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G. Oldenziel

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12 records found

Ultrasound imaging velocimetry in particle-laden flows

Counteracting attenuation with correlation averaging

Journal article - A. Dash, W.J. Hogendoorn, G. Oldenziel, G. Oldenziel, C. Poelma

Abstract: Ultrasound imaging velocimetry (UIV) refers to the technique wherein ultrasound images are analysed with 2D cross-correlation techniques developed originally in the framework of particle image velocimetry. Applying UIV to opaque, particle-laden multiphase flows have long been considered to be an attractive prospect. In this study, we demonstrate how fundamental differences in acoustical imaging, as compared to optical imaging, manifest themselves in the 2D cross-correlation analysis. A chief point of departure from conventional particle image velocimetry is the strong variation in the intensity profile of the acoustic wavefield, primarily caused by the attenuation of ultrasonic waves in particle-laden flows. Attenuation necessitates using a larger ensemble of correlation planes to obtain satisfactory time-averaged velocity profiles. For a given combination of imaging and flow conditions, attenuation sets upper limits on volume fraction, penetration depth, as well as temporal resolutions that may be accessed confidently. This behaviour is demonstrated in two experimental datasets and is also supported by a modified cross-correlation theory. The modification is brought about by incorporating a lumped model of ultrasonic backscattering in suspensions into existing spatial cross-correlation analysis. The two experimental datasets correspond to two distinct particle-laden pipe flows: (1) a neutrally buoyant non-Brownian suspension in a laboratory-scale flow facility, wherein particle sizes are comparable to the ultrasonic wavelength and (2) a non-Newtonian slurry in an industrial-scale flow facility, wherein particle sizes are much smaller than the ultrasonic wavelength. We illustrate how and to what extent correlation averaging can counteract the adversity caused by attenuation. The work herein offers a template for one to evaluate the performance of UIV in particle-laden flows. Graphical abstract: [Figure not available: see fulltext.].@en

The effect of bubble size on lock-exchange density currents through bubble screens

Journal article - Tom S.D. O'Mahoney, G. Oldenziel, G. Oldenziel, Pepijn Van Der Ven

Bubble screens are used at sea locks to mitigate salt intrusion into inland water systems. In this paper the effectiveness of a bubble screen in delaying the mixing of salt and freshwater via lock exchange was studied. Laboratory-scale experiments investigating the flow field and ...

Experimental study on the 3D-flow field of a free-surface vortex using stereo PIV

Journal article - S.P.A. Duinmeijer, G. Oldenziel, G. Oldenziel, F.H.L.R. Clemens, F.H.L.R. Clemens

In order to analyse the flow characteristics of free-surface vortexes and to validate the Burgers vortex model by using stereo particle image velocimetry, experiments are conducted in a 600 mm diameter vortex tank. Measured axial velocities indicate that 10–25% of the flow is tra ...

Assessing the Effectiveness of the IJmuiden Salt Screen Design for Nonuniform Selective Withdrawal by Physical and Numerical Modeling

Journal article - Anton De Fockert, Tom S.D. O'Mahoney, Helena I.S. Nogueira, G. Oldenziel, Arnout C. Bijlsma, Hans Janssen

Salt water intrusion through the New Sea Lock of IJmuiden, Netherlands requires mitigation to ensure availability of enough fresh water further inland. For this purpose, a salt screen has been proposed for selective withdrawal of salt water from the Noordzeekanaal in the vicinity ...

Pulsed LED line light for large-scale PIV -development and use in wave load measurements

Journal article - W. Bakker, W. Bakker, Bas Hofland, E. de Almeida Sousa, G. Oldenziel, G. Oldenziel, E.F.J. Overmars

In this paper the development of a high-power pulsed LED line light and its use to apply particle image velocimetry (PIV) during wave impact measurements are described. An electrical circuit that generates high-current pulses is designed and built, which is used to overdrive a nu ...

Measurement of high-Re turbulent pipe flow using single-pixel PIV

Review - G. Oldenziel, G. Oldenziel, S. Sridharan, S. Sridharan, J. Westerweel

In this paper are presented PIV measurements of turbulent pipe flow at bulk Reynolds numbers Re D between 3.4 × 10 5 and 6.9 × 10 5 . So-called single-pixel correlation is applied that yields a superior spatial resolution that is slightly larger than the equivalent size of a pixe ...

Wave field measurements of regular wave–monopile interaction using Free-Surface Synthetic Schlieren

Journal article - G. Oldenziel, G. Oldenziel, A. Moreno-Rodenas, N Bruinsma, W. Bakker

