Flow regimes during fluid-filled crack propagation in elastic media: Applications to volcanology and magma flow within dykes

Scaled analogue experiments were conducted to explore the effect of magma flow regimes, characterised by the Reynolds number (Re), on the transit of magma through the lithosphere via fractures. An elastic, transparent gelatine solid (the crust analogue) was injected by a fluid (magma analogue) to create a thin, vertical, and penny-shaped crack that is analogous to a magma-filled crack (dyke). A vertical laser sheet fluoresced passive-tracer particles suspended in the injected fluid, and particle image velocity (PIV) was used to map the location, magnitude, and direction of flow within the growing dyke from its inception to its surface rupture. Experiments were conducted using water, hydroxyethyl cellulose (HEC) or xanthan gum (XG) as the magma analogue. The results suggest that Re has significant impact on the direction of fluid flow within propagating dykes: Re > 0.1 (jet-flow) is characterised by a rapid central rising fluid jet and downflow at the dyke margin, whereas Re < 0.1 (creeping flow) is characterised by broadly uniform velocities across the dyke plane. Re may be underestimated by up to two orders of magnitude if tip velocity rather than internal fluid velocity is used. In nature, these different flow regimes would affect the petrological, geochemical, geophysical, and geodetic measurements of magma movement, key information upon which reconstructions of volcanic plumbing system architectures and their growth are based.

Design of a High Uniformity Laser Sheet Optical System for Particle Image Velocimetry

Particle image velocimetry (PIV) is a non-contact, instantaneous and full-flow velocity measurement method based on cross-correlation analysis of particle image. It is widely used in fluid mechanics and aerodynamics. Laser sheet optical system is one of the key equipment of PIV, and it is an important guarantee to obtain high definition particle image. In the PIV measurement task of large low speed wind tunnel, in order to solve the problem of sheet light illumination uniformity of large size model and take into account the requirements of PIV technology on the thickness of the sheet light, a hybrid algorithm is used to design a high uniformity laser sheet optical system based on the theory of physical optics. The simulation results show that the size of the sheet light is 400 mm ×1 mm, the diffraction efficiency reaches 97.77%, and the non-uniformity is only 0.03%. It is helpful to acquire high-resolution images of particles in the full field of view. It also can be applied to a series of non-contact flow field measurement techniques such as plane laser induced fluorescence, filtered Rayleigh scattering and two-color plane laser induced fluorescence temperature measurement.

novel method to accurately align the laser sheet for planar and stereoscopic PIV

Several techniques including two-dimensional (2D) and three-dimensional (3D) calibration are used for the calibration of two-component two-dimensional (2C-2D) particle image velocimetry (PIV) and three-component two-dimensional (3C-2D) stereoscopic PIV (SPIV) systems. A major requirement of these techniques is to keep the calibration target exactly at the position of the laser sheet within the field of view (FOV), which is very difficult to achieve (Raffel et al., 2018). In 3C-2D SPIV, several methods offer different correction schemes based on the disparity between the FOV of two stereo cameras produced due to misalignment, to account for the misalignment error. These techniques adjust the calibration or the measured displacement field in different ways to reduce the error which may introduce an unintended error in the measurement position and/or velocity such as a bias in the measured three-component 3C displacements. This paper introduces a novel method to align the laser sheet with the calibration target so that the uncertainty in displacement measurements is minimal. Ideally, it should be of the order of the uncertainty associated with PIV measurement so that no ad hoc post-correction scheme is required.

Particle pair statistics of inertial particles at small separation using stereoscopic particle tracking

Particle pair statistics of inertial particles having average Stokes numbers of 2.1 and 14 are measured in isotropic turbulence at a Reynolds number of Reλ = 240. The radial distribution function (RDF) and mean relative approach velocity are obtained at small separation distances using 2-frame stereoscopic particle tracking velocimetry (stereo-PTV). At small separation distance, the RDF varies by an order of magnitude in the range of Stokes numbers investigated. However, the mean relative approach velocity is found to have a weak dependence on Stokes number. The results are shown to have high accuracy when compared to analogous mono-PTV datasets, and can be used to provide a more reliable estimate of the inter-particle collision rate. The main limitation of the measurement is observed at separation distances less than the laser sheet thickness, where the technique tended to underestimate the mean relative approach velocity.

High Speed OH PLIF Measurements of Combustor Effusion Films in a High Pressure, Liquid Fueled Combustor

This paper presents measurements of 10 kHz OH planar laser induced fluorescence (PLIF) with an objective to study the interaction of effusion cooling with the flame and hot combustion products in the liquid fueled combustor. The combustor rig is a single sector representation a rich-burn/quick-quench/lean-burn (RQL) configuration. It consists of a swirl nozzle, dilution, and effusion jets. The rig is operated under realistic aircraft conditions, including elevated combustor inlet temperature, and elevated pressure. The PLIF laser sheet was arranged perpendicular and parallel to the liner at distinct liner locations. Parametric variations of important parameters, namely equivalence ratio, and effusion cooling air blowing ratio are conducted to investigate their effect on flame-effusion jet interactions. The PLIF images were analyzed using several data reduction techniques to de-noise the images and identify patterns in the effusion jet-flame interactions. Results show that the effusion jets are highly unsteady, interacting strongly with the turbulent flame from the swirl nozzle and the dilution jets. This work is an extension of recent effusion film mixing studies that were performed with acetone PLIF under non-reacting conditions.

