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Rotorcraft Engine-Nacelle Cooling Model Calibration Project

College of Engineering and Natural Sciences. Rotorcraft Engine-Nacelle Cooling Model Calibration Project. Nacelle Cooling Solutions Senior Design Team Mechanical Engineering. Nacelle Cooling Solutions: The Team. Presentation Overview. Project Objectives Breakdown of tasks

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Rotorcraft Engine-Nacelle Cooling Model Calibration Project

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  1. College of Engineering and Natural Sciences Rotorcraft Engine-Nacelle Cooling Model Calibration Project Nacelle Cooling Solutions Senior Design Team Mechanical Engineering

  2. Nacelle Cooling Solutions: The Team NCS

  3. Presentation Overview • Project Objectives • Breakdown of tasks • Discussion of Computational Model • Discussion of Experimental Model • Our Vision of the project’s future NCS

  4. Industry Standard Model • Methodology for engine cooling analysis is described in SAE, ARP-996A, “Cooling Data for Turbine Engines in Helicopters”. • Originally written in 1967, and last revised in 1986. NCS

  5. What is ARP-996A? • Describes a standard method of presenting needed data and calculating the required cooling air for a given engine-nacelle installation in rotorcraft. • “Purpose: Efficient design of a turbine engine installation requires … Cooling margins developed by these methods would be subject to full scale testing for verification.” NCS

  6. Project Statement • Our Objective: Determine a confidence interval to be associated with results obtained from the industry standard model. • Our study is based upon the AH-64 installation of the Apache Longbow helicopter. NCS

  7. AH-64 Data NCS

  8. Project Execution • Three Main Phases: • Computational Model Development • Experimental Development • Results and Recommendations. • Current Status: Completing Computational Stage and beginning Conceptual stage of the test model. NCS

  9. Computation: Phase I • Major Tasks • Understanding the underlying theory behind the model described by ARP-996A. • Develop a numerical algorithm for the model. • Implement a computer program to execute the algorithm. NCS

  10. Experimental: Phase II • Major Tasks • Develop an appropriately scaled model of the engine-nacelle installation. • Design and execute an appropriate experiment. • Analyze experimental data and determine a confidence interval. NCS

  11. Results: Phase III • Major Tasks • Based on results of data analysis, determine a recommendation for improvements, and/or advice on interpretation of results from ARP-996A methodology. • i.e. a fudge factor for the methods described in ARP-996A NCS

  12. Computational Model • Used to provide numbers for comparison with experiment • Based on the model described in SAE ARP-996A • Engine is broken lengthwise into several elements • Energy balance on each element NCS

  13. 1-D Model Schematic NCS

  14. Nodal Energy Balance Equations • Engine surface: • Nacelle: • Annulus flow: NCS

  15. Solving the Energy Balance for Each Element • Energy balance equations • Three equations • Non-Linear • Use Newton’s Method for Non-Linear Systems NCS

  16. Newton's Method for Nonlinear Systems • Given a vector of n functions, find simultaneous roots for all of them • The messy part: calculating the Jacobian matrix NCS

  17. Newton's Method for Nonlinear Systems • Solve linear system (J(x))y = F(x) • Gaussian elimination or Cramer's rule • ARP uses Cramer's rule • Easiest to just use \ operator in Matlab • set new x = x + y • repeat until y is close to zero NCS

  18. Find T1, or W? • ARP uses mass flow rate of the annulus as one of the variables in the node equations • Using the engine surface temperature instead has advantages • Mass flow rate must be the same for each node • Temperature can change • The math is simpler • Required mass flow rate can still be found NCS

  19. Finding the Required Mass Flow:The ARP Way • Calculate T2, Ta, W for first element • Calculate T2, Ta, W for next element • Take maximum W • Re-Calculate temperatures of previous elements • Repeat from 2. for each element • Re-calculate required flows from step 1. until converged NCS

  20. Finding the Required Mass Flow:The New Way • Make a guess for the required mass flow W • Calculate temperatures throughout engine • Are the temperatures all low enough? • if yes, then the flow rate is high enough • if no, then increase the flow rate and try again NCS

  21. Advantages of the New Way • Flow rate is automatically held constant over the entire engine • Easier to non-dimensionalize the node equations • Easier to calculate the Jacobian matrix • Don’t have to deal with changing h with W NCS

  22. Non-dimensional Nodal Energy Balance NCS

  23. Test Model Development • Based on data for the AH-64 installation, a simplified model can be described. • A series of cylinders, with nominal diameters given by scaled AH-64 data. NCS

  24. Our Physical Model Geometry NCS

  25. Physical Model Concepts • Scale 1:2, 6061 Aluminum to be used, or 15 gauge sheet metal • Nacelle circular cross-section to simplify airflow velocity profiles NCS

  26. Experimental Heat Source Concepts • Resistance wire and a current source. • Propane burners NCS

  27. Engine with Nacelle NCS

  28. The Next Steps to Our Goal • Material Selection • Heating Element Selection • Model Construction • Test Rig Design and Construction • Data Acquisition • Execution NCS

  29. Phase II: Schedule Phase II Experimental Development: Including Test model development Design of Experiment Procurement and Construction Experiment Execution: Including Data Analysis NCS

  30. Experimental Development • What are we trying to achieve? • What will the measurements be? • Engine Surface Temperature • Nacelle Surface Temperature • Cooling Air Temperature • How will we get the data from the experiment? • Appropriate Data Acquisition NCS

  31. Data Analysis • What do we do with the data when we’ve run the experiment? • Compare surface temperature profiles with those obtained from the computational model. • Based on this comparison, determine the confidence interval for the methods described in ARP-996A. NCS

  32. Results and Recommendations • Based upon the results from the data analysis, we can recommend one of two things: • A revision to ARP-996A, consisting of the addition of a warning section describing the accuracy of the methods described there in. • A complete revision of ARP-996A, including a new model describing new methods. NCS

  33. In Conclusion: • What are we trying to accomplish? • A measure of “goodness” for the 1-D model described in SAE, ARP-996A. • Provide data from an appropriate experimental test to back up our conclusions. NCS

  34. Any Questions? NCS

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