Spatio-temporal wave patterns due to wave field–structure interaction can be very complex to measure and analyze when using (intrusive) point probes. Free-surface field measurements can offer much needed insight in this domain. Nevertheless, to the best of the authors’ knowledge, these methods are rarely used in experimental offshore engineering and research. In these fields, typical domain sizes are at least in the order of several m2, whereas (optical) free-surface field measurements are often not performed in domains with dimensions larger than roughly 0.5 × 0.5 m2. In the current work, the optical free-surface measurement technique named Free-Surface Synthetic Schlieren (FS-SS) is applied to measure the interaction between an incident wave field and a surface piercing cylinder, or monopile, in a domain of several m2 for the first time. The FS-SS method is validated for wave fields with wavelengths λ ≪ L to λ ≫ L, where L is the domain size in the direction of wave propagation. It is found that the incorporation of an additional water level measurement improves the agreement between intrusive wave height meters and the FS-SS measurement for large wavelengths (λ / L> 0.5) as compared to assuming a zero-mean free-surface. Wave field–monopile interaction is measured for two values of D/ λ: D/ λ= 0.1 and D/ λ= 0.2 , where D is the monopile diameter. For the case D/ λ= 0.2 the interaction wave field is analyzed by subtracting the measured wave field in the absence of a structure, from the measured interaction wave fields. The measured difference wave field reveals many interaction phenomena such as locations of amplification, both near the monopile and further away, a wake that has certain similarities with a Kelvin wake, and a circular small wavelength diffraction pattern. Additionally, the embedding of the measurements in a wave breaking regime map is presented. In this map, the applicability for certain wave conditions can be clearly visualized. It is concluded that the FS-SS method, including the proposed improvement using additional sensor data, is a useful addition to the toolbox of hydraulic engineers and researchers, and that especially the measured locations of wave amplification in the far field will not be easily detected using (arrays of) point probes.@en

Single-pixel PIV measurements of high-re turbulent pipe flow

Conference paper - J. Westerweel, S. Sridharan, G. Oldenziel

In this paper we present PIV measurements of turbulent pipe flow at Reynolds numbers between 3.4×105 and 6.9×105. We apply a so-called 'single-pixel correlation' that yields a superior spatial resolution (Westerweel et al., 2004). We use the location and shape of the averaged cor ...

Droplet collisions in turbulence

Doctoral thesis - G. Oldenziel

Measurements of liquid film thickness for a droplet at a two-fluid interface

Journal article - G. Oldenziel, R. Delfos, J. Westerweel

Measurements of liquid film thickness for a droplet at a two-fluid interface

Journal article - G. Oldenziel, R. Delfos, J. Westerweel

Closure on discussion Experimental study on the 3D-flow of a freesurface vortex using stereo PIV

Journal article - Alex Duinmeijer, G. Oldenziel, G. Oldenziel, F.H.L.R. Clemens, F.H.L.R. Clemens

Contributed

2 records found

Towards high resolution Particle Image Velocimetry

Estimating turbulence statistics from the ensemble correlation

Master thesis - S. Sridharan, J. Westerweel, G. Oldenziel

The research in resolving the smaller scales of turbulence has gained significant attention in recent years, owing to the advancements in the measurement techniques. High resolution experimental studies are required to investigate high Reynolds number flows where the scales of turbulence are very small. This is of particular importance in addressing the theoretical issues in studying high Reynolds number wall turbulence which finds applications in transport, energy, and aerospace industries. Hot-Wire Anemometry (HWA) is often employed to reach very high spatial resolution. Early research in Particle Image Velocimetry (PIV), a qualitative flow visualization technique, was not able to achieve a higher resolution as comparable with that of HWA. However, recent developments in PIV allow high resolution measurements, using information on the time averaged ensemble correlation. The ensemble correlation can be used to reduce the size of the interrogation windows employed in a PIV analysis, without compromising for the particle image density in an interrogation window. This is achieved by using a large number of image pairs. In this thesis, ensemble correlation is used to study the turbulence in two specific cases: a turbulent jet and high Reynolds number pipe flow. The ensemble correlation, though being a time averaged quantity, contains information on the velocity Joint Probability Distribution Functions (JPDFs) which can be used to estimate the turbulence statistics. This information can be retrieved from the shape of the ensemble correlation. It is assumed that the ensemble correlation is the convolution of the auto-correlation and the velocity JPDFs. The velocity JPDFs are retrieved by estimating the second moments of the ensemble correlation by fitting a Gaussian profile, and further using a correction for auto-correlation. The second moments can be used to estimate the Reynolds stresses in the flow. The proposed method is validated by implementing it to study the turbulent jet. For this purpose, 9000 image pairs are acquired. The results show that the retrieved moments predict the Reynolds stresses accurately. Further, high Reynolds number pipe flow experiments are performed in the Alpha Loop facility at Deltares. The bulk Reynolds number is varied from 0.3 to 0.6 million, acquiring 20,000 image pairs per measurement series. Also, the pressure drop is measured across the pipe along with the PIV measurements to estimate the roughness of the pipe. The results from the PIV measurements show that the mean velocity profile follows a similar trend as observed in the literature. A small bias is observed between the mean velocity obtained from the ensemble correlation and that obtained by averaging the instantaneous velocity vectors, in regions of high velocity gradients. The Reynolds shear stress estimated from the shape of the ensemble correlation is underestimated. However, the streamwise turbulent fluctuations estimated follow a trend, similar to that observed in the literature.

On the free-surface vortex driven motion of buoyant particles

Doctoral thesis - S.P.A. Duinmeijer

This is an experimental and theoretical research on the motion of buoyant particles in the flow of a free-surface vortex at moderate to high particle Reynolds numbers. @en