# Search results

- Title
- Effects of Fluctuating Energy Input on the Small Scales in Turbulence
- Creator
- Chien, Chen-chi (Chen-chi Chien) (Author), (Greg Voth) (Thesis advisor)
- Date
- 2013-05-23
- Description
- 2013, In Copyright – Non-Commercial Use Permitted (InC-NC)

- Title
- Experimental Measurement of the Stress Tensor in a Quasi-2D Granular Gas
- Creator
- Yang, Wan Jun (Wan Jun Yang) (Author), (Greg Voth) (Thesis advisor)
- Date
- 2011-04-15
- Description
- 2011, Old URL: https://wesscholar.wesleyan.edu/etd_hon_theses/745, In Copyright – Non-Commercial Use Permitted (InC-NC)

- Title
- Experimental Study of Lagrangian Velocity and Energy Statistics in Inhomogeneous Turbulence
- Creator
- Kunwar, Surendra Bahadur (Surendra Bahadur Kunwar) (Author), (Greg Voth) (Thesis advisor)
- Date
- 2010-04-15
- Description
- We study Lagrangian statistics in a flow stirred by two oscillating grids. We quantify the dependence of small scales on the inhomogeneous large scales in a complex flow. We also describe the method we developed to study the measurement volume bias while investigating Lagrangian structure functions. We identify the important factors in energy transport by estimating the terms of the turbulent kinetic energy equation., 2010, Old URL: https://wesscholar.wesleyan.edu/etd_hon_theses/506, In Copyright – Non-Commercial Use Permitted (InC-NC)

- Title
- Fiber Orientation Fields in Turbulence
- Creator
- Masi-Phelps, Andrea Jean (Andrea Jean Masi-Phelps) (Author), (Greg Voth) (Thesis advisor)
- Date
- 2018-04-15
- Description
- We study the orientation field of fibers in homogeneous isotropic turbulence. As small rod-like particles (referred to as fibers) are advected through a turbulent flow, they rotate and follow Jeffery's equation, which may be used to calculate their orientations at any time in the flow. However, this method depends on the initial orientation chosen for each particle. Instead, we examine the preferential alignment of the particles, which is given by the largest stretching direction of the surrounding fluid. We calculate this using the left Cauchy-Green strain tensor, which measures the strain deformation undergone by the fluid over a finite time interval. The most extensional eigenvector of the left Cauchy-Green strain tensor gives the stretching direction and thus the preferential fiber orientation. This does not depend on the initial orientation of the particle. We show that the independence of initial conditions extends further: as we calculate this field using longer integration times (by considering earlier initial sampling times), the field converges to an invariant state. We visualize the spatial structures of the orientation field and observe, for the first time in 3D turbulence, surfaces across which the orientation rapidly rotates by pi. These surfaces become thinner as we increase integration time, and create regions of very sharp change in the otherwise smooth orientation field. We measure these spatial structures statistically through the orientation structure function and demonstrate the fractal structure of the field caused by these alignment-inversion surfaces., 2018, Old URL: https://wesscholar.wesleyan.edu/etd_hon_theses/1918, In Copyright – Non-Commercial Use Permitted (InC-NC)

- Title
- Granular Gravitational Collapse in Realistically Simulated Granular Gases
- Creator
- Kachuck, Samuel Benjamin (Samuel Benjamin Kachuck) (Author), (Greg Voth) (Thesis advisor)
- Date
- 2010-04-15
- Description
- Gravitational granular collapse (GGC) occurs whenever a granular gas is allowed to evolve freely in gravity without the additional input of kinetic energy. The system dissipates its remaining energy through inelastic collisions as it settles into a granular solid at rest at the bottom of its enclosure in &amp;#64257;nite time. We are interested in the reasons for an observed divergence between experimental and theoretical results of the rate of decay. The use of realistic simulations con&amp;#64257;rms that, even in more closely ideal settings, the theory is not as universal as expected. We test the relative e&amp;#64256;ects of a variety of system parameters on GGC dynamics and conclude that the second-power granular temperature decay law during GGC theoretically derived involves the somewhat unphysical approximation of particles that interact with a constant coe&amp;#64259;cient of resititution that is very far into the elastic limit., 2010, Old URL: https://wesscholar.wesleyan.edu/etd_hon_theses/497, In Copyright – Non-Commercial Use Permitted (InC-NC)

