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Invited Paper for ASM 2004

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Invited Paper for ASM 2004

  1. 1. Generic process for air vehicle concept design and assessment (Paper AIAA-2004-0895) John J Doherty and Stephen C McParlin Aerodynamics, QinetiQ Ltd, Farnborough AIAA Aerospace Sciences Conference, 5-8 January 2004
  2. 2. Contents (1 of 2) <ul><li>1 Introduction </li></ul><ul><ul><li>MOD customer requirements </li></ul></ul><ul><li>2 The assessment process </li></ul><ul><ul><li>Conceptual design </li></ul></ul><ul><ul><li>Detailed configuration design </li></ul></ul><ul><ul><li>Analysis and WT testing </li></ul></ul><ul><ul><li>Synthesis of performance </li></ul></ul>
  3. 3. Contents (2 of 2) <ul><li>3 Underlying technologies </li></ul><ul><ul><li>CAD Integration </li></ul></ul><ul><ul><li>DoE and RSM </li></ul></ul><ul><ul><li>CFD methods </li></ul></ul><ul><li>4 Future directions </li></ul><ul><ul><li>Systems of systems </li></ul></ul><ul><ul><li>Multidisciplinary aspects </li></ul></ul><ul><li>5 Conclusions </li></ul>
  4. 4. Introduction Section 1
  5. 5. UK MOD customer requirements <ul><li>Capability developed to meet MOD needs in the procurement of future air vehicles. </li></ul><ul><li>Complex systems need to be assessed against Operational Requirements considering a range of attributes: </li></ul><ul><ul><li>Capability </li></ul></ul><ul><ul><li>Affordability </li></ul></ul><ul><ul><li>Flexibility </li></ul></ul><ul><li>Intelligent Customer status implies an ability to understand trade-offs and their implications at system level. </li></ul>Introduction
  6. 6. The assessment process Section 2
  7. 7. Rationale for improved process <ul><li>Limitations of the historical assessment process. </li></ul><ul><ul><li>Data sheet methods fast, cheap but often inaccurate. </li></ul></ul><ul><ul><li>Wind tunnel tests accurate, but slow and expensive. </li></ul></ul><ul><li>New processes, using new technologies, have been matured: </li></ul><ul><ul><li>Adoption of CFD-based methods. </li></ul></ul><ul><ul><li>Increasing power and fidelity of design tools. </li></ul></ul><ul><li>New processes improve accuracy, speed and flexibility. </li></ul><ul><ul><li>Particularly for novel concepts. </li></ul></ul>The assessment process
  8. 8. Conceptual design synthesis <ul><li>Multi-Variate Optimisation (MVO) has a long pedigree. </li></ul><ul><ul><li>Civil transport MVO from late ‘60s. </li></ul></ul><ul><ul><li>Combat aircraft MVO from early ‘80s. </li></ul></ul><ul><li>A parametric concept model is evolved to meet performance requirements at minimum mass or cost. </li></ul><ul><ul><li>Performance modelling via data-sheet type methods </li></ul></ul><ul><ul><li>MVO run-time typically 5 minutes CPU </li></ul></ul><ul><li>MVO has evolved to meet changing MOD requirements. </li></ul><ul><ul><li>Wider range of air-vehicle concept types </li></ul></ul>The assessment process
  9. 9. MVO synthesis - requirements capture Requirements capture process including formulation of design constraints E.g. mission profile E.g. point performance The assessment process Opt climb / cruise climb FLOT Opt Alt & A/S Release A/A Weapons Penetration CV to FLOT O/H Fuel SUTTO No Credit Combat No Distance Credit
  10. 10. Performance requirements. Design constants. Engine data. Start point for design variables. The assessment process MVO synthesis - optimisation process Synthesise geometry, mass, aerodynamics, performance Meets performance? & Sensible design? & Minimum mass? NO Change values of design variables Optimisation loop Solution Aircraft YES
  11. 11. MVO conceptual design example (1 of 2) <ul><li>Manned aircraft concept requirements </li></ul><ul><ul><li>Deep strike/penetration role </li></ul></ul><ul><ul><li>Defined mission profile </li></ul></ul><ul><ul><li>Defined payload/range </li></ul></ul><ul><ul><li>Point performance requirements </li></ul></ul><ul><li>MVO optimises concept layout/sizing </li></ul><ul><ul><li>Final design meets requirements </li></ul></ul><ul><li>MVO output provides 2D definition of concept </li></ul>The assessment process
