Laser Light Sheet Research Articles

S054101 周囲と密度の異なる噴流のプリファード周波数([S05410]噴流,後流,およびはく離流れの基礎と応用:最前線(10))

This report aims at investigating the relationship between preferred frequency of jets and density. The disturbance frequency for mixing control based on the preferred frequency occur in a jet flow initial area of a jet column mode is often selected to enhance the diffusion of the jet flow. Air, CO_2, and He were used for jets and surroundings. Nozzle was used converging round nozzle (d=10mm). The laser light sheet technique was applied to the visualization of a cross section of vortex ring. The variation of velocity of a jet flow was measured by the hot wire anemometry and PIV to investigate the preferred frequency to determine the Strouhal number. The distance until rolling up to the vortex ring goes away from the nozzle as increasing the density ratio. The Strouhal number does not depend on Reynolds number and keep an almost constant value. These show the relationship between preferred frequency and diffusion by jet density with different surrounding gas.

A NEW QUALITY METHODOLOGY AND METRICS FOR SPRAY PATTERN ANALYSIS

A new quality procedure and metrics for detecting quality problems in various applications, including medical device coating, spray drying, mass spectrometry, inhalation (drug delivery), heat transfer, and combustion, is presented. The novel spray characterization method facilitates the evaluation of data relating to spray surface area, spray density distribution, and/or mass distribution by visualizing deviations (spray errors) with respect to an ideal distribution in a two-dimensional plane. In this paper an optical patternation experiment was performed using a custom diagnostic system based on a 2D laser light sheet (Mie scattering) technique to control the quality of a series of air-assisted micronozzles for medical device coating. The novel spray error metrics were evaluated and compared to traditional quality measures such as the pattern index (P.I.). It was noted that the new spray error patternation methodology and error metrics SEt, SEo, and SEu provide a more informative indicator than conventional measures for detecting the spray quality. Besides the spray symmetry, the spray size and accurate location and type of spray density deviations are assessed. The results show that by obtaining quantitative information on spray density deviations, nozzle comparability is facilitated, and otherwise- "invisible" spray under-representation and/or over-representations are detected. A new insight into the spray characteristics of a series of micronozzles could be gained.

Laser stripe measurements of near-wall solid fraction in channel flows of liquid-granular mixtures

A simple, robust, and accurate imaging technique is proposed to measure granular concentration profiles in channel flows of liquid-granular mixtures. We focus on moderate to high granular concentrations (5–50%), for which optical access is restricted to regions close to a transparent wall. To measure concentrations in this range, we illuminate solid grains moving near the wall using a transverse laser light sheet. The evolving shape of the laser stripe, deformed by passing grains, is then monitored using an oblique camera. Statistics of the granular distance to wall can thus be acquired and converted to volumetric solid fraction measurements. The method is verified using fluidization cell tests and applied to open-channel sheet flow experiments. Free of any parameter adjustment, the laser stripe method is found to yield good results, and allows joint measurements of granular velocity and solid fraction profiles.

Acoustic Doppler velocimeter-induced acoustic streaming and its implications for measurement

The acoustic Doppler velocimeter (ADV) is widely used for the characterization of fluid flow. Secondary flows (“acoustic streaming”) generated by the ADV’s acoustic pulses may affect the accuracy of measurements in experiments with small velocities. We assessed the impact of acoustic streaming on flow measurement using particle image velocimetry. The probes of two different ADVs were successively mounted in a tank of quiescent water. The probes’ ultrasound emitters were aligned with a laser light sheet. Observed flow was primarily in the axial direction, accelerating from the ultrasound emitter and peaking within centimeters of the velocimeter sampling volume before dropping off. We measured the dependence of acoustic streaming velocity on ADV configuration, finding that different settings induce streaming ranging from negligible to more than 2.0 cm s−1. From these results, we describe cases where acoustic streaming affects velocity measurements and also cases where ADVs accurately measure their own acoustic streaming.

