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Reflections on Applied Computational Aerodynamics (ACA) My Journey on a Long and Winding Road in the Quest for Fully Effective ACA—A Bridge Too Far!

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Reflections on Applied Computational Aerodynamics (ACA) My Journey on a Long and Winding Road in the Quest for Fully Effective ACA—A Bridge Too Far! Reflections on Applied Computational Aerodynamics (ACA) My Journey on a Long and Winding Road in the Quest for Fully Effective ACA—A Bridge Too Far! Pradeep Raj, Ph.D. Professor, Kevin T. Crofton Department of Aerospace and Ocean Engineering Virginia Tech, Blacksburg, Virginia, USA http://www.aoe.vt.edu/people/faculty/raj.html Program Management Director, Lockheed Martin (Retired) Deputy Director, Technology Development & Integration The Skunk Works®, Palmdale, California, USA Fully Effective ACA ≡ ACA Nirvana*! 07 July 2021 (*a goal hoped for but apparently unattainable) 1 Copyright © 2021 by Pradeep Raj. All Rights Reserved. About the Author Pradeep Raj • Virginia Tech, Blacksburg, VA – Professor (2012 - present) o Teaching: AOE Air Vehicle Design and ACA o Research: Applied Aerodynamics for Aircraft Design • Lockheed Martin (Retd.) – Prog. Mgmt. Director (2011) The Skunk Works®, Aeronautics Co., Palmdale, California • Lockheed, Burbank – Sr. Aero. Engineer (1979) • UMR*, Rolla, Missouri – Asst. Prof. (1978) • ISU, Ames, Iowa – Res. Asst. Prof. (1976) • GT, Atlanta, Georgia – Ph.D. Aerospace Engineering (1976) • IISc, Bangalore, India – B.E. Elec. Tech. (1970) – M.E. Aero. Engr. (1972) • Fellow of AIAA, RAeS, and IAE Image Source: Internet 2 *now Missouri S&T University Copyright © 2021 by Pradeep Raj. All Rights Reserved. Why Raj Joined VT After Retirement from LM? Clarence Leonard “Kelly” Johnson (1910-1990) Legendary Aircraft Designer Founder of World-renowned Skunk Works® “Hang with young people; they mostly have it right” 3 Copyright © 2021 by Pradeep Raj. All Rights Reserved. About This Presentation This is a revised, updated, and much expanded version of the Lead Presentation: Applied Computational Aerodynamics: An Unending Quest for Effectiveness presented at the Royal Aeronautical Society Applied Aerodynamics Conference— The Future of Aerodynamics, Bristol, U.K., July 24-26, 2018. Download at URL: https://www.aoe.vt.edu/people/faculty/raj/personal-page/ACA.html MOTIVATION To Provide a Historical Context for the Capabilities and Shortcomings of Today’s ACA and the Prospects for a Fully Effective Capability NOTE: Focus is on Air Vehicle Design CAUTION: It’s NOT a history of ACA! 4 Copyright © 2021 by Pradeep Raj. All Rights Reserved. DISCLAIMERS The material contained herein reflects the views, thoughts, and convictions solely of the author, and not necessarily those of the author’s employers or other groups or individuals. The author has gathered and compiled this material from publicly available sources and personal archives. Although a good-faith attempt has been made to cite all sources of material, the author deeply regrets any inadvertent errors or omissions. Being a perspective, the material is based on the author’s opinions shaped by some knowledge, years of experience, and many biases. 5 Copyright © 2021 by Pradeep Raj. All Rights Reserved. Outline 1. Introductory Remarks 2. Genesis of Fluid Dynamics (Antiquity to 1750) 3. Fluid Dynamics as a Mathematical Science (1750–1900) 4. Emergence of Computational Fluid Dynamics (1900–1950) 5. Evolution of Applied Computational Aerodynamics (1950–2000) 5.1 Infancy through Adolescence (1950–1980) Level I: Linear Potential Methods (LPMs) Level II: Nonlinear Potential Methods (NPMs) 5.2 Pursuit of Effectiveness (1980–2000) Level III: Euler Methods Level IV: Reynolds-Averaged Navier-Stokes (RANS) Methods 6. ACA Effectiveness: Status and Prospects (2000 and Beyond) 6.1 Assessment of Effectiveness (2000–2020) 6.2 Prospects for Fully Effective ACA Capability (Beyond 2020) 7. Closing Remarks 6 Copyright © 2021 by Pradeep Raj. All Rights Reserved. What is Applied Computational Aerodynamics? Applied Computational Aerodynamics (ACA) is an engineering discipline that deals with analysis and design of arbitrarily-shaped bodies moving through air using Computational Fluid Dynamics (CFD) methods (codes). CFD methods (codes) simulate fluid flow by numerically solving governing mathematical equations using digital computers. Image Source: Internet 7 Copyright © 2021 by Pradeep Raj. All Rights Reserved. Applied Computational Aerodynamics (ACA) is purpose-driven application of CFD… …and the purpose is to help designers solve engineering problems related to the design of vehicles that move through air, not just to run CFD codes and produce data! In Today’s World of Engineering Design, ACA is a Necessity—Not a Luxury—for All Vehicles that Move Through Air 8 Copyright © 2021 by Pradeep Raj. All Rights Reserved. Fully Effective ACA Delivers credible solutions of aerodynamic problems to designers of vehicle