bluuebunny/crossref_metadata_2025 huggingface dataset:
Interracial Trust between Black Doctoral Student Protégés and White Mentors
Authors: Brown Eric Montrece , Grothaus Tim
Published: September 2021

Psychologists have found that many Black persons in the United States have significant levels of mistrust of White persons. This serves as a protective factor in response to pervasive structural and systemic racism. Yet interracial trusting relationships exist. In this phenomenological study, 10 Black counseling doctoral students described their interracial trust experiences with White faculty and/or clinical supervisor mentors. The authors constructed six themes from the data: setting less rigid boundaries, practicing transparency, taking the initiative, being congruent, honoring the proteges’ strengths and experiences, and advocating for equity. Implications and strategies for supervisors and educators are shared.
Beyond “Feeling Blessed”: Using International Documentary Film to Foster Global Awareness in an Online College Course
Authors: Blum Denise , Smythe Jon L.
Published: September 2021

As US colleges and universities incorporate an international requirement for undergraduate students, this study assesses the value of an online international documentary course. The effect of documentary viewing was evaluated using students’ reflective essays, noting possible shifts in perspectives on international issues after film viewing. Findings show that students gained new knowledge, displayed empathy, felt “blessed” for their privileges, and were inspired to help others. Findings also reflected an ignorance about inequitable power relationships between the United States and other countries, producing an “othering” effect. Recommendations are provided for engaging students in more critical research and reflection about local-global connections.
Subaltern Praxis: A Vygotskian and Freirean Framework in NGO Education
Authors: Keyl Shireen
Published: September 2021

This article examines the functionality and ideological underpinnings of an NGO system in Beirut, Lebanon. This grassroots NGO, in partnership with the Migrant Community Center and migrant domestic workers from African and Southeast Asian countries, creates an educational space that is both transformative and libratory. This activist space is informed by an anti-racist and feminist ideology. Based on the narratives of this system’s stakeholders, I forward a subaltern praxis, a transformative model for the development sector informed by Vygotsky’s constructivist frameworks and Freirean ideology.
Influencia de los sistemas de puesta a tierra descritos en el estándar IEEE 1243 en la tasa de fallas por rayos de líneas de transmisión
Authors: Mariño-Rojas Jaime Alejandro , Muñoz-Delgado Jonathan Armando , Soto-Ríos Edison Andrés
Published: September 2021

Este trabajo trata sobre los dos diferentes modelos resistivos de puesta a tierra usados en líneas de transmisión presentados en el estándar IEEE 1243-1997: tierra suplementaria con varillas y con contrapesos. Se analizó el efecto de variar los parámetros internos de cada modelo que afectan el valor resistivo de puesta a tierra en la reducción o aumento de la tasa de fallas por flameo inverso por impactos de rayos sobre la torre o el cable de guarda sobre terrenos con diferentes conductividades. El software ATPDraw se usó para obtener las corrientes críticas, para luego con estas obtener la tasa de fallas de la línea. Se simuló el efecto del número, la longitud, radio y enterramiento de los electrodos en las tasas de fallas por flameo inverso de una línea de transmisión para diferentes valores de conductividad del terreno. Se obtuvieron porcentajes de reducción de la tasa de fallas que van en general desde el 50 hasta el 95%.
Innovative Instrument for the Field Continuous Monitoring of Dissolved Gases in Environmental Studies
Authors: Eliot Chatton , Thierry Labasque , Guillou Aurélie , Paul Floury , Luc Aquilina , Vergnaud Virginie
Published: September 2021

Dissolved gases are particularly relevant tools for the investigation of environmental processes. Indeed, their solubility being a function of the variables of physical state of the medium (temperature, pressure, salinity), the dissolved noble gases are for instance good indicators of equilibrium conditions with the atmosphere and mixing of water bodies. Dissolved gases can also inform the biogeochemical functioning of natural systems by providing information on major processes such as photosynthesis, respiration or denitrification. Classical methods relying on the sampling, the storage and the ex situ analysis of water samples for the measurement of dissolved gases suffer from the difficulty of taking sufficiently frequent and representative samples as well as the analyte preservation. High-frequency in situ measurement of dissolved gases is therefore the most relevant for the study of environmental processes. The use of Membrane Inlet Mass Spectrometer (MIMS) technology provides access to high frequency measurements of a large set of dissolved gases in the field (He, Ne, Ar, Kr, Xe, N2, O2, CO2, CH4, N2O, H2) which offers a real opportunity for environmental studies.
Concept of Using Eye Tracking Technology to Assess and Ensure Cybersecurity, Functional Safety and Usability
Authors: Gordieiev Oleksandr , Kharchenko Vyacheslav , Illiashenko Oleg , Morozova Olga , Gasanov Magomediemin
Published: September 2021