P04. Dissecting the contribution of non-neural ectoderm to the vertebrate neural tube closure

Neural tube closure is one of the most prominent morphogenetic events during vertebrate development with dynamic cell shape changes and reorganization of cells. These cell behaviors are observed not only in a forming neural tube (neural ectoderm) itself but also in epidermal (non-neural) ectoderm. Cells in the neural ectoderm undergo apical constriction and mediolateral intercalation, which allow the neural tissue to form a groove along the anteroposterior axis and converge toward the midline, respectively. Although the knowledge on cellular and molecular mechanisms within neural ectoderm during vertebrate neurulation is accumulating, contribution of non-neural ectoderm is not well understood. In tissue level, non-neural ectoderm intensively moves toward the dorsal side of the embryo, probably contributing to the actual closure event, and it has been shown by studies with chick embryos that explants of neural ectoderm isolated from non-neural ectoderm fail to form neural tube, demonstrating the importance of non-neural ectoderm for neural tube closure. To clarify cellular and molecular basis of non-neural ectoderm that contributes to neural tube closure, we have analyzed possible mechanisms that may generate a force causing the movements, using Xenopus laevis embryos as a vertebrate model system. We first tested a contribution of cell divisions by treating the embryos with hydroxyurea and aphidicolin (HUA), inhibitors for cell division, throughout neurulation. Time-lapse images and sections of fixed embryos revealed that neural tube closure of the HUA-treated embryos were indistinguishable from the untreated controls with cell divisions suppressed significantly, suggesting that cell divisions may be dispensable for the tube closure. We are currently examining other cellular mechanisms, including surface expansion, mediolateral and/or anteroposterior rearrangement, and radial intercalation of non-neural ectoderm cells, using digital scanned laser light sheet microscopy (DSLM) as one of powerful tools enabling live imaging of cell morphogenesis in neural tube closure.

Investigation of Blade Tip Interaction With Casing Treatment in a Transonic Compressor—Part I: Particle Image Velocimetry

A single-stage transonic axial compressor was equipped with a casing treatment (CT), consisting of 3.5 axial slots per rotor pitch in order to investigate the predicted extension of the stall margin characteristics both numerically and experimentally. Contrary to most other studies, the CT was designed especially accounting for an optimized optical access in the immediate vicinity of the CT, rather than giving maximum benefit in terms of stall margin extension. Part I of this two-part contribution describes the experimental investigation of the blade tip interaction with casing treatment using particle image velocimetry (PIV). The nearly rectangular geometry of the CT cavities allowed a portion of it to be made of quartz glass with curvatures matching the casing. Thus, the flow phenomena could be observed with essentially no disturbance caused by the optical access. Two periscope light sheet probes were specifically designed for this application to allow for precise alignment of the laser light sheet at three different radial positions in the rotor passage (87.5%, 95%, and 99%). For the outermost radial position, the light sheet probe was placed behind the rotor and aligned to pass the light sheet through the blade tip clearance. It was demonstrated that the PIV technique is capable of providing velocity information of high quality even in the tip clearance region of the rotor blades. The chosen type of smoke-based seeding with very small particles (about 0.5 μm in diameter) supported data evaluation with high spatial resolution, resulting in a final grid size of 0.5×0.5 mm2. The PIV database established in this project forms the basis for further detailed evaluations of the flow phenomena present in the transonic compressor stage with CT and allows validation of accompanying computational fluid dynamics (CFD) calculations using the TRACE code. Based on the combined results of PIV measurements and CFD calculations of the same compressor and CT geometry, a better understanding of the complex flow characteristics can be achieved, as detailed in Part II of this paper.

Behaviors of Flame and Flow of Swirling Wake During Fuel Jet Oscillation Due to Acoustic Excitations

AbstractThe flame and flow behaviors along with the fuel jet oscillations of non-premixed and axisymmetric swirling wake during acoustic excitations are studied experimentally. Visual observations on the reaction zones are carried out to identify the flame behaviors. Close-up images at the flame base as well as the whole flame images are captured and discussed. Traditional photography techniques are adopted to illustrate the dimensional characteristics of every flame mode. The central jet oscillations are diagnosed by a two component laser Doppler anemometer. Combined images of the flame and flow are gathered using the laser-light sheet assisted Mie scattering method. Results showed that the short and wide flame which was induced during acoustic forcing is principally because of the severe premixing at the tip of the burner tube. Wake recirculation bubble enhanced premixing at low swirl number while it damped the jet oscillation at higher swirl number. Mechanics of mixing at every flame mode during acoustic excitation are reported and discussed.

