Utilization of I–Q signals of ultrasound Doppler velocimeter to obtain 1-D turbulence quantities in pipe flow

Abstract

A new method based on using inphase–quadrature (I–Q) ultrasound (US) signals was developed in order to overcome time resolution limitations encountered in turbulent flow measurements by ultrasound Doppler velocimetry (UDV). First, mathematical relations to be used in obtaining probability density function (PDF) and auto correlation function (ACF) of randomly fluctuating velocity (u) in the probe direction were derived in the form of the experimental I–Q signals. The results were evaluated with respect to those obtained by UDV or other conventional techniques whenever possible. In terms of general trend, velocity PDFs obtained from analytical relation along with the I–Q signals and from UDV compare well with each other for Reynolds numbers (NRe) of 16730 and 26300 at the pipe center. Smaller standard deviation of velocity PDF from spectrum of I–Q US signals than that of UDV measurements was the only major difference that could be attributed to the enhanced time resolution of the former technique. Effect of increased time resolution was also observed in the measurement of velocity auto correlation coefficients (ACC). Time correlations of the velocity fluctuations could be captured by using I–Q signals as opposed to UDV that resulted in correlations going to zero in one or two time steps.ACC from I–Q signals was used to get turbulence spectrum at the pipe center. In addition Reynolds number and radial position dependency of integral and Taylor microlength scales, Kolmogorov length scale, rate of energy dissipation and eddy diffusion coefficient were also established.