Noise in Turbulence Measurements Using Acoustic Doppler Velocimetry

Khorsandi, Babak; Mydlarski, Laurent; Gaskin, Susan

doi:10.1061/(asce)hy.1943-7900.0000589

Cited by 40 publications

(37 citation statements)

References 32 publications

(85 reference statements)

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“…These errors are caused by intrinsic Doppler noise, aliasing of the Doppler signal and perhaps due to the velocity gradient in the sampling volume [30,31]. Specific post-processing methods have been developed to remove such spikes in the raw velocity signal, aiming at the removal of any outliers and filtering of the records, such as the algorithms of Goring and Nikora [30] and Khorsandi et al [32]. Herein, the raw velocity data collected by the ADV were post-processed using the method developed by Goring and Nikora [30].…”

Section: Methodsmentioning

confidence: 99%

Flow Hydrodynamics across Open Channel Flows with Riparian Zones: Implications for Riverbank Stability

Valyrakis

Williams

2017

Water

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Riverbank vegetation is of high importance both for preserving the form (morphology) and function (ecology) of natural river systems. Revegetation of riverbanks is commonly used as a means of stream rehabilitation and management of bank instability and erosion. In this experimental study, the effect of different riverbank vegetation densities on flow hydrodynamics across the channel, including the riparian zone, are reported and discussed. The configuration of vegetation elements follows either linear or staggered arrangements as vegetation density is progressively increased, within a representative range of vegetation densities found in nature. Hydrodynamic measurements including mean streamwise velocity and turbulent intensity flow profiles are recorded via acoustic Doppler velocimetry (ADV)-both at the main channel and within the riverbank. These results show that for the main channel and the toe of riverbank, turbulence intensity for the low densities (λ ≈ 0 to 0.12 m −1 ) can increase up to 40% compared the case of high densities (λ = 0.94 to 1.9 m −1 ). Further analysis of these data allowed the estimation of bed-shear stresses, demonstrating 86% and 71% increase at the main channel and near the toe region, for increasing densities (λ = 0 to 1.9 m −1 ). Quantifying these hydrodynamic effects is important for assessing the contribution of physically representative ranges of riparian vegetation densities on hydrogeomorphologic feedback.

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Section: Methodsmentioning

confidence: 99%

Flow Hydrodynamics across Open Channel Flows with Riparian Zones: Implications for Riverbank Stability

Valyrakis

Williams

2017

Water

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“…Experiments have been carried out with the Vectrino both fixed in an axisymmetric turbulent jet (Reynolds number ca. 11,000), and translated at constant speed through approximately homogeneous isotropic turbulence with zero mean flow produced by a randomly-actuated jet array (RJA) [5]. The axisymmetric jet results indicated that RMS turbulence levels measured with the Vectrino were 30% greater than expected on the basis of earlier hotfilm and laser Doppler velocimetry measurements.…”

Section: Introductionmentioning

confidence: 88%

“…The axisymmetric jet results indicated that RMS turbulence levels measured with the Vectrino were 30% greater than expected on the basis of earlier hotfilm and laser Doppler velocimetry measurements. The RJA experiments indicated that the noise was not a function of mean flow speed, and on this basis [5] concluded that the higher RMS levels were not Doppler noise.…”

Section: Introductionmentioning

confidence: 93%

Turbulence measurements in a jet: Comparing the vectrino and vectrinoii

Zedel

Hay

2011

2011 IEEE/OES 10th Current, Waves and Turbulence Measurements (CWTM)

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Results are reported from an experiment carried out with the newly developed Nortek VectrinoII and the standard Nortek Vectrino in a turbulent axisymmetric jet at a Reynolds number of 5000. The mechanical and acoustic characteristics of these instruments are identical. However, the electronics and signal processing scheme in the VectrinoII represent advancements over those in the original Vectrino (referred to as VectrinoI in this paper). In addition, the VectrinoII provides for profiling over a ca. 3 cm range interval thereby allowing direct measurement of the spatial structure of the flow. The two instruments deliver comparable performance as measured by mean velocity profiles, turbulent kinetic energy spectra, and the derived values of Reynolds stress and dissipation. The Vectrino measurements are compared to the mean and turbulent properties observed by [1] using hot-film and Laser Doppler anemometry. Here, there is good agreement in mean velocity and Reynolds stress measurements. Significant differences are seen in dissipations and velocity variance.

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“…Thus, the device actually measures the velocity of the particles in the flow, rather than that of the flow itself [Nortek, 2009], but the assumption that the particle velocity is equal to the water velocity is valid for fine sediment traveling as washload [Hosseini et al, 2006;Elci et al, 2009]. ADV's have several advantages over other velocity measurement techniques, including robustness, capability to measure instantaneous 3D velocities at high sampling rates, a lack of calibration requirements, and portability [Khorsandi et al, 2012]. Additionally, since the measurement sampling volume is approximately 5 cm below the probes [Nortek, 2009], measurements are collected nonintrusively in the flow ].…”

Section: Acoustic Doppler Velocimetermentioning

confidence: 99%

Sediment Transport Dynamics around an Emergent Vegetation Patch in Unsteady Flows

Waters

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While recent efforts have promoted riverine vegetation because it can create habitats, enhance biodiversity, and improve nutrient dynamics and bank stability, its geomorphic impact when located in the main channel is not fully understood. This dissertation investigates the influence of an in-stream emergent vegetation patch on sediment transport rates and channel bed morphology for two sediment mixtures over repeated unsteady flows, with the overall goal being to assess the potential of vegetation vi TABLE OF CONTENTS Abstract i Acknowledgements iii Table of Contents vi List of Tables x List of Figures xii List of Symbols xv CHAPTER 1-INTRODUCTION 1.1-Background 1.

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Noise in Turbulence Measurements Using Acoustic Doppler Velocimetry

Cited by 40 publications

References 32 publications

Flow Hydrodynamics across Open Channel Flows with Riparian Zones: Implications for Riverbank Stability

Flow Hydrodynamics across Open Channel Flows with Riparian Zones: Implications for Riverbank Stability

Turbulence measurements in a jet: Comparing the vectrino and vectrinoii

Sediment Transport Dynamics around an Emergent Vegetation Patch in Unsteady Flows

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