Eye tracking technology is based on tracking the trajectory of human eye movement. As a rule, it is implemented in the form of an additional device attached under the monitor or in the form of glasses. On the basis of a mathematical model, the focus of a person's attention is calculated and, accordingly, the user's visual route is built. Eye tracking technology is used to solve various problems, e.g. for marketing research, assessing the quality of user interfaces, developing simulators for operators, etc. The article discusses the concept of using eye tracking technology to assess and ensure cyber security, functional safety and usability. The possibility of using eye tracking technology (ETT) to solve the problem of identifying a person's personality is considered separately. The solution is achieved by reproducing a certain trajectory by a person's vision. This technique can be used as a basic or additional technique for identifying a person's personality. It also analyzes the results of using eye tracking to study the interface of an automated information system for operator support based on algorithms for symptom-oriented emergency instructions (ASOEI), which is used at nuclear power plants (NPP).
Design of Miniaturized Sensors for a Mission-Oriented UAV Application: A New Pathway for Early Warning
Authors: Di Giovanni Daniele , Fumian Francesca , Chierici Andrea , Bianchelli Mattia , Martellucci Luca , Carminati Gaetano , Malizia Andrea , d’Errico Francesco , Gaudio Pasqualino
Published: September 2021

In recent decades, the increasing threats associated with Chemical and Radiological (CR) agents prompted the development of new tools to detect and collect samples without putting in danger first responders inside contaminated areas. A particularly promising branch of these technological developments relates to the integration of different detectors and sampling systems with Unmanned Aerial Vehicles (UAV). The adoption of this equipment may bring significant benefits for both military and civilian implementations. For instance, instrumented UAVs could be used in support of specialist military teams such as Sampling and Identification of Biological, Chemical and Radiological Agents (SIBCRA) team, tasked to perform sampling in contaminated areas, detecting the presence of CR substances in field and then confirming, collecting and evaluating the effective threats. Furthermore, instrumented UAVs may find dual-use application in the civil world in support of emergency teams during industrial accidents and in the monitoring activities of critical infrastructures. Small size drones equipped with different instruments for detection and collection of samples may enable, indeed, several applications, becoming a tool versatile and easy to use in different fields, and even featuring equipment normally utilized in manual operation. The authors hereby present the design of miniaturized sensors for a mission-oriented UAV application and the preliminary results from an experimental campaign performed in 2020.
The Effectiveness of Table-Top Exercises in Improving Pandemic Crisis Preparedness
Authors: Thornton Michael I. , Iannotti Alba , Quaranta Riccardo , Russo Colomba
Published: September 2021

The World Health Organization carried out a global survey in 2018 to ascertain the level of preparedness for pandemic influenza. It was discovered that simulation exercises to test national pandemic influenza preparedness plans were carried out in the previous 5 years, by 42 out of the 104 countries that completed the survey. The table-top exercise (TTX) being the preferred format, with 86% of the countries using them. Although no table-top exercise can convey a realistic picture of a pandemic, they can be used to assess plans, policies, and procedures, clarify roles and responsibilities, and identify resource gaps in an operational environment. However, table-top exercises are only effective if they are properly designed, carefully conducted, fully evaluated, and most importantly, the results and recommendations identified are actually implemented. TTXs used as part of preparedness for pandemics are not cost free, a failure to implement the lessons learned from them can have both human and economic consequences. To understand the value of TTXs, a sample of national and large scale TTXs are examined in an effort to identify the effectiveness of table-top exercises, as a part of improving pandemic crisis preparedness.
Kamu Çalışanlarının Liyakat İhlali Algısı, Kaynakları ve Etkileri
Authors: Yılmaz Feride , Çakıcı Ayşehan
Published: September 2021

Liyakat ihlali; işe alım, yükseltme, atamalarda ve göreve son vermelerde kadrolara ehil, nitelikli, hak eden kişilerin getirilmemesi ve tüm bu konularda adaylara fırsat eşitliği tanınmaması durumudur. Bu kapsamda, üniversitelerde çalışan kamu personelinin, liyakat ihlalinin kaynakları ve etkileri konularındaki görüşlerini belirlemek üzere bir keşifsel araştırma yapılmıştır. Veriler, iki farklı kamu üniversitesinin 132 personelinden kolayda örnekleme yöntemiyle, 2019 yılı Ocak-Ekim ayları arasında görüşme yoluyla toplanmış ve içerik analizine tabi tutulmuştur. Liyakatsizliğin temel nedeninin, kayırmacılık olduğu ve siyasi kayırmacılık türünün ön safta yer aldığı belirlenmiştir. Liyakat ihlalinin kuruma en önemli etkisinin performans düşüşü olduğu tespit edilmiştir. Liyakat ihlalinin, mağdurda daha çok duygusal/psikolojik etkilere yol açtığı, ancak diğer çalışanlarda davranışsal ve bilişsel etkilere sebebiyet verdiği bulgulanmıştır. Başta yasa ve yönetmeliklere uygunluğun gözetilmesi olmak üzere uzmanlık, bilgi, beceri, deneyim, kişilik uygunluğunun dikkate alınması ve sağlıklı bir işe alım, terfi ve atama sistemi oluşturulması önerilmektedir.
Combining high-speed planar PIV and motion tracking of a flexible cylinder in cross-flow
Authors: Gundersen Diego George , Christensen Kenneth Thor , Blois Gianluca
Published: September 2021

Most modeling studies investigating the flow dynamics in vegetation canopies are limited to rigid models as proxies for vegetation elements. However, most canopies embody some degree of structural flexibility, resulting in aeroelastic mechanisms coupling the motion of the vegetation with the surrounding flow. Studies addressing flexible canopies typically quantify either the flow or the plant motion independently, thus missing the instantaneous coupling between turbulent stresses and structural deformations. Few experiments have been devoted to measuring both quantities simultaneously. Okamoto and Nezu (2009) utilized a combined PIV-PTV technique to capture both flow and canopy motion. However, only the motion of the stem tips was captured, as opposed to the deformation of the entire stem. Py et al. (2006) employed digital image correlation (DIC) to quantify the motion of crop canopies using in-field images. However, the wind itself was not measured across the domain.

