Seminars

DCSE seminar on computational modeling of soot formation in flames

Tuesday, May 15, 2012

Delft University of Technology
Faculty of EEMCS, Snijder Room, Mekelweg 4, Delft

Organizer: Delft Centre for Computational Science and Engineering
Registration: Please send an e-mail to Deborah Dongor (D.M.Dongor@remove-this.tudelft.nl)
There is no registration fee

The modeling of soot formation in principle requires particularly complex chemical reaction kinetics. Important steps in soot formation from gas-phase hydrocarbons are formation of polycyclic aromatic hydrocarbons (PAH), soot inception and soot growth. Gas phase composition and temperature have a significant influence on these processes. The prediction of soot formation in practical systems requires the modeling of the coupling to fluid flow. To describe the influence of soot in turbulent flames, often semi-empirical models are used in the context of a statistical description of the flow.

In this DCSE seminar the detailed modeling of soot particle formation and growth and the modeling of laminar sooting flames is described in the lecture by Prof. Markus Kraft (University Cambridge). The modeling of sooting turbulent flames is considered in a presentation by Dr Michael Stoellinger (Delft University of Technology). The modeling of counteracting ring formation in rotary kilns is considered in a presentation by Michele Pisaroni.

http://ta.twi.tudelft.nl/nw/users/domenico/rotary_kiln/rotary_kiln.html

Markus Kraft is professor of Chemical Engineeering and head of the computational modelling group in the Department of Chemical Engineering and Biotechnology at the University of Cambridge.

http://como.cheng.cam.ac.uk/index.php?Page=People&Section=mk306

Program:

14:00-14.15
Arrival with coffee and tea
14:15-15:00
Markus Kraft
Title: Modelling soot formation: particle formation

Abstract:
Soot particles are formed from polycyclic aromatic hydrocarbons (PAHs). First, we present the PAH-primary particle (PAH-PP) model where soot particles are described by primary particles which are made up of PAHs. The model describes the formation, growth and oxidation of soot in laminar premixed ethylene flames. The connectivity between primary particles is stored to calculate the rounding of soot particles due to surface growth and condensation. We then show that a model intermolecular potential based on the simple Lennard-Jones potential supports the physical binding of PAHs as a viable mechanism for soot formation. We then present the kinetic Monte Carlo-aromatic site (KMC-ARS) model which describes the structure and growth of planar PAHs. The PAH processes are represented as jump processes, and the energetics and kinetics were de-termined by quantum chemistry calculations. Lastly, we use a simple potential parameterised using high accuracy interaction energies and the combined PAH-PP/KMC-ARS model to show that pyrene dimerization is unlikely to be the critical soot formation step at flame temperatures of about 1,500 – 2,000 K.

15:00-15:30
Michael Stoellinger, Department of Multi-Scale Physics, Delft University of Technology
Title: PDF modelling of soot formation and radiation in turbulent non-premixed flames

Abstract:
The nucleation, surface growth and oxidation of soot particles depend non-linearly on the gas phase temperature and composition. These processes typically occur on time scales that are larger than the gaseous chemical reactions and comparable to the turbulent mixing time scale. To treat the effects of the turbulent fluctuations of the gas phase temperature and composition on the soot process in closed form, an equation for the joint PDF of gas composition, enthalpy, soot number density and soot mass concentration is solved. To account for the radiative heat transfer, the Reynolds averaged radiative transfer equation (RTE) is solved by means of a discrete transfer method. The adopted PDF approach allows to treat the emission turbulence-radiation interaction in closed form. The proposed modelling approach is applied in simulations of two turbulent non-premixed flames at different pressures.

15:30-16:00
Michele Pisaroni, Department of Applied Mathematics, Delft University of Technology
Title: Counteracting Ring Formation in Rotary Kilns

Abstract:
Avoiding the formation of rings in rotary kilns is an issue of primary concern to the cement production industry. We developed a numerical combustion model that revealed that in our case study rings are typically formed in zones of maximal radiative heat transfer. This local overheating causes the overproduction of the liquid phase of the granular material that tends to stick to the oven’s wall and to form rings. To counteract for this phenomenon, we propose to increase the amount of secondary air injected to cool the oven. Experimental validation at the plant has repeatedly shown that our solution is indeed effective. For the first time in years, the kiln has been operation without unscheduled shut-downs, resulting in hugely important cost savings.

