Effect of Number of Pulse Repetition and Noise on Velocity Profile Measurement in Ultrasonic Pulse Doppler Method

Abstract

Ultrasonic pulse Doppler method has been widely used in many engineering field referred to as UVP (ultrasonic velocity profiler). Analysis algorithm in the UVP, number of pulse repetition (N_pulse), noise and reflector conditions, etc. may affect on the measurement accuracy. The N_pulse is related to the temporal resolution, and must be set as low as possible in order to improve the temporal resolution. However, it is known that accuracy of instantaneous velocity becomes worse with decreasing of the N_pulse. In this study, effect of analysis algorithm in the UVP on velocity data was investigated with changing of the N_pulse and SNR by simulation and experiments. As a result, it is shown that there is an appropriate N_pulse in each algorithm depending on the SNR. An algorithm which decides the Doppler frequency from maximum value in the power spectrum, FFT-max, was relatively hard to be affected by noise. Difference of velocity standard deviation was small between lower and higher noise conditions when FFT-max with N_pulse over the appropriate value was used for the calculation. Hence, FFT-max was the best analysis algorithm for measuring flow field compared with the autocorrelation.