Single camera volumetric shadowgraphy system for simultaneous droplet sizing and depth location, including empirical determination of the effective optical aperture

Legrand, Mathieu; Nogueira, J.; Lecuona, A.; Hernando, Ana

doi:10.1016/j.expthermflusci.2016.03.018

Cited by 10 publications

(8 citation statements)

References 7 publications

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“…They can even be classified further into techniques based on the gray level gradient [29] or contrast value [28], or both [30]. Another approach is to estimate particle size from both focused and defocused images [27,31], which can increase the depth of the measurement volume and allow a larger number of drops to be validated from the same image. The methods can also be classified according to how to define the effective depth of field or the measurement volume, being dependent [29,32] or independent [27,28] of the particle size.…”

Section: Depth From Defocusmentioning

confidence: 99%

“…The ultimate goal of these techniques is to realize three-dimensional visualization and characterization of sprays. Legrand et al [31] considered estimation of particle size and depth location from defocused images, but a directional ambiguity of depth location remained. The present study offers a strategy to solve the ambiguity problem for depth location estimation by using two cameras with different imaging distances on the same optical axis.…”

Section: Depth From Defocusmentioning

confidence: 99%

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Spray drop measurements using depth from defocus

Zhou

Tropea

Chen

et al. 2020

Meas. Sci. Technol.

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Sprays are typically characterised by providing local drop size and velocity distributions and number density. The present work examines the possibility of obtaining such information using backlight photography, whereby two cameras are employed and the size and position of each imaged drop is obtained using a depth from defocus approach. A simple algorithm for estimating size and position from the two camera images is introduced and the sensitivity of this algorithm to various system parameters is investigated with simulations using synthetic images, measurements from a calibration facility, and measurements conducted in a sparse spray. Comparison measurements using the analysis of focused images are provided.

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Section: Depth From Defocusmentioning

confidence: 99%

Section: Depth From Defocusmentioning

confidence: 99%

Spray drop measurements using depth from defocus

Zhou

Tropea

Chen

et al. 2020

Meas. Sci. Technol.

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“…Direct imaging of particles is a straightforward technique for determining velocity and size even from irregular-shaped particles. Multiple names were used for this technique in the past: shadowgraphy technique (Castanet et al 2013, Dehnadfar et al 2012, Legrand, Nogueira, Lecuona and Hernando 2016, Wang et al 2017, particle droplet image analysis (PDIA) (Anand et al 2012;Castanet et al 2013;Ju et al 2012;Kashdan et al 2003;Senthilkumar et al 2020), backlight photography (Zhou et al 2020), image processing technique (Koh et al 2001;Lee and Kim 2004), imagebased drop-sizing techniques (Fdida and Blaisot 2009), shadow imaging (Putkiranta et al 2008), or just imaging (Kim and Kim 1994). In the following, the term shadowgraphy is used.…”

Section: Shadowgraphy Approachmentioning

confidence: 99%

“…Depending on the implemented optics, it can be described as a function of particle/dot diameter. Following the remark made in (Legrand, Nogueira, Lecuona andHernando 2016, Senthilkumar et al 2020), it is necessary to control if all dots within a defined measurement volume thickness are detected. To check whether this was the case for d shadow minGS , the number of detected dots was counted for each z-position.…”

Section: Shadowgraphy Approachmentioning

confidence: 99%

“…As discussed in (Kapulla et al 2008), several detection settings of the DaVis software can have a significant effect on the detected particle size and, hence, on the particle mass flow rate. As mentioned in (Legrand et al 2016;Senthilkumar et al 2020), a check of how many particles are detected within the shadowgraphy measurement volume is recommended. These two aspects -influence of particle detection settings on G p and the particle detection rate, are missing in the uncertainty analysis made in (Allofs et al 2022).…”

Section: Introductionmentioning

confidence: 99%

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Particle mass flow determination in dust-laden supersonic flows by means of simultaneous application of optical measurement techniques

Allofs¹,

Neeb²,

Gülhan³

2023

Exp Fluids

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Particle mass flow rate and particle mass concentration are key parameters for describing two-phase flows, especially for particle-induced heating augmentation analysis. This work addresses the question of how accurate particle mass flow rate can be determined with three non-intrusive measurement approaches, based on shadowgraphy, particle tracking velocimetry (PTV), and scattered light intensity, in supersonic flows. In terms of shadowgraphy and PTV, the particle mass flow rate was determined by measuring individual particle characteristics, namely particle size, velocity, and density, as well as the measurement volume. The presented shadowgraphy procedure is based on the commercial LaVision DaVis software and additional shadowgraphy corrections. Multiple tests were conducted in the experimental test facility GBK of DLR with varying flow conditions, at a Mach number of 2.1, unit Reynolds number (Re∞) ranging from 5e7 1/m to 1.5e8 1/m, total temperature (T0) ranging from 303 to 544 K, and particle materials, namely Al2O3, MgO, and SiO2, in the size range of 1 to 60 µm. Particle size distributions of Al2O3 and MgO particles could be reproduced with shadowgraphy quite well, while the PTV procedure resulted in non-similar distributions. Pycnometer measurements indicated MgO particle density to be significantly lower than reference values. A DaVis parameter variation analysis resulted in a particle mass flow rate uncertainty of shadowgraphy of up to 30%. The particle mass flow rate uncertainty of PTV is approx. 76%, and the respective uncertainty of scaled PTV and scattered light intensity approach is 28%. The particle mass flow rate, measured with shadowgraphy, is 58% higher than those of the semi-axisymmetric scattered light intensity approach, which can be explained by a higher particle concentration at the injection plane.

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Depth from defocus technique: a simple calibration-free approach for dispersion size measurement

Rao,

Sharma,

Basu

et al. 2024

Exp Fluids

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Particle size measurement is crucial in various applications, be it sizing droplets in inkjet printing or respiratory events, tracking particulate ejection in hypersonic impacts or detecting floating target markers in free-surface flows. Such systems are characterised by extracting quantitative information like size, position, velocity and number density of the dispersed particles, which is typically non-trivial. The existing methods like phase Doppler or digital holography offer precise estimates at the expense of complicated systems, demanding significant expertise. We present a novel volumetric measurement approach for estimating the size and position of dispersed spherical particles that utilises a unique ‘Depth from Defocus’ (DFD) technique with a single camera. The calibration-free sizing enables in situ examination of hard to measure systems, including naturally occurring phenomena like pathogenic aerosols, pollen dispersion or raindrops. The efficacy of the technique is demonstrated for diverse sparse dispersions, including dots, glass beads and spray droplets. The simple optical configuration and semi-autonomous calibration procedure make the method readily deployable and accessible, with a scope of applicability across vast research horizons.

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Single camera volumetric shadowgraphy system for simultaneous droplet sizing and depth location, including empirical determination of the effective optical aperture

Cited by 10 publications

References 7 publications

Spray drop measurements using depth from defocus

Spray drop measurements using depth from defocus

Particle mass flow determination in dust-laden supersonic flows by means of simultaneous application of optical measurement techniques

Depth from defocus technique: a simple calibration-free approach for dispersion size measurement

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