Effects of Acoustic Excitation on a Swirling Diffusion Flame

A swirling double concentric jet is commonly used for nonpremixed gas burner application for safety reasons and to improve the combustion performance. Fuel is generally spurted at the central jet while the annular coflowing air is swirled. They are normally separated by a blockage disk where the bluff-body effects further enhance the recirculation of hot gas at the reaction zone. This paper aims to experimentally investigate the behavior of flame and flow in a double concentric jet combustor when the fuel supply is acoustically driven. Laser-light sheet assisted Mie scattering method has been used to visualize the flow, while the flame lengths were measured by a conventional photography technique. The fluctuating velocity at the jet exit was measured by a two-component laser Doppler velocimeter. Flammability and stability at first fuel tube resonant frequency are reported and discussed. The evolution of flame profile with excitation level is presented and discussed, together with the reduction in flame length. The flame in the unforced reacting axisymmetric wake is classified into three characteristic modes, which are weak swirling flame, lifted flame, and transitional reattached flame. These terms reflect their primary features of flame appearances, and when the acoustic excitation is applied, the flame behaviors change with the excitation frequency and amplitude. Four additional characteristic modes are identified; e.g., at low excitation amplitudes, wrinkling flame with a blue annular film is observed because the excitation induces vortices in the central fuel jet and hence gives rise to the wrinkling of flame. The central jet vortices become larger with the increase in excitation amplitude and thus lead to a wider and shorter flame. If the excitation amplitude is increased above a certain value, the central jet vortices change the rotation direction and pacing with the annular jet vortices. These changes in the flow field induce large turbulent intensity and mixing and therefore make the flame looks blue and short. Further increase in the excitation amplitude would lift the flame because the flow field would be dramatically modified.

An Autonomous Open-Ocean Stereoscopic PIV Profiler

Abstract Over the past decade, a novel free-fall imaging profiler has been under development at the Scripps Institution of Oceanography to observe and quantify biological and physical structure in the upper 100 m of the ocean. The profiler provided the first detailed view of microscale phytoplankton distributions using in situ planar laser-induced fluorescence. The present study examines a recent incarnation of the profiler that features microscale turbulent flow measurement capabilities using stereoscopic particle image velocimetry (PIV). As the profiler descends through the water column, a vertical sheet of laser light illuminates natural particles below the profiler. Two sensitive charge-coupled device (CCD) cameras image a 25 cm × 25 cm × 0.6 cm region at a nominal frame rate of 8 Hz. The stereoscopic camera configuration allows all three components of velocity to be measured in the vertical plane with an average spatial resolution of approximately 3 mm. The performance of the PIV system is evaluated for deployments offshore of the southern California coast. The in situ image characteristics, including natural particle seeding density and imaged particle size, are found to be suitable for PIV. Ensemble-averaged velocity and dissipation of turbulent kinetic energy estimates from the stereoscopic PIV system are consistent with observations from an acoustic Doppler velocimeter and acoustic Doppler current profiler, though it is revealed that the present instrument configuration influences the observed flow field. The salient challenges in adapting stereoscopic PIV for in situ, open-ocean turbulence measurements are identified, including cross-plane particle motion, instrument intrusiveness, and measurement uncertainty limitations. These challenges are discussed and recommendations are provided for future development: improved alignment with the dominant flow direction, mitigation of instrument intrusiveness, and improvements in illumination and imaging resolution.

