Fire Safety Journal 40 (2005) 65–78

The transport of water sprays past generic clutter

elements found within engine nacelles$

Peter J. Disimilea,, James R. Tuckera, Brian Croswellb,

John M. Davisb

a

USAF 46 Test Wing, Aerospace Survivability and Safety Flight, 2700 D Street, Bldg 1661,

Wright-Patterson AFB, OH 45433-7605, USA b

Department of Aerospace Engineering, UC-FEST Research Group, University of Cincinnati,

Cincinnati, OH 45221-0070, USA

Received 23 July 2003; received in revised form30 June 2004; accepted 15 August 2004

Available online 23 November 2004

Abstract

The current work is presented as part of an effort to develop a spray transport model that

would be used within the computational fire code currently under development by Sandia

National Laboratory. As part of a halon replacement research program, new high-boilingpoint chemical suppressants have been identified. These agents would discharge in a liquid

state and initially result in the transport of liquid droplets through a portion of the nacelle,

impinging on various objects prior to reaching the fire zone. The goal of this research effort is

to enhance the fundamental knowledge of spray interactions with clutter (e.g., obstacles

representing fuel and hydraulic lines, electrical wire bundles, etc). This paper reports on an

experimental investigation into the effect of generic cylindrical clutter elements on the

performance of a suppressant spray impinging on various clutter densities and porosities.

Specifically the amount of agent (water/air spray) that is transported through a generic clutter

configuration is presented as a function of clutter spacing and surrounding air. The air coflow

speed was set between 0.5 and 6.5 m/s at nominal turbulence levels of 10%.

r 2004 Elsevier Ltd. All rights reserved.

Keywords: Fire suppression; Engine nacelle; Clutter; Two-phase coflow

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www.elsevier.com/locate/firesaf

0379-7112/$ - see front matter r 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.firesaf.2004.08.003

$This research is part of the Department of Defense’s Next Generation Fire Suppression Technology

Program, funded by the DoD Strategic Environmental Research and Development Program. Corresponding author. Tel.: +1 937 255 6302x212; fax: +1 937 255 2237.

E-mail address: peter.disimile@wpafb.af.mil (P.J. Disimile).
1. Introduction

Aircraft engine nacelles represent a unique environment for fires and fire

protection. Many nacelles are characterized by high air exchange rates and a strong

degree of nonuniformity and turbulence within the airflow [1]. In addition, nacelles

contain large amounts of plumbing, wiring, avionics and mechanical components

mounted on the engine or along the nacelle walls. Some nacelles also have large ribs

for structural purposes. This combination of a highly turbulent airflow, flammable

fluids, and numerous ignition sources make aircraft engine nacelles a difficult fire

zone to protect.

For the past several decades, halogenated agents, notably Halon 1301, have

protected engine nacelles. Since the production ban on halon, scientists and

engineers in the public and private sectors have been working on replacement agents

and new technologies that attempt to replicate Halon 1301’s beneficial attributes.

Thus far none have succeeded completely. Of the technologies that have been

deemed acceptable, based on environmental friendliness, toxicity, materials

compatibility, etc. all lack fire-suppression efficiency as measured by weight and/or

volume [2].

To improve the fire-suppression efficiency of these candidate technologies, one

area of focus is suppressant distribution. Since Halon 1301 was so efficient, research

into understanding the engine nacelle airflow offered little payoff. Today, however, a

better understanding of the nacelle airflow and how it impacts fires within a nacelle,

as well as suppression distribution, can have a large payoff in reducing the design

time and/or weight of a halon replacement system.

An additional complication is due to the fact that some halon replacements have a

high boiling point, when compared to Halon 1301. These fluids can prove to be

especially challenging to distribute in an aircraft engine nacelle. To understand how

these systems would perform and thereby optimize a design, engineers must

understand better how a cloud of liquid droplets behaves when convecting within a

highly turbulent airflow through a cluttered engine nacelle.

