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Abstract Hypersonic Application of Focused ABSTRACT Title of thesis: HYPERSONIC APPLICATION OF FOCUSED SCHLIEREN AND DEFLECTOMETRY Colin VanDercreek, Master of Science, 2010 Thesis directed by: Associate Professor Kenneth Yu Department of Aerospace Engineering A non-intrusive diagnostic capability for determining the hypersonic shock and boundary layer structure was developed, installed, and successfully tested at the AEDC Hypervelocity Tunnel 9. This customized diagnostic involves a combi- nation of a focused schlieren system, which relies on creating multiple virtual light sources using a Fresnel lens and a source grid, and a deflectometry system, which uses the focused schlieren and a photomultiplier tube. It was used for obtaining spatially resolved images of density gradients with a depth of focus less than one centimeter, while allowing high frequency measurements of density fluctuations. The diagnostic was applied in investigating the second mode instability waves present in the boundary layer of a sharp-nosed cone submerged in a Mach 10 flow. The waves were successfully imaged and their frequencies were measured even though kg the flow density was below 0:01 m3 and the frequencies over 200 kHz. This adds a new capability to hypersonic testing. HYPERSONIC APPLICATION OF FOCUSED SCHLIEREN AND DEFLECTOMETRY by Colin Paul VanDercreek Thesis submitted to the Faculty of the Graduate School of the University of Maryland, College Park in partial fulfillment of the requirements for the degree of M.S. in Aerospace Engineering 2010 Advisory Committee: Associate Professor Kenneth H. Yu, Chair Associate Professor Chris Cadou Professor Mark Lewis c Copyright by Colin VanDercreek 2010 Dedication To Badger ii Acknowledgments I would like to thank the extremely knowledgeable and dedicated staff of Tunnel 9, especially Mike Smith for their support and assistance. My advisor Dr. Yu has been very helpful by giving me excellent advice on improving my research. Additionally, I would like to thank AFOSR, Purdue University, and Dr. Settles group at Penn State University for their support and assistance. iii Table of Contents List of Tables vi List of Figures vii List of Abbreviations ix 1 Introduction 1 1.1 Motivation . .2 1.2 Focused Schlieren and Deflectometry . .4 1.3 Research Objectives . .6 1.4 Scope . .8 2 Theoretical Considerations 9 2.1 Literature Review . .9 2.2 Theory . 20 2.2.1 Conventional Schlieren . 20 2.2.2 Focused Schlieren . 23 2.2.3 Deflectometry . 33 3 Diagnostics Development 36 3.1 Focusing Schlieren . 36 3.1.1 Light Source and Source Grid . 38 3.1.2 Cutoff Grid . 40 3.1.3 Recording Schlieren Images . 45 3.1.4 Design Trade-offs . 46 3.1.5 Final Set-up . 50 3.1.6 Design Summary . 57 3.2 Deflectometry Development . 60 3.2.1 Deflectometry Optimization . 63 3.2.2 Signal Processing . 67 3.2.3 Design Summary . 69 4 Experimental Demonstration of Diagnostics 73 4.1 Calibration Laboratory . 73 4.1.1 Focused Schlieren . 74 4.1.2 Deflectometry . 80 4.2 Transition Cone Experiment at Tunnel 9 . 82 4.2.1 Focused Schlieren . 89 4.2.2 Deflectometry . 96 iv 5 Summary and Conclusions 103 5.1 Summary of Results . 104 5.1.1 Focused Schlieren Visualization . 105 5.1.2 Deflectometry . 107 5.2 Technical Contributions . 108 5.3 Future Research . 112 A Matlab FFT script 114 v List of Tables 3.1 Design parameters, calibration Lab . 52 3.2 Focused schlieren diagnostic components . 52 3.3 Component spacing of Tunnel 9 focused schlieren set-up . 55 3.4 Design parameters of Tunnel 9 focused schlieren set-up . 55 3.5 Comparison of focusing schlieren and conventional schlieren . 59 3.6 Components used in the deflectometry diagnostic . 61 3.7 Comparison of diagnostics used to measure fluctuations in a flow . 72 4.1 Pipe lengths tested in Mach 3 nozzle . 83 4.2 Tunnel 9 nominal test conditions . 90 4.3 Transition cone deflectometry results . 99 vi List of Figures 2.1 Conventional schlieren . 22 2.2 Focused Schlieren Theory, Object in Focus . 25 2.3 Focused Schlieren Theory, Object Out of Focus . 25 2.4 Focused schlieren set-up . 29 2.5 Cutoff grid dimensions . 29 3.1 Focused schlieren set-up . 41 3.2 Example cutoff grid . 43 3.3 Change in field of view with model location . 46 3.4 Change in sensitivity with model location . 47 3.5 Change in depth of field with model location . 48 3.6 Change in sensitivity with number of grid lines . 49 3.7 Change in depth of field with number of grid Lines . 49 3.8 Calibration laboratory focused schlieren sensitivity . 51 3.9 Focusing schlieren, detailed component layout . 53 3.10 Tunnel 9 focused schlieren sensitivity . 54 3.11 Tunnel 9 focused schlieren components . 56 3.12 Deflectometry, detailed component layout . 62 3.13 Tunnel 9 deflectometry fiber optic location . 65 3.14 Run 37, before signal to noise ratio improvement . 