Two-Pulse 3D particle tracking with Shake-The-Box

The problem of reconstructing the three-dimensional position of particle flow tracers from their projection on multiple cameras lies at the heart of several 3D particle-image-based velocimetry and Lagrangian particle tracking (LPT) measurement techniques. While cross-correlation-based techniques such as tomographic-PIV (Tomo-PIV, Elsinga et al. 2006) make use of algebraic methods (e.g. MART, Herman and Lent 1976) to reconstruct particles as intensity peaks in a discretized voxel space, triangulation-based methods (3D-PTV, Nishino et al. 1989, Maas et al. 1993 and Iterative Particle Reconstruction, IPR, Wieneke 2013, Jahn et al. 2021) leverage epipolar geometry to reconstruct individual particles as positions and peak-intensity values in the 3D domain. Despite the inherent differences concerning accuracy, robustness and computational cost between the two approaches, in both cases the 3D reconstruction represents a bottleneck when the spatial resolution (i.e. particle image density, indicated in particles per pixel, ppp) of the measurement is considered. In fact, as the number of particles to be reconstructed increases (assuming constant properties of the imaging system), the reconstruction process become increasingly difficult due to the underdetermined nature of the problem. This typically results in a lower number and positional accuracy of the reconstructed particles, as well as an increasing number of spurious particles (ghost particles, Elsinga et al. 2011) which affect the accuracy of the measurement. As a consequence, during the last decade, several methods have been developed to increase the performances of the reconstruction technique; an overview of these developments can be found in Scarano 2012 and Jahn et al. 2021

Variable-Timestep Shake-The-Box (VT-STB) for flows with high dynamic range

In recent years, Lagrangian Particle Tracking (LPT) has become more and more important in the field of 3D flow measurements, largely due to the introduction of the methods of Iterative Particle Reconstruction (IPR, Wieneke 2013) and Shake-The-Box (STB, Schanz et al. 2016). Applying the STB algorithm, particles can be tracked in large numbers, with a nearly complete suppression of ghost particles. The introduced extension to the STB method extends its working range to flows with high vleocity range, i.e. large areas within the measurement region that exhibit very slow flow velocities compared to the fastest ones, which determine the applied frame-rat

Shake-The-Box particle tracking with variable time-steps in flows with high velocity range (VT-STB)

In recent years, Lagrangian Particle Tracking (LPT) has become more and more important in the field of 3D flow measurements, largely due to the introduction of the methods of Iterative Particle Reconstruction (IPR, Wieneke 2013) and Shake-The-Box (STB, Schanz et al. 2016). Applying the STB algorithm, particles can be tracked in large numbers, with a nearly complete suppression of ghost particles. The ability of the STB algorithm to discern real particles from ghost particles is largely stemming from the observation that for real particles the change of acceleration is small between time-steps, while ghost particles are generated in quasi-random locations all over the measurement volume. However, this assumption only holds if the particles exhibit a certain amount of movement relative to each other, such that the ambiguities ‘de-correlate’ within few time-steps. However, flows with a high velocity range can exhibit regions in space with only very little movement of the particles (e.g. jet flows). As the time separation has to be chosen such that the fastest particles are reliably tracked, particles in the surrounding flow might move only a fraction of a pixel in the same time. Another potentially problematic effect of slowly moving particle clouds is that situations of overlapping particle images are retained over several time-steps. In this work we propose an extension to the standard STB evaluation, which applies multiple iterations of particle tracking with variable time-separation Δ. The idea is to start the evaluation with a Δ at iteration 1 such that the slowest particles of the flow can be optimally tracked. From there, the time-separation is iteratively reduced, tracking faster particles with every iteration. Finally, the original time-separation of the recording is reached, where only the fastest particles - remain to be tracked

Development of new methods for analysis of LPT data and application to high-subsonic jet measurements

