Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session U35: Atomization and Sprays III |
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Chair: Theodore Heindel, Iowa State University Room: 243 |
Tuesday, November 22, 2022 8:00AM - 8:13AM |
U35.00001: A quantitative analysis of atomization mechanisms from high-fidelity simulations Brendan V Christensen, Mark F Owkes Recent advances in computational efficiency and numerical methods have allowed researchers to simulate atomizing liquid systems. These simulations have yet to result in a significantly deeper understanding of the underlying processes of atomization. The primary obstacle limiting simulations' usefulness is the massive size of resultant datasets, which contain millions to billions of spatial cells per timestep and can fill hundreds of terabytes of storage. The present work focuses on utilizing a methodology to extract relevant information from simulations, as they run, to produce easily accessible databases full of novel, statistically relevant information. This methodology will be applied to two simulations. First, a diesel-type high-pressure round jet injected into quiescent air. And second, an air-blast atomizing round jet. Novel statistics describing the local flow fields and droplet characteristics from breakup events throughout these simulations will be processed and compared. Special consideration will be given to comparing the two jets for an analysis of the effects of aerodynamic stresses on liquid breakup. This work will result in a foundation for future higher-resolution studies of jets and the development of new physics-based reduced-order atomization models. |
Tuesday, November 22, 2022 8:13AM - 8:26AM Author not Attending |
U35.00002: The fluid mechanics of medical sprays: physics-informed design of low-emissions metered dose inhalers Daniel Duke, Lingzhe Rao, Harry N Scott, Paul Young, Damon Honnery, David Schmidt Pressurised metered dose inhalers (PMDIs) have been used for over 60 years to treat a range of respiratory conditions such as asthma. The microscale inhaled aerosol particles produced by these devices are generated through the flash-evaporation of a volatile propellant. Originally these were chlorofluorocarbons. They were replaced with hydrofluorocarbons (HFCs) by the early 2000s. The Kigali amendment to the Montreal Protocol is now phasing down the use of HFCs worldwide due to their high global warming potential. New propellants are again required. Given the expansive parameter space for pMDI design (droplet chemistry and nozzle design) and broad use cases, trial and error parametric product design is not cost effective or practical. A more nuanced understanding of the fluid mechanics of the pMDI are required to develop new products. We demonstrate how multiphase Large Eddy Simulations can be combined with synchrotron X-ray diagnostics, droplet evaporation models, laser diffraction and high speed imaging measurements to unravel the complex multi-physics problem of volatile propellant evaporation and guide the selection of new propellants, solvents and nozzle designs. We show that sonic flow phenomena and previously hidden standing evaporation wave in the core of the jet plays a dominant role in the primary atomisation process, and that manipulation of nozzle geometry can be used to offset the lower spray momentum of more environmentally friendly propellants with lower vapour pressures and densities. The outcomes of this research are being used to drive the design of new inhaled pharmaceutical products with 10x to 100x lower CO2-equivalent emissions with equivalent or even enhanced performance. |
Tuesday, November 22, 2022 8:26AM - 8:39AM |
U35.00003: Investigation of two-way coupled euler-lagrange spray simulations with swirl Jungyun Kim, Kai Liu, S Balachandar This work aims at the effect of inlet swirl on the turbulent inflow specification for Euler-Lagrange simulations. Euler-Lagrange simulations of the mid-field region of liquid sprays are performed of both the single-phase flow without injected droplets and two-phase simulations with injection model where droplets are injected to the computational domain. Two later set of simulations consider several different swirl strengths of ranging up to a non-dimensional value of 2.0 at an inlet jet Reynolds number of 50000. From time- and circumferential-averaged velocities, we obtain and investigate the effect of inlet swirl on the self-similar profiles of velocity and Reynolds stress for single-phase simulations and the normalized number flux, mean and standard deviation of droplet velocity distributions for two-phase simulations. The swirl effect on the behavior of spray and the radial distribution of the different sized droplets is quantified. |
Tuesday, November 22, 2022 8:39AM - 8:52AM |
