Date of Award

3-22-2007

Document Type

Thesis

Degree Name

Master of Science in Aeronautical Engineering

Department

Department of Aeronautics and Astronautics

First Advisor

Raymond C. Maple, PhD

Abstract

This research modeled low-speed flow past idealized engine nacelle clutter in support of aircraft re suppression research. The idealized clutter was comprised of three vertical rows of staggered circular cylinders approximating typical nacelle obstructions such as fuel lines and wire bundles. Single-phase, Detached-Eddy Simulations (DES) were conducted using the commercial CFD solver, Fluent(TradeMark), to resolve the flow-field dynamics inside the clutter element and determine mechanisms accounting for the failure of suppressant spray droplets from traversing the array under low-speed, free-stream conditions (ReD = 1, 575). The numerical models provided no evidence that span-wise vorticity or non-uniform shedding was responsible for transporting dispersed-phase particles towards the tunnel walls for deposition. However, the simulations demonstrated that suppressant droplets would likely follow a path governed by the vector sum of the local carrier fluid velocity and the velocity imposed by gravity. Additionally, the Stokes number was computed from time-accurate data to determine the ability of dispersed particles to negotiate the clutter element without impinging on a cylinder. For slower free-stream velocities, U(infinity) = 1 m/s, suppressant droplets (D = 90 m/) will likely be entrained in vortices shed from the intermediate row of cylinders and subsequently deposited on the last row of cylinders as the Karman vortex directly collides with the clutter. At free-stream velocities, U(INFINITY) = 5 m/=s, the droplet particles will likely fail to track the carrier fluid streamlines in the cylinder wake and remain free of any shed vortices. Thus, the suppressant will conceivably transit the cylinder array without impact. These findings imply that a bluff-body turbulent diffusion flame in a cylinder wake could be nearly impossible to extinguish under high-speed, co-flow conditions.

AFIT Designator

AFIT-GAE-ENY-07-M08

DTIC Accession Number

ADA468376

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