1. 22nd AIAA Aerodynamic Measurement Technology and Ground Testing Conference June 24th-26th, 2002 Adams Mark Hotel - St. Louis, MS Modeling Inert Gas Distribution in Commercial Transport Aircraft Fuel Tanks William M Cavage Project Manager - Fuel Tank Inerting FAA AAR-440, Fire Safety R&D Branch

2. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Outline Background Equipment & Procedures –B-747SP Ground Test Article –24% Scale Tank Data Analysis Modeling Methods Results Summary

3. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Background Ongoing FAA Rulemaking Seeks to Improve on the Existing and Future Fuel Tank Safety –Consistent Accident Trends are a Concern –Focus of Concern is on Heated Center Wing Tanks (CWTs) Fuel Tank Inerting is a Well Established Method of Reducing/Eliminating Ullage Vapor Flammability –Has Been Meet with Resistance by Industry Leaders FAA Would Like to Develop Cost Effective Methods of Modeling Inert Gas Distribution in Commercial Transport Fuel Tanks

4. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Equipment Boeing 747SP Full-Scale Inerting Test Article –Decommissioned from Airline Service and Purchased by the FAA for Ground Testing Only All Major Systems Fully Operational Has Independent Power for Test Equipment and Instrumentation –Full Complement of Ground Service Equipment Aircraft Modified to Study Inerting –Inert Gas Deposit System Installed on Aircraft Inerts CWT from Ground Source of Nitrogen Enriched Air (NEA) –Instrumentation Gas Sample Tubing at 8 Locations for Oxygen/THC Analysis 32 Thermocouples in Tank (Ullage, Fuel, Walls, Floor, and Ceiling)

5. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Boeing 747SP Aircraft

6. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Boeing 747-100/SP Center Wing Tank

7. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Boeing 747SP CWT Top Diagram

8. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Scale Tank Test Article –24% Scale Model of Boeing 747 SP CWT was Built from 3/4 Inch Plywood By Scaling Drawings from Shepherd Report Spars and Spanwise Beams Simulated with ¼ Inch Plywood Installed in Slats with Scaled Penetration Holes Vent System Simulated with PVC Tubing Plumbed to an Aluminum Vent Channel Plumbed Similar to Aircraft –Instrumentation Oxygen Sensor in Each Bay and in One Vent Channel Plumbed in Unique Sample “Drafting” Method Returned to Each Bay Thermocouple in Each Bay –“Variable NEA Manifold” Allowed for NEA to be Deposited in Any and All Bays of the Tank at Different Flow Rates Equipment

9. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Scale Plywood CWT Model

10. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Procedures 24% Scale Tank Testing –Series of Tests Done to Examine Different Deposit Schemes Deposited Different Amounts of NEA in Different Bays to Determine the most Efficient Method of Deposit in a Half Blocked Venting Configuration All Work Presented is for 95% NEA and 128 CFH Total Flow Rate –Focus of Testing was to Find Best Method of Depositing NEA Boeing 747SP Full-Scale Inerting Testing –Series of Tests Done to Examine the Efficiency of Inerting Single Deposit (Optimal from Scale Testing)and Venting Case Tested for Different Day and Operational Conditions All Work Presented is for 95% NEA and 140 CFM Total Flow Rate with ACMs Running (Vertical Mixing Stimulated) –Focus of Testing was on Operational Effects and Predictability

11. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Data Reduction Analysis Volumetric Tank Exchange is the Ratio of the Volume of Deposited Gas to the Volume of the Tank –This Gives a Dimensionless Quantity of Inert Gas Given the Volume of the Tank Average Tank Oxygen Concentration –This Gives a Representation of the Tank Oxygen Constituency Given Varying Oxygen Concentrations in Different Bays

12. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Inert Gas Distribution Engineering Model Model Calculates Inert Gas Distribution in 6 Bay Tank, in terms of Oxygen Concentration Evolution, Given NEA Purity and Bay Deposit Flow Rates –Based on Original Single Bay Inerting Model, by FAA CSTA for Fuel Systems, which Tracks Oxygen In and Out of Each Bay Assuming Perfect Mixing During the Time Step –Assumes an “Outward” Flow Pattern and Splits Flow into a Bay to Adjacent Bays Using Out Flow Area Relationships Basic Formula for Volume of Oxygen in a Bay:

13. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Bay 1 Flow Out Bay 2 Flow In Bay 3 Bay 4 Bay 5Bay 6 Flow Out Assumed Engineering Model Flow Pattern

14. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D CFD Model A CFD Model was Developed with the Analysis Package FLUENT –Used the Fluent CFD Solver Which Uses a Finite Volume Method Where the General Conservation (transport) Equation (Mass, Momentum, Energy, etc.) is Solved for Each Finite Volume –Has Ability to Track Fluid Species (O 2 Concentration) at Given Locations –Model was Solved Using a Laminar Flow Throughout (Oxygen Evolution is Based Entirely on Flow Diffusion) –For Administrative Reasons, Model was Developed of the Scale Tank and not Full-Scale Test Article –The Model Developed had Approximately 700K Cells and Ran on Several Platforms Over a Weekend.

15. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Scale Tank Test Data Compares Well with Full-Scale Test Article Data –Bay 4 Does Not Compare Well for Any Modeling Method Engineering Model Compares Fair –Trend Data Very Good but Some Bays have Large Discrepancy in Some Bay Oxygen Concentration Values when Compared with Full- Scale Data CFD Model Comparisons Initially Poor –Trend Data Marginal with Large Discrepancies in Some Bay Oxygen Concentration Values when Compared with Full-Scale Data –Subsequent Data Has Much Better Agreement Results - Full Scale Comparison

16. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Scale Tank Data Comparison

17. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Engineering Model Data Comparison

18. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D CFD Model Data Comparison

19. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Modeling Methods Compared

20. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Comparing Scale Tank Test Article Data with Engineering Model Data for Different Deposit Scenarios Has Mixed Results –Bay to Bay Oxygen Concentration Comparisons Vary for Different Deposit Scenarios –The Average Oxygen Concentration Trend Data for the Different Deposit Scenarios is Consistently Biased High for the Engineering Model Except for the Single Deposit Case –This Results in a Discrepancy Between Which Deposit Method is Optimal (Most Efficient) for Each Modeling Method Results - Mock Trade Study

21. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Engineering Model Compared with Scale Tank

22. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Engineering Model Compared with Scale Tank

23. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Full-Scale Data Compared with Modeling Methods

24. Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Summary Scale Tank Testing Produced Good Results when Compared with the “Good Mixing” Full-Scale Testing –Cost Effective Modeling Method Simple Engineering Modeling Methods Can Produce Fair Results in a Very Cost Effective Way –Additional Work Needed to Improve Model –Additional Research Required to Resolve Discrepancies between Engineering Model and Scale Tank for for Multiple Deposits CFD Data Labor/Resource Intensive and Eventually Resulted in Good Comparison to Full-Scale Data