The present work presents an experimental technique that can be utilized to study the flow–structure interaction in flexible canopies, and that could be extended to other flexible and/or moving objects. High-speed PIV data of the flow surrounding an idealized canopy element, consisting of a flexible cylinder, together with the corresponding displacement field throughout the cylinder were simultaneously obtained combining fluorescent imaging and refractive index matching (RIM).
Three-dimensional density measurements of a heated jet using laser-speckle tomographic background-oriented schlieren
Authors: Amjad Shoaib , Soria Julio , Atkinson Callum
Published: September 2021

Three-dimensional density field measurement techniques can be used to understand the complex heat transfer and mixing processes that occur in turbulent flows. Tomographic background-oriented schlieren (BOS) is an optical technique that can be used to measure the instantaneous three-dimensional density field in turbulent flows. Light rays propagating through the flow are deflected from their ambient path due to variations in refractive index related to the spatial density gradients. In BOS, a camera is placed looking through the flow at a reference image, which captures path-integrated information on the refractive index gradients in the form of apparent image displacements Richard and Raffel (2001). The displacements recorded simultaneously from many cameras placed around the flow form the basis of a tomographic reconstruction of the three-dimensional refractive index gradients Goldhahn and Seume (2007), from which the density field is obtained through integration of the gradients and application of the Gladstone-Dale relation.
Energy spectra of Sub-Surface Velocity Fields Beneath Faraday Waves
Authors: Colombi Raffaele , Rohde Niclas , Schlüter Michael , Von Kameke Alexandra
Published: September 2021

Faraday waves form on the surface of a fluid which is subject to vertical forcing, and are researched in a large range of applications. Some examples are the formation of ordered wave patterns and the controlled walking or orbiting of droplets (Couder et al. (2005); Saylor and Kinard (2005)). Moreover, recent studies discovered the existence of a horizontal velocity field at  the fluid surface, called Faraday flow, which was shown to exhibit an inverse energy cascade and thus properties of two-dimensional turbulence (von Kameke et al., 2011, 2013; Francois et al., 2013). Additionally, three-dimensionality effects have been part of recent investigations in quasi-2D flows (both electromagnetically-driven (Kelley and Ouellette, 2011; Martell et al., 2019) or produced by parametrically-excited waves (Francois et al., 2014; Xia and Francois, 2017)). Furthermore, the occurrence of an inverse cascade in thick layers is also subject of current studies on the coexistence of 2D and 3D turbulence (Biferale et al., 2012; Kokot et al., 2017; Biferale et al., 2017). By performing 2D PIV measurements at horizontal planes beneath the Faraday waves, we recently showed that pronounced three dimensional flows occur in the bulk, with much larger spatial and temporal scales than those on the surface (Colombi et al., 2021), when the system is not shallow in comparison to typical length scales of the surface flow (fluid thickness exceeding half the Faraday wavelength λF). This in turn reveals that an inverse energy cascade and aspects of a confined 2D turbulence can coexist with a three dimensional bulk flow. In this work, 2D PIV measurements of the velocity fields are carried out at a vertical cross-section xz-plane and at four distinct horizontal xy-planes at different depths in Faraday waves. The results reveal that small and fast vertical jets penetrate from the surface into the bulk with fast accelerating bursts and strong momentum transport in the z−direction. Furthermore, the fraction of flow kinetic energy in the vertical direction is found to peak inside a layer of approximately 10 mm (one Faraday wavelength) below the fluid surface.
Plunging jets from orifices of different geometry
Authors: Moscato Giorgio , Romano Giovanni Paolo
Published: September 2021

Plunging jets are used in many industrial and civil applications, as for example in sewage and water treatment plants, in order to enhance aeration and mass transfer of volatile gases. They are also observed in natural processes as rivers self-purification, waterfalls and weirs.
Many investigations dealt with the plunging jets in different configurations, but the dependence on Reynolds number and jet geometry were still not sufficiently addressed. For example, Mishra et al. (2020) studied an oblique submerged water impinging jet at different nozzle-to-plate distances and impingement angles, but only at a rather small Reynolds numbers (2600). On the other hand, different jet geometries have been extensively considered, but not for the plunging jet configuration (Mi, 2000; Hashiehbaf &Romano, 2013).
In this work, plunging water jets issuing in air from orifices of different shape are considered. The aim of the work is to detail and compare jet behaviors in terms of velocity fields generated after impacting the air-water interface, as a function of Reynolds number and orifice geometry. However, air bubbles entrainment is mainly avoided in order to study the jet characteristics in a simpler case and use it as a reference starting point for future works.
Investigating Optimal Training and Uncertainty Quantification for CNN-based Optical Flow
Authors: Kurinara Daiki , Blois Gianluca , Sakaue Hirotaka , Schiavazzi Daniele
Published: September 2021

