The One-Dimensional Turbulence Model Applied to Spray Atomization
Doctoral thesis, 2018
Numerical simulation of the spray behavior is an important part of engine research and is critical for combustion optimization. Successful implementation of the advanced modeling tools for sprays is strongly dependent on our current understanding of the physical processes involved. One of the main processes occurring close to the nozzle is primary atomization. It governs the initial size and velocity distribution of droplets formed at the liquid jet surface. This process is not yet fully understood due to challenges in experimental observation of the region close to the nozzle. This has kept the primary atomization as one of the least developed model components in spray simulation and in need of mprovement.
In this dissertation, a new primary atomization model is proposed based on the One-Dimensional Turbulence (ODT) model framework. ODT is a stochastic turbulence model simulating turbulent flow evolution along a notional 1D line of sight by applying instantaneous maps to represent the effect of individual turbulent eddies on property profiles. This approach provides affordable high resolution at the liquid/gas interface, which is essential for capturing the local behavior of the breakup process.
This new approach is assessed under different operating conditions parameterized by the liquid jet Reynolds and Weber numbers. ODT primary atomization results have been provided as an input to a spray model in conventional form to evaluate its predictive capability. These efforts are reported in several manuscripts attached to this dissertation.
Furthermore, to better understand the physics behind primary atomization, a canonical simulation configuration is developed that isolates the interaction between surface tension and surrounding turbulence. The ability of the model to capture the breakup is assessed with the available Detailed Numerical Simulation (DNS) data for further improvements.
Lastly, a new strategy is proposed to use ODT as a subgrid resolution model in LES/VOF simulations to describe/model unresolved subgrid interface dynamics.
In this dissertation, a new primary atomization model is proposed based on the One-Dimensional Turbulence (ODT) model framework. ODT is a stochastic turbulence model simulating turbulent flow evolution along a notional 1D line of sight by applying instantaneous maps to represent the effect of individual turbulent eddies on property profiles. This approach provides affordable high resolution at the liquid/gas interface, which is essential for capturing the local behavior of the breakup process.
This new approach is assessed under different operating conditions parameterized by the liquid jet Reynolds and Weber numbers. ODT primary atomization results have been provided as an input to a spray model in conventional form to evaluate its predictive capability. These efforts are reported in several manuscripts attached to this dissertation.
Furthermore, to better understand the physics behind primary atomization, a canonical simulation configuration is developed that isolates the interaction between surface tension and surrounding turbulence. The ability of the model to capture the breakup is assessed with the available Detailed Numerical Simulation (DNS) data for further improvements.
Lastly, a new strategy is proposed to use ODT as a subgrid resolution model in LES/VOF simulations to describe/model unresolved subgrid interface dynamics.
Primary breakup
Turbulence
One Dimensional Turbulence(ODT)
HA2
Opponent: Professor. Mikhael Gorokhovski, École Centrale de Lyon, France
Author
Amirreza Movaghar
Chalmers, Mechanics and Maritime Sciences (M2), Combustion and Propulsion Systems
Parameter dependences of the onset of turbulent liquid-jet breakup
Journal of Fluid Mechanics,;Vol. 811(2017)
Journal article
Numerical investigation of turbulent-jet primary breakup using one-dimensional turbulence
International Journal of Multiphase Flow,;Vol. 89(2017)p. 241-254
Journal article
Sensitivity of VOF simulations of the liquid jet breakup to physical and numerical parameters
Computers and Fluids,;Vol. 136(2016)p. 312-323
Journal article
Modeling and numerical study of primary breakup under diesel conditions
International Journal of Multiphase Flow,;Vol. 98(2018)p. 110-119
Journal article
To have a clean and less polluted environment we need to have optimized and well-designed combustion systems for automotive transport. Most new engines today use direct injection of fuel, making the fuel spray breakup an important physical process. Fuel spray atomization and breakup has a major impact on engine performance and emissions. The fuel spray starts forming by disintegration and break-up of the liquid fuel jet just after injection. This initial breakup process is called primary breakup or primary atomization. The lack of proper predictive models for fuel spray primary breakup is strongly recognized in industrial applications. The current models often rely on crude assumptions and phenomenological modelling approaches leading to inaccurate predictions and time consuming model tuning.
The main objective of this study is the development of a new computational model for primary spray breakup that is both computationally efficient and more predictive than before. Here, we propose a new model for simulating and predicting primary jet breakup that is based on a stochastic one-dimensional approach, namely one-dimensional turbulence (ODT). The low computational costs of ODT compared to fully resolved three-dimensional Direct Numerical Simulation (DNS) overcomes the limitation of DNS to moderate Reynolds and Weber numbers and makes it a promising tool for industrial applications.
This thesis presents extensions to the ODT model to capture spray primary atomization and turbulence interface interactions. It covers the assessment process to validate and improve the model for different flow scenarios, from a simple configuration to a real engine conditions.
The main objective of this study is the development of a new computational model for primary spray breakup that is both computationally efficient and more predictive than before. Here, we propose a new model for simulating and predicting primary jet breakup that is based on a stochastic one-dimensional approach, namely one-dimensional turbulence (ODT). The low computational costs of ODT compared to fully resolved three-dimensional Direct Numerical Simulation (DNS) overcomes the limitation of DNS to moderate Reynolds and Weber numbers and makes it a promising tool for industrial applications.
This thesis presents extensions to the ODT model to capture spray primary atomization and turbulence interface interactions. It covers the assessment process to validate and improve the model for different flow scenarios, from a simple configuration to a real engine conditions.
Subject Categories
Aerospace Engineering
Applied Mechanics
Fluid Mechanics and Acoustics
ISBN
978-91-7597-730-0
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4411
Publisher
Chalmers
HA2
Opponent: Professor. Mikhael Gorokhovski, École Centrale de Lyon, France