+publisher:"Clemson University" +contributor:("Dr. John Saylor")

Clemson University

1. Bergen, Jesse Edward. Intrinsic Geometrical Constraints of Spontaneously Excited Leidenfrost Drops.

Degree: MS, Mechanical Engineering, 2018, Clemson University

URL: https://tigerprints.clemson.edu/all_theses/2971

A liquid drop placed on a heated surface above the Leidenfrost temperature will levitate on a vapor cushion. The static shape of these non-wetting Leidenfrost drops is that of a flattened sphere, reflecting the balance between gravitational, surface tension and lubrication pressures. In this thesis, we study Leidenfrost drops on curved substrates where we observe spontaneous star-shaped surface oscillations of characteristic frequency and mode number. Experiments are conducted using six different liquids and the temporal response of the observed modes n = 2 – 13 is analyzed to dene the oscillation spectrum. We observe that large drops oscillate with a constant frequency, while small drop frequencies are strongly dependent upon liquid volume. A simple mathematical model is developed using a hydrodynamic stability analysis and shows reasonable agreement with our large experimental data set. Scaling arguments are used to collapse the data which allows generalized statements to be made regarding the physics governing star oscillations. In addition, we observe more complex dynamics such as mode doubling where two distinct modes are simultaneously excited at different frequencies and modal dominance where one mode persists over large ranges of parameter space previously thought to be occupied by another mode. Lastly, we conclude by offering some qualitative observations of Leidenfrost shape instabilities in other complex substrate geometries. Advisors/Committee Members: Dr. Joshua Bostwick, Committee Chair, Dr. John Saylor, Dr. Daniel Fant.

Subjects/Keywords: Drop; Instability; Interfacial; Mechanics; Oscillation; Surface

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APA (6^th Edition):

Bergen, J. E. (2018). Intrinsic Geometrical Constraints of Spontaneously Excited Leidenfrost Drops. (Masters Thesis). Clemson University. Retrieved from https://tigerprints.clemson.edu/all_theses/2971

Chicago Manual of Style (16^th Edition):

Bergen, Jesse Edward. “Intrinsic Geometrical Constraints of Spontaneously Excited Leidenfrost Drops.” 2018. Masters Thesis, Clemson University. Accessed January 24, 2021. https://tigerprints.clemson.edu/all_theses/2971.

MLA Handbook (7^th Edition):

Bergen, Jesse Edward. “Intrinsic Geometrical Constraints of Spontaneously Excited Leidenfrost Drops.” 2018. Web. 24 Jan 2021.

Vancouver:

Bergen JE. Intrinsic Geometrical Constraints of Spontaneously Excited Leidenfrost Drops. [Internet] [Masters thesis]. Clemson University; 2018. [cited 2021 Jan 24]. Available from: https://tigerprints.clemson.edu/all_theses/2971.

Council of Science Editors:

Bergen JE. Intrinsic Geometrical Constraints of Spontaneously Excited Leidenfrost Drops. [Masters Thesis]. Clemson University; 2018. Available from: https://tigerprints.clemson.edu/all_theses/2971

Clemson University

2. Quinones, Matthew. Numerical Analysis of Scramjet Cavity Flameholders at Varying Flight Mach Numbers.

Degree: MS, Mechanical Engineering, 2018, Clemson University

URL: https://tigerprints.clemson.edu/all_theses/3010

Various types of air breathing engines are used as propulsion devices in aviation. At high flight velocities, the use of a ramjet or supersonic combustion ramjet (scramjet) may be preferred due to the natural compressibility of air at high speed. A scramjet, while similar to the ramjet, does not slow air to subsonic speeds prior to combustion, allowing it to operate at much higher flight velocities at very high altitude. For this reason, however, the residence time of air inside of the combustor is on the order of milliseconds, requiring rapid mixing and ignition of the fuel to generate adequate thrust. To do this, a flameholder is often used, which generates turbulence, shock waves, and maintains a recirculation region through geometric effects. In this study, four geometry types involving eighteen separate designs were chosen and analyzed using CFD software. Isolator inlet Mach numbers of 2.2, 4, 6, 8, and 10 were selected to model varying flight velocity, and hydrogen fuel was injected sonically at all injector locations with a single step reaction mechanism applied for combustion. An existing square cavity model was chosen and modified to produce slanted cavity, double cavity, and combined strut-cavity designs. The flameholders were analyzed in a non-reacting simulation to observe their effects on the flow field and fuel mixing efficiency. Reacting simulations were performed for each flameholder to investigate flame stabilization capabilities, thermal choking, stagnation pressure losses and drag generated inside of the combustor. Results show that all designs sustain a flame during combustion at all flight Mach numbers. However, the square cavity with a back cavity injector does this while limiting losses and drag due to shock wave formation, thermal choking, and geometric effects in the flow. Advisors/Committee Members: Dr. Richard Miller, Committee Chair, Dr. John Saylor, Dr. Xiangchun Xuan.