Optical Flow (OF) techniques provide “dense estimation” flow maps (i.e. pixel-level resolution) of timecorrelated images and thus are appealing to applications requiring high spatial resolutions. OF methods revolve around mathematical descriptions of the image as a collection of features, in which the pixel-level light intensity is the primary variable (Horn and Schunck, 1981). Feature tracking often involves the notion of scale invariance. Traditional OF approaches, merely based on mathematical formulations, have suffered from many challenges, especially when directly applied to images of fluid flows textured with tracer particles (hereafter PIV-like images). Due to the limited number of computationally manageable features and suboptimal regularization methods, successful implementation of past approaches has been limited to highly textured images and small displacement dynamic ranges.
Super-large-scale flow visualization using natural snowfall for the study of utility-scale wind turbine flows
Authors: Abraham Aliza , Hong Jiarong
Published: September 2021

With the rapid growth of wind turbine installation in recent decades, fundamental physical understanding of the flow around wind turbines and farms is becoming increasingly critical for further efficiency increases. However, the effort to develop this understanding is hindered by the significant challenges involved in modelling such a complex dynamic system with a wide range of relevant scales (blade boundary layer thickness at ∼ 1 mm to atmospheric scales at ∼ 1 km). Additionally, conventional methods used to measure air flow around wind turbines in the field (e.g., lidar) are limited by low spatio-temporal resolutions.
PIV measurement of buffer and logarithmic layers with detached eddies which mimics the neutral atmospheric surface layer
Authors: Hattori Yasuo , Suto Hitoshi , Nakao Keisuke , Hirakuchi Hiromaru
Published: September 2021

Accurate comprehension of turbulence characteristics in the atmospheric surface layer (ASL) under near neutral conditions, which is a lower part of the atmospheric boundary layer and a very high-Re number flow, is critically required in view of the increasing and broadening use of numerical weather prediction models. The models need to estimate turbulence fluxes of momentum, heat and moisture in the ASL as boundary conditions. On the other hand, observations (Högström 1990, Drobinski et al. 2007) have revealed that the fluxes under near-neutral conditions are often inconsistent with Monin-Obukhof theory, which has been widely used in models. The observations were conducted over flat surfaces with homogeneous roughness, and thus the violation from the theory might not be due to the underlying surface conditions. Thus, aiming to investigate an origin of the violation from the theory, we have carried out a wind tunnel experiment on the logarithmic layer along a smooth flat wall with a larger-scale disturbance, which mimics the near-neutral atmospheric surface layer (Hattori et al. 2010). In the present study, we especially examine a PIV measurement with a long-distance microscope lens to discuss the interaction of turbulences structures between buffer and logarithmic layers, which must give a clue on Reynolds number effects
Uncertainty Estimation for Ensemble Particle Image Velocimetry
Authors: Ahmadzadegan Adib , Bhattacharya Sayantan , Ardekani Arezoo M. , Vlachos Pavlos P.
Published: September 2021

We present a novel approach to estimate the uncertainty in ensemble particle image velocimetry (PIV) measurements. Ensemble PIV is widely used when the cross-correlation signal-to-noise ratio (SNR) is insufficient to perform a reliable instantaneous velocity measurement. Despite the utility of ensemble PIV, uncertainty quantification for this type of measurement has not been studied. The existing uncertainty quantification algorithms for PIV are developed and used only for instantaneous PIV measurement and do not account for the improved SNR in ensemble PIV. Existing instantaneous uncertainty quantification methods can be divided into direct and indirect categories. Indirect methods require calibration based on the effect of various image parameters (such as noise, particle size, density, velocity gradient, etc.) on the correlation SNR. Indirect methods have not been calibrated for error sources relevant in an Ensemble PIV measurement. Also, they have lower sensitivity to the error sources compared to direct approaches. Direct methods, such as the moment of correlation (MC) and Image Matching (IM), find the uncertainty based on the images and correlation planes without any calibration and are more reliable (Bhattacharya et al., 2018; Sciacchitano et al., 2013). Ensemble PIV is based on ensemble correlations; therefore, MC, which uses the generalized cross-correlation (GCC) plane as a measure of uncertainty, is the most suitable method to be modified to be applicable for the ensemble PIV. The GCC plane is the inverse Fourier transform of the phase correlation and represents the probability density function (PDF) of particles’ displacements (Bhattacharya et al., 2018; Eckstein and Vlachos, 2009). We replaced instantaneous GCC with ensemble GCC and modified MC’s normalization factor to account for the number of ensembles. The MC’s primary limitation is that it assumes a Gaussian shape for the PDF of displacements and estimate the standard deviation of the underlying PDF using a fitted Gaussian. However, the PDF deviates from Gaussian distribution due to velocity gradient or non-Gaussian random displacements. Therefore, MC’s reliability and applicability are reduced for flow fields with non-Gaussian PDFs. Also, our analysis shows that ensemble MC consistently underestimates the uncertainty. So, a generalized and reliable method for uncertainty quantification for ensemble PIV is needed.
TR-PIV in highly pulsatile flow: pulsation frequency and wake dynamics case study
Authors: Carr Ian A. , Plesniak Michael W.
Published: September 2021