Influence of Atomization Characteristics on Lean Blow-Out Limits in a Gas Turbine Combustor

In order to investigate the effects of atomization characteristics on the lean blow-out (LBO) performance, an experimental study was carried out on the spray and the combustion. The LBO limits and the outlet temperature near the LBO condition of different atomizers were measured in a single dome rectangular model combustor with a dual-radial and a dual-axial swirl cup, respectively. In the combustor, the spray analysis was performed on different atomizers (without combustion) at the LBO condition. The Malvern particle size analyzer was used to measure the Sauter Mean Diameter (SMD), and the laser sheet was used to take spray images. First of all, the spray pattern determines the minimum heat release required to maintain the combustion, which corresponds to the ideal LBO fuel/air ratio (FAR), which is the maximum potential for the lean combustion. Secondly, the matching of the spray SMD, the droplet size spatial distribution and the droplet initial velocity with the flow field determines the ratio of the completely burned fuel to the total fuel ejected from the atomizer, which determines the extent to which the combustor exerts its lean combustion potential. In addition, the numerical simulation of the flow field of the combustor with two structures was carried out, which provided an important basis for the theoretical analysis of this paper.

Evaluation of High Flow Local Extraction on control of the aerosol plume in an operating theatre

Background Engineering controls are a necessity for minimising aerosol transmission of SARS-CoV-2, yet so far, little attention has been given to such interventions. High flow local extraction (HFLE) is a standard in other industries that deal with airborne contaminants. This study provides a quantitative evaluation of an HFLE concept feasible to implement in most real clinical settings. Method A unique combined experimental model of Laser sheet illumination videography paired with continuous nanoparticle counts was used to quantitatively assess the impact of HFLE in an operating theatre. Propylene Glycol was aerosolised via a customised physiological lung simulator and dispersion was measured in 3 dimensions. Cumulative probability heat maps were generated to describe aerosol behaviour. Continuous particle counts were made at 15 locations throughout the room to validate laser assessments. Results HFLE effectively reduced dispersion of simulated exhaled aerosols to undetectable levels. With the HFLE in operation and optimally positioned, the aerosol plume was tightly controlled. Particle counts remained at baseline when HFLE was active. HFLE becomes less effective with increasing distance from source. Plume behaviour in the absence of HFLE was highly variable and unpredictable. Conclusions This analysis demonstrates great potential for HFLE to have a significant impact in reducing aerosol transmission. Simple HFLE devices can be easily engineered and could be widely deployed without impacting on the safe delivery of care. Keywords: aerosol; high flow local extraction; aerosol-generating procedure; tracheal intubation; SARS-CoV-2; COVID-19; plume; personal protective equipment; engineering controls

Sizing of airborne particles in an operating room

Medical procedures that produce aerosolized particles are under great scrutiny due to the recent concerns surrounding the COVID-19 virus and increased risk for nosocomial infections. For example, thoracostomies, tracheotomies and intubations/extubations produce aerosols that can linger in the air. The lingering time is dependent on particle size where, e.g., 500 μm (0.5 mm) particles may quickly fall to the floor, while 1 μm particles may float for extended lengths of time. Here, a method is presented to characterize the size of <40 μm to >600 μm particles resulting from surgery in an operating room (OR). The particles are measured in-situ (next to a patient on an operating table) through a 75mm aperture in a ∼400 mm rectangular enclosure with minimal flow restriction. The particles and gasses exiting a patient are vented through an enclosed laser sheet while a camera captures images of the side-scattered light from the entrained particles. A similar optical configuration was described by Anfinrud et al.; however, we present here an extended method which provides a calibration method for determining particle size. The use of a laser sheet with side-scattered light provides a large FOV and bright image of the particles; however, the particle image dilation caused by scattering does not allow direct measurement of particle size. The calibration routine presented here is accomplished by measuring fixed particle distribution ranges with a calibrated shadow imaging system and mapping these measurements to the in-situ imaging system. The technique used for generating and measuring these particles is described. The result is a three-part process where 1) particles of varying sizes are produced and measured using a calibrated, high-resolution shadow imaging method, 2) the same particle generators are measured with the in-situ imaging system, and 3) a correlation mapping is made between the (dilated) laser image size and the measured particle size. Additionally, experimental and operational details of the imaging system are described such as requirements for the enclosure volume, light management, air filtration and control of various laser reflections. Details related to the OR environment and requirements for achieving close proximity to a patient are discussed as well.