16:00-17:00
Drinks

Thursday, November 10, 2011

Delft University of Technology
Faculty of EEMCS, Lecture room D, Mekelweg 4, Delft 

Organizer: Delft Centre for Computational Science and Engineering

Registration: Please send an e-mail to Deborah Dongor (D.M.Dongor@remove-this.tudelft.nl)
                     There is no registration fee

Program

13:45 Coffee

14:00 Opening by Prof.dr.ir. Chris Kleijn

14:05 Prof. Tom Schwartzentruber (Department of Aerospace Engineering and Mechanics, University of Minnesota, USA) 

14:35 Discussion

14:40 Ira Livshits (Department of Mathematical Sciences, Ball State University, USA) 

15:10 Discussion

15:15 Coffee break

15:30 Dr. Jurriaan J. J. Gillissen (Department of Mathematical Sciences, Ball State University, USA) 

16:00 Discussion

16:05 Closing by Prof.dr.ir. Chris Kleijn

Speaker 1. Prof. Tom Schwartzentruber,
Department of Aerospace Engineering and Mechanics, University of Minnesota, USA

Particle Simulation of Nonequilibrium Hypersonic Flows
During hypersonic reentry, a high temperature gas in thermal and chemical nonequilibrium surrounds the vehicle. Understanding the precise thermo-chemical state within the shock layer, boundary layer, and at the vehicle surface is a necessary first step in predicting processes such as radiative heating and catalytic or ablative processes occurring on the heat shield surface. In addition to chemical and thermal nonequilibrium, the gas may also be in a state of collisional-nonequilibrium where gas molecules may not have equilibrium (Maxwell-Boltzmann) velocity and internal energy distributions. An accurate approach for modeling such flows is the direct simulation Monte Carlo (DSMC) particle method. The DSMC method moves a representative number of simulated molecules through a computational mesh, allowing for collisions including those with the vehicle surface. If the correct collision rates, probabilities of internal energy exchange and chemical reactions, as well as collision outcomes are prescribed, the DSMC method can accurately simulate complex hypersonic flows.

Specifically, DSMC collision models are typically parameterized by forcing consistency with existing continuum models in the limit of continuum flow (Maxwell-Boltzmann molecular distributions). Examples including models for viscosity, thermal conductivity, vibrational relaxation, and finite rate chemistry are highlighted in context with hybrid CFD-DSMC simulations. In some cases, when the continuum models must be interpreted from relatively few experimental data sets and are often extrapolated far outside of experimental conditions, their use for informing DSMC collision models is questionable.

Instead, Computational Chemistry simulations are employed that require only a Potential Energy Surface (PES) describing each collision and do not rely on collision rules or constitutive closure laws. A novel combined event-driven/time-driven numerical technique will be described that greatly accelerates the first-principles simulation of dilute gas flows. Simulation results are presented for normal shock waves and are compared with experimental data and DSMC simulations with regards to viscosity, mass diffusion, and rotational excitation processes within the shock.

Speaker 2. Dr. Ira Livshits
Department of Mathematical Sciences, Ball State University, USA

Application of algebraic multigrid approach to solving the Helmholtz equation with large wave numbers
Multigrid algorithms are known to be efficient for many  partial differential equations. However, Helmholtz equations with large wave numbers posses properties that standard iterative solvers do not handle well. In this talk, we discuss the challenges that the Helmholtz equations present and some ways to overcome them using multigrid, including algebraic multigrid, techniques.

Speaker 3. Dr. Jurriaan J. J. Gillissen
Department of Multi-Scale Physics, Delft University of Technology, The Netherlands

Lattice Boltmann Simulations of Turbulent Drag Reduction using Spherical Additives
We have used lattice Boltzmann and immersed boundary methods to simulate turbulent Couette flow of suspensions of particles whose radii are large compared to the viscous sub-layer VSL thickness. Drag reduction is observed. We explain the drag reduction by considering the finite size of the particles. Due to their large size, the particle volume fraction decays to zero in the VSL, when approaching the wall. Consequently, the particles induce a negligible effect in the VSL, while at the same time they dampen the eddies in the turbulent region. This mechanism is similar to the case of polymers, which exemplifies the universal nature of drag reduction.