  12. 12. <ul><li>For manned aircraft example, the key performance requirement driving concept sizing was the transonic to supersonic acceleration time. </li></ul>MVO conceptual design example (2 of 2) The assessment process Acceleration time derived from (thrust - drag) integration
  13. 13. High-fidelity concept assessment <ul><li>MVO performance levels for designed concept are based on semi-empirical estimates. </li></ul><ul><li>Wish to validate MVO performance levels using higher fidelity analysis methods ( e.g. CFD, Wind-tunnel). </li></ul><ul><ul><li>MVO output is limited to 2D geometry representation. </li></ul></ul><ul><ul><li>A corresponding high-fidelity 3D geometry is required. </li></ul></ul><ul><li>Initial 3D model produced automatically from MVO output. </li></ul><ul><ul><li>Process based on parametric, rules-based CAD (CATIA V5) </li></ul></ul>The assessment process
  14. 14. Initial 3D CAD definition (1 of 2) <ul><li>CAD created from MVO output using rules-based CAD </li></ul><ul><ul><li>3-D layout </li></ul></ul><ul><ul><li>packaging </li></ul></ul><ul><ul><li>control surfaces </li></ul></ul>The assessment process
  15. 15. Initial 3D CAD definition (2 of 2) <ul><li>External CAD surfaces also created using rules-based CAD </li></ul>The assessment process <ul><li>Process allows initial aerodynamic design choices to be made: </li></ul><ul><ul><li>aerofoil sections </li></ul></ul><ul><ul><li>radome shaping </li></ul></ul><ul><ul><li>fuselage shaping </li></ul></ul><ul><li>For manned aircraft example, initial CAD model was 25% short on fuel volume </li></ul>
  16. 16. Detailed 3D concept design <ul><li>To predict the realistic performance achievable for a concept, a realistic level of detailed design must be incorporated. </li></ul><ul><li>The 3D geometry must first be designed, and then the performance assessed. </li></ul><ul><li>This detailed design should aim to satisfy the same constraints as the original MVO design. </li></ul><ul><ul><li>Or, identify that the performance cannot be realised. </li></ul></ul><ul><li>The CODAS aerodynamic shape optimisation process is used to achieve this detailed design. </li></ul>The assessment process
  17. 17. Design conditions. Performance objective. Aerodynamic/geometric constraints. Initial values. The assessment process CODAS shape optimisation process Optimised Geometry YES Surface geometry creation (Parametric CAD) Satisfies constraints & no further improvement? NO Change values of design variables Performance analysis (CFD & Empirical Methods) Optimisation loop
  18. 18. CODAS detailed design example (1 of 3) <ul><li>Manned aircraft designed using CODAS, with Euler CFD. </li></ul><ul><li>MVO identified acceleration time as a key driver. </li></ul><ul><ul><li>Acceleration time used as optimisation objective. </li></ul></ul><ul><ul><li>Multi-point transonic/supersonic design. </li></ul></ul><ul><li>Numerous constraints within shape optimisation. </li></ul><ul><ul><li>Packaging constraints. </li></ul></ul><ul><ul><li>Fuel volume (starting CAD shape is 25% too low). </li></ul></ul><ul><ul><li>Control hinge lines. </li></ul></ul><ul><li>Concept trimmed throughout. </li></ul>The assessment process
  19. 19. <ul><li>Extensive design of external surfaces. </li></ul>CODAS detailed design example (2 of 3) The assessment process <ul><ul><li>Full wing design. </li></ul></ul><ul><ul><li>Control deflections. </li></ul></ul><ul><ul><li>Tailplane & deflection. </li></ul></ul><ul><ul><li>Fin setting angle. </li></ul></ul><ul><ul><li>Fuselage upper surface. </li></ul></ul><ul><li>Final design satisfies constraints. </li></ul><ul><ul><li>Corresponds to a detailed representation of MVO concept. </li></ul></ul>
  20. 20. <ul><li>Acceleration time bettered by 20% compared to MVO. </li></ul>CODAS detailed design example (3 of 3) The assessment process
  21. 21. Post design CFD analysis The assessment process Euler and RANS methods are used to predict the off-design performance.
