Begell House Inc.
Atomization and Sprays
AAS
1044-5110
23
11
2013
ON SIMULATING PRIMARY ATOMIZATION
v-ix
10.1615/AtomizSpr.2013010013
Marcus
Herrmann
School for Engineering of Matter, Transport and Energy, Arizona State University, P.O. Box 876106, Tempe, AZ 85287-6106, USA
primary atomization; simulation; modelling
The prediction of the initial breakup of injected liquids to form sprays remains, to date, an unsolved problem. While progress has been made in recent years to develop experimental techniques to help study the dynamics of the phase interface during the primary atomization process, spatial and temporal resolution constraints remain a challenge. On the other hand, significant advances in both numerical methods and available computational resources have enabled simulations to emerge as a viable tool to study primary atomization, help in the derivation and verification of new classes of atomization models, and even serve as a predictive tool in engineering applications. The purpose of this and a subsequent special issue of Atomization and Sprays is to provide an overview of the current state of the art in this emerging field of primary atomization research.
TOWARD USING DIRECT NUMERICAL SIMULATION TO IMPROVE PRIMARY BREAK-UP MODELING
957-980
10.1615/AtomizSpr.2013007439
Francois-Xavier
Demoulin
CORIA-UMR 6614 – Normandie Université, CNRS-Université et INSA de
Rouen, Campus Universitaire du Madrillet, 76800 Saint Etienne du Rouvray,
France
Julien
Reveillon
CORIA-UMR 6614 – Normandie Université, CNRS-Université et INSA de
Rouen, Campus Universitaire du Madrillet, 76800 Saint Etienne du Rouvray,
France
Bernard
Duret
UMR6614-CORIA, Technopole du Madrillet, BP 12, Avenue de l'Universite, 76801 Saint-Etienne du Rouvray Cedex, France
Zakaria
Bouali
ISAE-ENSMA / Pprime Institute
P.
Desjonqueres
UMR 6614 CNRS CORIA, Rouen University, bp 12−Site universitaire du Madrillet, 76801 St Etienne du Rouvray, France
Thibaut
Menard
CNRS, CORIA UMR 6614, University of Rouen, Technopole du Madrillet, BP 12, 76801 Saint- Etienne-du-Rouvray Cedex, France
spray
atomization
direct numerical simulation
modeling
two-phase flows
interface
This paper focuses on the use of direct numerical simulation (DNS) in the context of spray atomization modeling. Key features of such liquid/gas simulations, which are necessary for confidence in model accuracy, are recalled and discussed together with their inherent limitations. Particular attention is given to the lack of theories relating to the determination of the smallest length scale in turbulent liquid-gas flows. To demonstrate how direct numerical simulation can serve modeling purposes, this paper discusses three major areas of possible applications of DNS. First, DNS databases were created to validate modeling approaches inflow areas where no experimental measurements are available. In this paper, this approach is applied to diesel injection conditions to validate the Eulerian−Lagrangian spray atomization (ELSA) model. Second, because models are necessary to mitigate computational costs, which constitute the main drawback of DNS, this paper proposes the development of a large eddy simulation formulation of the liquid atomization, thereby enabling results that are no longer mesh resolution dependent. Finally, once the large scale is correctly captured, it is necessary to ensure an accurate representation of the liquid structure falling below the subgrid scale. To this end, a source term for the surface density equation is established based on direct numerical simulations of liquid-gas flows embedded in an isotropic turbulence and covering both dense and moderately dense ranges.
AN INVESTIGATION ON THE BREAKUP OF UNDERWATER BUOYANT OIL JETS: COMPUTATIONAL SIMULATIONS AND EXPERIMENTS
981-1000
10.1615/AtomizSpr.2013007484
Leandre R.
Berard
Department of Mechanical Engineering, University of Massachusetts-Dartmouth
Mehdi
Raessi
Department of Mechanical Engineering, University of Massachusetts-Dartmouth
Michael T.
Bauer
Department of Mechanical Engineering, University of Massachusetts-Dartmouth
Peter
Friedman
University of Massachusetts Dartmouth
Stephen R.
Codyer
Department of Mechanical Engineering, University of Massachusetts-Dartmouth
underwater buoyant oil jets
jet breakup
primary atomization
immiscible plumes
underwater oil spill
GPU acceleration
We present experimental and computational results on the breakup of underwater buoyant oil jets and plumes at a wide range of Reynolds, Weber, and Richardson numbers and viscosity ratios. The results show three main jet breakup regimes: atomization, skirt-type, and pinch-off. The threshold Weber number for the atomization regime is around 100, which varies slightly with the jet Eotvos number. Furthermore, it is demonstrated that the correlation proposed by Masutani and Adams as the boundary for the atomization regime applies to our broader data set too. The experimental and computational results both suggest that in a buoyancy-driven jet breakup occurs only when the jet is accelerated to a point where the local Richardson number, defined based on properties at breakup, becomes less than 0.4, in which case the local Weber number is above 10. The computational results reveal the mechanisms leading to formation of small droplets around the perimeter of energetic jets and umbrella-shaped jet separations at less energetic cases. The time-averaged lateral expansion of the simulated jets, representing four different conditions, is presented as a function of the height along the jet. The computational results were obtained by using a GPU-accelerated MPI parallel two-phase flow solver, which provides acceleration factors between 3 to 6, compared to running on CPUs only.
