A Correction Method for Turbulence Measurements with a 3D Acoustic Doppler Velocity Profiler

Hurther, David; Lemmin, Ulrich

doi:10.1175/1520-0426(2001)018<0446:acmftm>2.0.co;2

Cited by 124 publications

(115 citation statements)

References 12 publications

(23 reference statements)

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“…However it adds a positive bias to the high frequency range of the power spectrum, affecting the turbulence statistics (Dombroski and Crimaldi, 2007). Hurther and Lemmin (2001) ADVs. These include the phase-space thresholding method of Goring and Nikora (2002) and the despiking filters of Cea et al (2007).…”

Section: Acoustic Doppler Velocimetrymentioning

confidence: 99%

Effect of background turbulence on an axisymmetric turbulent jet

2013

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The effect of background turbulence on a turbulent jet was investigated experimentally. The primary objective of this work was to study the effect of different levels of the background turbulence on the dynamics and mixing of an axisymmetric turbulent jet at different Reynolds numbers. The secondary objective, which arose during the experiments, was to improve the acoustic Doppler velocimetry measurements which were found to be inaccurate when measuring turbulence statistics.In addition to acoustic Doppler velocimetry (ADV), flying hot-film anemometry was employed in this study. To move the hot-film probe at constant speeds, a high precision traversing mechanism was designed and built. A data acquisition system and LabVIEW programs were also developed to acquire data and control the traversing mechanism. The experiments started by benchmarking the two measurement techniques in an axisymmetric turbulent jet. Comparing the results with those of the other studies validated the use of flying hot-film anemometry to estimate the mean and the root-mean square (RMS) velocities.The experiments also validated the use of ADV for measurement of the mean velocities (measured in three Cartesian directions) and the RMS velocity (measured in the z-direction only). RMS velocities measured by the ADV along the x-and y-direction of the probe were overestimated.Attempts to improve the turbulence statistics measured by the ADV using the post-processing and noise-reduction methods presented in the literature were undertaken. However, the RMS velocities remained higher than the accepted values. In addition, a noise-reduction method was presented in this study which reduced the RMS velocities down to the accepted values. It was also attempted to relate Doppler noise to current velocity, and thus improve the results by iv subtracting the Doppler noise from the measured RMS velocities in the jet. However, no relationship was found between the Doppler noise and the mean velocity.The effect of different levels of background turbulence on the dynamics and mixing of an axisymmetric turbulent jet at different Reynolds numbers was then investigated. The background turbulence was generated by a random jet array. To confirm that the turbulence is approximately homogeneous and isotropic and has a low mean flow, the background flow was first characterized. Velocity measurements in an axisymmetric jet issuing into two different levels of background turbulence were then conducted. Three different jet Reynolds

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Section: Acoustic Doppler Velocimetrymentioning

confidence: 99%

Effect of background turbulence on an axisymmetric turbulent jet

2013

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“…For the present measurements, a multistatic configuration of the ADVP was used, consisting of four receivers that surround the emitter, providing one redundancy in the three-dimensional velocity component calculation. This redundancy eliminates the signal noise and improves the data quality (Hurther & Lemmin 2000). Pulse repetition frequencies (PRF) of 1667 Hz and 1111 Hz, with a number of pulse pairs (NPP) equal to 32 were used, which results in velocity data acquisition frequencies of 52 and 35 Hz, respectively.…”

Section: Velocity Measurementsmentioning

confidence: 99%

“…The ADVP consists of two independent working subsystems in the longitudinal and spanwise flow sections, which make a redundant measurement of the instantaneous vertical velocity field in order to correct the data. Hurther & Lemmin (2000) demonstrated that the AVDP mean flow and turbulence data compare well with data obtained by more conventional techniques.…”

