Mechanical Engineering PhD Thesis Defense by Muhammad Irfan

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KOÇ UNIVERSITY

GRADUATE SCHOOL OF SCIENCES & ENGINEERING

MECHANICAL ENGINEERING

PhD THESIS DEFENSE BY MUHAMMAD IRFAN

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Title: Direct Numerical Simulation of Evaporation and Burning of a Droplet using Front Tracking Method.

Speaker: Muhammad Irfan

Time: September 06, 2017, 11:00

Place: ENG 208

Koç University

Rumeli Feneri Yolu

Sariyer, Istanbul

Thesis Committee Members:

Prof. Dr. Metin Muradoglu (Advisor, Koc University)

Assoc. Prof. Dr. Murat Sozer (Koc University)

Prof. Dr. Alper Kiraz (Koc University)

Assoc. Prof. Dr. Mehmet Sahin (Istanbul Technical University)

Assoc. Prof. Dr. Onur Tuncer (Istanbul Technical University)

Abstract:

A front-tracking method is developed for the direct numerical simulation of droplet evaporation and combustion in a liquid-gas multiphase system. One field formulation is used to solve the flow, energy and species equations with suitable jump conditions. Both phases are assumed to be incompressible; however, the divergence-free velocity field condition is modified to account for the phase change at the interface. Both temperature and species gradient driven phase change processes/models are simulated in 2D planar configuration. For the species gradient driven phase change process, the Clausius-Clapeyron equilibrium relation is used to find the vapor mass fraction and subsequently the evaporation mass flux at the interface. Extensive validation studies are performed using the benchmark cases: The Stefan and the sucking interface problems, d² law and the wet bulb temperature comparison with the psychrometric chart values. The models are then applied to simulate the evaporation of a single and two droplets systems that move, evaporate, interact and undergo significant deformation in a gravitational field. The implementations have been demonstrated to be grid convergent and the global mass conservation is satisfied for all the studied cases.

The temperature gradient based phase change model is then incorporated into the axisymmetric multiphase solver and comprehensive validation studies are performed. This is then further extended to model the burning process following the evaporation as a first step towards the development of a computational framework for the direct numerical simulations of spray combustion. We used single step as well as reduced chemical kinetic mechanism, constant thermodynamic properties, unity Lewis number for all the species and an ideal gas behaviour for a n-heptane droplet combustion; the chemical kinetics being handled by the CHEMKIN. An operator-splitting approach is used to advance temperature and species mass fractions in time. The numerical results of the droplet burning rate, flame temperature, flame standoff ratio and ignition delay times show good agreement with the experimental and previous numerical studies.