Date of Graduation

2013

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Gary J Morris

Committee Co-Chair

Douglas S Dierdorf

Committee Member

Wade W Huebsch

Committee Member

John M Kuhlman

Committee Member

David C Lewellen

Abstract

Over the past few decades, aircraft rescue firefighting (ARFF) research has made technical strides on multiple fronts. Continuing efforts have helped develop computer-aided engineering tools to quantify risk assessment for a variety of ARFF aspects like aircraft pool fire combustion and dynamic crash-related events. To continue this work, a study was conducted to characterize firefighting agent application behavior and to quantify the flow characteristics that differentiate water and AFFF jets. Progress will lead to further simulation capability including a combined aircraft crash-fire-suppression application risk assessment model. An aqueous firefighting agent application laboratory was specially constructed to carry out experiments on firefighting jets ranging from 1 to 11 megapascals and 4 to 25 liters per minute at AFFF concentration levels ranging from 0 (pure water) to 12 percent by volume. Experimental flow characterization consisted of flow visualization, agent ground pattern distribution analysis, and 2-D phase Doppler particle analysis (PDPA). Flow visualization results depicted minimal differences in terms of overall jet structure between AFFF versus water jets. However, PDPA results showed AFFF enhances jet break-up generating droplet sizes 25 to 100 percent less compared to water jets with AFFF jets lagging water jet velocities by as much as 10 percent in certain instances. Agent ground pattern results confirmed flow performance factors such as ground coverage area, reach, and maximum span all benefit from an increase in nozzle pressure flow rate. An Euler-Lagrange, large eddy simulation computational fluid dynamic (CFD) strategy accounting for droplet collision and break-up was employed to predict firefighting jet flow dynamics with and without the addition of AFFF. AFFF influence was handled computationally via material property variation from pure water in terms of density, viscosity, and surface tension effects. CFD model results were agreeable with flow visualization and phase Doppler data reproducing global trends in both droplet velocity and size data, particularly with respect to the influence of AFFF. However, oversimplified nozzle injection conditions led to greater differences than expected. CFD model result errors were difficult to quantify entirely due to PDPA upper particle size range limitations and complexities associated with direct comparisons to data. High fidelity, near field characterization of AFFF-surface interactions is needed to better understand agent accumulation fluid mechanics with eventual application to fire suppression of aircraft bodies engulfed in fire.

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