14th International Symposium on Particle Image Velocimetry
type: channel
description: Welcome to the collection of final two-page abstracts and full-length papers (author's choice about which to submit) for the 14th International Symposium on Particle Image Velocimetry (ISPIV21). Particle Image Velocimetry (PIV) is an advanced optical measurement technique for non-intrusive analysis of microscopic and macroscopic flow fields in transparent fluids with high resolution. Thanks to the enormous developments in recent years in the fields of lasers, light emitting diodes (LEDs), digital cameras, computer performance, memory capacity, and processing algorithms, very precise measurements are now possible in many research areas and the field of application is being continuously expanded. Due to its performance and efficiency, PIV is also increasingly used in industry to answer various research questions. The technique can be extended by complementary techniques (e.g. laser-induced fluorescence) to simultaneously measure scalars such as concentration, pressure and temperature. At the same time, the measured 2D or 3D flow fields can be used to determine physical quantities that cannot be measured with other techniques. The measurement technology thus provides deep insights into the flow phenomena, no matter how high the flow velocities are. This biannual symposium series brings together leading PIV experts and users from all over the world to exchange and discuss the latest innovative developments and applications of the technology. The 14th edition of this symposium series was originally planned as an in-person meeting in Chicago, Illinois USA for August 1-4, 2021, following successful previous symposia in Munich (2019) and Busan (2017). However, owing to COVID-19 circumstances, it was moved to a virtual modality. In addition to these written contributions, authors also pre-recorded 15-minute presentations of their work that were shared with conference participants on demand. Finally, live keynote presentations were given by leading researchers in the PIV fiel…
publisher: Illinois Tech - Galvin Library
language: en
publication name: 14th International Symposium on Particle Image Velocimetry
issn: 2769-7576
copyright: Copyright for all articles and abstracts is retained by their respective authors
items: Particle position prediction based on Lagrangian coherency for flow over a cylinder in 4D-PTV
items: Development of Echo-LPT for the study of particle-wall interactions in dense suspensions
items: Spatially and temporally resolved measurements of turbulent Rayleigh-Bénard convection by Lagrangian particle tracking of long-lived helium-filled soap bubbles
items: Robust approach to monitoring Lagrangian transport in very large volume
items: Three-dimensional temperature and velocity measurements in fluids using thermographic phosphor tracer particles
items: Large-scale 3D flow investigations around a cyclically breathing thermal manikin in a 12 m³ room using HFSB and STB
items: Tracer-based 3D surface reconstruction
items: Aerodynamics of a cycling wheel in crosswind by coaxial volumetric velocimetry
items: Investigation on computed pressures from PIV, a study of how boundary definitions affect pressure accuracy along objects on the example of a cylinder flow.
items: An experimental investigation on stall flutter over a vertically mounted rigid finite wing
items: Particle Image Velocimetry Measurements of a Dry Powder Inhaler Flow
items: Main results of the first Data Assimilation Challenge
items: Main results of the first Lagrangian Particle Tracking Challenge
items: PIV and deformation measurements on the rotor blade of a rotating, scaled model wind turbine with flexible blades under tailored inflow conditions
items: Peregrine falcon wakes examined using Volumetric PIV
items: Physics-based universal outlier detector for flow statistics
items: A novel volumetric velocity measurement method for small seeding tracers in large volumes
items: Velocity measurements of dilute suspensions over and through various porous media models
items: Lagrangian Strain- and Rotation-Rate Tensor Evaluation Based on Multi-pulse Particle Tracking Velocimetry (MPTV) and Radial Basis Functions(RBFs)
items: Error propagation dynamics of velocimetry-based pressure field calculations (2): on the error profile
items: An experimental approach to analyze aerosol and splatter formation in a dental practice
items: Quantification of Brownian motion under presence of flow using particle diffusometry
items: Lagrangian Particle Tracking: a link between localization error and fraction of missed particles
items: Numerical Uncertainty in Density Estimation for Background Oriented Schlieren
items: PIV measurements of entrainment process of directly injected media in internal combustion engines
items: Development of micro soap bubble generator for PIV tracer using home stereolithography 3D printer
items: Particle Detection by means of Machine Learning in Defocusing PTV
items: Noise canceling to compute second order statistic from SPIV
items: Pressure reconstruction of a planar turbulent flow field within a multiply-connected domain with arbitrary boundary shapes
items: Investigation of the shear-layer instabilities in supersonic impinging jets using dual-time velocity measurements

