Abstract
Ultrasonic pulsed Doppler method is a powerful tool to measure velocity distribution in a flow field. However, the method has the maximum measurable velocity. In addition, the measurement volume of this method is relatively large and it is known that the measurement volume affects measured velocities in near-wall region. To measure higher velocity, feedback method which is a dealiasing method and a multi-wave ultrasonic transducer were introduced. Using the transducer, velocities in the near-wall region were measured by 8 MHz ultrasonic with small sensor diameter, velocities far from the transducer were measured by 2 MHz ultrasonic with large sensor diameter. Thus, measurement volume was minimized in the near-wall region. Experiments were carried out at flow rate calibration facility at AIST, and the effects of the measurement volume and the number of pulse repetitions for obtaining an instantaneous velocity profile, N_<pulse>, was discussed. As a result, reduction of the measurement volume improved measurement accuracy in the near-wall region by using the multi-wave transducer, and the measurement accuracy of flow rate was improved. Increasing the N_<pulse> was found to be effective for improving the measurement accuracy even though the total echo signals are the same for calculating the average velocity distribution.
