The NASA Langley Research Center hypersonic wind tunnels serve a vital role in the field of hypersonics in both helping validate CFD predictions and producing experimental results. These tunnels have been heavily utilized for decades by numerous planetary missions, such as MSL and Orion, commercial and academic partnerships, such as Sierra Space and the University of Maryland, and flight projects such as Artemis and LOFTID. The data acquisition method used in these tunnels is thermography, primarily phosphor and infrared. Image data are not collected during model injection, resulting in a data gap in the time-history of temperature. Historically, an approximate method has been used to obtain heating data with the data gap, but a new, higher-fidelity method has been developed that patches the data gap and performs integral heat transfer analysis on the temperature data, directly solving the heat equation and avoiding unnecessary assumptions. This method has been shown to model the surface heating much more accurately, agree with computational predictions better than the current method, and be an overall more robust method that collapses to a constant film coefficient value much more quickly. The culmination of these aspects results in a method that is a significant improvement over the approximate method and increases the fidelity of the heating results obtained from the NASA Langley Research Center hypersonic wind tunnels. / Master of Science / A new heat transfer analysis method that reduces image data taken of wind tunnel models in the NASA Langley Research Center hypersonic wind tunnels has been developed as a higher-fidelity successor to the existing approximate method. This new method patches the data gap that occurs during injection due to the fact that no images are taken of the model until it reaches the centerline of the tunnel. Then, this method performs integral heat transfer analysis on the image temperature data, directly solving the heat equation and avoiding unnecessary assumptions. This method has been shown to model the surface heating better, agree with computational predictions better, and be a more robust method that obtains a film coefficient value more quickly. This method is shown to be a significant improvement over the approximate method.

Mississippi State University has a subsonic closed return wind tunnel facility with an open test section configuration. This research analyzes the test section flow quality using a numerical approach and explain how the diffuser's collector suppresses unsteadiness. Previous experiment assessed the flow quality at the wind tunnel without the collector, and velocity was measured using a pitot-static probe and hot wire. The results show a numerical comparison between the two configurations, with and without the collector, understand the effect of the diffuser 's collector on steadiness and uniformity. This paper will describe the wind tunnel facility and give further details about the measurements tools and the set up, and then introduce the numerical method used and analyze the cases of study and their results.

This Research explores hydrogen combustion in a Jet-in-Crossflow configuration through computational fluid dynamics using ANSYS Fluent commercial CFD software. Three fuel-only hydrogen jets with a momentum flux ratio J of 10, 50, and 115 were introduced axially, using a large eddy simulation with a WALE sub grid model. Detailed chemistry was computed directly with a 9 species hydrogen/air kinetic mechanism. The 4mm jet and crossflow domain utilized an automatic mesh adaptation method centered around the flame shear layer. The study models the second stage of a lab-scale gas turbine test facility at a pressure level of 5atm,a crossflow temperature of 1620K, and crossflow velocity of 75m/s. The models were compared to physical experiments conducted and analyzed with line-of-sight CH* chemiluminescence to create more insight into the phenomena of the combustion process. Flame position along the windward and leeside stabilization points were overlaid, and the validated CFD model utilized to characterize reaction progress as a function of jet entrainment with hot oxidizer. At elevated momentum flux ratio, increased reaction rates along the shear layer of the diffusion flame were attributed to the enhanced contact area between the fuel jet and crossflow oxidizer. The results outline the potential of carbon-free combustion technology and highlight the importance of tuning the operating condition for application in gas turbines.