Particle position prediction based on Lagrangian coherency for flow over a cylinder in 4D-PTV
type: item
description: Recent developments in time-resolved Particle Tracking Velocimetry (4D-PTV) consistently improved tracking accuracy and robustness. We propose a novel technique named ”Lagrangian coherent predictor” to estimate particle positions within the 4D-PTV algorithm. We add spatial and temporal coherency information of neighbour particles to predict a single trajectory using Lagrangian Coherent Structures (LCS). We found that even a weak signal from coherent neighbour motions improves particle prediction accuracy in complex flow regions. We applied Finite Time Lyapunov Exponent (FTLE) to quantify local boundaries (i.e. ridges) of coherent motions. Synthetic analysis of the wake behind a smooth cylinder at Reynolds number equal to 3900 showed enhanced estimation compared with the recent predictor functions employed in 4D-PTV. Results of the experimental study of the same flow configuration are reported. We compared predicted positions with the optimised final positions of Shake The Box (STB). It was found that the Lagrangian coherent predictor succeeded in estimating particle positions with minimum deviation to the optimised positions.
subject: 3D Methods and Applications
  topic: section
subject: 4D-PTV
  topic: keywords
subject: particle prediction
  topic: keywords
subject: Lagrangian Coherent Structures (LCS)
  topic: keywords
creator: Ali Rahimi Khojasteh
creator: Dominique Heitz
creator: Yin Yang
rights: Copyright (c) 2021 Ali Rahimi Khojasteh, Dominique Heitz, Yin Yang
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.211

Development of Echo-LPT for the study of particle-wall interactions in dense suspensions
type: item
description: Examining the behaviour of dense suspensions has proven to be difficult, both experimentally and numerically. Using super water–absorbent polymer, PIV measurement was successfully conducted in a hydrogel suspension with a volume fraction (VF) of Φ =20% (see Zhang and Rival, 2018). However, due to the slightly refractive index mismatch, the image quality will degrade significantly as the particle loading of the hydrogel is increased. In order to achieve flow measurements in suspensions with high volume fractions, non-optical based techniques such as ultrasound imaging velocimetry (UIV) should be implemented. UIV has been developed for fluid dynamics applications and embraced by many researchers to study fluid flows (Gurung and Poelma, 2016; Jeronimo et al., 2019). Although, UIV provides useful information about the flow physics, it is unable to provide Lagrangian quantities such as particle trajectories, which is a key parameter to study entrainment and particle-wall interactions.
subject: Echo PIV
  topic: section
subject: Lagrangian Particle Tracking
  topic: keywords
subject: Ultrasound Imaging Velocimetry
  topic: keywords
creator: Milad Samie
creator: Kai Zhang
creator: Mohammad Reza Najjari
creator: David E. Rival
rights: Copyright (c) 2021 Milad Samie, Kai Zhang, Mohammad Reza Najjari, David E. Rival
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.209

Spatially and temporally resolved measurements of turbulent Rayleigh-Bénard convection by Lagrangian particle tracking of long-lived helium-filled soap bubbles
type: item
description: We present spatially and temporally resolved velocity and acceleration measurements of turbulent RayleighBénard convection spanning the whole volume (~ 1 m³) of a cylindrical sample with aspect ratio one. With the "Shake-The-Box" (STB) Lagrangian particle tracking (LPT) algorithm, we were able to instantaneously track up to 560,000 particles, corresponding to mean inter-particle distances down to 6 - 8 Kolmogorov lengths. We used the data assimilation scheme ‘FlowFit’, which involves continuity and Navier-Stokesconstraints, to map the scattered velocity and acceleration data on cubic grids, herewith recovering the smallest flow scales. Lagrangian and Eulerian visualizations reveal the dynamics of the large-scale circulation and its interplay with small scale structures, such as thermal plumes and turbulent background fluctuations. As a result, the complex time-dependent behavior of the LSC comprising azimuthal rotations, torsional oscillation and sloshing can be extracted from the data. Further, we found more seldom dynamic events, such as spontaneous reorientations of the LSC in the data from long-term measurements.
subject: 3D Methods and Applications
  topic: section
subject: Shake-the-Box
  topic: keywords
subject: Lagrangian particle tracking
  topic: keywords
subject: Rayleigh-Bénard convection
  topic: keywords
subject: helium-filled soap bubbles
  topic: keywords
creator: Johannes Bosbach
creator: Daniel Schanz
creator: Phillip Godbersen
creator: Andreas Schröder
rights: Copyright (c) 2021 Johannes Bosbach, Daniel Schanz, Phillip Godbersen, Andreas Schröder
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.208

Robust approach to monitoring Lagrangian transport in very large volume
type: item
description: 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.
subject: 3D Methods and Applications
  topic: section
subject: large volume
  topic: keywords
subject: particle tracking
  topic: keywords
subject: single camera
  topic: keywords
subject: soap bubbles
  topic: keywords
subject: glare points
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creator: Frieder Kaiser
creator: Andreas Haramis
creator: Joshua Galler
creator: David E. Rival
rights: Copyright (c) 2021 Frieder Kaiser, Andreas Haramis, Joshua Galler, David E. Rival
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.207