Experimental study of highly pulsatile flows presents a number of challenges, primarily the inherently large dynamic range of velocities. Herein, we use time-resolved particle image velocimetry processed with a technique known as pyramid sum-of-correlation to study highly pulsatile flow around a surface-mounted hemisphere. The frequency of pulsation is varied from low- frequency, quasi-steady pulsation to high frequency pulsation. We present a conceptual overview of the wake regimes observed and compare the flow physics of the high-frequency case to that of a vortex ring produced by a single impulse of fluid.
Three-Dimensional Particle Tracking Velocimetry using a Single Time-of-Flight Camera
Authors: Morris Sarah , Goldman Ari , Thurow Brian
Published: September 2021

Time of Flight (ToF) cameras are a type of range-imaging camera that provides three-dimensional scene information from a single camera. This paper assesses the ability of ToF technology to be used for threedimensional particle tracking velocimetry (3D-PTV). Using a commercially available ToF camera various aspects of 3D-PTV are considered, including: minimum resolvable particle size, environmental factors (reflections and refractive index changes) and time resolution. Although it is found that an off-the-shelf ToF camera is not a viable alternative to traditional 3D-PTV measurement systems, basic 3D-PTV measurements are shown with large (6mm) particles in both air and water to demonstrate future potential use as this technology develops. A summary of necessary technological advances is also discussed.
Towards the closure of Collar’s triangle by optical diagnostics
Authors: Gonzalez Saiz Gabriel , Sciacchitano Andrea , Scarano Fulvio
Published: September 2021

An experimental methodology is proposed for the study of aeroelastic systems. The approach locally evaluates the forces involved in Collar’s triangle, namely aerodynamic, elastic, and inertial forces. The position of flow tracers as well as of markers on the object surface is monitored by a volumetric PIV system. From the recorded images, the flow tracers and surfare markers are separated based on their optical characteristics. The resulting images are then analysed by Lagrangian particle tracking. The inertial and elastic forces are obtained solely analysing the motion and the deformation of the solid object, whereas the aerodynamic force distribution is obtained via the pressure-from-PIV technique. Experiments are conducted on a benchmark problem of fluid-structure interaction, featuring a flexible panel installed at the trailing edge of a cylinder. A polynomial fit of the markers’ positions is carried out to determine the panel’s instantaneous shape, from which the inertial and elastic forces are evaluated. The pressure loads on the panel are determined via solution of the Poisson equation for pressure, imposing adaptive boundary conditions that comply with the panel. The simultaneous measurement of the three forces allows to assess the equilibrium of forces, and in turn to close Collar’s triangle.
Validation of model-based correction for non-Stokesian tracers
Authors: Galler Joshua Noah , Rival David Emory
Published: September 2021

In-situ flow-tracking measurements at scales on the order of 10 m3 and larger remain a challenge. The large size of the tracers required for optical visibility results in an inertial lag and inherently low seeding density. For instance, natural snowfall, fake snow and soap bubbles on the order of 2 cm have been used as tracers for field measurements and extracted statistical quantities (Nemes et al., 2017; Wei et al., 2021; Rosi et al., 2014). There is also growing interest in networks of sensors for remote- measurement where optical access is impossible (Bolt et al. 2020; Villa et al. 2016). Onboard inertial measurement units (IMU) are a promising tool for high-resolution measurements over large spatial domains without optical access. However, due to the intrinsic lag, a dynamic-model-based correction is required for the tracking of transient phenomena, sketched in figure 1. In the present study, the tracer-velocity correction is evaluated by quantifying the residual error in measured flow velocity after the method of Galler et al. (2021) is applied.
On the unsteady dynamics of synthetic leaves: Laboratory experiments using synchronized PIV and DIC
Authors: Wing Lai , Troolin Dan , Cheng Shyuan , Sun Jiao , Chamorro Leonardo
Published: September 2021

The unsteady 3D dynamics of various synthetic leaves and the induced turbulence are systematically studied experimentally for representative Cauchy numbers in a wind tunnel under nearly uniform incoming flows. Synchronized digital image correlation (DIC) and high-frame-rate particle image velocimetry (PIV) are employed to track the structure dynamics simultaneously and the surrounding flow field to uncover the fluid-solid interaction. A high-resolution six-axis load cell is also used to quantify the synthetic leaves' induced force and torque under various flows. The shapes of synthetic leaves inspected are representative of selected environments (e.g., calm to windy weather; tropical to temperate climate). The Cauchy number is set to resemble those observed in natural conditions. This presentation will discuss insights from synchronized PIV-DIC techniques on the synthetic leaves' distinct behavior and wake flow response. Particular emphasis is placed on characterizing flow instability and the leave shape's role in the motions and force. For this purpose, we inspected the instantaneous force and torque as well as their structure. We will also discuss the relationship between leave shapes with force and torque fluctuations linking them with the leaf motion obtained from DIC measurements. In particular, the results show that selected leaf shapes experience significantly larger and distinct force and torque fluctuations and larger pitch magnitude, as shown in Fig. 5. A shared monotonically decreasing trend of the nondimensional frequency (Strouhal number, St = fL/U) is evidenced for standard environmental conditions.
Flow characteristics analysis for flow past the porous spheres: wake structures and drag force coefficients
Authors: Ma Likun , Kashanj Sina , Xu Shuliang , Ye Mao , Nobes David
Published: September 2021