  22. 22. Wind tunnel testing <ul><li>Wind tunnel testing is the most cost-effective way of generating bulk aerodynamic data. </li></ul><ul><li>More accurate than CFD. </li></ul><ul><li>Generates data up to and beyond limits of flight envelope. </li></ul><ul><li>Low speed tests are much cheaper than high speed tests. </li></ul><ul><li>Generates force and pressure measurements for validation. </li></ul><ul><li>Flow visualisation is important for understanding physics. </li></ul><ul><li>CFD informs testing process. </li></ul>The assessment process
  23. 23. CODAS design wind tunnel tested <ul><li>Low-speed, transonic & supersonic testing completed. </li></ul>The assessment process
  24. 24. Synthesis of performance <ul><li>Neither wind tunnel or CFD data is fully representative </li></ul><ul><li>CFD can provide some points, but not all </li></ul><ul><li>Wind tunnel data is usually untrimmed and sub-scale. </li></ul><ul><li>Response surface techniques can generate trimmed drag. </li></ul><ul><li>Same methods can also generate device schedules. </li></ul><ul><li>CFD can correct zero-lift drag from model to full scale. </li></ul>The assessment process
  25. 25. MVO predicted vs. experimental trimmed drag The assessment process C L C D - (C L 2 / (   AR )) Wing LE -5, TE 0, Trimmed Wing LE 0, TE 0, Trimmed Wing LE 5, TE 0, Trimmed Wing LE 5, TE 5, Trimmed Mission performance targets (MVO) Point performance targets (MVO)  C D = 0.01
  26. 26. Closing the loop <ul><li>MVO results are based on low-fidelity methods. </li></ul><ul><li>MVO predictions should be supported by high-fidelity data. </li></ul><ul><li>CFD methods should agree with experimental data. </li></ul><ul><li>Differences between MVO, CFD and experiment should be accounted for. </li></ul><ul><ul><li>Systematic errors can be identified and reduced. </li></ul></ul>The assessment process
  27. 27. Assessment and optimisation process MVO modelling validated. Improved data-sheet methods derived from CFD and WT data (Response Surface Models). The assessment process Rules-based CAD MVO design synthesis Aerodynamics: CFD, CODAS, WT testing
  28. 28. Underpinning Technologies Section 3
  29. 29. Integration of CAD into assessment <ul><li>CAD methods are essential for handling complex configurations. </li></ul><ul><ul><li>But, geometry generation and input to CFD was previously the slowest step in the process. </li></ul></ul><ul><li>Rules-based CAD now allows automated generation of 3D CAD models. </li></ul><ul><ul><li>Now forms the basis of a multidisciplinary capability. </li></ul></ul><ul><li>Tailored CAD-CFD interface (GEMS) developed to allow rapid meshing of CAD geometry. </li></ul><ul><ul><li>Common front-end for many CFD tools. </li></ul></ul>Underpinning technologies
  30. 30. Parametric, knowledge-based, CAD <ul><li>Wide range of air-vehicle types generated from single parametric, rules-based CAD model. </li></ul>Underpinning technologies
  31. 31. Response surface modelling (RSM) <ul><li>The majority of aerodynamic methods in MVO are similar to those in data sheet methods. </li></ul><ul><ul><li>Limited to “classical” configurations. </li></ul></ul><ul><ul><li>Underlying technology dates from 1940s-1950s. </li></ul></ul><ul><li>There is a need to generate more accurate and flexible data sets, and represent these as algebraic functions. </li></ul><ul><ul><li>Design of Experiments (DoE) for minimum error samples. </li></ul></ul><ul><ul><li>CFD methods to generate data bases. </li></ul></ul><ul><ul><li>RSM software fits relationships to data. </li></ul></ul>Underpinning technologies
  32. 32. CFD methods (1 of 2) <ul><li>Mature CFD mesh generation and flow solution techniques: </li></ul><ul><ul><li>Panel & Euler methods are fast and consistent. </li></ul></ul><ul><ul><li>Accuracy levels and applicability are well understood. </li></ul></ul><ul><ul><li>These methods can mass produce data for RSM. </li></ul></ul><ul><li>Areas for improvement with RANS CFD: </li></ul><ul><ul><li>Robustness, accuracy and especially consistency. </li></ul></ul><ul><ul><li>Prediction of flow separation onset. </li></ul></ul><ul><ul><li>Unsteady, separated flows. </li></ul></ul>Underpinning technologies
  33. 33. <ul><li>Manned aircraft concept at transonic manoeuvre condition. </li></ul>CFD methods (2 of 2) Underpinning technologies Euler effective when flow primarily attached. RANS can give false flow features - in this case flow separation from leading edge control surface. Euler RANS Experiment +
  34. 34. Future directions Section 4
  35. 35. Systems of systems <ul><li>Top level drivers for MOD requirements are clear. </li></ul><ul><li>Roles and capabilities required are less so. </li></ul><ul><li>End user focus on effects, rather than technologies. </li></ul><ul><li>MVO gives the effect of technology on system performance. </li></ul><ul><li>Need for MVO to cover the full range of systems. </li></ul><ul><ul><li>HALE concepts. </li></ul></ul><ul><ul><li>Weapons concepts. </li></ul></ul>Future directions
  36. 36. Multidisciplinary aspects <ul><li>These techniques are suitable for wider application. </li></ul><ul><li>Generic means of inserting analyses into simpler tools. </li></ul><ul><li>More accurate, more flexible synthesis methods are possible. </li></ul><ul><li>Detailed assessment is now much faster and cheaper. </li></ul><ul><li>More understanding of detail than is feasible with MVO. </li></ul><ul><ul><li>Feedback to improve MVO. </li></ul></ul>Future directions
  37. 37. Conclusions Section 5
  38. 38. Conclusions <ul><li>Requirements will change and evolve. </li></ul><ul><li>The process needs to be more flexible to assess novel concepts accurately. </li></ul><ul><li>An improved assessment process has been described. </li></ul><ul><li>New generic technologies reduce time and cost. </li></ul><ul><li>New aerodynamic technologies have been matured. </li></ul><ul><li>There are continuing areas for improvement: </li></ul><ul><ul><li>CFD for the whole flight envelope. </li></ul></ul><ul><ul><li>Multidisciplinary trade-offs. </li></ul></ul>
  39. 39. Thank You

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