CFD as Applied to the Design Of Short Takeoff and Landing Vehicles Using Circulation Control A Thesis Presented to the Faculty of California Polytechnic State University, San Luis Obispo In Partial Fulfillment of the Requirements for the Degree of Master of Science in Aerospace Engineering By Tyler Matthew Ball June 2008 © 2008 Tyler Matthew Ball ALL RIGHTS RESERVED ii Approval Page Title: CFD as Applied to the Design of Short Takeoff and Landing Vehicles Using Circulation Control Author: Tyler Matthew Ball Date Submitted: June 2008 Dr. David D. Marshall ______________________ Advisor/Committee Chair Signature Dr. Jin Tso __ ______________________ Committee Member Signature Dr. Robert A. McDonald ______________________ Committee Member Signature Dr. Kim Shollenberger _ ______________________ Committee Member Signature iii Abstract Title: CFD as Applied to the Design of Short Takeoff and Landing Vehicles Using Circulation Control Author: Tyler Matthew Ball The ability to predict the distance required for an aircraft to takeoff is an essential component of aircraft design. It involves aspects related to each of the major aircraft systems: aerodynamics, propulsion, configuration, structures, and stability and control. For an aircraft designed for short takeoffs and landings (STOL), designing the aircraft to provide a short takeoff distance, or more precisely the balanced field length (BFL), often leads to the use of a powered lift technique such as circulation control (CC). Although CC has been around for many years, it has never been used on a production aircraft. This is in part due to the lack of knowledge as to how well CC can actually perform as a high lift device. This research provides a solution to this problem. By utilizing high fidelity computational fluid dynamics (CFD) aerodynamic data, a four-dimensional design space which was populated and modeled using a Monte Carlo approach, and a Gaussian Processes regression technique, an effective aerodynamic model for CC was produced which was then used in a BFL simulation. Three separate models were created of increasing quality which were then used in the BFL performance calculations. A comprehensive gridding methodology was provided as well as computational and grid dependence error analysis. Specific consideration was given to the effect of resolving the turbulent boundary layer in both the gridding and solving processes. Finally, additional turbulence model validation work was performed, both to match previously performed experimental data and to provide a comparison of different models’ abilities to predict separation. iv Acknowledgments There are a number of people which need to be mentioned for their support throughout my time spent here at Cal Poly. First, I want to thank my wife Amanda who has spent countless nights waiting for me to finish my work and often fell asleep in the process because I took too long. I want to apologize to my daughter Lillian for the many hours which I spent sitting at a computer instead of helping her litter toys around the apartment. I want to say thanks to my parents Mark and Darlene for supporting me in my five years at Cal Poly as well as the Navy and the Department of Naval Research for supporting me over the first summer of research on CCW. I would also like to say thanks to the rest of my family who continually asked me “so what are you doing?” and “so when will you be finished.” It’s finished now. I would like to thank Dr. Marshall for the years of guidance and direction which he provided on this project. Thanks to Scott Turner for his companionship in a building without windows for an entire summer. This project would have been much different without him and the GPs. I am grateful for the other two guys who spent their days in the ATL along with Scott and me: Brian Saponas and Robert Perry. Many hours of gridding, coding, solving, and analysis was performed alongside these people and everyone was always willing to help out. Thanks to Cal Poly for the 26 computers and the 90 plus cores on which this research were performed. Of those 26 computers, I am proud to say I crashed all but three, which were the three Windows machines which I used to write this report. And finally, I’d like to thank SSH, which provided the means for me to crash those 23 computers in five different buildings without having to leave my chair in the ATL. v Table of Contents List of Tables............................................................................... viii List of Figures ................................................................................ix Nomenclature.................................................................................xi 1 Introduction ..............................................................................1 1.1 Balanced Field Length ........................................................................................ 1 1.2 Problems with BFL Calculations for Powered Lift Aircraft............................... 4 1.3 Circulation Control – How it Works................................................................... 7 1.4 CFD Process and Methods.................................................................................. 9 1.4.1 CFD Basics ................................................................................................. 9 1.4.2 Computational use of Governing Equations............................................. 11 1.4.3 Turbulence Models ................................................................................... 14 1.5 Current Research on Circulation Control ......................................................... 18 1.5.1 Circulation Control and Turbulence Models ............................................ 18 2 Research of de la Montoya ....................................................29 2.1 Circulation Control Wing Geometry ................................................................ 29 2.2 Results............................................................................................................... 30 2.2.1 Grid Dependence ...................................................................................... 30 2.2.2 Turbulence Model Validation................................................................... 31 2.2.3 Three-Dimensional Analysis .................................................................... 32 3 Turbulence Model Validation...............................................34 3.1 Spalart-Allmaras and Y + Analysis .................................................................... 34 3.2 Turbulence Model Separation Verification ...................................................... 35 4 Design of Experiments ...........................................................41 5 Modeling and Simulation ......................................................44 5.1 Metamodeling and Gaussian Processes ............................................................ 44 5.2 BFL Simulation................................................................................................. 49 5.2.1 Performance Validation ............................................................................ 51 6 Preliminary Model .................................................................55 6.1 Gridding with Gambit ....................................................................................... 55 6.1.1 Gambit Limitations ................................................................................... 55 6.1.2 Gridding Techniques................................................................................. 56 6.1.3 Gridding Automation................................................................................ 57 6.2 Solving Methods ............................................................................................... 58 6.2.1 Setting up Fluent ....................................................................................... 58 6.2.2 Y+ Adaption .............................................................................................. 60 6.2.3 Multigridding ............................................................................................ 62 6.2.4 Fluent Automation Scripting .................................................................... 64 6.3 2D Results......................................................................................................... 67 6.4 3D Typical Flowfield Results........................................................................... 68 6.5 High Separation Results.................................................................................... 69 6.6 Preliminary Performance of CCW STOL Aircraft ........................................... 71 vi 7 Interim Model.........................................................................78 7.1 Improved Thrust Model .................................................................................... 78 7.2 Improved Aerodynamic Model......................................................................... 79 7.3 Interim BFL Results.......................................................................................... 82 8 Final Model .............................................................................85 8.1 Gridding with Icem ........................................................................................... 85 8.2 Solution Comparisons and Grid Improvements................................................ 93 8.2.1 Grid Resolution........................................................................................