High time resolution ultrasonic velocity profiler

The objective of the present study is to develop a high time resolution ultrasonic velocity profiler (UVP) system by improving a signal processing and apply it to turbulent flow. The UVP system is able to obtain one-dimensional velocity distribution on an ultrasonic beam line from echo signals reflected at tracer particles. The position is determined from a time delay between emission of ultrasound pulse and reception of corresponding echo signals. The time resolution of conventional UVP systems is limited to the order of 10 ms at the best due to its signal processing technique, that needs more than a few ten echo signals to obtain the velocity distribution. In order to improve the time resolution of the UVP, we use a cross-correlation technique to estimate a time difference between two echo signals of a pair of emissions of ultrasound pulses. The pipe flow was examined by the present UVP system with the new signal processing. The result showed in a good agreement with that of laser doppler velocimetry measurement. In this experiment, we could improve the time resolution of UVP up to 500 mus to obtain a line profile of velocities and demonstrated a possibility to realize measurements of a smaller time scale velocity fluctuation in flows. (C) 2002 Elsevier Science Inc. All rights reserved.