The leading-edge tubercle is a type of airfoil modification that inspired by the humpback whale. It was found that the aerodynamic performance of the wing would increase compared to the wing without tubercles. In the past several years, a lot of numerical and experimental studies have been accomplished to explore this leading-edge modification. Besides the aerodynamic performance change, this research explores the aeroacoustics behavior of airfoils with leading-edge tubercles. A numerical study based on Computational Fluid Dynamics (CFD) is established, and simulations using Star CCM are accomplished based on reasonable set-ups. The airfoil chosen to create the wing is NACA 4412 which is an asymmetric airfoil. Two different tubercle wavelengths were used: 20 mm and 25 mm. The baseline airfoil is the wing that made of the same airfoil but without any modifications. For wings with leading-edge tubercles, the wavelength of the tubercles is the only changing parameter. It was found that the wings with leading-edge tubercles can reduce the noise generation, and the best noise reduction is achieved for a value of 2.525 dB (Decibel) at Point Receiver 10 for the wing that has 25 mm wavelength leading-edge tubercles. However, the wavelength of tubercles does not affect the aeroacoustics performance in an obvious way.

Computational Field Simulation processes are typically complex and involve execution of multiple software tools in the form of pipelines to perform simulations successfully. Very often, handling the input and output communication between the tools and allocating computing resources for the processes becomes an essential but an unimportant task for the user. A well written script can often reduce these peripheral tasks and allow the user to concentrate on the analysis. This thesis studies the aspects of design and implementation of a framework called the Integrated Simulation Environment or ISE, that not only forms a scripted environment for high level integration of simulation software tools, but is also flexible enough to accommodate new tools on the fly, while maintaining ease of use and reliability. A hierarchy based design methodology was used to implement the ISE. Hierarchies provide the framework with the flexibility to decompose the complexities of simulation process pipelines and physical entities such as grids and geometries into managable components. Also hierarchies are easily translated into standards such as XML for saving and restoring, and external communication. An Overset CFD simulation process pipeline was integrated into the framework and tested for ease of use, reliability and extensibility. Both simple and complex tools such as a curve extraction tool, a surface grid generation tool, a volume grid generation tool and tools for preparing flow solver inputs were integrated into the system and tested successfully.

A generalized grid based technique was developed for handling the relative motion of grids in CFD simulations involving rotating machineries. In the present method, the relative motion between the grid blocks is handled by splitting the cellaces at the interface and updating the grid data structure appropriately. The resulting grid will have cells and cellaces with an arbitrary number of nodes and which are stored in a cellace based data structure. The current methodology is developed for cells with any number of nodes. However, the present work supports only tetrahedral elements at the interface of the rotating grid-blocks at the beginning of the simulation. Also the present approach can handle multiple objects in the domain of interest which are rotating in arbitrary directions. The current approach was tested by rotating a generalized grid for a single un-ducted SR7 propeller with eight blades designed with 41 degrees of sweep at the tip. This was also tested for two counter rotating SR7 propellers. After every rotation the new grid was tested for negative volumes, folded cellaces, proper connectivity of nodes forming the cellaces, and for gaps. Preliminary work has been conducted to couple the grid generation strategy to a generalized grid based flow solver.

This study reports the development and validation of a modified two-equation eddy-viscosity turbulence model for computational fluid dynamics prediction of transitional and turbulent flows. The existing terms of the standard k-w model have been modified to include transitional flow effects, within the framework of Reynolds-averaged, eddy-viscosity turbulence modeling. The new model has been implemented into the commercially available flow solver FLUENT and the Mississippi State University SimCenter developed flow solver U2NCLE. Test cases included flow over a flat plate, a 2-D circular cylinder in a crossflow, a 3-D cylindrical body and three conical geometries, which represent the nose-cones of aerodynamic vehicles such as missiles. The results illustrate the ability of the model to yield reasonable predictions of transitional flow behavior using a simple modeling framework, including an appropriate response to freestream turbulence quantities, boundary-layer separation, and angle of attack.

This document describes the design of an axisymmetric aerospike nozzle to replace the conical converging-diverging nozzle of a commercially available hybrid rocket motor. The planar method of characteristics is used with isentropic flow assumptions to design the nozzle wall. Axisymmetric adjustments are made with quasi-one-dimensional flow approximations. Computational Fluid Dynamics (CFD) simulations verify these assumptions, and illustrate viscous effects within the flow. Nozzle truncations are also investigated. Development of a hybrid-rocket-specific data acquisition system is also detailed.

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