Three-dimensional temperature and velocity measurements in fluids using thermographic phosphor tracer particles
type: item
description: 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.
subject: Environmental Flows
  topic: section
creator: Moritz Stelter
creator: Fabio J. W. A. Martins
creator: Frank Beyrau
creator: Benoît Fond
rights: Copyright (c) 2021 Moritz Stelter, Fabio J. W. A. Martins, Frank Beyrau, Benoît Fond
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.205

Large-scale 3D flow investigations around a cyclically breathing thermal manikin in a 12 m³ room using HFSB and STB
type: item
description: Exhalation of small aerosol droplets and their transport, dispersion and (local) accumulation in closed rooms have been identified as the main pathway for indirect or airborne respiratory virus transmission from person to person, e.g. for SARS-CoV 2 or measles (Morawska and Cao 2020). Understanding airborne transport mechanisms of viruses via small bio-aerosol particles inside closed populated rooms is an important key factor for optimizing various mitigation strategies (Morawska et al. 2020), which can play an important role for damping the infection dynamics of any future and the ongoing present pandemic scenario, which unfortunately, is still threatening due to the spreading of several SARS-CoV2 variants of concern, e.g. delta (Kupferschmidt and Wadman 2021). Therefore, a large-scale 3D Lagrangian Particle Tracking experiment using up to 3 million long lived and nearly neutrally buoyant helium-filled soap bubbles (HFSB) with a mean diameter of ~ 370 µm as passive tracers in a 12 m³ generic test room has been performed, which allows to fully resolve the Lagrangian transport properties and flow field inside the whole room around a cyclically breathing thermal manikin (Lange et al. 2012) with and without mouth-nose-masks and shields applied. Six high-resolution CMOS streaming cameras, a large array of powerful pulsed LEDs have been used and the Shake-The-Box (STB) (Schanz et al. 2016) Lagrangian particle tracking algorithm has been applied in this experimental study of internal flows in order to gain insight into the complex transient and turbulent aerosol particle transport and dispersion processes around seated breathing persons.
subject: 3D Methods and Applications
  topic: section
subject: Shake-The-Box
  topic: keywords
subject: Lagrangian Particle Tracking
  topic: keywords
subject: COVID-19
  topic: keywords
subject: HFSB
  topic: keywords
subject: particle dispersion
  topic: keywords
creator: Andreas Schröder
creator: Daniel Schanz
creator: Johannes Bosbach
creator: Matteo Novara
creator: Reinhard Geisler
creator: Janos Agocs
creator: Andreas Kohl
rights: Copyright (c) 2021 Andreas Schröder, Daniel Schanz, Johannes Bosbach, Matteo Novara, Reinhard Geisler, Janos Agocs, Andreas Kohl
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.204

Tracer-based 3D surface reconstruction
type: item
description: The continuous advancements of particle imaging techniques for flow field measurements have led to imaging systems and processing approaches matching the demands for 3D velocimetry at large scale (Schanz et al., 2016; Discetti and Coletti, 2018). Often, the flow past an object immersed in the fluid is of key interest, and in some cases the experimentalist exploits the velocimetry data for analysis of the near-surface flow properties such as pressure. It follows that knowledge of the object shape and position is essential. For 2D studies, the issue of identifying the fluid-solid interface often reduces to detection of the intensity gradient resulting from the light sheet striking the object. The latter task is well explored, with a variety of methods providing the object interface in the measurement plane (Canny, 1986; Malik et al., 2001; Gui et al., 2003, among others). These approaches, however, are not applicable in volumetric studies where the illumination is diffuse. A frequently applied alternative in fluid-structure-interaction studies is a dual-measurement approach, where a second measurement system tracks the object shape (e.g., Acher et al., 2019; Zhang et al., 2019) The complexity of operating two measurement systems may not be affordable however, motivating the development of 3D interface detection methods that rely solely on the flow imaging system. Particle imaging based interface detection approaches in 3D have been addressed from various perspectives, containing the detection of fluid-fluid interfaces. Examples utilizing tomographic PIV measurements include the studies of Adhikari and Longmire (2012), Im et al. (2014), and Ebi and Clemens (2016). The two latter examples identify the fluid-solid interface by discriminating a seeded phase (the fluid) from a void phase (the solid). The present work is inspired by this principle, but it assumes a discrete 3D particle distribution as obtained from a generic particle tracking algorithm such as IPR by Wienek…
subject: 3D Methods and Applications
  topic: section
subject: Surface recognition
  topic: keywords
subject: Interface detection
  topic: keywords
subject: PTV processing
  topic: keywords
subject: Data visualization
  topic: keywords
creator: Constantin Jux
creator: Fulvio Scarano
creator: Andrea Sciacchitano
rights: Copyright (c) 2021 Constantin Jux, Fulvio Scarano, Andrea Sciacchitano
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.203