- Title
- Lord Kelvin's Error? An Investigation into the Isotropic Helicoid
- Creator
- Collins, Darci Katarina (Darci Katarina Collins) (Author), (Greg Voth) (Thesis advisor)
- Date
- 2018-04-15
- Description
- In a publication in 1871, Lord Kelvin, a notable $19^\text{th}$ century scientist, hypothesized the existence of an isotropic helicoid. He predicted that such a particle would be isotropic in drag and rotation translation coupling, and also have a handedness that causes it to rotate. Since this work was published, theorists have made predictions about the motion of isotropic helicoids in complex flows. Until now, no one has built such a particle or quantified its rotation translation coupling to confirm whether the particle has the properties that Lord Kelvin predicted. In this thesis, we show experimental, theoretical, and computational evidence that all conclude that Lord Kelvin's geometry of an isotropic helicoid does not couple rotation and translation. Even in both the high and low Reynolds number regimes, Lord Kelvin's model did not rotate through fluid. While it is possible there may be a chiral particle that is isotropic in drag and rotation translation coupling, this thesis presents compelling evidence that the geometry Lord Kelvin proposed is not one. Our evidence leads us to hypothesize that an isotropic helicoid does not exist., 2018, Old URL: https://wesscholar.wesleyan.edu/etd_hon_theses/1910, In Copyright – Non-Commercial Use Permitted (InC-NC)

- Title
- Ramified Deformable Particles in Simple Shear
- Creator
- Krellenstein, Michael Gregory (Michael Gregory Krellenstein) (Author), (Greg Voth) (Thesis advisor)
- Date
- 2017-04-15
- Description
- Abstract The behavior of deformable structures in fluid flows is a standard problem, but normally involves the interaction between a complex flow and a complex structure. Fibers are an example such an interaction: the curvature of a fiber in a fluid flow will correspond to the derivative of the velocity gradient tensor. In simpler flows however, where the velocity gradient tensor remains constant over time, fibers exhibit no deformation, making them no more useful than non-deformable structures. [1] We have identified a new opportunity for deformable structures by using deformable ramified particles. These particles interactions with linear velocity fields (i.e. flows with constant velocity gradient tensors) are simple enough that we can extract the full velocity gradient from a single deformable particle. Normally, numerous non-deformable particles would be required to extract the same information. This is of particular value when studying turbulent flows. Turbulent flows exhibit linear behavior at the kolmogorov length, but because this length is often exceedingly small, the seed density (density of tracer particles) needed to re-assemble the full velocity gradient tensor is prohibitively high. Using deformable ramified particles, which extract far more information on a per particle basis, we can make the same measurements while maintaining a low seed density. The use of ramified deformable particles represents a novel development in the field of fluid dynamics. As a proof of concept, we set out to test them in a simple, well understood fluid flow with well known fluid structure interactions., 2017, Old URL: https://wesscholar.wesleyan.edu/etd_hon_theses/1813, In Copyright – Non-Commercial Use Permitted (InC-NC)

- Title
- Rotational Dynamics of Anisotropic Particles in Turbulence: Measurements of Lagrangian Vorticity and the Effects of Alignment with the Velocity Gradient
- Creator
- Geyer, Guy (Guy Geyer) (Author), (Greg Voth) (Thesis advisor)
- Date
- 2013-05-23
- Description
- 2013, Old URL: https://wesscholar.wesleyan.edu/etd_hon_theses/1065, In Copyright – Non-Commercial Use Permitted (InC-NC)

- Title
- Sedimentation and Orientation of Slender Particles in a Laminar Flow
- Creator
- Tierney, Lydia Helen (Lydia Helen Tierney) (Author), (Greg Voth) (Thesis advisor)
- Date
- 2016-04-15
- Description
- The motions of high aspect ratio particles settling in fluid flow are of importance in a range of scientific fields, including atmospheric science and biological fluid dynamics. In the past, calculations for the orientation and sedimentation velocities of long slender particles were conducted in the Stokes flow limit, valid only in the absence of fluid inertia. This thesis work presents series of experiments designed to extend the theory for the sedimentation of high aspect ratio particles to the finite Reynolds number regime. Additionally, experiments are presented which examine the effect of particle asymmetry on the inertial torques on the sedimenting bodies. Of particular interest in the case of the asymmetric particles is the discontinuity in the transition from a horizontal to vertical sedimentation orientation as the particle asymmetry increases. Each experiment that I conducted was designed to accompany theoretical developments by collaborators at Cornell. In addition to experimental work, this thesis presents a review of the mathematics and theoretical development of slender body theory, including recent work completed by collaborators in the the Cornell department of Chemical and Biomolecular Engineering., 2016, Old URL: https://wesscholar.wesleyan.edu/etd_hon_theses/1535, In Copyright – Non-Commercial Use Permitted (InC-NC)