Image enhancement in ultramicroscopy by improved laser light sheets

In the majority of implementations of light sheet microscopy, such as ultramicroscopy, the laser beam illuminating the specimen is truncated by a slit aperture before it is focused to a light sheet by a single cylindrical lens. A light sheet generated in this way can be made very thin near to the focal point, but unfortunately its Rayleigh range is severely limited. This problem can be partially solved by using a smaller slit aperture. However, this also causes a major loss in power, a severe broadening of the beam waist, and thus a significant loss of resolution along the detection axis. We developed improved light-sheet-generation optics, which provide longer Raleigh ranges, whilst retaining beam waists comparable to our standard system with one cylindrical lens. Using the modified system we achieved a marked improvement in the resolution of ultramicroscopy reconstructions of representative biological specimens.

Digital Scanned Laser Light Sheet Fluorescence Microscopy

Modern applications in the life sciences are frequently based on in vivo imaging of biological specimens, a domain for which light microscopy approaches are typically best suited. Often, quantitative information must be obtained from large multicellular organisms on the cellular or even subcellular level and with a good temporal resolution. However, this usually requires a combination of conflicting features: high imaging speed, low photobleaching, and low phototoxicity in the specimen, good three-dimensional (3D) resolution, an excellent signal-to-noise ratio, and multiple-view imaging capability. The latter feature refers to the capability of recording a specimen along multiple directions, which is crucial for the imaging of large specimens with strong light-scattering or light-absorbing tissue properties. An imaging technique that fulfills these requirements is essential for many key applications: For example, studying fast cellular processes over long periods of time, imaging entire embryos throughout development, or reconstructing the formation of morphological defects in mutants. Here, we discuss digital scanned laser light sheet fluorescence microscopy (DSLM) as a novel tool for quantitative in vivo imaging in the post-genomic era and show how this emerging technique relates to the currently most widely applied 3D microscopy techniques in biology: confocal fluorescence microscopy and two-photon microscopy.

Muscle activity and hydrodynamic function of pelvic fins in trout (Oncorhynchus mykiss)

Contrary to the previous premise that pelvic fins lacked obvious function, recent work on three-dimensional fin motions suggests that pelvic fins actively control stability and speed in slowly swimming trout. This study used electromyography to measure pelvic fin muscle activity and particle imaging velocimetry to quantify flow along the ventral body region to test this hypothesis. Fish swam at slow speeds (0.13-1.36 BL s(-1)) while being filmed with three high speed cameras. Three-dimensional kinematics were captured for all trials. During EMG trials pelvic fin muscle activity was synchronized to kinematic motion, during particle imaging velocimetry trials, a laser light-sheet was used to visualize the flow surrounding the ventral aspect of the fish. Four main conclusions are reached: first, pelvic fins are actively oscillated during slow-speed swimming; antagonistic abductor and adductor muscles contracted simultaneously, their collective action producing a unique contralateral oscillating behaviour in the fins. Second, pelvic fins slow the flow along the ventral side affecting pitch and yaw instabilities; flow upstream of the pelvic fins is slowed by 0.02 m s(-1) and flow downstream of the pelvic fins is slowed by 0.034 m s(-1) compared with free stream flow. Third, pelvic fin wake influences anal fin angle of attack; flow angle in the wake of the pelvic fin was 33.84+/-2.4 deg. (max) and -11.83+/-11.2 deg. (min) compared with the free stream flow angle of 1.27+/-0.1 deg. Fourth, pelvic fins appear to actively damp body oscillation during slow-speed swimming, providing drag to help control speed and stabilize the body position during slow-speed swimming.

Physical modelling of pile penetration in clay using transparent soil and particle image velocimetry

A small-scale physical modelling method was developed to study the movement of clay during pile installation. The clay was simulated using a mixture of amorphous silica and mineral oil, which becomes almost transparent when the refractive indices of the oil and the silica are well matched. After adding reflective particles and consolidating the mixture in a transparent container, cylindrical model piles were driven vertically at the centre. A vertical section aligned with the pile centreline was illuminated by a laser light sheet, and a sequence of digital images was recorded. These were analysed using particle image velocimetry, and the complete displacement distribution during the pile installation was obtained. Notwithstanding some discrepancies at shallow depths, the observed displacements generally showed fairly good agreement with the theoretical predictions of the shallow strain path method (SSPM) once the effect of some soil trapped beneath the flat pile tip was taken into account. Normalisation of the horizontal and vertical components of movement employing both the pile length and radius, based on SSPM theory, was shown to be valid. The normalised vertical displacement contours were similar to those published by previous researchers. The results of this study could be used to assess the impact of disturbance due to pile installation on, for example, buried services or archaeology.

