Vortex flow meters are used to measure the flow of liquids, gases, and steam. They operate based on the principle of the Von Karman effect, which occurs when a fluid flows past a bluff body inserted into the flow stream. This creates alternating vortices downstream of the bluff body. The frequency of these vortices is directly proportional to the velocity of the fluid, allowing for the measurement of flow rate. Vortex flow meters are commonly used in industrial applications due to their reliability and accuracy.