- Title
- The Alignment of Rods and Disks in Turbulence
- Creator
- Hunt, Conor Gerard (Conor Gerard Hunt) (Author), (Greg Voth) (Thesis advisor)
- Date
- 2016-04-15
- Description
- We study the orientation and rotational dynamics of anisotropic particles in homogenous isotropic turbulence. By analyzing direct numerical simulation (DNS) data at Taylor-microscale Reynolds number of 180, we quantify the preferential alignment between particle orientations and vorticity, as well as alignment with principal stretching directions defined by the Cauchy-Green strain tensor. This tensor quantifies stretching experienced by material elements in turbulence and provides a natural basis for studying particle alignment in turbulence. While previous work has focused primarily on thin rods, we extend the study to oblate disks. Both rods and disks are a specific class of anisotropic particles known as axisymmetric ellipsoids. These particles are defined by their aspect ratio, the ratio of their length, L, to their diameter, d. Rods have an aspect ratio greater than 1 while disks have an aspect ratio less than 1. The case of aspect ratio equalling 1 is a sphere. In this thesis, we compare the preferential alignments of rods with disks in turbulence. Rods preferentially align with vorticity as a result of both quantities independently aligning with the strongest extensional stretching direction, as defined by the maximum eigenvector of the Cauchy-Green strain tensor. In contrast, disks orient perpendicular to vorticity and preferentially align with the strongest compressional stretching direction, as defined by the smallest Cauchy-Green eigenvector. Furthermore, we study the relationship between the principle stretching eigenframe defined by the eigenvectors of the Cauchy-Green strain tensor and the principle rate of stretching eigenframe defined by the eigenvectors of the strain rate tensor, the symmetric part of the velocity gradient tensor., 2016, Old URL: https://wesscholar.wesleyan.edu/etd_hon_theses/1679, In Copyright – Non-Commercial Use Permitted (InC-NC)

- Title
- Turbulence Generated by a Randomly Pulsed Through Flow Jet-Array
- Creator
- Rees, Wyatt Jackson (Wyatt Jackson Rees) (Author), (Greg Voth) (Thesis advisor)
- Date
- 2017-04-15
- Description
- We study the turbulence generated by a through flow jet-array in our newly constructed vertical water tunnel. This apparatus was designed to facilitate the measurement of dynamics of sedimenting particles in turbulence. It circulates water through a vertical, square channel, passing through a grid of 40 water jets that each fire at two 45 degree angles from the horizontal axis. We pulse the jet-array in several randomized patterns and intensities, while maintaining a constant total flow rate for each configuration. In its minimum turbulence configuration, the jets eject no fluid, allowing the jet-array to essentially function as a passive grid. When the jets are activated, the jet-array maintains a constant number of jets that will be on at any moment, an average duration for each jet to remain on, a through-flow rate, and a total jet-flow rate. This thesis characterizes the flow generated by the jet-array with different jet configurations and intensities. We see turbulence that is highly isotropic in the lateral plane, and homogeneous in the upper half of the test section. We also see varying levels of skewness of the flow with a high dependence on the number of jets firing. We study the flow at 36 cm, 60 cm, 90 cm, and 120 cm above the jet-array to analyze how various properties of the turbulence dissipate through space., 2017, Old URL: https://wesscholar.wesleyan.edu/etd_hon_theses/1829, In Copyright – Non-Commercial Use Permitted (InC-NC)

- Title
- Two Point Correlations Between Velocity Sums and Differences, and Their Implications for Large-Small Scale Correlations in Fluid Turbulence
- Creator
- Rotile, Nicholas Joseph (Nicholas Joseph Rotile) (Author), (Greg Voth) (Thesis advisor)
- Date
- 2012-04-15
- Description
- 2012, Old URL: https://wesscholar.wesleyan.edu/etd_hon_theses/885, In Copyright – Non-Commercial Use Permitted (InC-NC)