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Expanded Model for Determining the Effects of Vertical Plumes on

Aviation Safety

David GouldeyJoe Hopper

Dr. Jonathan Schwalbe

The MITRE CorporationCenter for Advanced Aviation System Development

McLean, VA


Outline• Background of expanded plume model

– Plume definition– Potential hazards with plumes– Plume model description– Turbulence model description– Aircraft response models– Comparison to Australian model

• Case studies at three representative power plants• Graphical User Interface (GUI) description• Helicopter Risk• Conclusions

2


Background


What is an exhaust plume?

• This study focuses on the vertically-discharged effluent from a single or multiple smoke stacks from power plants or other industrial facilities

4

Plume Region

Transition Region

Jet Region

ZOFE


Hazards Caused by Plumes –Fixed-Wing Aircraft

• Upward motion of plume has caused reported cases of severe turbulence

• Motion of the plume has two main driving forces: initial momentum and buoyancy

• Significant turbulent gusts can be experienced inside of the plume

• Mostly an issue for light aircraft on final approach

5


Hazards Caused by Plumes –Helicopters

• Elevated temperatures can create pockets of low density air, in which helicopters have trouble maintaining lift

• Depleted oxygen concentration in plume can inhibit combustion

• Reported cases of engine flame-out caused by industrial plumes and by burning excess oil on offshore oil platforms

• Hazardous for helicopters flying slowly or hovering in the vicinity of a plume

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Source: Ireland Air Accident Investigation Unit (AAIU), Synoptic Report No. 2004-001


Hazards Caused by Plumes –Health

• Exposure time to the pollutants and depleted oxygen inside of the plume is too short to cause any significant health concerns for the crew or passengers

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Study Timeline

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January 2006 - FAA releases initial study on risk of exhaust plumes

December 2008 -Colgan Air flight experiences severe turbulence attributed to smokestack on final approach to MGW

2006 2007 201020092008 2011 2012 2013

September 2010 - SAIC delivers plume model to FAA with several deficiencies

March 2011 –MITRE CAASD tasked with creating revised plume model

September 2012 – Final report and plume model delivered to AOSC


Method Overview

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Stack Inputs Environmental Inputs

Mean Flow Plume Model(Spillane)

Turbulence Model to predict Possible Gusts(Papanicoloau and List)

Gust Loads Formula to determine Maximum Vertical Acceleration (specified in the FAR)

Houbolt Roll Model to determine if aircraft upset criteria were reached

Aircraft Inputs

Areas of Aviation Risk Around Exhaust Plumes

User Inputs

Models from Literature

Outputs


User Inputs

• Stack Inputs– Diameter– Height of Stack– Initial Velocity of Effluent– Initial Temperature of Effluent– Number of Stacks– Distance Between Stacks (if multiple stacks exist)

• Environmental Inputs– Ambient Temperature– Potential Temperature Lapse Rate (0°C/m is neutral stratification)– Ambient Winds

• Aircraft Inputs– Weight– Lift-curve slope– Approach airspeed– Surface Area– Rolling Moment of Inertia– Mean Chord Length

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Plume Models

• Jirka Model– Used in SAIC’s plume model

• The Air Pollution Model (TAPM)– Used by Australian plume model

• Spillane Model– Used in previous plume studies (i.e. Katestone

Environmental)• All models output mean centerline velocity,

coordinates of the plume, and temperature

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Model Comparison

• The three plume models were compared to experimental data in terms of mean centerline velocity and plume trajectory

• On average, Spillane has the smallest errors

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Turbulence Model

• Total gust possible from plume is the sum of the mean velocity and the turbulent gusts

• Papanicolaou and List (1988) found that the Root-mean-square (RMS) values of turbulent gusts are ~ .

• The turbulent gusts have an approximately Gaussian distribution, so the probability of a gust of a particular amplitude could be calculated

• Gusts were chosen so that a Target Level of Safety (TLS) of 10-7 was reached to be consistent with prior FAA Plume Safety Studies and TERPS criteria

13


Aircraft Response• Gust Loads Formula

– Calculates vertical acceleration (or load factor) on aircraft when it encounters a vertical gust Specified in FAR 23.341 and referenced in FAR 25.335

– A vertical acceleration of greater than 1g was deemed hazardous

• Houbolt Roll Formula– Calculates aircraft roll when encountering a vertical gust

and no corrective action is taken– Compared to defined upset criteria (bank angle > 45°)

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Maximum Roll Angle Maximum Load Factor


NOAA’s Forecasting Guide on Turbulence Intensity

Derived Gust(feet per second)

Derived Gust (converted to meters per second)

Peak Vertical Acceleration (g’s)

Turbulence Intensity

Description of Turbulence

5 - 20 1.52 – 6.10 0.2 – 0.5 Light

Momentarily causes slight, erratic changes in altitude and/or attitude (pitch, roll, and yaw).