Although the current problem may be thought to be related to common two phase

flow separation processes (i.e. flow demisters, cooling towers and steam separators)

the flow fields in these areas of study differ greatly. In these two phase flow processes

the flow fields are typically homogenously droplet laden and impinge on wires or

wires meshes smaller than the mean droplet diameter. In the current problem, the

drops are two to three orders of magnitude smaller than the elements on which they

locally impinge and emanate from a simple concentrated point source at relatively

high velocity. Therefore, the common area of two phase flow separation offers little

assistance to the current problem.

Earlier studies of spray impingement involved the development of spray to wall

interaction models. An example of these studies can be seen in [3]. The termwall

indicates that the impacted surface is much larger than the spray jet. Although these

studies help in describing and modeling the phenomena of the droplet to wall

interactions, they do not provide insight into the effect of solid obstacles of finite

dimensions in a coflow regime.

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66 P.J. Disimile et al. / Fire Safety Journal 40 (2005) 65–78
A study involving spray impingement on a solid object in the presence of coflow

air was done by Ghielmetti [4]. In this study, Ghielmetti analyzes droplet impacts on

a conical surface with an air coflow around a surface. However, the main focus of

this study was on secondary droplet behavior (droplets formed after impact), and

does not investigate the overall spray interaction in the field either upstreamor

downstreamof the impacted surface.

A more relevant study was conducted by Hung [5] investigating droplet impaction

with a cylindrical object of a finite size relatively close to that of the diameter of the

droplet, i.e. spray impingement on single wires. This study provides knowledge on

how the size of the droplets dripping off wires can be predicted, but again does not

include an air coflow and is more focused on the impact phenomena rather than the

volume of the spray dripping off the wires.

More recent investigations were done as part of the same NGP program of which

the current work is included [6–9]. DesJardin et al. [6] presented a subgrid CFD

spray model that could possibly predict the effects of a liquid spray in a cluttered

aircraft engine nacelle. However, to the understanding of the authors, this CFD

model has only been tested against experimental data for airflow over a single

circular cylinder. Another investigation was conducted by Presser et al. [7] predicting

a suppressant spray impacting a circular cylinder. This investigation predicted the

spray flow field around the cylinder using a numerical model and tested the

numerical model with experimental data for fog droplets over a single circular

cylinder. The experimental data consists of particle image velocimetry (PIV) velocity

measurements of fog injected using a pencil fogger with a specified tight range of

drop sizes. Velocity measurements of the fog droplets were taken over a single

circular cylinder in the presence of a turbulent coflow. The experimental

arrangement of Presser’s study is mounted vertically such that the main coflow

direction is vertically upward over the cylinder. Both of the above-described studies

indicate that further experimental data is needed for verification and modification of

their derived models.

DesJardin et al. [8] provides the derivation of a numerical model describing the

impact of a 1 mm liquid droplet on a singular circular cylinder. This model is useful

in explaining the physics of the liquid droplet impaction on the cylinder and can be

used in future models to explain the droplet interaction with the clutter elements.

However, this investigation does not include any experimental measurements of

spray impingement on a circular clutter element.

The most recent investigation directly related to the current one presents droplet

velocity and diameter measurements in the field surrounding a heated cylinder in the

presence of a droplet-laden homogenous turbulent flow field [9]. Measurements were

taken over both a heated and an unheated cylinder, mainly to highlight the different

effects of fire suppressants flowing over structures when heated well above the

boiling point of the fire suppressant.

Even though several researchers have investigated various aspects of the current

project, experimental research has yet to be done that includes the volume flow of a

sprayed suppressant through a multi element clutter in the presence of a turbulent

coflow. By finding the dependency of the suppressant volume transported through

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P.J. Disimile et al. / Fire Safety Journal 40 (2005) 65–78 67
clutter as a function the coflow airspeed and clutter density, the amount of

suppressant needed to effectively extinguish fires in aircraft engine nacelles can more

appropriately be sized. To this end the present study focuses the ability of water

drops to pass through a series of cylindrical obstacles, representing generic clutter,

while moving in a turbulent coflow.

