The optimum distribution of cavitation bubbles for a flow rate measurement using ultrasonic Doppler method

An ultrasonic Doppler method (UDM) can achieve high accurate flow rate measurement in underdeveloped flow or transient flow. In the conventional method, the UDM for flow rate measurement requires suspending particles in fluid as reflectors. However, in some applications, for example, a flow rate measurement in clean water, any particle does not exist in the flow and hence, the conventional UDM cannot be applied to the measurement. The authors group has proposed the ultrasonic cavitation bubbles as reflectors in the flow measurement by UDM. The cavitation bubbles inside the pipe are excited by the low frequency Langevin transducer attached to the outside wall. The distribution of the cavitation bubbles has a large influence on the accuracy of the measurement. In this report, the optimum distribution of the cavitation bubbles was examined. The intensity of the harmonic components of the measure sound pressure corresponds to the intensity of cavitations bubbles. In order to examine the measurement accuracy of the flow rate against the intensity of cavitation bubble, the sound pressure distribution in the cavitation excitation part was measured by the hydrophone.