Analysis, presentation, and understanding in experimental fluid flow studies: A colourful evolutionary story

The digital computer has revolutionised the ability of the experimentalist to obtain, analyse and interpret physical data, and no-where is this more apparent than in the study of fluid flow and heat transfer problems. The emergence of digital methods is reviewed, with the discussion reflecting the first author's personal experience over the past 50 years. To illustrate how modern experimental study relies heavily on digital technology, representative results are presented for a number of fluid flow problems that have been investigated using advanced forms of optical instrumentation—namely laser light sheet visualisation, three-component laser Doppler anemometry (LDA), and particle image velocimetry (PIV). These examples are used to emphasise the importance of digital methods for data capture and analysis, with samples of the reduced results being presented in the form of multi-functional colour graphs and images. The discussion shows how the processed data can yield improved understanding, revealing complex three-dimensional flow features that probably could not have been identified, and certainly could never have been quantified, in previous years. Colour, specifically, is shown to have emerged with increasing prominence in the last few decades, and its various uses are now seen to be crucial for the modern experimentalist. These aspects are comprehensively discussed.

J0501-3-6 PTVとDNSを融合した非定常流シミュレーションアルゴリズムとその応用([J0501-3]流体機械の研究開発におけるEFD/CFD(3))

We acquire particle velocities on a laser-light sheet with PTV and generate time-resolved velocity fields compatible with DNS by rectifying PTV velocity fields to satisfy the continuity. By synchronizing the DNS time step with the PTV frame rate, we feed a rearranged velocity field at each time step and compute the two-dimensional incompressible Navier-Stokes equations over time. At each time step, velocity components are given by the linear combination between those from PTV and those updated with DNS, and their weight is determined so that the hybrid velocity field is directed toward the measured one with a minimum noise level. Thus, unsteady velocity and pressure fields satisfying the governing equations can be simultaneously obtained with the resolution comparable to the numerical simulation. The algorithm and features of this hybrid algorithm are introduced by taking examples from flows past a NACA0012 airfoil and a planar jet.

G0600-2-4 衝突噴流群を用いた流路内の流動および熱移動解析(熱工学部門一般講演(2):伝熱(2))

This paper shows the influence of flow behavior of multiple impingement jets on characteristics of heat transfer of narrow spaces. The jets were set a 5×5 nozzles of sharp edged orifice type with D=5 mm in diameter. The jet-to-jet space is 10 mm. The experiments were performed for the separation distance, H, between jet exit and impingement plate ranging from H/D=1 to 3, at Reynolds number 1600〜3300. The time and spatial temperature profiles over the impingement plate were measured using at infrared camera (TVS-8500, Avio) with a two-dimensional array of Indeum-Antimony (In Sb) sensors. To clarify the influence of the flow behavior on heat transfer fields, we visualized a smoke flow field by means of a laser light sheet method (LLS). Based on these experimental data, the relationships between the fluid flow and the heat transfer characteristics were clarified.

Novel processing tools for automated doppler picture veocimetry (DPV) evaluation

A unique technique, the Doppler Picture Velocimetry (DPV), for measuring and visualizing velocities especially in hypersonic gas flows is presented. By means of a Michelson interferometer (MI) the Doppler shifted light scattered by tracers is transformed into an image showing Fizeau fringes. The image fringe distribution provides information on the Doppler frequency shift which is related to the velocity of the particles crossing a light sheet plane. To overcome former disadvantages of DPV, the optical set-up as well as the processing scheme have been improved significantly. Two schemes have been tested in recent times for fringe processing: 1) an alternative process, the Least Square Estimators (LES) and 2) an algorithm based on a technique using Fast Fourier Transformations (FFT) to examine the DPV images in the frequency domain. The new DPV algorithms now allow an automated calculation of the velocity profiles from the Doppler pictures without manual fringe tracing as it had to be done in the past. Both methods are compared by means of Mach 6 flows around a wedge and a sphere produced in the ISL high energy shock tunnel STA. TiO$_2$ particles are illuminated by a laser light sheet which was perpendicularly arranged to the main flow direction. Light observation via the MI from the side (90° to illumination) informs on the vertically oriented velocity through the DPV images.

