Towards High Fidelity Particle-laden Simulations Based on Volume-filtering: From Point-particle to Interface-resolved Descriptions.

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Description
This dissertation presents a volume filtering framework to solve particle-laden flows. Particle-laden flows are studied, employing the well-established Euler-Lagrange method, using the point-particle approximation. This approach requires the filter width to be much larger than the particle diameter. The method

This dissertation presents a volume filtering framework to solve particle-laden flows. Particle-laden flows are studied, employing the well-established Euler-Lagrange method, using the point-particle approximation. This approach requires the filter width to be much larger than the particle diameter. The method assumes that the particle is smaller than the Kolmogorov length scale. This thesis investigates how inertial particles at semi-dilute volume fractions modulate the flow characteristics for particles smaller than 1 in wall units, when dispersed within wall-bounded channel flows at friction Reynolds number of 180. The simulations are performed with 4 way coupling in order to account for high local concentration of particles, to capture mechanisms such as turbophoresis and preferential concentration. We show that drag attenuation or augmentation is determined by the particle inertia. As particle size is increased greater than 1 in wall units, the regime becomes finite-sized, requiring an interface-resolved description. To do this a novel Immersed Boundaries (IB) framework based on the concept of volume-filtering called the Volume-Filtered Immersed Boundary (VF-IB) method is presented. Transport equations are obtained by volume-filtering the Navier-Stokes equation and accounting for the stresses at the solid-fluid interface. Boundary conditions are transformed into bodyforces that appear as surface integrals on the right hand side of the filtered equation. The approach requires the filter width to be much smaller than the particle diameter in order to accurately resolve the interfacial dynamics. Several canonical tests are conducted for both stationary and moving immersed solids and report comparable results to the experimental and/or body-fitted simulations. Keep in mind, the VF-IB method reverts back to the Euler-Lagrange formulation if the filter width is significantly greater than the particle diameter. An artifact of volume-filtering is the emergence of unclosed terms we define as the sub-filter scale term. In order to characterize the contribution of this term on the solution, a more simpler case of a 2-D varying coefficient hyperbolic equation that has an exact solution is looked into. It is observed that the sub-filter scale term scales inversely with the square of the filter width. For fine interface resolution (i.e. small filter width), this value can be ignored with negligible effect to the accuracy of the numerical solution. However for coarse interface resolution (i.e. large filter width), including the sub-filter scale term significantly increases the accuracy of the numerical solution
Date Created
2024
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Assessing Uncertainty in Surface Regression Models for Solid Rocket Motors

Description
The Level Set Method was implemented via a coupled two-dimensional G-equation approach in successive axial segments.
Date Created
2024-05
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Understanding Base Thrust of Highly Truncated Aerospike Nozzles

Description
This thesis examines how a recently proposed concept for a highly-truncated aerospike nozzle can be expected to perform at altitudes corresponding to ambient pressures from sea-level to full vacuum conditions, as would occur during second-stage ascent and during second-stage descent and return to

This thesis examines how a recently proposed concept for a highly-truncated aerospike nozzle can be expected to perform at altitudes corresponding to ambient pressures from sea-level to full vacuum conditions, as would occur during second-stage ascent and during second-stage descent and return to Earth. Of particular importance is how the base pressure varies with ambient pressure, especially at low ambient pressures for which the resulting highly underexpanded flows exiting from discrete thrust chambers around the truncated aerospike merge to create a closed (unventilated) base flow. The objective was to develop an approximate but usefully accurate and technically rooted way of estimating conditions for which the jets issuing from adjacent thrust chambers will merge before the end of the truncated aerospike is reached. Three main factors that determine the merging distance are the chamber pressure, the altitude, and the spacing between adjacent thrust chambers. The Prandtl-Meyer expansion angle was used to approximate the initial expansion of the jet flow issuing from each thrust chamber. From this an approximate criterion was developed for the downstream distance at which the jet flows from adjacent thrust chambers merge. Variations in atmospheric gas composition, specific heat ratio, temperature, and pressure with altitude from sea-level to 600 km were accounted for. Results showed that with decreasing atmospheric pressure during vehicle ascent, the merging distance decreases as the jet flows become increasingly under-expanded. Increasing the number of thrust chambers decreases the merging distance exponentially, and increasing chamber pressure results in a decrease of the merging distance as well.
Date Created
2024-05
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Aerodynamic Nuances on Wings Subjected to Ground Effect

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Description
This thesis aims to determine how finite wing aerodynamic loads change in proximity to the ground. In this study, the primary design tool is an inviscid panel method code, VORLAX. The validation tool is a commercial volume grid CFD package,