systems on time and within budget • Pervasive Role of ACA in engineering design makes it imperative that its effectiveness be maximized Luis R. Miranda • Miranda in 1982 defined ACA Effectiveness as a product of two factors Effectiveness = Quality x Acceptance “Q” Factors: quality of results . Credible prediction of aerodynamic characteristics for a wide variety of configurations and flow conditions (can we trust the data/ results?) “A” Factors: user acceptance Manager . Easy to use with rapid turnaround, i.e., short elapsed Computational Aerodynamics time from go-ahead to delivery Lockheed-California Co. Low cost (labor hours plus H/W-S/W costs) Fully Effective ACA Requires Simultaneous Maximization of Both Q and A Factors Source: Ref. 1.1 9 Copyright © 2021 by Pradeep Raj. All Rights Reserved. Credible Data is of Critical Importance for Aircraft Design “Design is an iterative decision-making activity performed by team of engineers to produce plans by which resources are converted, preferably optimally, into systems or devices to meet human need.” T.T. Woodson • Success of design efforts Introduction to Engineering Design, 1966 strongly depends on quality and timeliness of decisions. • On-time quality decisions depend on availability of credible data at the right time and the right cost. • The later a major configuration change is made, the higher the cost—exponentially higher! Quality Decisions Early Better Quality Final Product at Lower Cost Image Courtesy of L.R. Miranda 10 Copyright © 2021 by Pradeep Raj. All Rights Reserved. Computational Fluid Dynamics (CFD): A Subdiscipline of Fluid Dynamics Fluid Dynamics: The branch of applied science concerned with the movement of fluids (liquids and gases).* Fluid Dynamics Analytical E Computational Fluid Dynamics F Fluid Dynamics (AFD) (CFD) D Experimental Fluid Dynamics (EFD) Aerodynamics: A branch of Fluid Dynamics with air as the fluid. Synergistic Use of AFD, EFD, and CFD is Essential to Comprehensive Understanding of Fluid Dynamics *American Heritage Dictionary 11 Copyright © 2021 by Pradeep Raj. All Rights Reserved. EFD and CFD: Two Primary Means of Aerodynamic Simulations Today EFD (Experimental Fluid Dynamics) CFD (Computational Fluid Dynamics) S • Low cost t • Perceived as “Real” r • Credible data • Quick turnaround e . Quantified uncertainties • No scale effects n • Large excursions per entry • No wall interference effects g • No support interference effects t • Assess aeroelastic distortions effects h • Applicable to all flight conditions s W • Higher cost, longer elapsed time • Perceived as “Virtual” e a • Scale effects • Lack of credibility due to k • Wall interference effects . Computational uncertainties caused n • Support interference effects by limitations or deficiencies in e • Difficult to assess aeroelastic Numerical Modeling and Flow s distortions effect Physics Modeling s • Not practical for some flight e conditions s Highly Complementary Strengths 12 Copyright © 2021 by Pradeep Raj. All Rights Reserved. CFD Plays a Key Role in Air Vehicle Design • Generate Aerodynamic Data for Designing Air Vehicles o New Vehicles (clean-sheet designs) o Derivative Vehicles (improvements, upgrades and/or modifications) • Enable Multidisciplinary Analysis, Design & Optimization (MADO) Environments to Create Quality, Affordable Air Vehicles o CFD offers the most practical means (probably the only?) of producing data required for rapid design closure through extensive multidisciplinary trade-offs o CFD affords timely and cost-effective evaluation of the impact of geometric changes on performance, and of sensitivity of performance to numerous design variables o CFD provides inverse design and shape optimization capability that most clearly differentiates it from EFD CFD is the Linchpin of Simulation Based Design Source: Refs. 1.2 – 1.4 13 Copyright © 2021 by Pradeep Raj. All Rights Reserved. Role of CFD in Air Vehicle Design Generate Aerodynamic Data for Designing Air Vehicles • New Vehicles (clean-sheet designs) o Outer Mold Line (OML) Design: Forces, moments, and surface pressure distributions o Shape Optimization: Sensitivity of aerodynamic data to design variables o Flight Performance Prediction: Data to validate take-off, climb, cruise, maneuver, descent, landing Quieter Supersonic Aircraft o Airframe Propulsion Integration: Data to minimize installation losses o System Integration: Off-body flow field for safe carriage and deployment of stores & weapons o Structural Design: Steady and unsteady flight loads o Flight Control System Design: Stability & Control coefficients and rate derivatives A-380 o Etc. • Derivative Vehicles (improvements, C-5M upgrades and/or modifications) o Aerodynamic data to assess impact of shape change on performance when integrating new or improved subsystems to upgrade current product Reliability Enhancement & or design a derivative Re-engining Program (RERP) Source: Refs. 1.2 – 1.5 14 Copyright © 2021
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