Rene van Hout

Rene van Hout
Technion - Israel Institute of Technology | technion · Faculty of Mechanical Engineering

Doctor of Philosophy

About

67
Publications
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1,268
Citations

Publications

Publications (67)
Article
Full-text available
A combination of time resolved tomographic particle image velocimetry (tomo-PIV), refractive-index matching technique, and machine vision algorithms was used to measure the translational and rotational motion of freely moving, nearly neutrally buoyant spheres in a fully developed, turbulent boundary layer (TBL). Located in the buffer and logarithmi...
Preprint
Full-text available
The changing 3D vortex shedding topology of a heavy, tethered sphere exposed to uniform flow crossing the onset of vortex induced vibrations (VIV) is reported together with simultaneously tracked sphere positions. Transient upstream flow conditions were imposed by increasing the reduced velocity from U * = 2.2 to 4.5 ("lock-in", mode I). 3D vortex...
Article
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The flow field of an impulsively started round, confined nitrogen jet was investigated using combined high speed schlieren imaging and particle velocimetry (PIV) measurements. PIV measurements were carried out at five different, normalized times (55 ≤ t * ≤ 392) relative to jet intrusion into a constant volume chamber. Between 100 < t * < 250, the...
Article
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This review article focuses on the near-field flow characteristics of coaxial circular jets that, despite their common usage in combustion processes, are still not well understood. In particular, changes in outer to inner jet velocity ratios, r_u, absolute jet exit velocities and the nozzle dimensions and geometry have a profound effect on the near...
Article
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Since effective thermal insulation of buildings could significantly decrease energy consumption worldwide, this study examined the potential of concrete tiles with complex geometries at improving thermal performance in building envelopes. The study focused on air flow characteristics that occur near the external surface of the tile, and their influ...
Article
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We present experiments on rigid, nylon fiber translation, orientation and rotation dynamics (one-way coupled) in a fully developed turbulent channel flow (Re τ = 435). The experiments were performed using two orthogonal view, digital inline Fraunhofer holographic cinematography that allowed to track individual fibers and determine their 3D position...
Conference Paper
Full-text available
This paper presents the current stage of a study examining the potential of complex geometry concrete tiles to improve thermal performance in building envelopes. This stage focused on developing tile geometries and testing them using physical and digital CFD simulations. Tiles were developed taking two approaches: (i) developing variation from basi...
Article
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A combination of time-resolved particle image velocimetry (TR-PIV) and tomographic PIV was used to study the instantaneous 3D vortex shedding as well as mean velocities and turbulent stresses in the near wake of a smooth and rough sphere. Sphere roughness was modeled by spiraling grooves found in nature on pine cones. The measurements extended up t...
Article
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In this study, the effect of impinging air jet pulsation on the generation of toroidal (“primary”) vortices near to the nozzle exit, their subsequent downstream evolution, the creation of “secondary” vortices and their interaction along the radial wall jet was investigated. Experiments were performed using particle image velocimetry and data analys...
Preprint
Full-text available
In this study, the effect of impinging air jet pulsation on the generation of toroidal ("primary") vortices near to the nozzle exit, their subsequent downstream evolution, the creation of "secondary" vortices and their interaction along the radial wall jet was investigated. Experiments were performed using particle image velocimetry and data analys...
Article
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A pulsating round jet having a constant average mass flow rate may increase heat transfer in comparison to a steady jet impinging on a surface. However, while several studies have focused on the heat transfer, flow field characteristics remain poorly understood. Here, the mean and turbulent flow characteristics of a pulsating, round jet impinging o...
Article
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Flow in the wake of a sphere has been studied for at least the last hundred years. The three-dimensional (3-D) flow structure has been observed many times using dye visualization and prior to the direct numerical simulations by Johnson & Patel ( J. Fluid Mech. , vol. 378, 1999, pp. 19–70), its structure at a Reynolds number of approximately 300, wa...