Subjects/Keywords: Flame holder; Flame stability; Ramjet; Scramjet

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Quinones, M. (2018). Numerical Analysis of Scramjet Cavity Flameholders at Varying Flight Mach Numbers. (Masters Thesis). Clemson University. Retrieved from https://tigerprints.clemson.edu/all_theses/3010

Chicago Manual of Style (16^th Edition):

Quinones, Matthew. “Numerical Analysis of Scramjet Cavity Flameholders at Varying Flight Mach Numbers.” 2018. Masters Thesis, Clemson University. Accessed January 24, 2021. https://tigerprints.clemson.edu/all_theses/3010.

MLA Handbook (7^th Edition):

Quinones, Matthew. “Numerical Analysis of Scramjet Cavity Flameholders at Varying Flight Mach Numbers.” 2018. Web. 24 Jan 2021.

Vancouver:

Quinones M. Numerical Analysis of Scramjet Cavity Flameholders at Varying Flight Mach Numbers. [Internet] [Masters thesis]. Clemson University; 2018. [cited 2021 Jan 24]. Available from: https://tigerprints.clemson.edu/all_theses/3010.

Council of Science Editors:

Quinones M. Numerical Analysis of Scramjet Cavity Flameholders at Varying Flight Mach Numbers. [Masters Thesis]. Clemson University; 2018. Available from: https://tigerprints.clemson.edu/all_theses/3010

Clemson University

3. Abarotin, Cameron Alexander. An Experimental Study of Low Velocity Impact of Bistable Laminated CFRP Composites.

Degree: MS, Mechanical Engineering, 2018, Clemson University

URL: https://tigerprints.clemson.edu/all_theses/2961

In recent years, laminated carbon fiber reinforced polymer (CFRP) composites have gained popularity in engineering applications due to their lightweight and strong mechanical properties. One of this material's greatest weaknesses is that it performs poorly in out-of-plane impact resistance. Thus, it was the objective of this research to investigate the effect of bistability on the impact resistance of laminated CFRP composites. Bistable composites have the ability to alternate between two different geometric equilibria through external loading, and when unloaded, do not require external forces to maintain either geometry. An instrumented dropweight tower was designed and constructed according to ASTM standards with modifications to accommodate bistability. Laminated CFRP composite specimens of bistable, flat monostable, and curved monostable configurations were subjected to low velocity impacts of 20 J. The acceleration and force of each impact was recorded using an accelerometer and a load cell mounted on the dropweight tower's impactor. The sensor data was used to analyze the dynamic response and calculate the energy absorption of each impact. Post-impact crack length measurements and damage characterization were used to conduct a damage resistance analysis. The effects of moisture, geometry, stacking sequence, and bistability of the impacted specimens were determined. The results showed that bistability improves the low velocity impact damage resistance of laminated CFRP composites through increased energy absorption and specimen kinetic energy. Advisors/Committee Members: Dr. Oliver Myers, Co-Committee Chair, Dr. Garrett Pataky, Co-Committee Chair, Dr. John Saylor.

Subjects/Keywords: Bistable; CFRP; Composites; Experimental; Laminated; Low Velocity Impact

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Abarotin, C. A. (2018). An Experimental Study of Low Velocity Impact of Bistable Laminated CFRP Composites. (Masters Thesis). Clemson University. Retrieved from https://tigerprints.clemson.edu/all_theses/2961

Chicago Manual of Style (16^th Edition):

Abarotin, Cameron Alexander. “An Experimental Study of Low Velocity Impact of Bistable Laminated CFRP Composites.” 2018. Masters Thesis, Clemson University. Accessed January 24, 2021. https://tigerprints.clemson.edu/all_theses/2961.

MLA Handbook (7^th Edition):

Abarotin, Cameron Alexander. “An Experimental Study of Low Velocity Impact of Bistable Laminated CFRP Composites.” 2018. Web. 24 Jan 2021.

Vancouver:

Abarotin CA. An Experimental Study of Low Velocity Impact of Bistable Laminated CFRP Composites. [Internet] [Masters thesis]. Clemson University; 2018. [cited 2021 Jan 24]. Available from: https://tigerprints.clemson.edu/all_theses/2961.

Council of Science Editors:

Abarotin CA. An Experimental Study of Low Velocity Impact of Bistable Laminated CFRP Composites. [Masters Thesis]. Clemson University; 2018. Available from: https://tigerprints.clemson.edu/all_theses/2961

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