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LIF/Mie ratio-metric imaging was used to characterize sprays produced by a simple hollow-cone pressure atomizer, operating under elevated ambient pressures up to 10 atm. A structured laser sheet was used as the source of illumination to suppress the multiple scattered light, generating images that are free of the artefacts typically found in conventional laser sheet images. The resulting LIF/Mie ratio-metric images were calibrated using Phase Doppler anemometry to generate axial planar maps of the spray’s Sauter-mean diameter (SMD). This calibration methodology was applied over a range of ambient pressures and liquid flows to assess the robustness of the structured LIF/Mie ratio-metric imaging as a droplet sizing technique. The test fluids consisted of conventional and alternative jet fuels as well as nozzle calibration fluid. Results presented in the paper indicate both the effectiveness and certain limitations of the technique.

To control the evolution of a pandemic such as COVID-19, knowing the conditions under which the pathogen is being transmitted represents a critical issue, especially when implementing protection strategies like social distancing and face masks wearing. For viruses and bacteria that spread via airborne and/or droplet pathways, this requires understanding how saliva droplets evolve over time after their expulsion by speaking or coughing. Within this context, the transition from saliva droplets to solid residues, due to water evaporation, is studied here both experimentally, considering the saliva from 5 men and 5 women, and via numerical modeling to accurately predict the dynamics of this process. The model assumes saliva to be a binary water/salt mixture and is validated against experimental results using saliva droplets that are suspended in an ultrasound levitator. We demonstrate that droplets with an initial diameter smaller than 21 μm will produce a solid residue that would be considered an aerosol of

The implementation of high-pressure oxy-fired systems presents unique challenges to burner and combustor design. For the same throughput as an atmospheric or low-pressure system, high-pressure reactors have a much smaller footprint, and consequently the injectors, mixers, and combustion chambers are reduced in size. Adequate burner performance, heat dissipation, and solids handling are therefore challenging, especially at the pilot scale. CanmetENERGY−Ottawa has developed an 80-barg pilot test facility for the development of a range of applications, including high-pressure gasification and combustion. As part of this endeavor, an optically accessible cold-flow rig was designed and built to replicate the geometry of the pilot-scale combustor. This article presents the layout of this 80-barg optically accessible vessel and results of a test program that examined sprays produced by three effervescent atomizers. Techniques applied to the near-injector region of the spray included laser sheet imaging (LSI), particle image velocimetry (PIV), and phase Doppler anemome-try (PDA). The effect of spray configuration, water flow, nozzle diameter, and ambient pressure were studied. Cone angle, successfully measured with LSI, varied between ≈ 4° and 16°. Both PIV and PDA successfully provided velocity measurements throughout the flow field. Relationships between droplet velocity and location were recorded. Droplet size at a fixed measurement plane was affected most by the velocity of the bulk mixture at the orifice exit. Results of this study provide insight into the robustness of the injectors and the potential effect of deviations from target operating conditions on burner performance for the pilot-scale system. The results provide necessary input data for computational fluid dynamics models of the system in both cold and hot cases.

This paper is Part I in a series of articles focused on a fundamental study on liquid jet disintegration. The main goal of this work is to provide an extensive open access database of high-speed images and videos for modelers and researchers in the field of fluid mechanics studying the dynamics of a liquid jet transiting from the Rayleigh to the atomization regimes. The injector under examination has a single orifice 0.60 mm in diameter and was used to inject water into quiescent air at atmospheric temperature and pressure. In this study, only the liquid injection pressure was varied, reaching a maximum Reynolds number of approximately 60 000. Historically, high-speed videos of liquid jet disintegration have been captured via shadowgraphy imaging techniques. The alternate approach proposed here employs photographing a fluorescing liquid, using Laser Induced Fluorescence (LIF) allowing us to deduce the volume of the imaged liquid structures. The experiment is divided into two parts. In the first portion, the interrogation area measures a distance of 160 mm along the jet, and includes sets of ~800 images, recorded at 40 000 frames per second, corresponding to a temporal resolution of 25 µs. In the second part, the viewable area was reduced to 28 mm, and ~400 images were recorded at 50 000 frames per second resulting in a temporal resolution of 20 µs. This configuration enabled the finer structures of the jet to be resolved. In this case, two high-speed cameras orientated at 90˚ are used to simultaneously image the liquid jet. This two-angle detection configuration allows for the identification and more accurate account of the irregular liquid bodies formed in the jet. Descriptions of the optical arrangements, operating conditions, and the image post-processing methodologies used to obtain quantitative measurements of liquid depths from the LIF signal have been outlined. The resulting temporally resolved high-speed image series are openly downloadable on the website: https://spray-imaging.com/water-jet.html or alternatively on Open Science Framework at: https://doi.org/10.17605/OSF.IO/CG3DF