Aerodynamics of a cycling wheel in crosswind by coaxial volumetric velocimetry
type: item
description: 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◦.
subject: 3D Methods and Applications
  topic: section
subject: 3D PIV
  topic: keywords
subject: Wheel aerodynamics
  topic: keywords
subject: Cycling aerodynamics
  topic: keywords
subject: Pressure analysis
  topic: keywords
subject: Coaxial volumetric velocimetry
  topic: keywords
creator: Constantin Jux
creator: Andrea Sciacchitano
creator: Fulvio Scarano
rights: Copyright (c) 2021 Constantin Jux, Andrea Sciacchitano, Fulvio Scarano
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.202

Investigation on computed pressures from PIV, a study of how boundary definitions affect pressure accuracy along objects on the example of a cylinder flow.
type: item
description: This work discusses an approach to compute pressure fields from planar PIV measurement using standard CFD tools. In particular, we propose a combination of interpolation and mesh adaptation to import the PIV measurements on a grid that is morphed around objects, and is fine enough to solve the Poisson equation accurately. The whole process of meshing, interpolation and pressure computation is carried out using the popular open-source solver OpenFoam®. The method is tested and validated on a classic benchmark test case, namely, the unsteady flow past a cylinder. A 3D multiphase flow simulation is used to generate the reference data and analyze the impact of both, the PIV interrogation and the interpolation on the morphed grid. The simulation uses an Euler-Lagrangian one-way coupling approach to simulate the flow field and the dynamics of seeding particles. The analysis compares the pressure field from the 3D CFD simulation with the solution of a 2D Poisson equation based on the 2D velocity field obtained by either down-sampling the CFD data or by PIV interrogation of synthetic images built from the CFD data. Finally, we challenge the proposed method with the pressure reconstruction in a TR-PIV experiment in similar conditions.
subject: Pressure and Force
  topic: section
subject: Pressure
  topic: keywords
subject: from PIV
  topic: keywords
subject: pressure computation
  topic: keywords
subject: accuracy
  topic: keywords
creator: Francisco Felis-Carrasco
creator: David Hess
creator: Bo Beltoft Watz
creator: Miguel Alfonso Mendez
rights: Copyright (c) 2021 Francisco Felis-Carrasco, David Hess, Bo Beltoft Watz, Miguel Alfonso Mendez
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.201

An experimental investigation on stall flutter over a vertically mounted rigid finite wing
type: item
description: As stall flutter has relevant engineering implications, such as in blades of wind turbine and HALE (highaltitude long-endurance aircraft). This work presents the experimental investigation of rigid wing setup in a closed-circuit wind tunnel having 2.1 m × 1.5 m test section. The experimental campaign reached stable and symmetrical LCO within the freestream range from 9 m/s up to 14 m/s (1.69 × 105 < Re < 2.63 × 105 ). Two techniques were used for position tracking: one mechatronic and one image-based. The latter used ‘shakethe-box’ method applied to a body, which has proven a successful approach as a non-intrusive tool.
subject: 3D Methods and Applications
  topic: section
subject: Aeroelasticity
  topic: keywords
subject: wind tunnel
  topic: keywords
subject: PTV
  topic: keywords
subject: Shake-the-box
  topic: keywords
subject: loads
  topic: keywords
creator: Renan Francisco Soares
creator: Ilyas Karasu
creator: Bharath Ganapathisubramani
rights: Copyright (c) 2021 Renan Francisco Soares, Ilyas Karasu, Bharath Ganapathisubramani
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.200

Particle Image Velocimetry Measurements of a Dry Powder Inhaler Flow
type: item
description: Inhalation therapy for respiratory disorders is being increasingly delivered via dry powder inhalers (DPIs), which are breath-actuated devices that deliver pharmaceutical drug particles to the lungs. The motion of inhalation air, produced when a patient inhales through this device, supplies all energy for the entrainment, de-agglomeration, and dispersion of powder drug agglomerates into a fine drug particle aerosol. The aerosol performance is directly related to the fluid-mechanics of a given DPI device. These flow mechanisms are complex as they depend on the device design, inhalation flow rate, and the properties of the dry powder formulation used. Among these, the role of device design is crucial as it significantly affects not only the generation and properties of delivered aerosol, but also the capability of targeted regional drug deposition.
subject: Biological Flows
  topic: section
subject: dry powder inhaler
  topic: keywords
subject: swirling flow
  topic: keywords
subject: aerosol performance
  topic: keywords
subject: inhaler design
  topic: keywords
creator: Vishal Chaugule
creator: Larissa Gomes dos Reis
creator: David F. Fletcher
creator: Paul M. Young
creator: Daniela Traini
creator: Julio Soria
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.199