DIRECT NUMERICAL AND LARGE-EDDY SIMULATION OF PRIMARY ATOMIZATION IN COMPLEX GEOMETRIES
1001-1048
10.1615/AtomizSpr.2013007679
Olivier
Desjardins
Sibley School of Mechanical and Aerospace Engineering, Cornell University, 250 Upson Hall, Ithaca, NY 14853, USA
Jeremy
McCaslin
Sibley School of Mechanical and Aerospace Engineering Cornell University 245 Upson Hall, Ithaca, NY 14853 USA
Mark
Owkes
Department of Mechanical and Industrial Engineering, Montana State
University, Bozeman, MT, 59717-3800, USA
Peter
Brady
Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, New York 14853-7501, USA
multiphase flow
primary atomization
direct numerical simulation
large-eddy simulation
interface capture
conservative level set
immersed boundaries
A detailed understanding of the driving mechanisms behind primary atomization is crucial to the optimization of sprays for efficient combustion in modern propulsion systems. Many challenges are associated with simulating realistic turbulent atomization, such as the multiplicity of length and time scales of the turbulent flow field and gas-liquid interface, discontinuous fluid properties and pressure at the phase interface, high density ratios that degrade numerical robustness, and complex shapes of spray injectors. These challenges have hindered progress in computational modeling of atomizing two-phase flows, and as a result a complete characterization of all physical processes involved in turbulent atomization has remained elusive. This paper presents a suite of computational tools that have been developed in an effort to simulate primary atomization from first principles. The incompressible Navier-Stokes equations are handled in the context of a high-order accurate, discretely conservative, finite difference solver shown to be ideally suited for direct numerical and large-eddy simulations of turbulence. A conservative level set method is used for interface capture, improved through the use of local re-initialization enabled by an efficient fast marching method. A high-density ratio correction algorithm is employed that leads to tighter coupling between mass and momentum transport. Finally, the use of immersed boundaries allows for modeling of complex geometries without requiring body-fitted meshes, eliminating time spent generating complex grids. The framework outlined herein is shown to have the ability to capture important instabilities for atomizing flows, such as Rayleigh-Plateau and Kelvin-Helmholtz instabilities. Simulations of air-assisted breakup of both planar and coaxial liquid layers are shown to agree well with theoretical and experimental results. This strategy is employed to simulate the breakup of a turbulent liquid jet under diesel conditions, the atomization of a liquid sheet issued from a pressure swirl atomizer, and finally a complete dual-orifice atomizer, leading to qualitative insights on the atomization process. Detailed parallel scaling results are also provided.
HIGH-FIDELITY SIMULATION OF FUEL ATOMIZATION IN A REALISTIC SWIRLING FLOW INJECTOR
1049-1078
10.1615/AtomizSpr.2013007395
Xiaoyi
Li
United Technologies Research Center, East Hartford, Connecticut, 06108, USA
Marios
Soteriou
United Technologies Research Center
primary atomization
liquid breakup
two-phase
incompressible flow
level set
volume of fluid
ghost fluid
AMR
embedded boundary
DNS
Fuel injectors relevant to aerospace combustors exploit geometrical complexity to generate the aerodynamic forces that atomize the fuel and achieve the fuel-air mixing that enhances the combustion process. Detailed experimental analysis of the multiphase flow occurring in these injectors remains a challenge due to the extreme operating conditions, the geometrical complexity, and the challenges posed by dense spray measurements. High-fidelity, first-principles simulation offers an alternative analysis approach. Thus far, such simulations have been restricted to canonical problems with benign operating conditions. In this work, we present and apply a numerical framework that enables the simulation of a realistic multinozzle/swirler injector. This framework leverages the coupled level set and volume-of-fluid methodology for capturing the liquid−gas surface, the ghost fluid algorithm for reproducing the surface discontinuity, adaptive mesh refinement for efficiently resolving the surface features, Lagrangian droplet models for treating the smallest droplets, and an embedded boundary algorithm to flexibly handle the geometry. Optimization of this framework on massively parallel systems is discussed and so is its validation using the canonical problems of impinging liquid jets and liquid jet in crossflow. Results from the realistic injector simulations are presented, with emphasis on demonstrating the validity and feasibility of the approach via comparisons with experimental evidence. Moreover, it is shown that for the conditions simulated, the liquid jet atomization inside the swirling flow approximates that of a liquid jet in plain crossflow and that filming on the injector walls is minimal. Comparisons against coarse grid simulations indicate that in the latter case the flow fine scale features are compromised but jet penetration and breakup location are not.