Date of Award

12-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Civil Engineering

Advisor

Kaye, Nigel B

Committee Member

Aziz , Nadim M

Committee Member

Khan , Abdul A

Abstract

This thesis presents a study on ember flight modeling based on a series of wind tunnel experiments. The purpose of these experiments and the data collected was to provide the input conditions for an ember flight model in order to compare and validate the model predictions. An analysis was performed which determined the sensitivity of model predictions of downwind mass distribution to uncertainties in the model input parameters.
From the wind tunnel experiments, flight distances were measured and characteristic ember size distributions were obtained from the collected data. A flight model was developed based on standard models published in the literature that was modified to account for particle size variability. The model input conditions were based on the initial conditions observed during the experiments. The model output was compared to the mass distributions obtained from the experimental data. This flight model looks specifically at the propagation phase of ember flight while subject to combustion. Modeling including the lofting and deposition phases should be considered in future work.
The two main goals of the thesis were to compare the measured downwind mass distribution with the results of the model simulations, and to conduct a parameter sensitivity study to establish the experimental parameters that have the most influence on the downwind distribution of embers.
The first goal of the model was to replicate the mass distribution data collected from the experimental tests. Both the measured and simulated downwind mass distributions were very uneven. This is due to the large range of ember sizes measured and simulated, and the finite number of embers collected in the experiments. As such direct comparison was somewhat limited though for the section of the ember field measured, the simulations provided a reasonable first order approximation of the measured distribution.
The second goal was to examine the sensitivity of the predicted ember flight distance to changes in launch angle, launch speed, wind speed, and the size distribution of the embers. A reference case of input parameters was selected and a series of simulations were run varying each of these parameters one at a time to determine their effect on the model predictions. This was done by calculating the center of mass for the mass distribution and the standard deviation about that center of mass for each simulation. These values were compared to the values obtained from the reference case. The parameter sensitivity analysis shows that the particle launch velocity has the greatest impact on the predicted flight distance. A 20% increase in the launch velocity increased distance to the center of mass by 40%, while decreasing the launch velocity 20% reduced the distance to the center of mass by 22%. Therefore, more accurate measurements of this parameter are needed to decrease the level of variability in this input parameter. This uncertainty most likely accounts for the bulk of the uncertainty in the downwind mass distribution.

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