Main results of the first Data Assimilation Challenge
type: item
description: This work presents the main results of the first Data Assimilation (DA) challenge, conducted within the framework of the European Union’s Horizon 2020 project HOMER (Holistic Optical Metrology for Aero-Elastic Research), grant agreement number 769237. The challenge was jointly organised by the research groups of DLR, ONERA and TU Delft. The same synthetic test case as in the Lagrangian Particle Tracking (LPT) challenge (also presented in this symposium) was considered, reproducing the flow in the wake of a cylinder in proximity of a flat wall. The participants were provided with three datasets containing the measured particles locations and their trajectories identification numbers, at increasing tracers concentrations from 0.04 to 1.4 particles/mm3 . The requested outputs were the three components of the velocity, the nine components of the velocity gradient and the static pressure, defined on a Cartesian grid at one specific time instant. The results were analysed in terms of errors of the output quantities and their distributions. Additionally, the performances of the different DA algorithms were compared with that of a standard linear interpolation approach. Although the velocity errors were found to be in the same range as those of the linear interpolation algorithm, typically between 3% and 12% of the bulk velocity, the use of the DA algorithms enabled an increase of the measurement spatial resolution by a factor between 3 and 4. The errors of the velocity gradient were of the order of 10-15% of the peak vorticity magnitude. Accurate pressure reconstruction was achieved in the flow field, whereas the evaluation of the surface pressure revealed more challenging.
subject: Deep Learning and Data Assimilation
  topic: section
creator: Andrea Sciacchitano
creator: Benjamin Leclaire
creator: Andreas Schroeder
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.198

Main results of the first Lagrangian Particle Tracking Challenge
type: item
description: This work presents the main results of the first Lagrangian Particle Tracking challenge, conducted within the framework of the European Union’s Horizon 2020 project HOMER (Holistic Optical Metrology for Aero-Elastic Research), grant agreement number 769237. The challenge, jointly organised by the research groups of DLR, ONERA and TU Delft, considered a synthetic experiment reproducing the wall-bounded flow in the wake of a cylinder which was simulated by LES. The participants received the calibration images and sets of particle images acquired by four virtual cameras, and were asked to produce as output the particles positions, velocities and accelerations (when possible) at a specific time instant. Four different image acquisition strategies were addressed, namely two-pulse (TP), four-pulse (FP) and time-resolved (TR) acquisitions, each with varying tracer particle concentrations (or number of particles per pixel, ppp). The participants’ outputs were analysed in terms of percentages of correctly reconstructed particles, missed particles, ghost particles, correct tracks and wrong tracks, as well as in terms of position, velocity and acceleration errors, along with their distributions. The analysis of the results showed that the best-performing algorithms allow for a correct reconstruction of more than 99% of the tracer particles with positional errors below 0.1 pixels even at ppp values exceeding 0.15, whereas other algorithms are more prone to the presence of ghost particles already for ppp < 0.1. While the velocity errors remained contained within a small percentage of the bulk velocity, acceleration errors as large as 50% of the actual acceleration magnitude were retrieved.
subject: 3D Methods and Applications
  topic: section
subject: Lagrangian particle tracking
  topic: keywords
subject: LPT challenge
  topic: keywords
subject: methods assessment
  topic: keywords
creator: Andrea Sciacchitano
creator: Benjamin Leclaire
creator: Andreas Schroeder
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.197

PIV and deformation measurements on the rotor blade of a rotating, scaled model wind turbine with flexible blades under tailored inflow conditions
type: item
description: Wind turbines face harsh inflow conditions when operating in the atmospheric boundary layer or in the wake of other wind turbines. The incoming velocity field can change within seconds due to the turbulent structures it contains, resulting in a rapid change of several degrees in the angle of attack for the rotating blade. Aerodynamics are hence rapidly altered, leading to changes of the occurring forces on the rotor. Such dynamic forces cause the blades to twist and bend, accelerating fatigue and reducing the lifetime of a turbine Spinato et al. (2009).
subject: Aerodynamics
  topic: section
subject: PIV
  topic: keywords
subject: Photogrammetry
  topic: keywords
subject: Model Wind Turbine
  topic: keywords
subject: Active Grid
  topic: keywords
subject: Wind Tunnel Experiments
  topic: keywords
creator: Tom T. B. Wester
creator: Lars Kröger
creator: Apostolos Langidis
creator: Simon Nietiedt
creator: Robin Rofallski
creator: Martina Goering
creator: Thomas Luhmann
creator: Joachim Peinke
creator: Gerd Gülker
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.195