This thesis aims to determine how finite wing aerodynamic loads change in proximity to the ground. In this study, the primary design tool is an inviscid panel method code, VORLAX. The validation tool is a commercial volume grid CFD package, ANSYS FLUENT. I use VORLAX to simulate wings with different incidences and aspect ratios to look at how ground effect impacts spanwise loading and incipient flow separation. Then the results were compared to widely published equations such as McCormick, Torenbeek, and Hoerner & Borst. Because I found that these “famous” equations function best only for specific conditions, I propose a new empirical equation to estimate ground effect lift as a function of aspect ratio and incidence. Using Stratford’s method to predict signs of flow separation in the inviscid solutions, I found that variations in the height above the ground were not significant enough to change the stall angle of low aspect ratio wings. I did find early signs of flow separation with increasing aspect ratio. I observe significant changes in spanwise loading when in ground effect; as I narrow the gap, the transverse loading builds higher near the center of the wing. These effects were more apparent in wings with smaller aspect ratio; higher aspect ratio wings experience a higher loading gradient near the tips in proximity to the ground. I found that high aspect ratio wings have a smaller stall angle compared to that of lower aspect ratio wings; these trends are consistent between the potential flow solution and the volume grid CFD viscous solution.
Date Created
2024
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Attainable Moment Sets - Approaches to Understanding Trim Capability in Conceptual Design

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Description
This thesis addresses the issue of assessing longitudinal and lateral-directional trim capability during the conceptual design process. Modern high-performance aircraft are likely to feature complex flight control systems where the control system may independently command every control surface to develo

This thesis addresses the issue of assessing longitudinal and lateral-directional trim capability during the conceptual design process. Modern high-performance aircraft are likely to feature complex flight control systems where the control system may independently command every control surface to develop necessary moments. However, to prove stability and controllability on such an aircraft requires a near-final set of control laws. This requirement is onerous at the conceptual design level, where engineering methods need to facilitate rapid, multidisciplinary design optimization trades. This work considers the differences in Attainable Moment Sets across a wide variety of airframes using a simplified “pre-mix” approach to controls as well as a model where the control systems have independent command authority over each control surface. This work indicates that the “independent-single-panel” model offers modest improvements in attainable moments over a “pre-mix” strategy. This suggests that a “pre-mix” approach used to assess basic combined trim problems will not lead to an overly conservative final design.
Date Created
2023
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A Dual Scale Approach to Modeling Hydrodynamic Instabilities on a Phase Interface

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Description
Advancements to a dual scale Large Eddy Simulation (LES) modeling approach for immiscible turbulent phase interfaces are presented. In the dual scale LES approach, a high resolution auxiliary grid, used to capture a fully resolved interface geometry realization, is linked

Advancements to a dual scale Large Eddy Simulation (LES) modeling approach for immiscible turbulent phase interfaces are presented. In the dual scale LES approach, a high resolution auxiliary grid, used to capture a fully resolved interface geometry realization, is linked to an LES grid that solves the filtered Navier-Stokes equations. Exact closure of the sub-filter interface terms is provided by explicitly filtering the fully resolved quantities from the auxiliary grid. Reconstructing a fully resolved velocity field to advance the phase interface requires modeling several sub-filter effects, including shear and accelerational instabilities and phase change. Two sub-filter models were developed to generate these sub-filter hydrodynamic instabilities: an Orr-Sommerfeld model and a Volume-of-Fluid (VoF) vortex sheet method. The Orr-Sommerfeld sub-filter model was found to be incompatible with the dual scale approach, since it is unable to generate interface rollup and a process to separate filtered and sub-filter scales could not be established. A novel VoF vortex sheet method was therefore proposed, since prior vortex methods have demonstrated interface rollup and following the LES methodology, the vortex sheet strength could be decomposed into its filtered and sub-filter components. In the development of the VoF vortex sheet method, it was tested with a variety of classical hydrodynamic instability problems, compared against prior work and linear theory, and verified using Direct Numerical Simulations (DNS). An LES consistent approach to coupling the VoF vortex sheet with the LES filtered equations is presented and compared against DNS. Finally, a sub-filter phase change model is proposed and assessed in the dual scale LES framework with an evaporating interface subjected to decaying homogeneous isotropic turbulence. Results are compared against DNS and the interplay between surface tension forces and evaporation are discussed.
Date Created
2023
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Increasing Lateral-Directional Controllability and Investigating Elevator-Body Flap Interaction for Shuttle Orbiter