Article
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While fiber-turbulence interactions are common in industrial and environmental applications, little is known about inertial fiber dynamics in isotropic turbulence. Here, rotational and translational dynamics of rigid, heavy fibers in air isotropic turbulence were measured using two-orthogonal-view, holographic cinematography. Measurements were cond...
Article
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Heat transfer and flow field characteristics of a pulsating round air jet, impinging on a flat heated target surface were measured and compared to those of a steady impinging jet. The jet was partially confined and the target surface stand-off distance equaled two nozzle diameters, D. Investigated Reynolds numbers ranged from Re = 4,606 to 13,513,...
Article
Full-text available
The 3D flow field in the wake of a tethered sphere (D=6 mm, m ∗ =7.77, L ∗ =4.1) undergoing vortex induced vibrations (VIV) in a water tunnel, was measured using tomographic particle image velocimetry (tomo-PIV). The flow field was investigated for four different reduced velocities ranging between 3.6<U ∗ <13.2, corresponding to Reynolds numbers ra...
Article
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Few studies have investigated the flow characteristics of jets impinging on dimpled surfaces that may increase or decrease their heat transfer capabilities. Here, particle image velocimetry (PIV) measurements have been performed on a round jet (diameter D) impinging on a surface having large spherical dimples (opening size d), D/d = 0.83. In partic...
Article
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Dimpled surfaces may enhance or decrease heat transfer compared to smooth surfaces. Here, the flow field of a round, axisymmetric air jet (diameter D) impinging on smooth and dimpled target surfaces (positioned at H/D ≈ 5) was measured using particle image velocimetry (PIV). Reynolds numbers based on the jet exit velocity and D were, Re = 1,473, 6,...
Article
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Nocturnal sky radiation cooling (NSRC) is a passive, sustainable, cooling method that utilizes the sky as a radiation heat sink. Here, a reliable, hybrid NSRC system including a heat pump is presented and analyzed for the cooling of remote, off-grid data centers. An analytical system model that incorporates thermal and life cycle cost analyses incl...
Chapter
Time-resolved tomographic particle image velocimetry (PIV) measurements (acquisition rate 250 Hz) were performed in a turbulent boundary layer on the side wall of an open channel, water flow facility (cross section 60×60 cm², W × H), 3.5m downstream of the inlet at a bulk flow velocity of Ub = 0.17m/s (Reb = UbH/v= 97, 679, δ0.99 = 45.0 mm, Reθ= 75...
Article
Full-text available
Impinging jets are widely used in cooling applications. Here, particle image velocimetry measurements were performed to study the flow field (focusing on the wall jet) and vortex characteristics of a round air jet, impinging on a flat surface at three Reynolds numbers, Re = 1,300, 6,260 and 12,354 (based on nozzle diameter, D, and jet exit velocity...
Article
Full-text available
In many applications, finite-sized particles are immersed in a turbulent boundary layer (TBL) and it is of interest to study wall effects on the instantaneous shedding of turbulence structures and associated mean velocity and Reynolds stress distributions. Here, 3D flow field dynamics in the wake of a prototypical, small sphere (D+=50, 692<ReD<959)...
Conference Paper
Full-text available
This paper presents the results of an investigation into the potential of complex geometry to create a microclimate by changing the airflow on building façades. The current stage of the research focused on developing a setup and a methodology for examining and comparing the results of a physical wind tunnel test to those of CFD (computational fluid...
Article
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A two orthogonal view, holographic cinematography system (volume of $17\times 17\times 17~\text{mm}^{3}$ ) was used to measure three-dimensional fibre translational velocities, orientations and rotation rates in near homogeneous isotropic air turbulence (HIT). Flow characteristics were determined from temporally resolved particle image velocimetry...
Chapter
In this chapter two experimental imaging techniques, holography and particle image velocimetry (PIV), and their application to particle dispersed flows are discussed. Special emphasis is put on particle deposition, re-suspension and agglomeration processes. In the first two chapters the theoretical background of the techniques is presented indicati...