The National Jet Fuel Combustion Program (NJFCP) is an initiative, currently being led by the Office of Environment & Energy at the FAA, to streamline the ASTM jet fuels certification process for alternative aviation fuels. In order to accomplish this objective, the program has identified specific applied research tasks in several areas. The National Research Council of Canada (NRC) is contributing to the NJFCP in the areas of sprays and atomization and high altitude engine performance. This paper describes work pertaining to atomization tests using a reference injection system. The work involves characterization of the injection nozzle, comparison of sprays and atomization quality of various conventional and alternative fuels, as well as use of the experimental data to validate spray correlations. The paper also briefly explores the application viability of a new spray diagnostic system that has potential to reduce test time in characterizing sprays. Measurements were made from ambient up to 10 bar pressures in NRC’s High Pressure Spray Facility using optical diagnostics including laser diffraction, phase Doppler anemometry (PDA), LIF/Mie Imaging and laser sheet imaging to assess differences in the atomization characteristics of the test fuels. A total of nine test fluids including six NJFCP fuels and three calibration fluids were used. The experimental data was then used to validate semi-empirical models, developed through years of experience by engine OEMs and modified under NJFCP, for predicting droplet size and distribution. The work offers effective tools for developing advanced fuel injectors, and generating data that can be used to significantly enhance multi-dimensional combustor simulation capabilities., ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, Monday 11 June 2018, Oslo, Norway

2018 AIAA Aerospace Sciences Meeting, 8–12 January 2018, Gaylord Palms, Kissimmee, Florida, USA

This paper presents an investigation of the spatial droplet distribution around a rotary atomizer in an air cross flow. The droplet size, velocity, and spray distribution were measured using a phase Doppler particle analyzer system. The spray was photographed using a high-speed camera. The rotary atomizer was driven at speeds of 5000 rpm, 10,000 rpm, and 15,000 rpm. The fuel flow rate was held constant at 15 kg/h, and the air cross-flow velocities varied from 25 m/s to 150 m/s. The overall spray shape was observed to shrink toward the axis of rotation with increasing cross-flow speeds. High-speed visualization showed that the injected ligaments disintegrate into fairly large droplets and spread out in the radial direction at lower cross-flow velocities. At higher cross-flow speeds, the injected ligaments are abruptly deflected and broken up in the downstream direction close to the surface of the atomizer and are mixed with the cross-flow air stream immediately. The axial velocity profile indicates that a strong recirculation zone is formed just below the rotating nozzle. A high tangential velocity is shown to exist close to the injection point. Further downstream, the radial velocity component is shown to be dominant, while the tangential velocity becomes weak. The axial velocities show similar trends for the same cross-flow velocities, as the droplets follow the dominant air stream formed by the cross flow regardless of rotational speed. Near the injection orifice, relatively larger droplets are concentrated in a narrow region close to the radius of the atomizer. As the liquid jet travels downstream, the droplets are dispersed by the cross flow and distributed over a wider area. The cross flow influences the Sauter mean diameter directly; however, the rotational speed of the nozzle only has a large effect on the spray at slower cross-flow conditions. This injector design is shown to have a circumferential uniformity of ±4 μm, making it an acceptable choice for combustion applications. © 2012 by Begell House, Inc.

The splitting of the airflow that passes through the openings in the combustor liner is vital to its performance. Traditionally, numerical simulations of the gas turbine combustor have limited the computational domain to only the flow field inside the liner, while the airflow distribution over the liner is estimated based on semi-empirical correlations. In addition, the airflow rates are assumed to be the same through the identical open passages at each combustor axial cross-section. In the present study, the internal and external flow fields of a practical gas turbine combustor liner are directly coupled, so the air splitting is determined by comprehensive simulations. The predicted results for the air distribution are closely correlated to the dataset estimated from recently improved semi-empirical correlations for passage discharge-coefficients. The simulations also show that the effects of the combustion process on the air splitting can be neglected. Lastly, the results reveal that the airflow through identical passages at the same axial cross-section are not equal, and can vary by up to ±25% of the mean. In summary, the present study suggests that when performing computational models of gas turbine combustor flows, the simulations should couple the liner’s internal and external air splits whenever possible., ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, June 16-20, 2014, Düsseldorf, Germany

This paper presents an experimental investigation of fuel sprays generated by a rotary atomizer exposed to a cross flow of air. The effects of two variables, the rotational speed and cross-flow velocity, on the droplet sizes were studied. The rotary atomizer was driven at speeds up to 15,000 rpm with a fuel flow rate of 15 kg/h and cross flow from 10 to 150 m/s. For any given rotational speed, the fuel droplet sizes decreased as the air cross flow increased, reaching an almost constant value of about 8 μm at 150 m/s cross-flow velocity. At cross-flow velocities less than about 50 m/s, the fuel droplet sizes decreased as the rotational speed increased. However, at a cross-flow velocity greater than 100 m/s, the fuel droplet sizes did not changed significantly as the rotational speed increased. Of the two variables studied, each influenced the droplet size differently in a certain cross-flow velocity region. The rotational speed influenced the droplet size at relatively low cross-flow velocity. By exceeding a cross-flow velocity of 75 m/s, the dynamic effect of high-speed cross flow became dominant. This effect can be generalized to the Weber number based on the orifice diameter and the non-dimensional droplet size. In this correlation, the following three distinct spray regimes were identified according to the Weber number based on orifice diameter: rotation dominant, intermediate, and cross flow dominant. © 2012 by Begell House, Inc.