U35.00004: An investigation on the influence of droplet deformation and internal circulation on drag coefficient Yushu Lin, John Palmore In this work, we use numerical approaches to investigate the effect of droplet deformation and internal circulation on droplet drag coefficient. In applications like spray combustion, droplets can be modeled as Lagrangian particles to reduce computational cost in simulations. A common starting assumption for the Lagrangian model is that droplets are spherical and have no internal flow. However, in spray, droplets are generated in a wide range of sizes, and the largest ones tend to have significant deformation which can fundamentally affect their behavior. Droplets are also subjected to high temperature and pressure, which enhances the internal circulation. Therefore, we need to improve the physical understanding of droplets to better predict the dynamics of droplets represented by Lagrangian particles. This work performs a numerical study on how the droplet drag coefficient is dependent on relevant parameters. We use DNS to simulate a non-evaporating droplet falling at terminal velocity in high pressure air. The drag coefficient is calculated, and the results are consistent with existing literature. Our study shows that droplet drag is increased by deformation and internal circulation. In addition, the acceleration effect of droplet lowers the actual drag compared to steady state. |
Tuesday, November 22, 2022 8:52AM - 9:05AM |
U35.00005: Data-driven surrogate modelling of drop-size distribution Tullio Traverso, Thomas Y Abadie, Omar K Matar, Luca Magri The accurate prediction of the drop size distribution (DSD) in liquid atomization and sprays is key to the optimization of multi-phase flows, from gas-turbine combustion, through agriculture to healthcare. The DSD is characterized from experiments and high-fidelity simulations, which provide data for surrogate modelling. With this data, we propose a multi-task Gaussian process regression (GPR) to model the DSD as a function of the spray angle, the Reynolds, and the Weber number of the jet. The prior knowledge of the approximate statistics of the distribution is embedded in the learning algorithm to provide physical predictions that conserve the total probability. We enforce conservation laws while reproducing the complex features of the surrogate model (i.e., a sharply peaked, long-tailed distribution) by including the uncertainty on the data. This model outputs predictions on the drop-size distribution with confidence intervals. The work opens up opportunities for data-driven surrogate modelling and optimization of atomizers. |
Tuesday, November 22, 2022 9:05AM - 9:18AM |
U35.00006: Modeling spray atomization by a hybrid Volume-of-Fluid Lagrangian-Eulerian approach Mario F Trujillo, Chia-Wei Kuo A hybrid Volume-of-Fluid Lagrangian-Eulerian (VoFLE) method for simulations of liquid jet atomization is presented. The solver is based on the combined use of the Volume-of-Fluid (VoF) method and the Lagrangian-Eulerian (LE) strategy. Compared with existing approaches, this work introduces a different way of implementing this hybrid method by considering the further hydrodynamic breakup of unstable unresolved elements. The calculation of breakup is based on a statistical model utilizing maximum entropy formalism conditional on mass, momentum, and energy conservation constraints. Three tests are implemented in this work. The first is a realistic Engine Combustion Network (ECN) Spray D configuration, which considers the needle, the nozzle, and the nozzle surface roughness effects. The second consists of the simplified ECN Spray A configuration where the needle and the nozzle surface roughness effects are ignored. The last test is associated with the breakup of a water jet injected from a canonical orifice under mild conditions, where the secondary breakup is absent. |
Tuesday, November 22, 2022 9:18AM - 9:31AM |
U35.00007: Adjoint-based Flow Control of Liquid-Gas Flows Modeled with a Sharp Interface Lam X Vu, Alexandru Fikl, Daniel J Bodony, Olivier Desjardins Spray formation plays a critical role in combustion systems where implementing control strategies can be highly beneficial. With advancements in numerical modeling of liquid-gas flows, we can now accurately predict complex two-phase flows. As a result, we are able to explore computational optimization strategies as an avenue for control. Adjoint methods are an efficient technique to calculate gradients because their cost is independent of the number of control variables. The gradients can then be input into a gradient optimization algorithm to solve the control problem. In this work, we present a computational adjoint method for incompressible, liquid-gas flows using a sharp interface. We verify our method by comparing adjoint calculated gradients against analytical gradients for canonical test cases. We then highlight the method's utility by controlling a temporally evolving liquid-gas mixing layer, a case that has relevance to spray formation. |
Tuesday, November 22, 2022 9:31AM - 9:44AM |
