2019 CSCE Annual Conference - Laval (Greater Montreal)

2019 CSCE Annual Conference - Laval (Greater Montreal) Conference


Title
A LABORATORY STUDY OF THE EFFECT OF ACOUSTIC DOPPLER VELOCIMETER SAMPLING FREQUENCY AND SAMPLING VOLUME ON MEASUREMENTS

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Author(s)
Dr. Babak Khorsandi, Amirkabir University of Technology (Tehran Polytechnic) (Presenter)
Dr. Laurent Mydlarski
Mr. Masoud Moeini
Mr. Mohammad Kazemi
Abstract

Acoustic Doppler velocimeters (ADVs) are popular devices for the measurement of velocity in hydraulic engineering applications. It has been found that ADVs accurately predict the mean velocity; however their turbulence measurements is affected by noise. It is expected that the turbulence measurements is further influenced by user adjustable ADV parameters, such as the sampling frequency and sampling volume. These parameters affect how the ADV outputs velocities (by the temporal and spatial averaging). Given this, an experimental work focusing on the performance of ADV operating at different sampling rates and sampling volumes has been conducted to evaluate how the turbulence statistics may be affected. The velocity field of a turbulent axisymmetric jet with a Reynolds number of 10,000 issued into a background of quiescent water was measured via an ADV. Measurements of the mean and RMS velocities at different sampling frequencies and sampling volumes were conducted and compared with those of other measurement techniques. The results show that mean velocities were not influenced by variations in neither the sampling frequency nor the sampling volume. On the other hand, the RMS velocities were damped as the sampling frequency decreased (resulting in more pings being averaged) or when the sampling volume increased (resulting in the velocity being averaged over more scattered particles). The present results offer an opportunity to choose proper sampling frequency and sampling volume for the ADV in measurements of turbulent flows.