A clamp-on ultrasonic cross correlation flow meter for one-phase flow

This correlation technique presents opportunities for measuring the average rate of flow of fluids through pipes. The only physical parameter required for the measurement principle is the well known distance between the sensors. The new system consists of ultrasonic sensors transforming the natural, stochastic fluctuations of velocity, pressure and density into two signals with a delay time T, and a real time correlator, extracting the delay time from the signals and calculating the average rate of flow of the fluid. Measurements have been carried out with 40 and 50 mm pipe diameters for direct fluid contact and clamp-on transducers. Measurement error has been found to be less than 2% from the reference value for a Reynolds number range 25,000-250,000; even down to a Reynolds number of 4000, the error was less than 3%. (Original abstract - amended)