2. Suppressant spray flow facility (SF)2

A low-speed flow facility with the test section air speed ranging from0.0 to 12 m/s

(0 to 40 ft/s) was modified for the current program. The major components of this

facility include an inlet contraction, turbulence generator, test section, clutter

section, and the return and separation plenum. A general overview of these

components is provided in the following text.

Air drawn froma large laboratory is accelerated towards the test section by a

3.5:1 inlet contraction that serves as the coflow supply. To minimize outside

disturbances frompropagating directly to the test section, a flow-conditioning unit

was placed over the inlet entrance. At the exit of this contraction, a turbulence

generation section was also attached. As the coflow exits the turbulence generation

section, it enters the test section. The test section was divided into two zones, A

and B. Fig. 1 is a digital image of the upstream portion of the facility test section

(zone A).

Zone A also contains the suppressant spray nozzle and the clutter package. Zone

B represents the remaining portion of the test section which is located downstream of

the clutter package. Both zones have a nominal 610 mm  914 (2400  3600) cross

sectional area. Zone A is 1220 (4800) in streamwise length, while zone B is 2440 mm

(9600) in streamwise length. As previously noted provisions have been made for the

insertion of clutter packages at the downstreamend of zone A. The leading edge of

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Fig. 1. (SF)2 zone A test section.

68 P.J. Disimile et al. / Fire Safety Journal 40 (2005) 65–78
the clutter package is held fixed at 952.50 mm (37.5000) fromthe turbulence

generation grid. The exit of the suppressant spray nozzle is located within the coflow,

596.9070.79 mm (23.500070.0300) downstreamof the turbulence generation grid.

Further the nozzle exit is positioned along the coflow centerline, located

304.8070.79 mm (12.000070.0300) vertically and 457.2070.79 mm (18.000070.0300)

horizontally fromthe test section walls. This also corresponds to the nozzle exit

being located 355.6070.79 mm (14.000070.0300) upstreamof the leading edge of the

clutter package.

Utilizing constant temperature anemometry, velocity surveys at selected streamwise locations within the coflow were performed. Specifically, hot film probes

were used to measure the velocity profile within the (SF)2 test section in the

absence of any turbulence generating grid, spray nozzle, or clutter package. Fig. 2

displays the results of vertical (y-direction) velocity traverses simultaneously

acquired using three hot filmprobes positioned in zone A, 723.9070.79 mm

(28.500070.0300) downstreamof the test section inlet, with the coflow air speed

set at 5.0070.25 m/s (16.4070.82 ft/s). Since the hot filmprobes were calibrated

for each test the maximum error in Fig. 2 was minimized to 70.1%. These

probes were positioned on the centerline (z=0), and at transverse locations,

z=7168 mm (76.6 in). The measurement survey was arranged such that

the y=0 position corresponded to the vertical center of the test section. Hot film

data were acquired at a sampling rate of 1 kHz for a period 20 s, providing 20,000

samples for each spatial location traversed. These data were analyzed and

both the time average and standard deviation computed. Results of these

surveys indicate that the mean velocity in the streamwise direction over the central

portion of the test section (vertical height of 508.0070.79 mm or 20.0070.03 in)

was 4.7570.17 m/s. Over the available span of the probe holder (approximately

16 in) the two dimensionality of the coflow was determined to be 72%.

Turbulent intensities (TI) of approximately 1% were also determined at all positions

across the (SF)2 test section except close to the walls where boundary layer effects

are observed.

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1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

5.50

6.00

-300 -250 -200 -150 -100 -50 0 50 100 150 200 250 300

Y Position (mm)

Velocity (m/s)

Probe A Probe B Probe C

Fig. 2. Streamwise velocity profiles with large grid.