Article
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Time resolved, PIV measurements were performed to investigate the flow field dynamics around an ovulate pine cone (P. halepensis) mounted in a windtunnel at Reynolds numbers ranging from = 246 to 955, based on the equatorial diameter. Scale/bract complexes arranged in helices characterized the cone’s surface morphology. The cone could be represente...
Article
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Single view, inline digital holographic cinematography (1 kHz) was used to track near neutrally buoyant, polystyrene beads in a turbulent water channel flow at bulk flow Reynolds number of 10,602. In-house developed algorithms, fine-tuned to tracking single and overlapping beads were developed. In total, 1616 beads were tracked using a nearest neig...
Article
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Digital holography was used to determine 3D positions of a dilute, polystyrene bead suspension in a turbulent, square channel water flow. Voronoi tessellation performed on bead positions collapsed onto a transverse plane indicated clustering, the result of coherent turbulent flow structures and associated, induced secondary flows. Cluster areas lac...
Article
Full-text available
High-speed particle image velocimetry (PIV) and digital holography were applied to dilute, rigid fiber suspensions without floc formation. PIV is suited to study the instantaneous interaction between the flow and the fiber motion down to the scale of the fiber. Based on the size difference between fibers and tracers, fibers were masked in the PIV i...
Article
Full-text available
Time-resolved particle image velocimetry measurements of vortex-induced vibrations of a negatively (“heavy”) and positively (“light”) buoyant tethered sphere in uniform flow, and its wake characteristics were performed in a closed-loop water channel. Experiments for both spheres were performed at similar bulk velocities, ranging between 0.048 < U <...
Article
Full-text available
The coupling between shear layer, near wake dynamics, and structural oscillations downstream of a tethered spherical pendulum undergoing vortex induced vibrations (VIV) has been experimentally investigated using time-resolved particle image velocimetry in a wind tunnel. One quarter of the sphere was imaged in the field of view (spatial resolution 0...
Article
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An active flow-control technique is used to reduce or eliminate vortex-induced vibrations (VIV) on a tethered body that is subjected to acoustic perturbations. Experiments were performed in a small blowdown wind tunnel having a 9.5:1 inlet contraction and square test section with transparent acrylic windows for optical access. The symmetric nature...
Article
Resuspension and saltation of nearly neutrally buoyant polystyrene beads in a turbulent boundary layer were studied using time-resolved particle image velocimetry and particle tracking velocimetry in a horizontal water channel facility . The time difference between frames was , comparable to the particle Stokes number, . Near-wall coherent structur...
Article
Vortex-induced vibrations (VIV) of a positively buoyant (light) tethered sphere in uniform flow as well as its wake characteristics were measured in a closed loop water channel. Experiments were performed at free stream velocities ranging between 0.048 and 0.22 m/s, corresponding to sphere Reynolds numbers ranging from Re-D=430 to 1925. The measure...
Article
Pollen dispersal is fundamental in a plant's reproductive ecology and as a result of fragmentation of the landscape, questions have been raised on how isolated plant populations can still exchange genetic information. A common mechanism for gene exchange is wind pollination (anemophily). A successful anemophilous species native to North America is...
Article
The dispersal of ragweed, pine and corn pollen as well as polystyrene spheres in still air and stationary, near homogeneous, isotropic turbulence (HIT) was investigated using high-speed, digital inline holographic cinematography enabling Lagrangian tracking of the particles. Mean still air settling velocities were similar as reported literature val...
Article
Time-Resolved Particle Image Velocimetry (TR-PIV) and digital holography measurements were carried out in a dilute particle-laden flow tracking both Polystyrene Spheres (PS, ˜0.583 mm, d^+˜10) as well as resolving the instantaneous velocity field of the turbulent flow. Measurements were performed in a closed loop, transparent, square channel facili...