20 – 35 6.10 – 10.67 0.5 – 1 Moderate

Similar to Light Turbulence but of greater intensity. Changes in altitude and/or attitude occur but the aircraft remains in positive control at all times. It usually causes variations in indicated airspeed.

35 - 50 10.67 – 15.24 1 – 2 Severe

Causes large, abrupt changes in altitude and/or attitude. It usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control.

> 50 > 15.24 >2 Extreme

The aircraft is violently tossed about and is practically impossible to control. It may cause structural damage.

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Accessed at http://www.nws.noaa.gov/wsom/manual/archives/ND229107.HTML#FORECASTING


Australian Model - AC 139-5(1)

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• Threshold value (10.6 m/s) is consistent with the NOAA chart for causing severe turbulence

• Use of 4.3 m/s or 10.6 m/s value is chosen by CASA


Concerns with Australian Model

• TAPM was not as accurate as the Spillane model in terms of mean centerline velocity and plume trajectory

• It doesn’t consider the possibility of a significant turbulent gust in addition to the mean centerline velocity

• It doesn’t model how aircraft with different parameters are affected by the plume

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Case Studies


Set-up• Three years of historical environmental data

sampled hourly was considered from NOAA’s RUC and RAP weather products at three different airports with near-by exhaust plumes (~25,300 hourly measurements)

• Gust amplitudes were chosen to achieve a total probability of 10-7

• Three aircraft types were modeled– Navion GA – comparable to Cessna 172– Lockheed Jetstar – comparable to Gulfstream 100– Convair CV-880M Jet – comparable to B737

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Total Probability

•

•

• A Target Level of Safety (TLS) of 10-7 was chosen to be consistent with prior FAA Plume Safety Studies and TERPS criteria (

• Gust amplitudes were chosen to reach the TLS

20


Stack Parameters

Fort Martin Power Station, WV

Mariposa Energy Project, CA

Towantic Energy Project, CT

Parameter Source Value Value Value

Stack Geometry

Height SAIC 168 m 24.2 m 45.7 mDiameter SAIC 10.7 m 3.66 m 5.64 mNumber of Stacks

SAIC 1 4 2

Stack Separation

SAIC - 47 m 39.6 m

Effluent Parameters

Exit Velocity SAIC 18.1 m/s 27.5 m/s 17.8 m/sExit Temperature

SAIC 55 °C 449 °C 94 °C

21

Taken from SAIC’s Report

Assumptions:• Aircraft are flying directly over the stack• Power plant is operating at full capacity


Morgantown, WV

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Red line = Median value

Blue box = 25th and 75th percentiles

Whisker = Maximum value


Morgantown, WV

23

GA Aircraft

Approximate Crossing Height on Glide Slope


Morgantown, WV – Probability of Severe Turbulence

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Morgantown, WV - Probability of Severe Turbulence

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Morgantown, WV - Probability of Severe Turbulence

26



Oxford, CT

27





Oxford, CT

28

GA Aircraft


Byron Airport, CA

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Byron Airport, CA

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GA Aircraft


GUI Description


GUI Background

• A GUI has been created to allow the user to input different stack and environmental parameters

• Output includes areas inside of plume where different levels of turbulence could be experienced, mean centerline velocity of the plume, temperature excess of the plume, and radius of the plume

• User can select the gust level and the aircraft type to model more detailed scenarios

32


GUI

33


Stack Inputs

34


Environmental Inputs

35


Aircraft Type Selection

36


Gust Selection

37


Figure Select

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Helicopters


Elevated Temperature Risk• MD 600N helicopter has a maximum operating temperature

of 52°C, so this was the temperature limit• Area of potential turbulence for fixed-wing aircraft is much

larger than area of elevated temperatures• Stack diameter of 10 m, ambient temperature of 0°C, initial

velocity of 15 m/s, neutral stratification

40


Reduced Oxygen Risk• >12% O2 by volume is required to ignite jet fuel below

10,000 feet (standard atmosphere has 20.9%)• Stack diameter of 10 m, ambient temperature 0°C, initial

effluent temperature 200°C, calm winds, neutral stratification, and varying initial velocity

• Assumes effluent has no oxygen• Elevated temperature risk is greater than reduced oxygen

risk

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Conclusions

• Turbulence caused by upward motion is the main hazard to aviation associated with plumes

• Our plume model considers mean flow, turbulent gusts, and aircraft parameters to determine hazardous regions around exhaust plumes

• In most situations, the hazardous region does not extend more than a few hundred feet above the stack

• Under extremely rare conditions (calm winds and cold temperatures OR calm winds and an unstable atmosphere), hazardous conditions can extend to further distances

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References• L.V. Schmidt, 1998. Introduction to Aircraft Flight Dynamics, AIAA Education Series, 397.