Peregrine falcon wakes examined using Volumetric PIV
type: item
description: This study presents time-resolved volumetric measurements in the wake of a peregrine falcon model. The experiments were performed in a water flume with a freestream velocity of 10 cm/s and at an angle of 3.25°. The TSI volumetric PIV system, using Insight V3V-4G software, was used to capture the time-resolved volumetric flow field. The results compare well with previous Stereo PIV measurements; however, the present results also provide true 3-dimensional flow field information which helps decode the reason for the superior maneuverability. This is attributable to the vortex dominated flow field promoted by its morphology.
subject: 3D Methods and Applications
  topic: section
subject: Volumetric PIV
  topic: keywords
subject: particle identification
  topic: keywords
creator: Edward Talboys
creator: Chetan Jagadeesh
creator: Martin Hyde
creator: Daniel Troolin
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.194

Physics-based universal outlier detector for flow statistics
type: item
description: 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 st…
subject: Post-Processing
  topic: section
subject: PIV
  topic: keywords
subject: outlier detection
  topic: keywords
creator: Edoardo Saredi
creator: Andrea Sciacchitano
creator: Fulvio Scarano
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.193

A novel volumetric velocity measurement method for small seeding tracers in large volumes
type: item
description: 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.
subject: 3D Methods and Applications
  topic: section
subject: volumetric velocity measurement
  topic: keywords
subject: turbulence
  topic: keywords
subject: PTV
  topic: keywords
creator: Yisheng Zhang
creator: Haim Abitan
creator: Simon Lautrup Ribergård
creator: Clara M. Velte
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.192

Velocity measurements of dilute suspensions over and through various porous media models
type: item
description: This study is focused on the motion of a dilute suspension containing rigid, spherical, non-Brownian, noncolloidal particles flowing over and through porous media models. The flow is confined to very low Reynolds numbers. To examine the velocity distribution particle image velocimetry (PIV) was applied in conjunction with refractive index matching (RIM) techniques. This study is the first of its kind analyzing the interaction between two common engineering systems: suspension fluid and porous media.
subject: Multiphase Flows
  topic: section
subject: planar PIV
  topic: keywords
subject: porous media
  topic: keywords
subject: suspension flows
  topic: keywords
creator: Eileen Haffner
creator: Theresa Wilkie
creator: Jonathan Higham
creator: Parisa Mirbod
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.191

Lagrangian Strain- and Rotation-Rate Tensor Evaluation Based on Multi-pulse Particle Tracking Velocimetry (MPTV) and Radial Basis Functions(RBFs)
type: item
description: Physical conservation laws are inherently Lagrangian. However, analyses in fluid mechanics using the Lagrangian framework are often forgone in favor of those using the Eulerian framework. This is perhaps due to a lack of experimental techniques with high temporal and spatial resolution that track the movement of fluid tracers in a flow domain. The development of time-resolved Particle Tracking Velocimetry/Accelerometry (TR-PTV/A) that measures flows with high seeding density has made the use of the Lagrangian framework more accessible. A challenge facing PTV/A is the need for robust mesh-free numerical schemes that handle random particle locations. Such a scheme can be created with high-order accuracy using Radial Basis Functions (RBFs). RBFs allow direct evaluation of derivatives of vector and scalar fields at random locations with infinite-order smoothness. The current work uses RBF-based differential schemes to develop a post-processing tool for PTV/A data, which can accurately evaluate spatial derivatives directly from Lagrangian particle tracks. This RBF-based strain/rotation-rate tensor evaluation tool is validated with two and three-dimensional flows from analytical solutions and is then tested with experimental data measured by a multi-pulse PTV/A system.
subject: Post-Processing
  topic: section
subject: Particle Tracking Velocimetry
  topic: keywords
subject: Radial Basis Functions
  topic: keywords
subject: Strain Rate Tensor
  topic: keywords
subject: Rotation Rate Tensor
  topic: keywords
creator: Lanyu Li
creator: Prabu Sellappan
creator: Peter Schmid
creator: Jean-Pierre Hickey
creator: Louis Cattafesta
creator: Zhao Pan
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.190

Error propagation dynamics of velocimetry-based pressure field calculations (2): on the error profile
type: item
description: This work investigates the propagation of error in a Velocimetry-based Pressure field reconstruction (VPressure) problem to determine and explain the effects of error profile of the data on the error propagation. The results discussed are an extension to those found in Pan et al. (2016). We first show how to determine the upper bound of the error in the pressure field, and that this worst scenario for error in the data field is unique and depends on the characteristics of the domain. We then show that the error propagation for a V-Pressure problem is analogous to elastic deformation in, for example, a Euler-Bernoulli beam or Kirchhoff-Love plate for one- and two-dimensional problems, respectively. Finally, we discuss the difference in error propagation near Dirichlet and Neumann boundary conditions, and explain the behavior using Green’s function and the solid mechanics analogy. The methods discussed in this paper will benefit the community in two ways: i) to give experimentalists intuitive and quantitative insights to design tests that minimize error propagation for a V-pressure problem, and ii) to create tests with significant error propagation for the benchmarking of V-Pressure solvers or algorithms. This paper is intended as a summary of recent research conducted by the authors, whereas the full work has been recently published (Faiella et al., 2021).
subject: Pressure and Force
  topic: section
creator: Matthew Faiella
creator: Corwin G. J. MacMillan
creator: Jared Whitehead
creator: Zhao Pan
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.189

