vortex flowmeters in oil applications are their simplicity, lack of moving parts, and wide flow range. They are suitable for pipeline sizes from DN25 to DN300, handle a broad temperature range, and are available in stainless steel and alloy wetted parts. Their output is a linear frequency signal that is easy to interface with control systems. In refineries and petrochemical plants, vortex meters are commonly used for light crude oil, condensate, naphtha, and other light hydrocarbons. They represent a reliable and cost-effective choice for applications where the fluid viscosity and flow velocity are within the meter's specified operating range.