P.J. Disimile et al. / Fire Safety Journal 40 (2005) 65–78 69
2.1. Turbulence generator

A large grid consisting of several 2.54 mm (1.00 in) wide, 6.35 mm (0.25 in) thick,

sharp-edged flat steel slats were assembled in a checkerboard pattern with open cell

dimension between the slats of nominally 51 mm  51 mm (2 in  2 in). This grid is

also visible in Fig. 1. Velocity surveys using hot filmprobes were acquired

downstreamof the turbulence generator, at x=711.2070.79 mm (28.0070.03 in),

Fig. 2. The spatial locations traversed are identical to those used in the clean test

section case. Readily apparent in this figure is the wave-like distribution of the

streamwise component of the mean velocity with velocities ranging between

approximately 3.7–5.0 m/s (12.0–16.4 ft/s). Although general symmetry can be

observed it appears that the lower portion of the test section seemed to have a greater

degree of unsteadiness. It is believed that additional unsteadiness was a result of

smoke generation supply tubes positioned at the entrance of the inlet contraction. In

a similar manner turbulent intensities are plotted in Fig. 3. This figure indicates that

the large disturbance grid produced TI levels in the range of 10–14%.

2.1.1. Suppressant spray nozzle

The suppressant spray nozzle used in the present study was a dual-fluid, solid cone

nozzle patented by the United States Navy as a Liquid Atomizing Nozzle, under the

US patent number of 5,520,331. Based on preliminary measurements using a Phase

Doppler Anemometer it was decided to reverse the gas liquid entrance locations as

opposed to the specifications listed in the patent. The nozzle was installed at the y–z

center of Zone A of the test section. This resulted in the centerline of the spray nozzle

being positioned tangent to the centerline of the test section. However, the spray

nozzle centerline was off center, ejecting its spray at a slight downward angle to the

test-section centerline. This caused the spray at the center of the flow to have a

nonzero velocity in the V and W directions. Froma visual inspection, it can also be

seen that the nozzle is slightly oriented in the negative y and positive z directions.

Although slight, this misalignment was also confirmed during an examination of the

velocity data.

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5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.0

13.0

14.0

15.0

16.0

17.0

18.0

19.0

-300 -250 -200 -150 -100 -50 0 50 100 150 200 250 300

Y Position (mm)

T.I. (%)

Probe A Probe B Probe C

Fig. 3. Streamwise turbulent intensity profiles with large grid.

70 P.J. Disimile et al. / Fire Safety Journal 40 (2005) 65–78
2.2. Clutter package

The clutter package used in the current test series can be seen installed within zone

A of the (SF)2 test section (Fig. 1). The present clutter package consists of 16 twodimensional elements, spanning the width of the test section. These elements were

cylinders and were made from sections of PVC plastic tubing. Elements were

assembled to form three separate arrays with equally spaced rows of 5, 6, and 5 tube

elements, separated vertically by 42.8870.79 mm (1.7570.03 in) between each

cylindrical element. The elements have an outer diameter of 50.8070.79 mm

(2.0070.03 in). The streamwise spacing between each clutter array is variable,

ranging from 13.27 mm (0.5 in) to 101.6 mm (4.0 in) with an error of 73.175 mm

(0.125 in). In terms of element diameter, the spacing ranges from 0.25D to 2.00D

with an error of 0.06D (Fig. 4).

The clutter arrangement for this investigation was selected based on its geometric

similarity to common elements found within aircraft engine nacelles. It can be seen in

Fig. 5 that many cylindrical elements fill the nacelle environment with various local

densities. With the capability of varying the streamwise distance between each array

of clutter elements in the chosen clutter package, the clutter densities found within

larger aircraft engine nacelles is simulated.

2.3. Return and separation plenum

Once the combined coflow air and suppressant mixture exit zone B of the test

section, the liquid component must be separated. The separation of the liquid was

achieved by first redirecting the flow downward into a recovery pan using a series of

turning vanes (see Fig. 6). Upon approaching the liquid pool, already present in the

recovery pan the flow is required to make a second, 180 degree turn. Due to the

combined mass and high momentum possessed by the liquid drops, the majority of

drops are unable to negotiate the tight 180-degree turn, thus impacting the liquid

pool. To further minimize suppressant from exiting the return plenum and leaving

the flow facility, a 10 mmfilter was installed.