Flow past a permeable sphere is different from that of a solid sphere due to the penetration of the fluid within porous structures, which can arise a change of flow fields. In this work, flow past porous spheres with Darcy numbers (Da) ranging from [0,10−3 ] were measured using planar Particle Image Velocimetry (PIV). The whole flow fields, including both leading edge and trailing edge, were captured at six different Reynolds numbers (Re) varying from 400 to 1400. Time-average flow fields were calculated based on instantaneous flow fields within fully-developed stages. Local minimum method was used to search for stagnation point positions. The results show positions of stagnation points are nearly proportional to the logarithm of Re. For most porous spheres, positions of stagnation points are extended to farther downstream positions than that of a solid sphere. However, at some certain Darcy numbers, ranging from 5 ∗ 10−6 to 2 ∗ 10−5, positions of stagnation points are closer to the sphere centers than that of an impermeable one.
Investigation of Large Scale Motions in Zero and Adverse Pressure Gradient Turbulent Boundary Layers Using High-Spatial-Resolution PIV
Authors: Jovic Daniel , Shehzad Muhammad , Sun Bihai , Cuvier Christophe , Willert Christian , Ostovan Yasar , Foucaut Jean-Marc , Atkinson Callum , Soria Julio
Published: September 2021

Particle image velocimetry (PIV) has been used to capture the high-spatial-resolution (HSR) two-component, two-dimensional (2C-2D) velocity fields of a zero-pressure-gradient (ZPG) turbulent boundary layer (TBL) and of an adverse-pressure-gradient (APG) TBL. Proper Orthogonal Decomposition (POD) is performed on the measured velocity fields to characterize the velocity fields as large or small scale motions (LSMs or SSMs), with further characterisation of the LSMs into high and low momentum events. This paper reports the findings of the PIV experiment and the subsequent analysis of the high Reynolds number ZPG and APG TBLs
Simultaneous two-phase flow measurements in a high-speed particle-laden under-expanded jet
Authors: Diaz-Lopez Miguel Xavier , Rubio Juan Sebastian , Ni Rui
Published: September 2021

The objective of this study is to understand the dynamics of a high-speed particle-laden under-expanded jet, motivated by landings on extraterrestrial bodies. In this setup, inertial particles are entrained and accelerated by an under-expanded jet. But, due to their inertia, the particle velocity is significantly lower than that of the surrounding gas close to the nozzle, so the two phases are coupled through aerodynamic drag. Sub-micron oil droplets are dispensed upstream to serve as tracers, whose velocity is determined through a PIV system; inertial particles, after image segmenting is performed to separate them from PIV data, will be tracked over time with a PTV system. This was accomplished with a single laser pulse and the camera straddle time to produce image pairs and shorten the pulse width. The results will help to understand particle-laden flow in a new regime where the background flow is compressible and the Mach number based on the slip velocity is not negligible, which may help to pave a foundation for future studies in compressible multiphase flows.
Investigation of the shear-layer instabilities in supersonic impinging jets using dual-time velocity measurements
Authors: Sikroria Tushar , Soria Julio , Karami Shahram , Sandberg Richard , Ooi Andrew
Published: September 2021

Motivated by applications in the propulsion industry, the fundamental study of phase-locked shear-layer instabilities in supersonic impinging jets has been of research interest for long time. While such flows have been experimentally investigated in various research studies using time-unresolved particle image velocimetry (PIV) techniques, the understanding of the shear-layer dynamics is limited, due to the absence of temporal information. Time-resolved PIV measurements for high-speed flows require a large bandwidth, which is challenging to achieve with the current state of technology. An alternate approach using time-unresolved double-PIV measurements is presented in the current study, which provides multiple samples of dual-time data, depicted in figure 1. Such data can be obtained using two co-visual PIV systems, triggered at a user-selectable time-offset, ∆t. As shown by Sikroria et al. (2020), the application of techniques like dynamic mode decomposition (DMD) on time-unresolved dual-time data provides valuable information about the flow structures governing the shear-layer instabilities. The experimental setup for such measurements in supersonic impinging jets, followed by the determination of the relevant dynamical flow structures from the data, will be presented in the conference.
Particle Detection by means of Machine Learning in Defocusing PTV
Authors: Dreisbach Maximilian , Leister Robin , Probst Matthias , Friederich Pascal , Stroh Alexander , Kriegseis Jochen
Published: September 2021

The accurate measurement of a fluid flow inside a measurement volume (MV) with limited optical access poses a challenge since the view on the MV is often partially obstructed for all but one viewing angle. Defocusing particle tracking velocimetry (DPTV) can be used to determine the instantaneous threedimensional velocity field of the flow with a standard PIV setup, requiring only a single optical axis. Current detection algorithms reach an out-of-plane accuracy in an order of magnitude lower than the planar accuracy, on top of a low rate of detected particles in comparison to other PTV approaches. These drawbacks originate from the low image quality due to noise, fluctuations in illumination, reflections and overlapping particle images. It has been shown that Machine Learning (ML) based detection is more robust against these adverse effects, due to the ability to leverage a higher amount of optical features for detection than conventional algorithms (Lecun et al. (1998)). Therefore, the present work addresses the applicability of ML algorithms in the post-processing of DPTV experiments, which will be evaluated on the ground of the DPTV experiments conducted by Leister and Kriegseis (2019). The setup of these experiments can be seen in Figure 1(a) and a section of a raw image recorded during the experiments in Figure 1(b).
PIV measurements of entrainment process of directly injected media in internal combustion engines
Authors: Abdelhameed Elsayed , Aoyagi Takahide , Tashima Hiroshi , Tsuru Daisuke
Published: September 2021

