Date of Graduation

2018

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

V'yacheslav Akkerman

Committee Co-Chair

V'yacheslav Akkerman

Committee Member

Hailin Li

Committee Member

Terence Musho

Abstract

Influence of the Lewis Number and Boundary Conditions on Finger Flame Acceleration Mohammed AlKhabbaz One of the mechanisms of premixed flame acceleration in pipes is devoted to the following scenario: an initially hemispherical flame embryo, ignited at a closed end of a tube or a channel with one end open, at a tube/channel centerline, eventually acquires a convex, finger-like shape. This is accompanied by powerful flame acceleration, which lasts until the flame skirt contacts a sidewall of the tube/channel and is followed by flame deceleration and formation of a concave, "tulip" flame shape. While this phenomenon has been observed and studied extensively in the past, experimentally, computationally, and analytically, the previous theoretical and numerical studies employed a set of conventional simplifying assumptions such as equidiffusive burning and ideally-slip, adiabatic walls of the pipe, which are not the cases in the practical reality.;The present work reduces such a gap between the research and practice. Specifically, the impacts of the Lewis number (the thermal-to-mass diffusivity ratio) Le and of the various wall boundary conditions on finger flame acceleration is investigated by means of the computational simulations of the reacting flow equations, with a fully-compressible hydrodynamics, transport properties (thermal conduction, diffusion and viscosity), and an Arrhenius chemical kinetics. The simulation results include the monitoring and analysis of the major flame parameters such as the evolutions of the locus and velocity of the flame tip, the flame surface area and the burning rate.;It is shown that the Le > 1 flames are intrinsically thickened and thereby propagate slower than the equidiffusive (Le = 1) flames, though the difference is minor. In contrast, the Le < 1 flames propagate faster due to the onset of the diffusional-thermal instability. As for the wall conditions, various isothermal (cold/preheated) and mechanistic (slip/non-slip) boundaries are employed and compared. Overall, it appears that sidewalls provide a minor impact on finger flame acceleration, which is different for another acceleration mechanism where wall friction plays a greater role. The latter result can be explained by the fact that finger acceleration occurs far from the walls, i.e. along the centerline and before the flame skirt contacts the side-walls.

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