Lagrangian particle tracking enables the accurate measurement of the position, velocity and acceleration of particles moving within fluid flows. Beyond the particle positions in each time step, an actual track of the individual particle is available over time. This can be exploited for new analysis methods that use this continuous nature of the tracks to improve binned statistics of the flow. Instead of considering just particle positions at each sampling time instance the movement of the tracked particle between those time steps can provide additional information. In the case of binning based averaging methods this results in better convergence of the statistics for a given amount of data. We apply such methods to a multi-pulse Shake-The-Box (STB) measurement of a Mach 0.84 jet in air and generate high resolution two-point correlation maps of the flow. Coherent structures in the shear layer are further investigated using event orientated conditional averaging based on quadrant analysis. As a novel approach for using the Lagrangian nature of the measurement data, we additionally show a control volume balance based calculation approach, which together with bin based statistics could provide a pathway towards investigating balance equations of flow quantitie

Volumetric Lagrangian particle tracking measurements of jet impingement on convex cylinder

Impinging jets are widely used for heat and mass transfer because they are applicable to any type of body and can be easily implemented. They are is also used in various industrial fields and design techniques. Previous researches usually have investigated a jet impinging onto a flat surface. However, since most of the mechanical parts have curvature on their surface, it is necessary to study more detailed properties using advanced measurements of the jet impinging on a curved surface. Therefore, in this study, three-dimensional flow structures of a round jet impinging on a convex cylinder surface were measured using volumetric Lagrangian particle tracking (LPT)

Multi-Resolution, Time-Resolved PIV Measurements of a Decelerating Turbulent Boundary Layer near Separation

We report on measurements of the time-evolving velocity profile of a turbulent boundary layer subjected to a strong adverse pressure gradient (APG) at Reynolds numbers up to Re_theta ~55000 with an upstream friction Reynolds number exceeding Re_tau ~10000. Near the point of flow separation high-resolution imaging at high camera frame rates captured the time evolving velocity profile using the so-called "profile-PIV" technique in a nested imaging configuration of two cameras operating at different image magnifications. One camera used an image magnification better than unity to resolve the viscous scales directly at the wall while the remainder of the roughly 200 mm thick boundary layer is simultaneous captured by the second camera. In the APG the variance of the stream-wise velocity exhibits no "inner peak" commonly found in turbulent boundary layers without pressure gradient influence. Spectral analysis further shows that the peak energy within the boundary layer shifts away from the wall toward lower frequencies. The overlap between the simultaneously imaged areas allows to assess and, to first order, correct for the effect of spatial smoothing on statistical quantities, spectra and related quantities. A multi-frame cross-correlation algorithm was used to process the extensive database. In addition, a newly developed 2D-2C "Shake-The-Box" algorithm(STB) provided highly resolved particle tracking data beyond the reach of conventional PIV processing

Experimental analysis of the log-law at adverse pressure gradient

The experimental data for the mean velocity are analysed in the inner layer for a turbulent boundary layer at significant adverse pressure gradient and Reynolds numbers up to Re-theta=57000. The aim is to determine the resilience of the log law for the mean velocity, the possible change of the von Karman constant kappa and the appearance of a square-root law above the log law at significant adverse pressure gradients. In the wind-tunnel experiment, the adverse pressure gradient is imposed by an S-shaped deflection of the contour model which is mounted on a wind-tunnel sidewall. A large-scale particle imaging velocimetry method is applied to measure the streamwise evolution of the flow over a streamwise distance of 15 boundary layer thicknesses. In the adverse pressure gradient region, microscopic and three-dimensional Lagrangian particle tracking velocimetry are used to measure the mean velocity and the Reynolds stresses down to the viscous sublayer. Oil-film interferometry is used to determine the wall shear stress. The log law in the mean-velocity profile is found to be a robust feature at adverse pressure gradient, but its region is thinner than its zero pressure gradient counterpart, and its slope is altered. A square-root law emerges above the log law, extending to the wall distance the log law typically occupies at zero pressure gradient. Lower values for kappa are found than for zero pressure gradient turbulent boundary layers, but the reduction is within the uncertainty of the measurement

