Turbulence modulation effects caused by small droplets using one-dimensional-turbulence
Doktorsavhandling, 2020

This thesis presents a stochastic model to study turbulence modulation effects on gas phases caused by small droplets or more generally speaking particles to achieve a better understanding about the physics and with the aim to provide data for a subgrid-scale (SGS) model for Large-eddy-simulations. The one-dimensional-turbulence (ODT) model addresses one of the major issues for multiphase flow simulations, namely computational costs. It is a dimension-reduced model resolving all turbulent time and length scales and reaching parameter ranges, which are inaccessible for Direct-Numerical-Simulations (DNS). ODT is a stochastic model simulating turbulent flow evolution along a notional one-dimensional line of sight by applying instantaneous maps which represent the effect of individual turbulent eddies on property fields.

For an efficient investigation of turbulence modulation effects, ODT has been extended in this thesis in many ways. First, the Lagrangian particle tracking method developed by Schmidt et al. was modified for spatial, cylindrical flow simulations. Therefore, the two-way coupling mechanism was extended as well. This case serves to study the overall influence of particles on a jet configuration, which conforms with the droplet-laden flow in the dilute region of a spray. Here, the most significant effects are expected. Secondly, a concept for developing a SGS model is presented. Based on this concept, ODT was modified to capture two canonical test cases of stationary, forced isotropic turbulence (HIT) and homogeneous shear turbulence (HST). For this purpose, a forcing scheme that maintains statistical stationarity and a new energy redistribution mechanism during  the eddy events are introduced. The latter enables ODT to predict anisotropic turbulent structures. ODT is validated against several data sets of DNS studies and showed its capability to access parameter ranges beyond previous limits. It turned out to have a lot of potential to contribute to a SGS closure of LES for turbulence modulation caused by small droplets.

Multiphase Flow

Turbulence

one-dimensional-turbulence (ODT)

Droplets

Opponent: John C. Hewson, Fire Science and Technology Department, Sandia National Laboratories, USA

Författare

Marco Fistler

Chalmers, Mekanik och maritima vetenskaper, Förbränning och framdrivningssytem, Förbränning och sprejer

Numerical studies of turbulent particle-laden jets using spatial approach of one-dimensional turbulence

28TH CONFERENCE ON LIQUID ATOMIZATION AND SPRAY SYSTEMS, ILASS-EUROPE 2017,; (2017)p. 83-89

Paper i proceeding

Turbulence modu- lation in particle-laden stationary homogeneous shear turbulence using one- dimensional turbulence, M. Fistler, A. Kerstein, S. Wunsch and M. Oevermann, submitted to Physical Review Fluids.

One-dimensional turbulence modeling for cylindrical and spherical flows: model formulation and application

Theoretical and Computational Fluid Dynamics,; Vol. 32(2018)p. 495-520

Artikel i vetenskaplig tidskrift

Around 30% of the global energy consumed for our economies is still produced by burning liquid fuel. For reaching the goal to lower the overall CO2emissions to decay or stop global warming, significant improvements in the combustion process are necessary. Therefore, this thesis aims to partially improve simulation frameworks predicting the fuel injection system to provide a better understanding of the physical mechanisms and to finally optimize the process itself.

In particular, we focus on the momentum and energy exchange between small droplets and the gas phase surrounding them. Because a very detailed assessment of this exchange is computationally very expensive, an approach is presented to bridge the gap between highly-detailed and affordable simulation frameworks, utilizing a dimension-reduced approach called one-dimensional-turbulence (ODT).

This thesis presents the modifications of the ODT approach to capture the desired exchange between small droplets and the gas phase. Additionally, it points out the opportunity ODT is giving to improve the current state-of-the-art frameworks, which are used to simulate the entire injection process.

The final outcome can serve as the foundation for many extension to study e.g. a wider variety of flows or different droplet properties. All of these studies will lead to a better understanding of the injection itself and will enable us to emit less exhaust gases.

Ämneskategorier

Teknisk mekanik

Annan fysik

Strömningsmekanik och akustik

ISBN

978-91-7905-350-5

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4817

Utgivare

Chalmers tekniska högskola

Online

Opponent: John C. Hewson, Fire Science and Technology Department, Sandia National Laboratories, USA

Mer information

Senast uppdaterat

2020-08-20