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U

12D

Clutter

D = 50.8 mm OD

PVC tubes 

(not to scale)

2D

1.875D

0.94D

Spray

Nozzle

Coflow Return & 

Separation

Plenum

7D

Turbulence

grid

18.75D

Fig. 4. Sideview schematic of SF2 test section.

P.J. Disimile et al. / Fire Safety Journal 40 (2005) 65–78 71
2.4. Phase Doppler anemometry system

A three-dimensional phase Doppler anemometer (PDA) was used to acquire the

velocity components as well as the diameter of the liquid drops exiting

the suppressant spray nozzle. Positioning the measuring volume in the center of

the test section required the use of 1000 mm lenses on both the transmitting and

receiving optics. In a separate study it was determined, for this measurement

configuration the largest spatial filter (Mask A) in the receiving optics was utilized.

In this configuration the maximum drop diameter capable of being measured

was 810.8 mm.

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Fig. 5. Typical aircraft engine nacelle clutter.

= Water 

Particle

Filter

Drain

= Air Stream

48”

6”

24”

16”

Air Outlet

1”

1”

Collection Pan

=Turning

vanes

Fig. 6. Side view schematic of SF2.

72 P.J. Disimile et al. / Fire Safety Journal 40 (2005) 65–78
3. Experimental strategy

The present experimental program utilized a dual-fluid nozzle emitting an air/

water spray. This spray was injected into the coflow and allowed to impinge directly

on the first array of cylindrical clutter elements. This measurement program was

divided into two phases: The first phase documented the transport behavior of a

liquid suppressant (water) and its ability to pass through a generic clutter package.

While the second phase focused on the measurement of water drop velocities and

diameters using the PDA system.

3.1. General strategy

The spray nozzle water flow rate was set and maintained at 17.170.4 L/min

(4.570.1 gal/min) at a corresponding nozzle water pressure of 158.0713.7 kPa

(23.072.0 psi). The water flow was monitored using a turbine type flow meter that was

positioned directly upstreamof a pressure gage. The incoming air was regulated to a

pressure of 171.873.4 kPa (25.070.5 psi). Five different clutter package densities were

evaluated during both phases of experimentation. These densities were varied by

changes in the streamwise spacing between individual clutter arrays. Array spacing was

selected to be 0.25D, 0.50D, 1.00D, 1.50D, and 2.00D with an error of 0.06D, where D

is the diameter of an individual tube. In the current study D=50.80 mm or 2.00 in.

3.2. Phase I: suppressant volume recovery

Experiments were initiated to determine the volume of water transmitted through

the clutter package as a function of the streamwise spacing of the clutter array and

coflow speed. Thirteen air speeds were investigated ranging from0.5070.03 m/s to

6.5070.33 m/s (1.5070.08 ft/s to 19.5070.98 ft/s) in increments of 0.50 m/s (1.60 ft/

s). To measure the volume of water passing through the clutter configuration

accurately, a repeatable procedure for measuring the liquid water volume was

followed. This included the water supply tanks being filled to the same initial starting

volume of 303.072.8 L (80.070.8 gal), the coflow set to the desired speed, and the

nozzle air pressure set. A run-time clock was then energized when the water pump

was powered on such that the water flow through the nozzle was set to 17.170.4 L

(4.570.1 gal/min). Due to gravity, water drops that wetted the clutter pooled on the

individual elements and dripped down into a collection pan located beneath the

clutter. Water droplets that passed through the clutter into zone B were deposited

within the return plenum. The volume of water that is collected directly under the

clutter package was carefully measured, as was the water collected in the return

plenumby using graduated containers.