Article
VIV of two heavy tethered spheres (D = 40 mm, m^* = msphere/ρfVsphere = 21 and 67, L^*=L/D = 2.50) were studied in a wind tunnel under uniform free stream velocities up to U^*=U/fnD = 15.9, with and without acoustic control. Control was achieved using two speakers mounted on either side of the spheres and driven in-phase at f = 35Hz (f^* = 22.3). I...
Article
Particle image velocimetry was used for measuring the velocity and Reynolds stress distributions in the latitudinal plane of counter-rotating Taylor-Couette flow at high Reynolds numbers (Re). The ratio of outer to inner cylinder angular velocity, μ, varied between −10.79 and −0.68, and Rei based on the inner cylinder velocity ranged between 2635 a...
Article
Time-resolved PIV measurements were performed in a dilute particle-laden flow tracking near-neutrally buoyant polystyrene beads and the velocity field of a near wall turbulent boundary layer. Data were taken in a vertical light sheet aligned in the streamwise direction at the center of a horizontal, closed loop, transparent square water channel fac...
Article
Full-text available
The motion of a heavy tethered sphere and its wake were measured in a closed loop water channel using a time resolved, high-speed particle image velocimetry technique in a horizontal plane. Measurements were performed for nondimensional reduced velocities ranging from 2.8 to 31.1 that include three bifurcation regions. In order to analyze the vorte...
Article
Full-text available
Time resolved, high-speed PIV measurements were performed to study the spatio-temporal dynamics of a tethered, stainless steel sphere (D = 5/16'', m^*=7.86, L^*=2.90), mounted in a water channel and exposed to uniform, free stream velocities up to 0.64 m/s. To study the coupled interaction between vortex and sphere dynamics, we performed measuremen...
Article
Field experiments were performed to study the diurnal cycle of corn pollen emission and its relation to local meteorological conditions, including temperature, relative humidity, solar radiation, mean wind speed, and turbulence quantities. Pollen concentrations were measured from canopy height to twice this level using four Rotorod samplers located...
Article
An expression for the vertical equilibrium concentration profile of heavy particles, including the effects of canopy on the eddy diffusivity as well as corrections for atmospheric stability, is proposed. This expression is validated against measurements of vertical concentration profiles of corn pollen above a corn field. The fitted theoretical pro...
Article
Particle image velocimetry (PIV) data obtained in a wind-tunnel model of a canopy boundary layer is used to examine the characteristics of mean flow and turbulence. The vector spacing varies between 1.7 and 2.5times the Kolmogorov scales. Conditional sampling based on quadrants, i.e. based on the signs of velocity fluctuations, reveals fundamental...
Article
Quadrant-hole (Q-H) analysis is applied to PIV data acquired just within and above a mature corn canopy. The Reynolds shear stresses, transverse components of vorticity, as well as turbulence production and cascading part of dissipation rates are conditionally sampled in each quadrant, based on stress and vorticity magnitudes. The stresses are repr...
Article
Full-text available
Turbulent flow in a corn canopy is simulated using large-eddy simulation (LES) with a Lagrangian dynamic Smagorinsky model. A new numerical representation of plant canopies is presented that resolves approximately the local structure of plants and takes into account their spatial arrangement. As a validation, computational results are compared with...
Article
Full-text available
Particle image velocimetry (PIV) measurements just within and above a mature corn canopy have been performed to clarify the small-scale spatial structure of the turbulence. The smallest resolved scales are about 15 times the Kolmogorov length scale ($\nu \approx$ 0.4 mm), the Taylor microscales are about $100\nu$, and the Taylor scale Reynolds numb...
Article
Full-text available
Large-eddy simulation (LES) of turbulence in plant canopies has traditionally been validated using bulk statistical quantities such as mean velocity and variance profiles. However, turbulent exchanges between a plant canopy and the atmosphere are dominated by large-scale coherent structures, and therefore LES must also be validated using statistica...
