Influence of individual variations of particle image intensities on high-resolution PIV

Nobach, Holger

doi:10.1007/s00348-010-0948-3

Cited by 15 publications

(11 citation statements)

References 17 publications

(22 reference statements)

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“…Prior to cross-correlation, reconstructions are normalised with a nonlinear filter to minimise variations in particle image intensity, which can impair accuracy (Nobach 2011). This consists of a subtract sliding minimum filter over the lengthscale of a cross-correlation window, followed by normalisation by a local maximum value obtained from a sliding maximum filter whose size is the lengthscale of a particle.…”

Section: Piv Processingmentioning

confidence: 99%

A scanning PIV method for fine-scale turbulence measurements

Lawson

Dawson

2014

Exp Fluids

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mechanics. It is a desirable aim, as the fine scales are responsible for (amongst other things) the dissipation of kinetic energy and chemical mixing (Tsinober 2009) and have an important role in phenomena such as cloud formation (Bodenschatz et al. 2010) and flame extinction (Sreenivasan 2004). The challenge stems from the fact that as the Reynolds number increases, the smallest length-and timescales become smaller and faster, requiring significant measurement or computational capability to capture even low Reynolds number flows.For laboratory investigations of turbulence, it would be valuable to have an accurate, three-dimensional, three-component (3D-3C) velocimetry technique with good space and time resolution. Of particular importance is access to the full velocity gradient tensor (VGT), as it embodies the fine scales of turbulence and provides direct access to the turbulent kinetic energy dissipation rate (Wallace 2009). Because of the wide range of lengthscales involved, a large spatial dynamic range (SDR, the ratio of the smallest measureable lengthscale to the largest) is also valuable.Hot wire probes with nine, twelve or even twenty wires (Wallace 2009) offer access to the full VGT with good temporal resolution, but are invasive, complicated to calibrate and only offer pointwise measurements. Dual plane PIV can offer a 3D-3C measurement with good accuracy, time and spatial resolution (Mullin and Dahm 2006), but the setup is complex: it requires four cameras and some means of differentiating between planes, usually chromatically by using two different wavelength laser sources. Furthermore, the depth of the measurement volume is very limited (i.e. between two planes), and the full VGT is only available in one plane. Cinematographic stereo PIV can be used to yield snapshots of 3D-3C velocity fields (Ganapathisubramani et al. 2007), but is only applicable to convective flows as it relies upon Taylor's frozen turbulence hypothesis.Abstract A hybrid technique is presented that combines scanning PIV with tomographic reconstruction to make spatially and temporally resolved measurements of the fine-scale motions in turbulent flows. The technique uses one or two high-speed cameras to record particle images as a laser sheet is rapidly traversed across a measurement volume. This is combined with a fast method for tomographic reconstruction of the particle field for use in conjunction with PIV cross-correlation. The method was tested numerically using DNS data and with experiments in a large mixing tank that produces axisymmetric homogeneous turbulence at R ≃ 219. A parametric investigation identifies the important parameters for a scanning PIV setup and provides guidance to the interested experimentalist in achieving the best accuracy. Optimal sheet spacings and thicknesses are reported, and it was found that accurate results could be obtained at quite low scanning speeds. The two-camera method is the most robust to noise, permitting accurate measurements of the velocity gradients and direct determination of the di...

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Section: Piv Processingmentioning

confidence: 99%

A scanning PIV method for fine-scale turbulence measurements

Lawson

Dawson

2014

Exp Fluids

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“…The assessment of the PIV intrinsic error has been discussed intensively in a number of technical papers, e.g., Norbach. 23 The algorithm used by PIV FFT determines the particle displacement with a typical 0.1 pixel uncertainty. Converted to the average pixel shift by the settings used in this experiment, the uncertainty is estimated to about 3%.…”

Section: Methodsmentioning

confidence: 99%

Evolution of turbulence and in-plane vortices in the near field flow behind multi-scale planar grids

Gan

Krogstad

2016

Physics of Fluids

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PHIT emerin snstitute of hysisF his rtile my e downloded for personl use onlyF eny other use requires prior permission of the uthor nd the emerin snstitute of hysisF he following rtile ppered in qnD vF urogstdD FE ¦ eF @PHITAF ivolution of turulene nd inEplne vorties in the ner (eld )ow ehind multiEsle plnr gridsF hysis of pluids PV@VAX HVSIHI nd my e found t httpsXGGdoiForgGIHFIHTQGIFRWTHHPS Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. In this experimental work, we carry out detailed two-dimensional particle image velocimetry investigations for the near field wakes behind a conventional and two multi-scale planar grids, using stitched camera fields of view. Statistical independent measurements are conducted focusing on the first few mesh distances downstream of the grid. It is found that the multiple integral length scales originated from the grids loose their importance on the turbulence development after about three mesh distances downstream, much earlier than the distance where the turbulence becomes homogeneous. The largest eddy size, represented by the integral length scales, does not show clear differences in its growth rate among the three grids after an initial development of three times the largest grid size downstream. Nevertheless, when examining individual vortex behaviours using conditional averaging and filtering processes, clear differences are found. The grids are found to have different decay rates of peak vorticity and projected vortex strengths. Despite these differences, the in-plane vorticity correlation function reveals that the mean vortex shape of all the grids shows a universal near-Gaussian pattern which does not change much as the turbulence decays. Published by AIP Publishing.[http://dx

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“…Furthermore, Nobach [146] and Fischer et al [79] studied the influence of fluctuations of the detected scattered light on PIV and DGV measurements, respectively. The scattered light fluctuations are a direct consequence of the discrete scattering particles moving through the measurement volume, but note that the light fluctuations also depend on the actual illumination and observation aperture of the measurement volume and the variation of the seeding particle concentration.…”

Section: Flow Sampling Phenomenonmentioning

confidence: 99%

Imaging Flow Velocimetry with Laser Mie Scattering

Fischer

2017

Applied Sciences

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Abstract:Imaging flow velocity measurements are essential for the investigation of unsteady complex flow phenomena, e.g., in turbomachines, injectors and combustors. The direct optical measurement on fluid molecules is possible with laser Rayleigh scattering and the Doppler effect. However, the small scattering cross-section results in a low signal to noise ratio, which hinders time-resolved measurements of the flow field. For this reason, the signal to noise ratio is increased by using laser Mie scattering on micrometer-sized particles that follow the flow with negligible slip. Finally, the ongoing development of powerful lasers and fast, sensitive cameras has boosted the performance of several imaging methods for flow velocimetry. The article describes the different flow measurement principles, as well as the fundamental physical measurement limits. Furthermore, the evolution to an imaging technique is outlined for each measurement principle by reviewing recent advances and applications. As a result, the progress, the challenges and the perspectives for high-speed imaging flow velocimetry are considered.

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Influence of individual variations of particle image intensities on high-resolution PIV

Cited by 15 publications

References 17 publications

A scanning PIV method for fine-scale turbulence measurements

A scanning PIV method for fine-scale turbulence measurements

Evolution of turbulence and in-plane vortices in the near field flow behind multi-scale planar grids

Imaging Flow Velocimetry with Laser Mie Scattering

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