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Stalcup, Erik JamesNumerical Modeling of Upward Flame Spread and Burning of Wavy Thin Solids
Master of Sciences, Case Western Reserve University, EMC - Aerospace Engineering
Flame spread over solid fuels with simple geometries has been extensively studied in the past, but few have investigated the effects of complex fuel geometry. This study uses numerical modeling to analyze the flame spread and burning of wavy (corrugated) thin solids and the effect of varying the wave amplitude. Sensitivity to gas phase chemical kinetics is also analyzed. Fire Dynamics Simulator is utilized for modeling. The simulations are two-dimensional Direct Numerical Simulations including finite-rate combustion, first-order pyrolysis, and gray gas radiation. Changing the fuel structure configuration has a significant effect on all stages of flame spread. Corrugated samples exhibit flame shrinkage and break-up into flamelets, behavior not seen for flat samples. Increasing the corrugation amplitude increases the flame growth rate, decreases the burnout rate, and can suppress flamelet propagation after shrinkage. Faster kinetics result in slightly faster growth and more surviving flamelets. These results qualitatively agreement with experiments.

Committee:

James T'ien (Committee Chair); Joseph Prahl (Committee Member); Yasuhiro Kamotani (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

modeling;simulation;numerical modeling;combustion;computational combustion;direct numerical simulation;flame spread;burning;wavy;corrugated;fire dynamics simulator;FDS;fuel structure;fuel geometry;complex geometry;cardboard;

Hashemi, Seyyed AmirrezaTransition to turbulent flow in finite length curved pipe using nek5000
Master of Science, University of Akron, Mechanical Engineering
Transition to turbulent flow in curved pipe has been well studied through experiments and numerical simulations. Numerical simulations often use helical pipe geometry with infinite length such that the inlet and outlet boundary conditions can be modeled as periodic which reduces computational time. In the present study, we examined a finite length curved pipe with a Poiseuille flow imposed at the inlet and a stress-free boundary condition at the outlet. Direct numerical simulation of the Navier-Stokes equations for rigid walls and a Newtonian fluid was performed using nek5000. Straight extensions were added to the inlet and the outlet such to diminish the impact of boundary conditions on the flow field in the region with curvature. The examined model has a pipe radius of curvature that is three times that of the pipe radius. The model has over 300 million nodes and required an order of magnitude greater computational time when compared to the infinite length curved pipe. Results show that the critical Reynolds number (initiation of instabilities) is greater compared to a straight pipe and occurs near Re=5000-5200. This Re is also larger than the critical Reynolds number typically reported for an infinite length curved pipe (Re= 4200-4300). As expected, flow patterns in the finite length curved pipe were shown to be evolving through the curvature as opposed to that of an infinite length curved pipe where it remains constant. In addition, the initial instabilities observed in the flow did not originate from a Dean flow instability, initiated through secondary flow, but rather were first observed near the outer wall.

Committee:

Francis Loth, Dr. (Advisor); Paul Fischer, Dr. (Committee Member); Sergio D. Felicelli, Dr. (Committee Member)

Subjects:

Fluid Dynamics

Keywords:

Transitional flow, Direct numerical simulation, Curved pipe, Secondary flow, Turbulent instabilities