Large-scale PIV surface flow measurements in shallow basins with different geometries

Shallow depth flow fields and low velocity magnitudes are often challenges for traditional velocity measuring instruments. As such, new techniques have been developed that provide more reliable velocity measurements under these circumstances. In the present study, the two-dimensional (2D) surface velocity field of shallow basins is assessed by means of Large-Scale Particle Image Velocimetry (LSPIV). The measurements are carried out at the water surface, which means that a laser light sheet is not needed. Depending on the time scales of the flow and the camera characteristics, it is even possible to work with a constant light source. An experimental application of this method is presented to analyze the effects of shallow basin geometry on flow characteristics in reservoirs where large coherent two-dimensional flow structures in the mixing layer dominate the flow characteristics. The flow and boundary conditions that give rise to asymmetric flow are presented. Asymmetric flow structures were observed starting from basin shape ratios that are less than or equal to 0.96. By decreasing the basin length and increasing the shape ratio to greater than 0.96, the flow structure generally tends towards a symmetric pattern.

Exhaled Air Dispersion Distances During Noninvasive Ventilation via Different Respironics Face Masks

BackgroundAs part of our influenza pandemic preparedness, we studied the exhaled air dispersion distances and directions through two different face masks (Respironics; Murrysville, PA) attached to a human-patient simulator (HPS) during noninvasive positive-pressure ventilation (NPPV) in an isolation room with pressure of −5 Pa.MethodsThe HPS was positioned at 45° on the bed and programmed to mimic mild lung injury (oxygen consumption, 300 mL/min; lung compliance, 35 mL/cm H2O). Airflow was marked with intrapulmonary smoke for visualization. Inspiratory positive airway pressure (IPAP) started at 10 cm H2O and gradually increased to 18 cm H2O, whereas expiratory pressure was maintained at 4 cm H2O. A leakage jet plume was revealed by a laser light sheet, and images were captured by high definition video. Normalized exhaled air concentration in the plume was estimated from the light scattered by the smoke particles.FindingsAs IPAP increased from 10 to 18 cm H2O, the exhaled air of a low normalized concentration through the ComfortFull 2 mask (Respironics) increased from 0.65 to 0.85 m at a direction perpendicular to the head of the HPS along the median sagittal plane. When the IPAP of 10 cm H2O was applied via the Image 3 mask (Respironics) connected to the whisper swivel, the exhaled air dispersed to 0.95 m toward the end of the bed along the median sagittal plane, whereas higher IPAP resulted in wider spread of a higher concentration of smoke.ConclusionsSubstantial exposure to exhaled air occurs within a 1-m region, from patients receiving NPPV via the ComfortFull 2 mask and the Image 3 mask, with more diffuse leakage from the latter, especially at higher IPAP.

Single-particle-sensitive imaging of freely propagating ultracold atoms

We present a novel imaging system for ultracold quantum gases in expansion. After release from a confining potential, atoms fall through a sheet of resonant excitation laser light and the emitted fluorescence photons are imaged onto an amplified CCD camera using a high numerical aperture optical system. The imaging system reaches an extraordinary dynamic range, not attainable with conventional absorption imaging. We demonstrate single-atom detection for dilute atomic clouds with high efficiency where at the same time dense Bose–Einstein condensates can be imaged without saturation or distortion. The spatial resolution can reach the sampling limit as given by the 8 μm pixel size in object space. Pulsed operation of the detector allows for slice images, a first step toward a three-dimensional (3D) tomography of the measured object. The scheme can easily be implemented for any atomic species and all optical components are situated outside the vacuum system. As a first application we perform thermometry on rubidium Bose–Einstein condensates created on an atom chip.