PIV measurements have been successfully applied to various flow fields relating internal combustion engines such as in-cylinder air motion, air flow in an intake port, and even a discharging passage of an ignition plug. Measurements of induced air motion around diesel sprays can be said to be a significant example of the PIV applications because the air motion is reflected in an unsteady complicated flow structure. Instead of the apparent entrainment exaggerated by spray droplet dispersing, substantial air entrainment through momentum exchange between liquid and gas was finally obtained by combining PIV and spray profile observation.

PIV measurements of this kind were extensionally applied to other direct fluid injection by the authors. The second object was a high-pressure gas jet directly injected under gas pressure as high as 30 MPa. It was found the gas jet has strong air entrainment through momentum exchange in a single gaseous phase between fuel gas and ambient air. The third directly injected medium in internal combustion engines should be torch flame ejected from nozzle holes of a pre-combustion chamber (PCC) to a main combustion chamber (MCC) of a so-called DF (dual-fuel) engine.

In this study, mixture entrainment process of torch flames is discussed on the PIV results for the first time. However, chamber configurations of a real DF engine are hard to simulate since itrequires several auxiliary PCC devices such as an ignition plug, a sub gas injector, and so on. All of them should be actuated synchronously with an engine crank angle. In the case of a constant volume vessel (CVV), the synchronization is not necessary, but the mixture control in the PCC becomes problematic because of the lack of compression and expansion strokes that assures PCCgas exchange. For overcoming the situation, rupture of a membrane was introduced in this study. The membrane turns the upper part of the PCC into an air pressure reservoir and low-pressure air jets eject from the nozzle holes after a solenoid-driven needle pierces the membrane for rupturing. The differential pressure between the upper chamber and the lower one was chosen as a main parameter of the experiment.

Since the measurements and analysis of the entrainment of the low-pressure air jets are yet to finalize, the outlook of the CVV, the PIV specifications, and prime results of the air entrainment are attached herewith. After all, the PIV measurements revealed essential difference among air entrainment processes of the above three directly injected media in internal combustion engines.
Lagrangian Particle Tracking: a link between localization error and fraction of missed particles
Authors: Cornic Philippe , Champagnat Frédéric , Leclaire Benjamin
Published: September 2021

This paper aims at analysing the behaviour of particle localisation error in 3D Lagrangian Particle Tracking (LPT) techniques, with a particular emphasis on general properties, independent of a specific algorithm. Based on the hypothesis that in LPT algorithms, errors on the image formation models are solely due to random noise, we show/prove the existence of a best achievable root mean square error (RMSE) on particle localisation, that, for a setup at a given seeding density, depends only on the noise level. We provide a procedure to estimate this lower bound, and show that it can only be reached if there are no missed detections; further on, we establish a link between localisation error and fraction of missed particles. We illustrate the consistency of this model on the results of the recent First Challenge on LPT (see ISPIV21 papers by Leclaire et al. and Sciacchitano et al.)
Quantification of Brownian motion under presence of flow using particle diffusometry
Authors: Lee Dong Hoon , Wereley Steven T.
Published: September 2021

Particle diffusometry (PD), a quantification method for the Brownian motion, is performed by recording temporally sequential images and using correlation analysis to obtain an ensemble diffusion coefficient for all particles captured in the imaging region (Clayton et al., 2017). PD is proven to be successful in the detection of the waterborne pathogen V. cholerae in environmental samples using different imaging techniques, including an inverted fluorescence microscope as well as a handheld hardware device operated with a smartphone (Clayton et al., 2019; Moehling et al., 2020). Although we intend to use PD to calculate diffusion coefficients in quiescent fluid, oftentimes unintentional fluid flows occur, creating measurement error when calculating the diffusion coefficient. In previous work, recordings under the presence of flow were discarded to avoid incorrect measurements of the sample.
A novel volumetric velocity measurement method for small seeding tracers in large volumes
Authors: Zhang Yisheng , Abitan Haim , Ribergård Simon Lautrup , Velte Clara M.
Published: September 2021

This paper presents the volumetric velocity measurement method of small seeding tracer with diameter 5µm ∼ 100µm for volumes of ≥ 500cm3. The size of seeding tracer is between helium-filled soap bubbles (HFSB) and di-ethyl-hexyl-sebacic acid ester(DEHS) droplets. The targeted measurement volume dimension is equivalent to the volume of HFSB, which will give a higher resolution of turbulence study. The relations between particle size, imaging and light intensity are formulated. The estimation of the imaging results is computed for the setup design. Finally, the methodology is demonstrated for turbulence velocity measurements in the jet flow, in which the velocities of averaged diameter 15µm air filled soap bubbles are measured in a volume of 7200cm3.
Physics-based universal outlier detector for flow statistics
Authors: Saredi Edoardo , Sciacchitano Andrea , Scarano Fulvio
Published: September 2021