70 3.15 Run 82, after signal to noise ratio improvement . 70 4.1 Layout of focused schlieren diagnostic in calibration laboratory . 75 4.2 Image of jet in focal plane . 76 4.3 Image of jet out of focal plane . 77 4.4 Image of sphere in Mach 3 flow . 78 4.5 Image of wedge in Mach 3 flow . 79 4.6 Run 51, L = 1.125" pressure transducer frequency measurement . 83 4.7 Run 51, L = 1.125" deflectometry frequency measurement . 84 4.8 Run 50, L = 1.5" pressure transducer frequency measurement . 84 4.9 Run 50, L = 1.5" deflectometry frequency measurement . 85 4.10 Run 38, L = 2.25" pressure transducer frequency measurement . 85 4.11 Run 38, L = 2.25" deflectometry frequency measurement . 86 4.12 Run 48, L = 3" pressure transducer frequency measurement . 86 4.13 Run 48, L = 3" deflectometry frequency measurement . 87 4.14 Transition cone . 89 4.15 Run 3317, frame 2661 . 91 4.16 Run 3317, frame 2661, Zoomed . 92 4.17 Run 3320, frame 1757 . 92 4.18 Run 3320, frame 1757 Zoomed . 93 4.19 Run 3320, frame 1790 . 94 4.20 Run 3320, frame 1790 Zoomed . 95 4.21 Run 3320, frame 1734 . 95 vii 4.22 Tunnel 9 test articles layout . 96 4.23 Run 3323, deflectometry frequency measurement . 100 4.24 Run 3324, deflectometry frequency measurement . 100 4.25 Run 3324, PCB gage 2 frequency measurement . 101 4.26 Run 3329, deflectometry frequency measurement . 101 4.27 Run 3329, PCB gage 3 frequency measurement . 102 viii List of Abbreviations n Index of Refraction k Gladstone-Dale coefficient ρ Density Angle of deflection n0 Refractive index of surrounding medium α The smallest ratio between the change in illumination due to a disturbance and the initial illumination E Image illumination a Light source image height above cut-off m Smallest detectable angle of deflection S Distance from disturbance to knife edge f Focal length L Distance from source grid to imaging lens l Distance from region of interest to imaging lens l0 Distance from imaging lens to imaging plane L0 Distance from imaging lens to cut-off grid w Resolution λ Wavelength of light b Spacing between opaque lines in the cut-off grid A Aperture of imaging lens DS Depth of sharp focus DU Depth of unsharp focus l R A θ Angle of ray bundle from individual source slit a2 Distance between center lines of adjacent slits φ Number of pairs of cutoff gridlines that blend together to form a schlieren image x Distance from plane of interest N Number of opaque and transparent line pairs Ω Ohms LF Fresnel Lens LS Schlieren Lens LR Relay Lens fLF Focal length of Fresnel Lens fLS Focal length of schlieren Lens fLR Focal length of relay Lens γ Ratio of specific heats L∗ Distance from shock to cavity base Rair Ideal gas constant for air To Stagnation Temperature AEDC Arnold Engineering Development Center AFOSR Air Force Office of Scientific Research PIV Particle Image Velocimetry LDI Laser Differential Interferometry ix Chapter 1 Introduction Sustained hypersonic flight is critical to the future of aerospace technology. Currently, re-entry vehicles such as spacecraft [1] are the dominant application of hypersonic aerodynamics. As technologies mature, hypersonic vehicles will increas- ingly be relied on for low cost access to space and rapid global transportation. How- ever there are many issues, such as transition prediction and thermal management, preventing sustained hypersonic travel from being practical. The accuracy of the prediction of the hypersonic flow over a vehicle is critical to designing an efficient ve- hicle [2]. Accurate prediction of where transition occurs is a critical area of research and is necessary to design hypersonic vehicles more effectively [3]. Knowledge of the transition location is important because it has a significant effect on the vehicle's lifting properties and the amount of heat transfer into a vehicle. Current hypersonic vehicle designs are conservative when it comes to thermal protection due to the uncertainty surrounding the prediction of transition. Increasing thermal protection adds more weight to the vehicle. With a more accurate understanding of the aero- dynamics, vehicles can be optimized to reduce weight, increase performance, and reduce operational cost. In order to develop new theories and computational mod- els, experimental data is critical. The focused schlieren and deflectometry diagnostic tools developed in this thesis will be a non-intrusive and flexible new capability for 1 acquiring hypersonic wind tunnel data to help improve the understanding of flow properties in order to improve hypersonic vehicle designs. 1.1 Motivation Wind tunnel testing is a critical part of the development and advancement of aerospace technologies [4]. Hypersonic wind tunnel testing is an important tool for investigating boundary layer transition and other hypersonic flow phenomena.
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