Article
An experimental investigation using Particle Image Velocimetry (PIV) was carried out to study the latitudinal planar velocity field in air counter-rotating cylindrical Couette flow at high Reynolds numbers. The facility consisted of two concentric cylinders with a radius ratio of eta=ri / ri ro . - ro= 0.55 and aspect ratio gamma=L/( ro-ri )= 11.2....
Article
Dispersion of airborne pollen by the wind has been a subject of interest for botanists and allergists for a long time. More recently, the development of genetically modified crops and questions about cross-pollination and subsequent contamination of natural plant populations has brought even more interest to this field. A critical question is how f...
Article
Particle image velocimetry (PIV) has been used to compare between turbulence characteristics just within and above a mature corn canopy and those of a model canopy setup in a wind tunnel (WT). The laboratory normalized mean velocity profile is adjusted using variable mesh screens to match the normalized mean shear of the corn field (CF) data. The s...
Article
The exchange between plants and the atmosphere is one of the main themes in ecohydrology. The realistic simulation of the turbulent flow around plants remains a major challenge. Canopy turbulence is characterized by momentum transfer through aerodynamic drag of foliage throughout the whole depth of the canopy, which leads to an unstable inflected m...
Article
This paper introduces a method to measure the density of irregularly shaped particles. The technique, demonstrated on corn pollen, is based on measuring the settling velocity of the particles at low Reynolds numbers (Stokes flow) in two fluids with different density and viscosity. If different samples are used, they should have statistically simila...
Article
Particle Image Velocimetry (PIV) measurements were performed in the turbulent boundary layer just above and within a mature corn canopy. Data were acquired at several heights, each at 4 Hz for 17min. The Kolmogorov length eta is about 0.4mm while the Taylor length scale is about 40mm. The Taylor microscale Reynolds numbers range between 2000-3000....
Article
Dispersal of pollen grains by wind and gravity (Anemophilous) is one of the oldest means of plant fertilization available in nature. Recently, the growth of genetically modified foods has raised questions on the range of pollen dispersal in order to limit cross-fertilization between organically grown and transgenic crops. The distance that a pollen...
Article
The development of slug flow along two long inclined pipes (2–90° from the horizontal) with internal diameters of 0.024 and was measured by three optical fiber probes. The probes were located in a measurement module at axial distances of between the fiber tips. To measure the evolution of slug flow, the module was placed at different positions alon...
Article
Full-text available
Prediction of the long distance dispersal of (biological) aerosol particles, such as pollen, in the atmosphere is of great importance in pollution control and allergy studies. The particle parameters affecting dispersal include size, shape and density. In this work a simple method has been tested and implemented for measuring the density of aerosol...
Article
The translational velocities of elongated bubbles in continuous slug flow were measured for various flow rates, pipe inclinations and pipe diameters. Measurements were carried out by cross-correlating the output signals of consecutive optical fiber probes and by image processing technique. In addition, the velocities of single elongated bubbles in...
Article
An experimental investigation of the flow field around a single Taylor bubble rising in a vertical pipe filled with stagnant water is presented. The Reynolds number of the flow based on the Taylor bubble rise velocity and the pipe diameter is 4350. The velocity field around the bubble was determined by Particle Image Velocimetry (PIV). The mean vel...
Article
The evolution of hydrodynamic and statistical parameters along the pipe was studied experimentally in gas–liquid slug flow for various flow conditions and two pipe diameters. The measuring modules comprise a set of three adjacent optical fiber probes and could be easily transferred to various positions along the pipes. The probes detect the passage...
Article
The structure of vertical upward slug flow in a pipe is studied. The distribution of the phases in the Taylor bubble zone and the liquid slug zone is investigated by simultaneous measurements with two optical fiber probes. In the Taylor bubble zone the shape of the Taylor bubble and the distribution of the bubble length is reported. In the liquid s...

Projects

Projects (4)
Project
The main research question that we aim to answer is: “Can the shear layer instabilities in the near-field flow of an impinging coaxial jet be fine-tuned in such a way that fiber separation and/or alignment can be controlled upon impingement and deposition of the fibers”.