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An Investigative Study of Gurney Flaps on a NACA 0036 Airfoil

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AN INVESTIGATIVE STUDY OF GURNEY FLAPS ON A NACA 0036 AIRFOIL

A Thesis presented to the Faculty of California Polytechnic State University, San Luis Obispo

In Partial Fulfillment Of the Requirements for the Degree Master of Science in Aerospace Engineering

by Greg F. Altmann March 2011

2011 Greg F. Altmann ALL RIGHTS RESERVED

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COMMITTEE MEMBERSHIPTITLE: INVESTIGATIVE STUDY OF GURNEY FLAPS ON A NACA 0036 AIRFOIL

AUTHOR:

Greg F. Altmann

DATE SUBMITTED:

February 2011

COMMITTEE CHAIR:

Dr. Jin Tso Advisor and Committee Chair Aerospace Engineering Dept.

COMMITTEE MEMBER:

Dr. Tina Jameson Committee Member Aerospace Engineering Dept.

COMMITTEE MEMBER:

Dr. David D. Marshall Committee Member Aerospace Engineering Dept.

COMMITTEE MEMBER:

Dr. Chee Tung Committee Member NASA Ames

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ABSTRACTInvestigative Study of Gurney Flaps on a NACA 0036 AirfoilGreg F. Altmann

This project examined the effect of Gurney flaps on a 2D, 2-ft chord NACA 0036 airfoil in the Cal Poly 3x4 low speed wind tunnel at 25 m/s. It also covered the numerical simulation of the experiment in computational fluid dynamics (CFD). During the study, problems with the wind tunnel data were seen. After a careful diagnosis, the problem was traced to dirty flow conditioners which were subsequently replaced. Five Gurney flaps at 1, 2, 3, 4, and 5% of the chord were tested. The Gurney flaps had the effect of eliminating the lift reversal effect and lowering the profile drag at low angles of attack, ranging from 4-27%. The optimal Gurney flap appeared to be 2% of the chord. CFD modeling of the problem had limited success, with the best results coming from Mentors k-w SST turbulence model. This model reproduced the non-linear lift curve, and captured the trend in rising drag fairly well, but failed to predict the correct point of separation. Attempts to model the Gurney flap in CFD were unsuccessful.

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ACKNOWLEDGEMENTSI would first like to thank Joshua Roepke for his support through this project. Throughout our partnership with first FSAE and then the wind tunnel, his assistance has been invaluable to help me become a better test engineer. I question how I would have ever solved my wind tunnel problems without his help. I would like to thank my advisor, Dr. Tso, for being readily available and devoting countless hours to the project. I also want to thank my college roommates, and over the last few months, my uncle, for helping me escape the stressful world of my thesis. Thanks to The Boeing Company for letting me see a light at the end of the (wind) tunnel, and getting me to wrap up the project in a timely manner for employment. And, finally, I thank my family for the support and encouragement that they provided and that prompted me to get this task accomplished.

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Table of ContentsForeword .......................................................................................................................... xiii 1 2 Introduction ................................................................................................................. 1 Background ................................................................................................................. 4 2.1 2.2 2.3 2.4 2.5 3 3.1 3.2 3.3 3.4 3.5 4 4.1 4.2 4.3 4.4 4.5 5 5.1 Non-linear Nature of a NACA 0036 .................................................................... 4 Boundary Layer Transition .................................................................................. 5 Transition Strips ................................................................................................... 7 Separation ............................................................................................................. 7 Gurney Flaps ........................................................................................................ 9 Wind Tunnel Facility ......................................................................................... 12 NACA 0036 Model ............................................................................................ 13 Transition Strips ................................................................................................. 15 Gurney Flaps ...................................................................................................... 17 Pressure Measurement........................................................................................ 18 Velocity and Dynamic Pressure Calibration ...................................................... 21 Angle of Attack Calibration ............................................................................... 22 Data Collection ................................................................................................... 22 Observable Error Analysis ................................................................................. 23 Force Calculation ............................................................................................... 24 Governing Equations .......................................................................................... 26 Continuity ................................................................................................... 26 Momentum Equation (Navier-Stokes Equations) ....................................... 26 Energy Equation.......................................................................................... 27 Reynolds Averaging.................................................................................... 27 The Boussinesq Approximation .................................................................. 28 Turbulence Models ..................................................................................... 29

Experimental Apparatus............................................................................................ 12

Experimental Procedure ............................................................................................ 21

Numeric Simulation .................................................................................................. 26 5.1.1 5.1.2 5.1.3 5.1.4 5.2 5.2.1 5.2.2 5.3 5.4 5.5

Turbulence Modeling ......................................................................................... 28

Mesh Approach .................................................................................................. 29 Solver Settings.................................................................................................... 32 Boundary Conditions.......................................................................................... 32

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5.6 5.7 5.8 6 6.1 6.2 7 7.1 7.2 8 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11

Convergence Criteria.......................................................................................... 33 Data Post-Processing .......................................................................................... 33 Mesh Independence ............................................................................................ 34 Wind Tunnel Experiment ................................................................................... 38 CFD Simulation.................................................................................................. 45 Conclusions ........................................................................................................ 52 Future Work ....................................................................................................... 53 Discovery of a Problem ...................................................................................... 55 Wall Boundary Layer Measurement .................................................................. 57 Smoke Visualization .......................................................................................... 61 Oil Visualization ................................................................................................ 62 Initial CFD Investigation .................................................................................... 64 Inlet Velocity Measurements ............................................................................. 65 Inlet Diagnosis.................................................................................................... 68 Honeycomb Selection ........................................................................................ 71 Screen Selection ................................................................................................. 74 Post-repair Inspection ..................................................................................... 76 Facility Improvement Recommendations ....................................................... 80

Results and Discussions ............................................................................................ 38

Final Remarks on Research ...................................................................................... 52

Wind Tunnel Facility Investigation .......................................................................... 55

Appendix A Complete Data ........................................................................................... 83 Appendix B Probe Dimensions ...................................................................................... 86 Appendix C Tunnel Geometry ....................................................................................... 86 Appendix D A/Aflow Equation Derivation...................................................................... 87 Appendix E Matlab Code for Honeycomb Pressure Drop Coefficient .......................... 88 Appendix F Matlab Code for Panel Method ............................................................

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