3.3. Phase II: phase Doppler anemometry

PDA measurements were also acquired upstream of the clutter package. At a

location in the center of the Zone A test section (z 1⁄4 0) and 2D (101.6070.79 mm or

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P.J. Disimile et al. / Fire Safety Journal 40 (2005) 65–78 73
4.0070.03 in) upstreamfromthe leading edge of the clutter package, velocity and

diameter traverses were performed. Specifically, the vertical upstream traverses

involved PDA measurements at 37 positions (in the y-direction @ z=0) through the

center of the water spray. At each location 20,000 data points were acquired. Each

vertical location was spatially separated by 3.15570.022 mm (0.12470.001 in). The

center of the spray nozzle was identified as the location where U, the streamwise

component of the mean velocity, reached a maximum, while the lowest Sauter and

arithmetic mean diameters were observed. Therefore, the starting and ending

position of the traverse could be slightly different depending on this offset, which

was within approximately 3.175 to 9.525 mm (0.125–0.375 in). The coflow air speed

was maintained at a constant value of 5.0070.25 m/s (16.4070.82 ft/s) during PDA

measurements. Optimal PDA data acquisition was achieved with a laser power

setting of 300 mW.

4. Phase I: suppressant volume results and discussion

Fig. 7 shows the percentage of water recovered directly under the clutter package

as a function of element spacing and air speed. The maximum error in the

suppressant volume measurements in Fig. 7 varies from 72% for coflow airspeeds

of approximately 0.5 m/s to 710% at coflow airspeeds of approximately 4.0 m/s.

The general trend of the data suggests that the volume of the liquid collected

decreases with increasing coflow speed. In fact above 4.5 m/s (15 ft/s) less than 5%

of the liquid is captured and the differences between the five clutter densities

diminish. However, with the coflow speed set to 0.50 m/s (1.60 ft/s) the amount of

water collected under the clutter ranged from61.25%70.85% (at 0.25D spacing) to

37.50%70.72% (at 2.00D). As the spacing between the individual clutter arrays is

reduced, the amount of water captured increases. Specifically, as the streamwise

spacing was reduced from2.00D to 0.25D, thereby increasing the clutter package

density, the water collected increases by over 50%. Data regression using a third

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0

10

20

30

40

50

60

70

0123456

Cofow Airspeed (m/s)

Clutter Volume (% of Initial Supply)

0.25 D 

0.5 D

1.0 D

1.5 D

2.0 D

0.25 D

0.5 D

1.0 D

1.5 D

2.0 D

7

Fig. 7. Clutter recovery vs. airspeed.

74 P.J. Disimile et al. / Fire Safety Journal 40 (2005) 65–78
degree polynomial was also applied to each clutter-spacing data set and excellent

correlation resulted.

Likewise, Fig. 8 indicates the amount of water collected in the return plenum, as

function of the coflow speed and clutter spacing. The maximum error for Fig. 8 is

72% for all data points. All five clutter densities are represented in this figure. The

volume in Fig. 8 is also represented as a percentage of the total starting supply volume.

The trends shown in Fig. 8 are the inverse of those seen in Fig. 7. The volume

collected in the plenumincreases as the coflow airspeed increases. The change in

clutter density also has the opposite effect on the plenum recovery volume compared

to that of the clutter recovery volume. With the coflow airspeed set to 0.50 m/s the

amount of water collected under the clutter ranged from 37.50%70.72% (at 0.25D)

to 58.75%70.83% (at 2.00D). The differences between the five clutter spacings also

diminish at speeds of approximately 3.5–4.0 m/s and higher. Also it can be seen that

the volume recovered in the plenum approaches 100% as the test section speed

increases.

During the test evaluation (five clutter spacings and 13 coflow speeds) the

percentage of unaccounted water volume between water supply and total liquid

recovered was determined. In all cases the difference was random and less than 4%.

Due to this small deviation measured in the present study any losses due to

evaporation and/or deposition on the tunnel walls can be neglected.

5. Phase II: PDA spray documentation

A velocity vector plot provides an indication of the behavior of the water spray in

two-dimensional space. Fig. 9 displays the results of a typical u, v vector plot

obtained by traversing across the spray in the y-direction at x=254.0070.79 mm

(10.0070.03 in) and z=0.0070.79 mm (0.0070.03 in), when the clutter array Xseparation was set to 2.00D. The drop velocities measured by the PDA system (Fig.

