Vortex flowmeters make use of a principle called the von Kármán effect. According to this principle, flow will alternately generate vortices when passing by a bluff body. A bluff body has a broad, flat front. In a vortex meter, the bluff body is a piece of material with a broad, flat front that extends vertically into the flowstream. Flow velocity is proportional to the frequency of the vortices. Flowrate is calculated by multiplying the area of the pipe times the velocity of the flow.