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Viscous Modeling of Ground Effect Aerodynamics Of VISCOUS MODELING OF GROUND EFFECT AERODYNAMICS OF AIRFOIL AND JET By ALEX EARLE OCKFEN A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN MECHANICAL ENGINEERING WASHINGTON STATE UNIVERSITY School of Mechanical and Materials Engineering DECEMBER 2008 To the Faculty of Washington State University: The members of the Committee appointed to examine the thesis of ALEX EARLE OCKFEN find it satisfactory and recommend that it be accepted. ___________________________________ Chair ___________________________________ ___________________________________ ii ACKNOWLEDGMENT First and foremost I would like to acknowledge my graduate advisor Dr. Konstantin Matveev, who made himself available for my questions and concerns at all times, no matter the subject or complexity. In addition to the vast technical and professional guidance from Dr. Matveev, I am thankful for his constant motivation and effort to provide diverse research, publication, and presentation opportunities. The members of my graduate committee, Dr. Prashanta Dutta and Dr. David Stock, have also been very helpful and provided feedback. Although my committee members have been instrumental, this educational experience would not have been possible without the handful of additional professors at Washington State University who provided the challenging coursework which has provoked my interest in the engineering field. In particular, Dr. Cecilia Richards provided the opportunity to complete an assistantship and related opportunities to gain experience with student interaction. All of these tasks could not have been completed without the constant support from members of the office staff, Jan Danforth, Bob Ames, and Gayle Landeen who have taken time on a weekly basis to make my experience as smooth as possible. Any additional technical difficulties were quickly addressed by Michael Shook and Giac Pham. Lastly, I would like to thank my family and friends whose support and advice have been a driving force for all of my achievements. iii VISCOUS MODELING OF GROUND EFFECT AERODYNAMICS OF AIRFOIL AND JET Abstract by Alex Earle Ockfen, M.S. Washington State University December 2008 Chair: Konstantin I. Matveev Wing-in-Ground craft and aerodynamically assisted marine vehicles take advantage of increased lift and reduced drag of wing sections in ground proximity. However, at relatively low speeds or heavily loaded craft, the passive aerodynamic lift may not be sufficient to provide vehicle support. In such cases, a flap at the wing trailing-edge or properly placed jet propulsor may be implemented to augment vehicle lift. Parametric design studies are completed for several ground effect configurations gaining insight into fundamental flow patterns and optimal performance regimes with flap and/or jet components implemented. This research takes advantage of efficient and low-cost numerical methods suited for design studies. The technique consists of a two-dimensional, steady-state, incompressible, viscous, finite volume method utilizing RANS turbulence models. Grid generation and solution of the Navier-Stokes equations are completed using Fluent 6.3. Validation of solution approach is provided with experimental validation of aerodynamic forces in and out of ground effect, plane turbulent jets, planar impinging jets, and static airfoil-flap-jet configurations. The influence of flap mechanization is first studied on the NACA 4412 airfoil in ground effect. Aerodynamic forces are calculated, and the effects of attack angle, Reynolds number, iv ground height, and flap deflection are presented for split and plain flaps. Overall, flap use on ground-effect vehicles with small attack angles is found to be beneficial for small flap deflections up to 5% of the chord, where an enhanced aerodynamic efficiency is realized. At low speeds where flap use is insufficient, the Power-Augmented-Ram (PAR) concept implements jet support to sufficiently augment vehicle lift. A simplified aerodynamic jet propulsor model, the ducted momentum source, is developed to account for upstream jet suction and downstream jet spreading. First, beneficial obliquely impinging propulsor configurations are studied with cross flow, and are then combined with a platform-flap to simulate a PAR vehicle. Results of PAR simulations suggest that in low-speed operation, harmful jet ingestion may occur. To avoid this phenomenon, the propulsor should be placed at impingement angles less than 30° and at moderate ground distances. With increasing PAR forward speed, performance may be increased by reducing flap deflection and impingement angle. v TABLE OF CONTENTS Page ACKNOWLEDGEMENT ....................................................................................................... iii ABSTRACT ............................................................................................................................. iv LIST OF TABLES ................................................................................................................... ix LIST OF FIGURES ...................................................................................................................x CHAPTER 1 INTRODUCTION ......................................................................................................1 1.1 MOTIVATION ...............................................................................................1 1.2 OBJECTIVE ...................................................................................................3 1.3 APPROACH ...................................................................................................5 1.4 VEHICLES BENEFITING FROM GROUND EFFECT ...............................7 1.4.1 WING-IN-GROUND ...................................................................................8 1.4.2 POWER-AUGMENTED-RAM ..................................................................9 2 NUMERICAL MODELING AND VALIDATION .................................................13 2.1 NUMERICAL MODELING ........................................................................13 2.1.1 GOVERNING EQUATIONS ....................................................................13 2.1.2 SPALART-ALLMARAS MODEL ...........................................................17 2.1.3 k-ε MODEL ...............................................................................................18 2.1.4 FINITE VOLUME METHOD ...................................................................20 2.1.5 DISCRETIZATION ...................................................................................21 2.1.6 PRESSURE-VELOCITY COUPLING .....................................................22 vi 2.1.7 SOLVER ....................................................................................................23 2.1.8 MESHING .................................................................................................24 2.1.9 CONVERGENCE CRITERIA ..................................................................25 2.2 VALIDATION ..............................................................................................26 2.2.1 UNBOUNDED TWO-DIMENSIONAL AIRFOIL ..................................26 2.2.2 TWO-DIMENSIONAL AIRFOIL WITH FLAP ......................................34 2.2.3 PLANAR TURBULENT FREE JET.........................................................37 2.2.4 MODELING CAPABILITIES ..................................................................45 3. WING-IN-GROUND EFFECT RESULTS ..............................................................47 3.1 NUMERICAL MODEL................................................................................48 3.2 EXPERIMENTAL COMPARISON .............................................................51 3.3 NUMERICAL RESULTS ............................................................................53 3.4 GROUND BOUNDARY CONDITION.......................................................61 3.5 DISCUSSION ...............................................................................................63 4. WING-IN-GROUND BEHAVIOR WITH FLAP ....................................................64 4.1 NUMERICAL MODEL................................................................................65 4.2 VALIDATION OF NUMERICAL TECHNIQUES .....................................70 4.3 PARAMETRIC CALCULATIONS .............................................................72 4.4 DISCUSSION ...............................................................................................84 5. OBLIQUE PROPULSORS FOR AERODYNAMIC APPLICATIONS .................86 5.1 SIMPLIFIED PROPULSOR MODELING ..................................................86 5.1.1 DEFINING THE SIMPLIFIED JET PROPULSOR MODELS ................87 vii 5.1.2 CHOOSING AN ADEQUATE JET PROPULSOR MODEL...................92 5.2 OBLIQUE JET IMPINGEMENT WITH CROSS-FLOW ...........................96 5.2.1 NUMERICAL MODEL...........................................................................100 5.2.2 NORMAL & OBLIQUE JET IMPINGEMENT VALIDATION ...........103 5.2.3 OBLIQUE JET IMPINGEMENT RESULTS .........................................106 5.3 CONCLUDING REMARKS ......................................................................119 6. PAR PLATFORM WITH JET AUGMENTATION AND FLAP ..........................122 6.1 INTRODUCTION ......................................................................................122 6.2 NUMERICAL TECHNIQUES ...................................................................123 6.3 EXPERIMENTAL
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