An experimental approach to analyze aerosol and splatter formation in a dental practice
type: item
description: The flow velocity, trajectories, and size distribution of droplets produced during a dental scaling procedure using a Cavitron ultrasonic scalar (CUS) has been investigated by optical flow tracking velocimetry and shadowgraphy measurements. The droplet sizes are found to vary from 5 -500 µm; these correspond to droplet nuclei that could carry viruses. The droplet velocities also vary between 0.7 m/s and 1.3 m/s. These observations confirm the critical role of aerosols in the transmission of disease during dental procedures, providing invaluable knowledge for developing protocols and procedures to ensure the safety of both dentists and patients especially during COVID-19 pandemic.
subject: Environmental Flows
  topic: section
subject: COVID-19
  topic: keywords
subject: droplets velocity
  topic: keywords
subject: experiments
  topic: keywords
subject: size distributions
  topic: keywords
creator: Parisa Mirbod
creator: Eileen A. Haffner
creator: Maryam Bagheri
creator: Jonathan E. Higham
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.188

Quantification of Brownian motion under presence of flow using particle diffusometry
type: item
description: 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.
subject: Micro Flows
  topic: section
creator: Dong Hoon Lee
creator: Steven T. Wereley
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.187

Lagrangian Particle Tracking: a link between localization error and fraction of missed particles
type: item
description: 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.)
subject: 3D Methods and Applications
  topic: section
subject: Double-frame 3D PTV
  topic: keywords
subject: Lagrangian Particle Tracking
  topic: keywords
subject: particles localization error
  topic: keywords
creator: Philippe Cornic
creator: Frédéric Champagnat
creator: Benjamin Leclaire
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.186

Numerical Uncertainty in Density Estimation for Background Oriented Schlieren
type: item
description: Background Oriented Schlieren (BOS) is an image-based density measurement technique. BOS estimates the density gradient from the apparent distortion of a target pattern viewed through a medium with varying density using cross-correlation, tracking, or optical flow algorithms. The density gradient can then be numerically integrated to yield a spatially resolved estimate of the density [1]. A method was recently proposed to estimate the a-posteriori instantaneous and spatially resolved density uncertainty for BOS [2] and showed good agreement between the propagated uncertainties and the random error. However, the density uncertainty quantification method could not account for the systematic uncertainty in the density field due to the discretization errors introduced during the numerical integration, which could be much larger than the displacement random errors [2]. In this work, we propose a method to estimate the numerical uncertainty introduced by the density integration in BOS measurements, using a Richardson extrapolation framework. A procedure is also introduced to combine this systematic uncertainty with the random uncertainty from the previous work to provide an instantaneous, spatially-resolved total uncertainty on the density estimates. The method will be tested with synthetic fields and synthetic BOS images.
subject: Uncertainty Quantification
  topic: section
subject: Background Oriented Schlieren
  topic: keywords
subject: Uncertainty Quantification
  topic: keywords
subject: Numerical Uncertainty
  topic: keywords
subject: Richardson Extrapolation
  topic: keywords
creator: Jiacheng Zhang
creator: Lalit Rajendran
creator: Sally Bane
creator: Pavlos Vlachos
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.185

PIV measurements of entrainment process of directly injected media in internal combustion engines
type: item
description: 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 it requires 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 PCC gas 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 noz…
subject: Combustion, Convection and Heat Transfer
  topic: section
subject: PIV
  topic: keywords
subject: Spray
  topic: keywords
subject: Gas jet
  topic: keywords
subject: Torch flame
  topic: keywords
subject: Air entrainment
  topic: keywords
subject: Engine
  topic: keywords
creator: Elsayed Abdelhameed
creator: Takahide Aoyagi
creator: Hiroshi Tashima
creator: Daisuke Tsuru
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.184

Development of micro soap bubble generator for PIV tracer using home stereolithography 3D printer
type: item
description: A micro soap bubble generator for tracers for PIV measurement was developed using a home stereolithography 3D printer. The nozzle has a coaxial triple pipe structure, and an orifice cap is attached to the nozzle head. The inner diameter of the central pipe is 0.7 mm, and the wall thickness of the central pipe is 0.7 mm. From the comparison of the smoke wire visualization result of the flow around the cylinder placed under the mainstream flow velocity of 3 m/s and the PIV measurement result, it was confirmed that the generated micro soap bubbles have good followability to the flow. Generated bubbles’ particle size was estimated to be Φ0.2 mm at the minimum and Φ6.3 mm at the maximum. The most common was Φ0.9 mm ± 0.1 mm, accounting for more than 50% of the total.
subject: Seeding
  topic: section
subject: soap bubble
  topic: keywords
subject: stereolithography3Dptinter
  topic: keywords
subject: nozzle design
  topic: keywords
subject: QFD expantion
  topic: keywords
subject: PIV
  topic: keywords
creator: Shu Shibata
creator: Takumi Yamazaki
creator: Hisashi Matsuda
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.183