Large-scale 3D flow investigations around a cyclically breathing thermal manikin in a 12 m³ room using HFSB and STB

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

Large-scale volumetric flow studies on transport of aerosol particles using a breathing human model with and without face protections

Exhalation of small aerosol particle droplets and their airborne transport, dispersion and (local) accumulation in closed rooms have been identified as the main pathways for direct and indirect respiratory virus transmission from person to person, e.g. for SARS-CoV-2 or measles (Morawska and Cao 2020) (Chen et al. 2021). Therefore, understanding airborne transport mechanisms of aerosol particles inside closed populated rooms is an important key factor for assessing and optimizing various mitigation strategies (Morawska et al. 2020) (Morawska et al. 2013). Unsteady flow features, which are typically evolving in such mixed convection flow scenarios, govern the respective particle transport properties. Experimental and numerical methods are required which enable capturing the related broad range of scales in such internal flows over many cubic meters in order to provide reliable data for the adaptation of proper mitigation measures (distances, masks, shields, air purifiers, ventilation systems etc.). In the present work we show results of a large-scale 3D Lagrangian Particle Tracking (LPT) experiment which has been performed in a 12 m³ generic test room capturing up to 3 million long lived and nearly neutrally buoyant helium-filled soap bubbles (HFSB) with a mean diameter of dHFSB~ 370 µm as (almost) passive tracers. HFSB are used as fluid mechanical replacements for small aerosol particles dP < 5µm and allow to resolve the Lagrangian transport properties and related unsteady 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 and the variable-time-step Shake-The-Box (VT-STB) (Schanz et al. 2016, Schanz et al. 2021) LPT algorithm have 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 a seated and breathing human model

Tolterodine extended release in the treatment of male oab/storage luts: A systematic review

Overactive bladder (OAB)/ storage lower urinary tract symptoms (LUTS) have a high prevalence affecting up to 90\% of men over 80 years. The role of sufficient therapies appears crucial. In the present review, we analyzed the mechanism of action of tolterodine extended-release (ER) with the aim to clarify its efficacy and safety profile, as compared to other active treatments of OAB/storage LUTS.A wide Medline search was performed including the combination of following words: "LUTS", "BPH", "OAB", "antimuscarinic", "tolterodine", "tolterodine ER". IPSS, IPSS storage sub-score and IPSS QoL (International Prostate Symptom Score) were the validated efficacy outcomes. In addition, the numbers of urgency episodes/24 h, urgency incontinence episodes/24 h, incontinence episodes/24 h and pad use were considered. We also evaluated the most common adverse events (AEs) reported for tolterodine ER.Of 128 retrieved articles, 109 were excluded. The efficacy and tolerability of tolterodine ER Vs. tolterodine IR have been evaluated in a multicenter, double-blind, randomized placebo controlled study in 1529 patients with OAB. A 71\% mean reduction in urgency incontinence episodes was found in the tolterodine ER group compared to a 60\% reduction in the tolterodine IR (p 29 cc) only the combination therapy significantly reduced 24-h voiding frequency (2.8 vs. 1.7 with tamsulosin, 1.4 with tolterodine, or 1.6 with placebo). A recent meta-analysis evaluating tolterodine in comparison with other antimuscarinic drugs demonstrated that tolterodine ER was significantly more effective than placebo in reducing micturition/24 h, urinary leakage episodes/24 h, urgency episodes/24 h, and urgency incontinence episodes/24 h. With regard to adverse events, tolterodine ER was associated with a good adverse event profile resulting in the third most favorable antimuscarinic. Antimuscarinic drugs are the mainstay of pharmacological therapy for OAB / storage LUTS; several studies have demonstrated that tolterodine ER is an effective and well tolerated formulation of this class of treatment.Tolterodine ER resulted effective in reducing frequency urgency and nocturia and urinary leakage in male patients with OAB/storage LUTS. Dry mouth and constipation are the most frequently reported adverse events