Abstract
Acoustic Doppler velocimetry (ADV) enables three-dimensional turbulent flow fields to be obtained with high spatial and temporal resolutions in the laboratory, rivers, and oceans. Although such advantages have led ADV to become a typical approach for analyzing various fluid dynamics mechanisms, the vagueness of ADV system operation methods has reduced its accuracy and efficiency. Accordingly, the present work suggests a proper measurement strategy for a four-receiver ADV system to obtain reliable turbulence quantities by performing laboratory experiments under two flow conditions. Firstly, in still water, the magnitude of noises was evaluated and a proper operation method was developed to obtain the Reynolds stress with lower noises. Secondly, in channel flows, an optimal sampling period was determined based on the integral time scale by applying the bootstrap sampling method and reverse arrangement test. The results reveal that the noises of the streamwise and transverse velocity components are an order of magnitude larger than those of the vertical velocity components. The orthogonally paired receivers enable the estimation of almost-error-free Reynolds stresses and the optimal sampling period is 150–200 times the integral time scale, regardless of the measurement conditions.
Highlights
Acoustic Doppler velocimetry (ADV) is one of the most popular instruments for measuring three-dimensional flow velocities in research related to water resources
The movement of particles shifts the phase of the emitted acoustic pulses to the back-scattered pulses due to the Doppler effect, and this shifted phase is converted into the radial flow velocity (Vi) based on the following equation (Lane et al, 1998): Vi where the subscript i can be from 1 to 4 and denotes the component in each receiver, c is the speed of sound in water, f ADV is the frequency of sound emitted by the ADV device, and dφ/dt is the phase difference given by dφ =
In a fixed sampling volume, the noises increase as the velocity range for setup increases, similar to the results obtained in previous studies (Nikora and Goring, 1998; Voulgaris and Trowbridge, 1998), in which experiments identical to the present cases were performed, but with threereceiver ADV
Summary
Acoustic Doppler velocimetry (ADV) is one of the most popular instruments for measuring three-dimensional flow velocities in research related to water resources It obtains velocity fields with high sampling rates for small sampling volumes and little data contamination. These advantages have led to the use of ADV in numerous studies to analyze the various physical mechanisms observed in the laboratory as well as in field studies (e.g., Kim et al, 2000; Reidenbach et al, 2006; Nystrom et al, 2007; Wang et al, 2012; Salim et al, 2017; Park and Hwang, 2019). The velocity data inevitably include measurement noises inherently produced by the measurement
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