Webinars

Making a Computational Splash: An Enhanced Volume-of-Fluid Framework for Multiscale Atomization Modeling

Liquid sprays surround us and play important roles in our daily lives, in obvious ways (taking a shower), in more subtle ways (drinking instant coffee produced via spray drying or driving a car powered via liquid fuel injection), or in more profound ways (with sea sprays playing a key part in ocean-atmosphere transfers impacting climate change). As such, we need to understand sprays better and for that we need to be able to predict how they form. Unfortunately, computational prediction of turbulent multiphase flows presents enormous challenges. This is especially true whenever break-up and topology changes happen, such as in spray formation, in part because of the wide range of length and time scales involved in the spray break-up process. In this work, we propose to tackle the challenge of high-fidelity modeling of liquid atomization with a novel multi-scale framework. New developments to the geometric volume of fluid method are presented that enable the tracking of sub-grid scale interfacial features. By reconstructing the liquid-gas interface with multiple planar surfaces, with paraboloids, or with cylindrical surfaces, we show that the small-scale ligaments and sheets that abound in spray formation can be represented accurately independently of mesh resolution while preserving exact conservation, excellent computational efficiency, and easy integration with finite-volume-based flow solvers. A consequence of such strategies is that lack of mesh resolution no longer induces topology change, which then need to be reintroduced explicitly using physics-informed models. We discuss various flavors of such models in the context of the break-up of thin liquid films, which are common features in aerodynamic liquid atomization, and show that this approach can accurately predict the size distribution of spray droplets even with limited resolution.

A comprehensive overview on the gaseous fuels jets investigation for a sustainable combustion process

The gradual decarbonization of means of transport is essential to achieve a sustainable mobility system, considering the sectors of road and off-road, industrial, naval and aeronautical transport. The contribution of a widespread, reliable and economical propulsion technology such as the internal combustion engine can be very important when using climate-neutral fuels, instead of conventional fossil fuels. Hydrogen and derived synthetic fuels (e-fuels) can play an important role in this area, making it possible to achieve zero CO2 emissions, similarly to the case of electric vehicles, and tailpipe polluting emissions with near-zero impact. Overall, engines fed by hydrogen and non-fossil synthetic fuels can provide a complementary solution to the electrification of part of transportation, being based on reliable, flexible and economical technology, contributing to a rapid transition towards zero CO2 emission mobility. Due to the possibility to apply different injection strategies as well as in-cylinder back pressures and temperatures, the comprehensive knowledge of gaseous injection process behavior and characteristics is fundamental for improving the combustion process in direct injection applications. In this context, the seminar will focus on the characterization of gaseous fuel jets in terms of mass flow rate and morphology under a wide range of engine-like conditions using injectors appropriate for direct injection applications. A measuring system, suitable for gaseous fuels, is used for measuring instantaneous and total flow rates as well as the dynamic behavior of the entire injection system. The spatial and temporal evolution of highly under-expanded gaseous jets is studied by the Z-type schlieren optical setup injecting into a constant-volume combustion vessel at typical engine conditions. The data can provide an useful database for the calibration of future numerical models for the simulation of the gaseous fuels direct injection process that could make it possible to give reliable results for the engine calibration to the full advantage of safety and development costs.

Marshall Award Talk - Conservative two-phase flow simulations using piecewise-quadratic interface reconstructions

Abstract: The volume-of-fluid (VOF) and moment-of-fluid (MOF) methods are widely regarded as state-of-the-art techniques for simulating atomization processes, largely because of their unique ability to conserve mass with machine precision. These methods traditionally employ piecewise-linear interface calculations (PLIC) to produce local geometric approximations of the interface that are used to calculate advective fluxes. However, this choice induces two key limitations: First, because the interface is approximated linearly, the transport of volume fractions is at best second-order accurate, while the estimation of curvature---and thus surface tension---is only zeroth-order accurate. Second, planar approximations often cannot adequately represent interfacial structures whose characteristic length-scales (e.g., radius of curvature or thickness) fall below the grid size. As a result, such features are prone to artificial numerical breakup or coalescence. This talk presents recent work on interface reconstruction using piecewise-quadratic surface patches, which aims to overcome both of these limitations. The effectiveness of these higher-order approximations is evaluated through convergence studies and advection test cases. Finally, we discuss extending the method to more general classes of implicit surfaces.