Particle Detection by means of Machine Learning in Defocusing PTV
type: item
description: 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).
subject: Deep Learning and Data Assimilation
  topic: section
subject: Machine Learning
  topic: keywords
subject: Deep Learning
  topic: keywords
subject: Defocusing Particle Tracking Velocimetry
  topic: keywords
subject: Post-processing
  topic: keywords
subject: Particle Detection
  topic: keywords
creator: Maximilian Dreisbach
creator: Robin Leister
creator: Matthias Probst
creator: Pascal Friederich
creator: Alexander Stroh
creator: Jochen Kriegseis
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.182

Noise canceling to compute second order statistic from SPIV
type: item
description: Stereoscopic PIV (SPIV) is performed near the wall in a turbulent boundary layer at high Reynolds numbers (Reτ = 2272, 3840) in the streamwise-wallnormal plane. A novel method for denoising the statistics is proposed by the use to two independent SPIV systems to capture the same field of view, with the objective being that the random noise associated with the velocity fluctuations are not correlated between two independent PIV systems. The derivatives in the third (spanwise) direction are obtained by axisymmetry assumptions [George and Hussein (1991)] and continuity equation. The statistics are in agreement with that of DNS at comparable Reynolds number, from y + = 25 for lower Reτ experiment and from y + = 40 for higher Reτ experiment.
subject: Uncertainty Quantification
  topic: section
subject: SPIV
  topic: keywords
subject: Noise characterisation
  topic: keywords
subject: Denoising
  topic: keywords
creator: Jean-Marc Foucaut
creator: Rakesh Yuvaraj
creator: Christophe Cuvier
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.181

Pressure reconstruction of a planar turbulent flow field within a multiply-connected domain with arbitrary boundary shapes
type: item
description: Over the past two decades, it has been demonstrated that the instantaneous spatial pressure distribution in a turbulent flow field can be reconstructed from the pressure gradient field non-intrusively measured by Particle Image Velocimetry (PIV). Representative pressure reconstruction methods include the omnidirectional integration (Liu and Katz, 2006; Liu et al., 2016; Liu and Moreto, 2020), the Poisson equation approach (Violato et al., 2011; De Kat and Van Oudheusden, 2012), the least-square method (Jeon et al., 2015), and most recently, the adjoint-based sequential data assimilation method, which also essentially utilizes the Poisson equation to reconstruct the pressure(He et al., 2020). Most of these previous pressure reconstruction examples, however, were applied to simply-connected domains (Gluzman et al., 2017) only. None of these previous studies have discussed how to apply the pressure reconstruction procedures to a multiply-connected domain (Gluzman et al., 2017). To fill in this gap, this paper presents a detailed report for the first time documenting the implementation procedures and validation results for pressure reconstruction of a planar turbulent flow field within a multiply-connected domain that has arbitrary inner and outer boundary shapes. The pressure reconstruction algorithm used in the current study is the rotating parallelray omni-directional integration algorithm, which, as demonstrated in reference (Liu and Moreto, 2020) based on simply-connected flow domains, offers high-level of accuracy in the reconstructed pressure. While preserving the nature and advantage of the parallel ray omni-directional pressure reconstruction at places with flow data, the new implementation of the algorithm is capable of processing an arbitrary number of inner void areas with arbitrary boundary shapes. Validation of the multiply-connected domain pressure reconstruction code is conducted using the DNS (Direct Numerical Simulation) isotropic turbulence field avai…
subject: Pressure and Force
  topic: section
subject: Pressure reconstruction
  topic: keywords
subject: multiply-connected domain
  topic: keywords
creator: Xiaofeng Liu
creator: Jose Roberto Moreto
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.180

Investigation of the shear-layer instabilities in supersonic impinging jets using dual-time velocity measurements
type: item
description: 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.
subject: Jets, Shear Layers and Wakes
  topic: section
subject: supersonic impinging jet
  topic: keywords
subject: double-PIV measurements
  topic: keywords
subject: shear-layer dynamics
  topic: keywords
subject: time-unresolved
  topic: keywords
creator: Tushar Sikroria
creator: Julio Soria
creator: Shahram Karami
creator: Richard Sandberg
creator: Andrew Ooi
rights: Copyright (c) 2021 14th International Symposium on Particle Image Velocimetry
date: 2021-08-01
publication date: 2021-08-01
doi: 10.18409/ispiv.v1i1.179