• K.T. Spillane, 1980. The Rise of Wet Plumes – Conservation Equations and Entrainment Assumptions. Report No. S0/80/10, State Electricity Commission of Victoria, Research and Development Department, Engineering Research Division.

• P. Best, L. Jackson, C. Killip, M. Kanowski, and K. Spillane, 2003. Aviation Safety and Buoyant Plumes. Clean Air Conference, Newcastle, New South Wales, Australia.

• J.C. Houbolt and A. Sen, 1971. Single-Degree-of-Freedom Roll Response Due to Two-Dimensional Vertical Gusts. NASA CR-111966. Aeronautical Research Associates of Princeton, Inc., Princeton, NJ.

• P. N. Papanicolaou and E. J. List, 1988. Investigations of round vertical turbulent buoyant jets. Journal of Fluid Mechanics, vol. 195, 341-391.

• SAIC, 2010. Analysis of the Impact of Vertical Plumes and Exhaust Effluent on Aviation Safety: Final Report for the Performed Scientific Analysis 1 October 2009 – 30 September 2010. Prepared for the FAA by SAIC. September 2010. DTFAWA-03-P-00117.

• G.L. Powell, A.B. Jones, M.A. Reisweber, Lt. Col. P. McCarver, Dr. J.H. Yates, J. Holman, and S. Bishop, 2006. Safety Risk Analysis of Aircraft Overflight of Industrial Exhaust Plumes.FAA, Flight Procedure Standards Branch, AFS-420, Oklahoma City, OK.

• S. Corrsin and M.S. Uberoi, 1950. Further Experiments on the Flow and Heat Transfer in a Heated Turbulent Air Jet. NACA Report 998.

• NOAA, “The Rapid Update Cycle.” Last update May 9, 2012. Accessed July 31, 2012. http://ruc.noaa.gov/

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This is the copyright work of The MITRE Corporation and was produced for the U.S. Government under Contract Number DTFAWA-10-C-00080 and is subject to Federal Aviation Administration Acquisition Management System Clause 3.5-13, Rights in Data-General, Alt. III and Alt. IV (Oct. 1996). No other use other than that granted to the U.S. Government, or to those acting on behalf of the U.S. Government, under that Clause is authorized without the express written permission of The MITRE Corporation. For further information, please contact The MITRE Corporation, Contract Office, 7515 Colshire Drive, McLean, VA 22102, (703) 983-6000.

The contents of this material reflect the views of the author and/or the Director of the Center for Advanced Aviation System Development, and do not necessarily reflect the views of the Federal Aviation Administration (FAA) or Department of Transportation (DOT). Neither the FAA nor the DOT makes any warranty or guarantee, or promise, expressed or implied, concerning the content or accuracy of the views expressed herein.

2012 The MITRE Corporation. The Government retains a nonexclusive, royalty-free right to publish or reproduce this document, or to allow others to do so, for “Government Purposes Only.”

This template is in compliance with FAA Logo and Branding Order 1700.6C


Backup Slides


Aircraft Parameters

Parameter North American Navion GA Aircraft

Lockheed Jetstar

Convair CV-880M Jet

Units

Surface Area, 180.0 542.5 2000.0 ft2

Wingspan, 33.4 53.75 120.0 ftMean Chord Length, ̅ 5.7 10.93 18.94 ftWeight, 2750 23,904 126,000 lbs.Lift-Curve Slope, 4.44 5 4.66 radians-1

Rolling moment of Inertia, 1048 42,550 1 x 106 slug-ft2

Approach Airspeed, 72 (value taken from discussions with pilots)

132 135 knots

46

Taken from Schmidt


Morgantown, WV – Probability of Moderate Turbulence

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Generic Scenarios


Areas of Risk Tables

• Assume neutral stratification, 0 knot winds, 0°C ambient temperature, and a 90th percentile gust

• Tables of varying stack diameter, effluent temperature, and initial velocity show maximum height above the stack where severe turbulence is possible for GA aircraft

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Temperature Excess (°C)

0 100 200 300 400 500

Initi

al V

eloc

ity (m

/s) 5 0 0 0 320 385 418

10 139 320 533 681 779 861

15 221 517 828 1025 1173 1288

20 303 714 1107 1386 1567 1714

25 369 894 1386 1731 1960 2141

30 451 1091 1681 2075 2354 2567

For Stack Diameter of 6 m


Buoyancy Flux• Buoyancy flux calculation contains stack diameter, initial

velocity, and effluent of temperature

1 /4

• 50,000 simulations were conducted using random effluent temperatures, stack diameters, and initial velocity

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