Section: Introductionmentioning

confidence: 99%

Near-field flow structure of a confined wall jet on flat and concave rough walls

Albayrak¹,

Hopfinger²,

Lemmin³

2008

J. Fluid Mech.

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Experimental results are presented of the mean flow and turbulence characteristics in the near field of a plane wall jet issuing from a nozzle onto flat and concave walls consisting of fixed sand beds. This is a flow configuration of interest for sediment erosion, also referred to as scouring. The measurements were made with an acoustic profiler that gives access to the three components of the instantaneous velocities. For the flat-wall flow, it is shown that the outer-layer spatial growth rate and the maxima of the Reynolds stresses approach the values accepted for the far field of a wall jet at a downstream distance x/b 0 ≈ 8. These maxima are only about half the values of a plane free jet. This reduction in Reynolds stresses is also observed in the shear-layer region, x/b 0 < 6, where the Reynolds shear stress is about half the value of a free shear layer. At distances x/b 0 > 11, the maximum Reynolds shear stress approaches the value of a plane free jet. This change in Reynolds stresses is related to the mean vertical velocity that is negative for x/b 0 < 8 and positive further downstream. The evolution of the inner region of the wall jet is found to be in good agreement with a previous model that explicitly includes the roughness length.On the concave wall, the mean flow and the Reynolds stresses are drastically changed by the adverse pressure gradient and especially by the development of Görtler vortices. On the downslope side of the scour hole, the flow is nearly separating with the wall shear stress tending to zero, whereas on the upslope side, the wall-friction coefficient is increased by a factor of about two by Görtler vortices. These vortices extend well into the outer layer and, just above the wall, cause a substantial increase in Reynolds shear stress.

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“…Rusello et al, 2006). Lastly, the Doppler noise removal procedure of Hurther & Lemmin (2001) was applied. This procedure corrects for the noise in the turbulent velocities by compensating for the covariance between the two vertical velocity signals that are obtained by the Vectrino.…”

Section: Data Collection and Processingmentioning

confidence: 99%

Model Versus Nature: Hydrodynamics in Mangrove Pneumatophores

Horstman

Bryan

Mullarney

et al. 2017

Int. Conf. Coastal. Eng.

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Water flows through submerged and emergent vegetation control the transport and deposition of sediment in coastal wetlands. Many past studies into the hydrodynamics of vegetation fields have used idealized vegetation mimics, mostly rigid dowels of uniform height. In this study, a canopy of real mangrove pneumatophores was reconstructed in a flume to quantify flow and turbulence within and above this canopy. At a constant flow forcing, an increase in pneumatophore density, from 71 m -2 to 268 m -2 , was found to cause a reduction of the within-canopy flow velocities, whereas the over-canopy flows increased. Within-canopy velocities reduced to 46% and 27% of the free-stream velocities for the lowest and highest pneumatophore densities, respectively, resulting in stronger vertical shear and hence greater turbulence production around the top of the denser pneumatophore canopies. The maximum Reynolds stress was observed at 1.5 times the average pneumatophore height, in contrast to uniform-height canopies, in which the maximum occurs at approximately the height of the vegetation. The ratios of the within-canopy velocity to the free-stream velocity for the pneumatophores were found to be similar to previous observations with uniform-height vegetation mimics for the same vegetation densities. However, maxima of the scaled friction velocity were two times smaller over the real pneumatophore canopies than for idealized dowel canopies, due to the reduced velocity gradients over the variable-height pneumatophores compared to uniform-height dowels. These findings imply that results from previous studies with idealized and uniform vegetation mimics may have limited application when considering sediment transport and deposition in real vegetation, as the observed turbulence characteristics in nonuniform canopies deviate significantly from those in dowel canopies.

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A Correction Method for Turbulence Measurements with a 3D Acoustic Doppler Velocity Profiler

Cited by 124 publications

References 12 publications

Effect of background turbulence on an axisymmetric turbulent jet

Effect of background turbulence on an axisymmetric turbulent jet

Near-field flow structure of a confined wall jet on flat and concave rough walls

Model Versus Nature: Hydrodynamics in Mangrove Pneumatophores

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