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Description
This thesis investigates the configurations needed to demonstrate positive lateraldirectional controllability across the flight envelope of a hypersonic vehicle. Itexamines the NASA Space Shuttle Orbiter as a baseline reference configuration, as it was a successful hypersonic vehicle. However, the Orbiter had

This thesis investigates the configurations needed to demonstrate positive lateraldirectional controllability across the flight envelope of a hypersonic vehicle. Itexamines the NASA Space Shuttle Orbiter as a baseline reference configuration, as it was a successful hypersonic vehicle. However, the Orbiter had limited high-speed maneuvering capability; it relied on reaction-control jets to augment controllability due to a strong tendency for its aerodynamics to “control couple.” It was seen that many problems associated with the control of the hypersonic Orbiter are due to its slender configuration. This work relies upon the Evolved-Bihrle-Weissman chart as an accurate indicator of lateral-directional stability and controllability. The also explores variant configurations of larger wing tip verticals to explore what configuration changes are needed to reduce dependence on reaction controls.
Date Created
2023
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Energy Neutral Orbital Plane Change Maneuvers Through the Use of Skyhooks and Momentum Exchange

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Description

The objective of this report is to discover a skyhook’s ability to change the plane of another spacecraft’s orbit while ensuring that each vehicle’s orbital energy remains constant. Skyhooks are a proposed momentum exchange device in which a tether is

The objective of this report is to discover a skyhook’s ability to change the plane of another spacecraft’s orbit while ensuring that each vehicle’s orbital energy remains constant. Skyhooks are a proposed momentum exchange device in which a tether is attached to a counterweight at one end and at the other, a capturing device intended to intercept rendezvousing spacecraft. Trigonometric velocity vector relations, along with objective comparisons to traditionally proposed uses for skyhooks and gravity-assist maneuvers were responsible for the ultimate parameterization of the proposed energy neutral maneuver. From this methodology, it was determined that a spacecraft’s initial relative velocity vector must be perpendicular to, and rotated about the skyhook’s total velocity vector if it is to benefit from an energy neutral plane change maneuver. A quaternion was used to model the rotation of the incoming spacecraft’s relative velocity vector. The potential post-maneuver spacecraft orbits vary in their inclinations depending on the ratio between the skyhook and spacecraft’s total velocities at the point of rendezvous as defined by the parameter called the alpha criterion. For many cases, the proposed maneuver will serve as a desirable alternative to currently practiced propulsive plane change methods because it does not costly require a substantial amount of propellant. The proposed maneuver is also more accessible than alternative methods that involve gravity-assist and aerodynamic forces. Additionally, by avoiding orbital degradation through the achievement of unchanging total orbital energy, the skyhook will be able to continually and self-sustainably provide plane changes to any spacecraft that belong to orbits that abide by the identified parameters.

Date Created
2023-05
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A Feasibility Study of Global Commercial SST, Building a Database on Routing Financials and Logistics for Major Airline Corporations

Description

Today, the vision of Commercial Supersonic Travel is often dreamed possible with innovation. Modern tech-business plans to reinvent commercial SuperSonic Transport (SST), while gaining reliable venture capital investment and proactive social backing. However, the concept’s global viability remains questionable, as

Today, the vision of Commercial Supersonic Travel is often dreamed possible with innovation. Modern tech-business plans to reinvent commercial SuperSonic Transport (SST), while gaining reliable venture capital investment and proactive social backing. However, the concept’s global viability remains questionable, as regulation opposes its integrability. As a result, SST has become industrially forgotten. This research paper challenges the neglect of SST through routing optimizations derived from an industry’s collective research, while outlining decisive use-cases. Initially, this paper describes the difficulty in SST’s integration through its logistical tasks, demanding designs, and lacking efficiency. After that, the paper defines an optimization strategy, through software-analyzed flight paths, for overall supersonic operations. This strategy was proven to shorten established SST flights by 6%, while enabling the implementation of newfound SST paths. Here, optimization averaged 3.3% on density-derived routes and 5.4% on software-derived routes. More importantly, this paper demonstrated routing optimization enables MACH 1.6 aircraft to achieve MACH 2 flight times. Further, this paper attempts to justify SST through an analysis of its market, financials, and social perspectives. With that, the paper justifies an ideal SST customer earns 630$/hr, while such measurements vary amongst flight types. Finally, this paper conceptualizes that SST, with optimization, promises a noteworthy business, while developments in aircraft designs may revamp the aerospace industry completely.

Date Created
2023-05
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