Outlier detection for PIV velocity fields is still nowadays an active field of research. In the last decades, several image pre-processing and processing algorithms have been developed aiming at increasing the dynamic velocity range of PIV measurements and reducing the measurement uncertainty. Nevertheless, PIV velocity fields are still often characterised by the presence of outliers, which potentially hamper the correct interpretation of the flow physics and negatively affect the evaluation of the flow statistics. The outlier detection strategies presented in literature are mainly based on the statistical analysis of the velocity vector with its immediate neighbour. Most of these algorithms have been demonstrated to be effective for instantaneous flow fields, where the errors associated with the outliers are order of magnitude larger than the expected measurement uncertainty. However, these approaches are not as effective for the flow statistics, where the outliers yield errors of the same order of the measurement uncertainty. To overcome this limitation, this paper proposed an outlier detection approach based on the agreement of the flow statistics to the constitutive equations, more specifically to the turbulent kinetic energy (TKE) transport equation. The focus is posed on the ratio between the local advection terms of TKE and a robust estimation of the TKE production along the local streamline. It is demonstrated that, in presence of outliers, the proposed principle yields a clear separation between the correct and the erroneous vectors. In order to assess the performance of the proposed principle, three different test cases are considered. For all of them, the results are compared with a reference outlier detection methodology, namely the universal outlier detection method proposed by Westerweel and Scarano (2005). The proposed turbulence transport-based approach exhibits higher performance in terms of percentage of outliers correctly identified in the flow statistics.
Aerodynamics of a cycling wheel in crosswind by coaxial volumetric velocimetry
Authors: Jux Constantin , Sciacchitano Andrea , Scarano Fulvio
Published: September 2021

The aerodynamic characteristics of a modern road cycling wheel in crosswind are studied through force measurements and 3D velocimetry in TU Delft’s Open Jet Facility. The performance of the 62 mm deep rim is evaluated for two tire profiles, and yaw angles up to 20◦ . All measurements are executed at 12.5 m/s (45 km/h) freestream- and wheel-rotational velocity. The wheel’s rim-tire section in crosswind is found to behave similar to an airfoil at incidence, ultimately resulting in a reduction of the wheel’s aerodynamic resistance with increasing yaw angle magnitude. This trend, also referred to as the sail-effect, is limited by the stall angle of the tire-rim profile. The stall angle is found to be dependent on the tire surface texture and varies between 14◦ and 20◦.
Three-dimensional temperature and velocity measurements in fluids using thermographic phosphor tracer particles
Authors: Stelter Moritz , Martins Fabio J. W. A. , Beyrau Frank , Fond Benoît
Published: September 2021

Many flows of technical and scientific interest are intrinsically three-dimensional. Extracting slices using planar measurement techniques allows only a limited view into the flow physics and can introduce ambiguities while investigating the extent of 3D regions. Nowadays, thanks to tremendous progress in the field of volumetric velocimetry, full 3D-3C velocity information can be gathered using tomographic PIV or PTV hence eliminating many of these ambiguities (Discetti and Coletti, 2018; Westerweel et al., 2013). However, for scalar quantities like temperature, 3D measurements remain challenging. Previous approaches for coupled 3D thermometry and velocimetry combined astigmatism PTV with encapsulated europium chelates particles (Massing et al., 2018) or tomographic PIV with thermochromic liquid crystals particles (Schiepel et al., 2021). Here we present a new technique based on solid thermographic phosphor tracer particles, which have been extensively used for planar fluid temperature and velocity measurements (Abram et al., 2018) and are applicable in a wide range of temperatures. The particles are seeded into a gas flow where their 3D positions are retrieved by triangulation from multiple views and their temperatures are derived from two-colour luminescence ratio imaging. In the following, the experimental setup and key processing steps are described before a demonstration of the concept in a turbulent heated jet is shown.
Robust approach to monitoring Lagrangian transport in very large volume
Authors: Kaiser Frieder , Haramis Andreas , Galler Joshua , Rival David E.
Published: September 2021

State-of-the-art flow measurements utilize four or more high-speed cameras to perform highly-accurate Lagrangian particle tracking (LPT) in small to medium-sized measurement volumes (Schanz et al., 2016). Hou et al. (2021) suggested a novel approach to allow measurements in significantly larger measurement volumes (O(10m3 )) while reducing the experimental effort. A single camera is used to track centimeter-sized soap bubbles in three dimensions by not only evaluating the bubble-center location but also the bubbleimage size. Possible applications of the suggested approach include - but are not limited to - measurements in industrial wind tunnels (Hou et al., 2021), full-scale measurements in the atmospheric boundary layer (Rosi et al., 2014; Toloui et al., 2014), and the characterization of airflow in indoor spaces, such as offices or classrooms (Kahler et al., 2020). In the context of the recent pandemic, the latter application could ¨help to reduce infection risk by designing appropriate air circulation. Hereby, frequent air exchange is recommended, while direct airflow from individual to individual should be avoided (WHO, 2020). The present study strives to optimize and simplify the experimental set-up as well as to characterize the accuracy of the novel single-camera approach. Figure 1(a) shows the set-up used to characterize the novel approach.