U35.00008: The Bombardier Beetle Fire Extinguisher: Development of a CFD Model to Simulate a Novel Firefighting Mechanism Elijah P Yoder, Wayne Strasser While modern fire extinguishers are adequate in extinguishing fires, they tend to have a short spray distance, a wide target area, and use chemicals that can harm humans. By creating a fire extinguisher that mimics the defense mechanism of the Bombardier Beetle, many of these downfalls can be corrected. When threatened, The Bombardier Beetle can facilitate a chemical reaction in its abdomen that builds pressure, eventually releasing the reactants at high velocities, high frequencies, and for long distances. This mechanism can be replicated in a fire extinguisher by vaporizing water in a pressure chamber. This would allow for fire to be fought from a safer distance, with a safer working fluid, and more effectively. To examine this effect, multiphase flow was simulated through an experimental chamber geometry using CFD. It was found that sufficient vaporization and pressure increase occurred to cause an increase in the velocity at the outlet. This proves that this technique can be viable as a mechanism in fire extinguishers. Various parameters of the model were modified to determine the presence of numerical diffusion. With the CFD model that minimizes numerical diffusion, pulsation, valve timing, and ejection mechanics should be investigated. |
Tuesday, November 22, 2022 9:44AM - 9:57AM |
U35.00009: Supersonic Spray Combustion Modeling for a Turbulent 3D Rotating Detonation Engine Model HyeJin Oh, Foluso Ladeinde In recent years, the rotating detonation engine (RDE) has been investigated extensively using experimental measurements and numerical simulations. One advantage of this type of engine is the pressure gain, which leads to higher propulsive force and efficiency when compared, for example, with the rocket engine. Most of the computational work has been based on premixed combustion. However, in a practical RDE, it is difficult to obtain premixed combustion, and undesirable issues such as flashback may occur. Therefore, the non-premixed case is of interest, where we focus on three-dimensionality, to complement our previous work, which has been based on two dimensional models. Furthermore, a liquid fuel is chosen to be mixed with ambient air. In our focus on airbreathing schemes, we develop a library for calculating the injection of a liquid state fuel into an ambient air stream and embed it to an existing high-accuracy CFD code. The physics of the flow, thermodynamic, and combustion variables are being investigated as functions of several critical non-dimensional parameters, using the explicit large-eddy simulation (LES) technique. Foundational results for several canonical conditions will be presented. |
Tuesday, November 22, 2022 9:57AM - 10:10AM |
U35.00010: CFD Modelling of Closed-Couple Gas Atomisation (CCGA) Process. Jo Samuel Joseph Subramanian, Andrew Mullis, Duncan Borman Eventhough gas atomisation process is the most viable method to produce metal powders, the process is chaotic, and extremely rapid, preventing a clear understanding of it. Due to this chaotic nature, the particle size and particle size distribution increases to a greater extent, making the process highly inefficient. Consequently, a huge amount of energy and capital is lost. In this research, CFD analysis is carried out to understand the instabilities present between the deep sub-ambient pressure formed in front of the melt nozzle tip known as aspiration pressure and the melt flow rate. Rapid variations in melt flow rate caused due to the change in aspiration pressure affects the particle size and particle size distribution. A two-phase flow is modelled using coupled Euler-Lagrange framework. Primary phase is Argon; Secondary phase is modelled as inert, constant diameter particles depicting the melt. The particles’ mass flow rate is coupled to the aspiration pressure using User-Defined Functions. This research confirms the presence of a pulsating flow field as postulated by TIng(2003), exhibiting repeated formation and disruption of a Mach disk causing fluctuation in aspiration pressure, which explains the rapid variations in melt flow rate and the chaotic nature of the process. |
Tuesday, November 22, 2022 10:10AM - 10:23AM Author not Attending |
U35.00011: Experimental investigation of spray from two-fluid nozzles: Universality of size distributions, dispersion of ethanol-water mixtures, and spray evaporation Moritz Sieber, Sebastian Schimek, Christian O Paschereit Within the scope of investigations on spray flame pyrolysis, the spray of different commercial two-fluid nozzles is investigated with phase doppler anemometry. The investigations cover a wide range of operating conditions where sprays with mean Sauter diameters in the order of 10 micrometres are produced from water-ethanol mixtures atomised with compressed air (Webber number > 10^3). |
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