9) have a maximum error of 1%. In general the flow appears to have a symmetric

spread with the maximum velocity occurring at the jet centerline. Immediately

evident as the water drops exit the nozzle, the drops decelerate in the streamwise

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20

30

40

50

60

70

80

90

100

01234

Coflow Airspeed (m/s)

Plenum Recovery Volume 

(% of Initial Supply)

0.25 D

0.5 D

1.0 D

1.5 D

2.0 D

5 6 7

Fig. 8. Plenumrecovery vs. airspeed.

P.J. Disimile et al. / Fire Safety Journal 40 (2005) 65–78 75
direction and spread in the y-direction. It was determined that the maximum

streamwise droplet velocity (U) was approximately 20 m/s (65 ft/s) in the center

(y=0), decreasing to 9 m/s (30 ft/s) at the edge of the spray. The V component of

velocity varied between 1.00 and 2.00 m/s (3.30 and 6.60 ft/s), however, the W

component was found to be approximately symmetric around y–z equal zero,

varying between 1.00 and +1.00 m/s (3.30 and +3.30 ft/s). An examination of

these profiles indicated that the spray centerline was pointed downward 0.8 degrees,

relative to the xz plane, which confirmed the visual indication.

The arithmetic mean and Sauter diameter profiles across the center of the jet are

shown in Fig. 10. Fromthis figure it can be seen that both the arithmetic and Sauter

mean diameter profiles are parabolic in nature. The smallest particles were measured

towards the center of the spray. By comparing the diameter and velocity profiles, it

can be seen that their diameters are inversely related to the drop velocity. Over the

extent of the traverse through the spray, Sauter diameters varied between

285711 mmat the center of the jet to 350714 mmat the edge of the jet. All mean

diameters in Fig. 10 are within an error of 4%.

6. Summary

To help provide insight into the transport of fire suppressants with high boiling points,

an air/-water spray was injected into a highly turbulent coflow of air. Documentation of

this coflow at a nominal test section setting of 5.00 m/s verified the presence of a highly

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Fig. 9. UV vector plot.

76 P.J. Disimile et al. / Fire Safety Journal 40 (2005) 65–78
turbulent coflow. Under these conditions the streamwise TI was estimated between 10

and 14% and mean velocity distribution between 3.70 and 5.00 m/s.

Once the nominal boundary conditions were documented, the suppressant volume

conservation experiments were performed. This evaluation indicated that, at low

coflow airspeeds, as much as 61.25% at 0.25D clutter spacing and 37.50% at 2.00D

clutter spacing of the total incoming water supply was collected directly under the

clutter element. This corresponded to only 37.50% (at 0.25D) and 58.75% (at 2.00D)

of the water volume passing through the clutter package. As a measure of

repeatability no less than 96% of the total supply volume was recovered in the

combined clutter and plenum return recovery tanks.

The results of this experiment provide valuable insight into the transport of liquid

agents through engine nacelles and provide essential data to develop first-generation

computer models to aid in the design of fire suppression systems for aircraft engine

nacelles. This work however, only addresses round elements of uniform size and

distribution. More data are needed to create a database of clutter information for

examining the effects of different-size, geometry and density of clutter elements as

well as different levels of turbulence.

Acknowledgments

This research is supported by the Department of Defense’s Next Generation Fire

Suppression Technology Program, funded by the DoD Strategic Environmental

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Arithmetic & Sauter Mean Diameter Profiles

100

150

200

250

300

350

400

-70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70

Y Position (mm)

Mean Diameter (μm)

Arithmetic Mean Sauter Mean

Fig. 10. Mean diameter profiles.

P.J. Disimile et al. / Fire Safety Journal 40 (2005) 65–78 77
Research and Development Program and monitored by Dr. Richard Gann. The

authors would like to thank Dr. Dave Keyser acting on behalf of Naval Air Systems

Command for coordinating this activity as well as providing invaluable discussion

relating to the experiments. We would also like to thank Mr. Nathaniel McElroy and

Veridian Engineering for their technical support in the experimentation.

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