PERSPECTIVES ON “REFERENCE SPRAYS” FOR ALIGNING THE SPRAY COMMUNITY

Abstract: Cold-flow spray researchers have an array of diagnostic tools to extract meaningful information on spray characteristics. The efficacy of many of these tools depends heavily on calibration, alignment, and human operation. This can lead to large discrepancies in data values for seemingly identical setups between research groups. The application of experimental data to numerical models is thereby hindered due to inconsistencies in results caused by experimental error. Previously, an attempt was made to produce a “standard spray” termed the “research simplex atomizer (RSA)”. As manufacturing processes and diagnostic tools have improved, the research simplex atomizer has been revisited. In this webinar, the background behind the RSA is overviewed. In addition, example results from a new version of the RSA are presented. Such fundamental datasets captured from detailed test conditions can potentially provide benchmark data with the intention of other researchers testing the reproducibility of the results as well as validate CFD simulations. Preliminary findings between laboratories show good agreement in droplet size measurements and spray patterns. Such collaborations generate thought exercises when trying to explain differences between diagnostics intending to provide the same information about the spray. Finally, outlook for additional varieties of reference sprays is provided.

Aerodynamic Effect on Liquid Breakup

Abstract: Dr. Sallam’s presentation will examine both experimental and phenomenological analyses of liquid jet and sheet breakup, drawing inspiration from the seminal work of Prof. G.M. Faeth—under whom Dr. Sallam trained as one of his last Ph.D. students at the University of Michigan. By leveraging these methodologies, the study aims to elucidate the influence of injector geometry, liquid turbulence, and aerodynamic forces on atomization phenomena, with relevance to applications in liquid atomization, agricultural spraying, spray coating, and other industrial processes. The work employs shadowgraphy and holography to visualize and characterize flow structures, linking the resulting measurements to phenomenological theories that help quantify how aerodynamic forces drive both primary and secondary breakup mechanisms. The analysis covers the breakup regimes of liquid jets and sheets in stationary gases and in crossflow, highlighting critical Weber number thresholds and identifying the aerodynamic conditions that govern transitions between distinct breakup modes. By integrating experimental observations with robust phenomenological frameworks, this presentation provides a deeper understanding of atomization mechanisms and the dominant aerodynamic factors at play.

Towards H2ICE: Characterization of Hydrogen Injection, Mixing, and Combustion

Abstract: Hydrogen-fueled internal combustion engines (H2ICE) have great potential for future carbon-free transportation but have not yet reached production due to a number of technical challenges. One of the most important issues is the design of hydrogen injector systems that achieve rapid mixing to fuel-lean mixtures while also ensuring stable combustion without combustion anomalies such as pre-ignition and knocking. The ILASS community has been at the forefront of research on liquid injection systems and is now encouraging needed research on hydrogen injection. This presentation will provide an overview of ongoing FUELCOM4 project with KAUST and Saudi Aramco in an effort to enhance our knowledge in hydrogen injection, mixing, and combustion characteristics by utilizing high fidelity laser diagnostics and simulations. First, hydrogen jet injection and mixing characteristics are investigated in high pressure constant volume chamber experiment with accompanying simulations for validation. Jet penetration and dispersion characteristics depending on different injector configurations are examined. Recent development in advanced laser diagnostic technique to quantify the hydrogen fuel distribution is also discussed. Finally, parametric studies of the effects of jet dispersion and mixing on engine combustion characteristics are presented.

Overview of imaging diagnostics for the characterization of sprays and droplet fields

This talk provides an overview of the evolution of imaging diagnostics techniques applied to sprays and droplet fields. Sprays and particle fields have been extensively studied over the years, delivering in-depth understanding of the droplet formation processes and its evolution. Most of this knowledge was acquired by the development and application of numerous diagnostics, often made possible by the combined power of innovations in equipment and methods. Beginning with an exploration of early imaging techniques, this review traces the development of methodologies such as shadowgraphy, schlieren imaging, and holography. These foundational techniques paved the way for contemporary advanced imaging methods aiming at characterizing particle fields in high-speed flows, where the droplet field features smaller particle sizes and higher velocities. Continuing with the advancements brought up by new diagnostic technologies, we will also explore the impact that the evolution of hardware and data processing capabilities have brought to the field.

Application of CFD Spray Models to Accelerate Industrial Product Design

The industrial sector faces the formidable challenge of swiftly deploying products and services in a fiercely competitive landscape. To expedite product development, computational models have become increasingly indispensable, particularly in driving upfront design. Virtual tools are now being heavily relied upon to shorten product development timelines. The efficacy of these tools hinges upon their accuracy, turnaround time, and widespread deployment through well-vetted workflow practices. This webinar will delve into the application of CFD spray simulations for automotive combustion and electrification applications. The subject matter will elucidate how advanced models are validated and used to propel advanced research and expedite near-term product development within the nuances of an industrial environment. The webinar will feature a multitude of application use cases, showcasing the practical implementation of these cutting-edge techniques.