22nd AIAA Aerodynamic Measurement Technology and Ground Testing Conference June 24th-26th, 2002 Adams Mark Hotel - St.

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

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

3. 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 AAR-422 Fire Safety R&D

4. 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) AAR-422 Fire Safety R&D

5. Boeing 747SP Aircraft AAR-422 Fire Safety R&D

6. Boeing 747-100/SP Center Wing Tank AAR-422 Fire Safety R&D

7. Boeing 747SP CWT Top Diagram AAR-422 Fire Safety R&D

8. Equipment • 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 AAR-422 Fire Safety R&D

9. Scale Plywood CWT Model AAR-422 Fire Safety R&D

10. 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 AAR-422 Fire Safety R&D

11. 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 AAR-422 Fire Safety R&D

12. 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: AAR-422 Fire Safety R&D

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

14. 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 (O2 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. AAR-422 Fire Safety R&D

15. Results - Full Scale Comparison • 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 AAR-422 Fire Safety R&D

16. Scale Tank Data Comparison AAR-422 Fire Safety R&D

17. Engineering Model Data Comparison AAR-422 Fire Safety R&D

18. CFD Model Data Comparison AAR-422 Fire Safety R&D

19. Modeling Methods Compared AAR-422 Fire Safety R&D

20. Results - Mock Trade Study • 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 AAR-422 Fire Safety R&D

21. Engineering Model Compared with Scale Tank AAR-422 Fire Safety R&D

22. Engineering Model Compared with Scale Tank AAR-422 Fire Safety R&D

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

24. 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 AAR-422 Fire Safety R&D