AE Theses and Dissertations

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    An investigation of the downwash field of aircraft in relation to problems involved in aerial refueling
    (Wichita State University, 1958-06) Holloway, Richard B.; Snyder, Melvin H.
    The purpose of solving the problem presented in this thesis is to provide an approximate method of predicting the downwash effects of a tanker airplane upon a receiver airplane when the two aircraft are flying in formation for the accomplishment of aerial refueling. To the best of the author’s knowledge, this study represents the first attempt at an analytical solution of the problem which is applicable to the general case or any tanker formatting with any receiver. Due to the great many variables involved, any attempt at constructing a generally applicable method implies that certain simplifying assumptions must be made. The results presented in this thesis are, then, probably most useful for obtaining a pre-flight test estimation of downwash effects.
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    An investigation of the core of a curved flow field
    (Wichita State University, 1958-07) Bleicher, Theodor; Razak, Kenneth, 1918-2010
    The purpose of this study was to investigate experimentally the flow of a jet of air over a curved surface. Only the area upstream of the point on the surface, where the flow ceases to follow the curvature, was considered. Along a longitudinal cross section of the jet, measurements were taken and the static pressure distribution, velocity distribution and flow direction were recorded. No close investigation of the boundary layer at the cylindrical surface nor of the mixing zone at the free jet boundaries was made. It was hoped to obtain a criterion as to the "stability" of the jet, i.e. how long the flow follows the· curved surface before breaking away.
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    Shear-web beam theories
    (Wichita State University, 1958-04) Cook, Everett L.
    Three theories for predicting the stresses in multistringer shear-web beams are presented. The stresses predicted by these theories are compared with experimental results obtained by the NACA. The agreement between the theoretical results was found to be poor in most cases; however, it appears that with the proper modifications this agreement could be improved.
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    Experimental investigation of acoustic absorption of additively manufactured spinodoid metamaterials
    (Wichita State University, 2023-07) Wojciechowski, Brittany Rose; Sharma, Bhisham N.
    Porous media have gained attention as a potential replacement for conventional acoustic liners in mitigating aircraft engine noise due to their superior broadband attenuation compared to honeycomb sandwich panels. Among these porous media, the spinodoid metamaterial stands out as a promising candidate. The spinodoid metamaterial is based on spinodal decomposition, a diffusion process in which a high-energy mixture splits into two phases to reduce the overall system energy. Previous investigations have explored the versatile stiffness properties of these materials, highlighting their potential for multifunctional applications, including acoustic liners. This thesis focuses on the experimental study of the acoustic properties of spinodoid materials. Gaussian Random Fields were employed to generate models, offering an alternative to the computationally expensive Cahn-Hillard equation. Additive manufacturing techniques were utilized to fabricate the samples, which were then subjected to experimental testing using a normal incidence impedance tube to measure their acoustic absorption coefficient. A microscopy analysis was conducted to assess any print defects resulting from the manufacturing process. The findings reveal intriguing acoustic performances among the various spinodoid types, indicating their potential for optimization in specific applications, such as acoustic liners for aircraft engines. Overall, this thesis contributes to the understanding of spinodoid materials and their acoustic properties through experimental investigations. The use of Gaussian Random Fields in generating models offers computational efficiency, while additive manufacturing enables the fabrication of complex structures. The results shed light on the acoustic behavior of spinodoid materials, paving the way for their further development and optimization. The potential multifunctionality of these materials, combined with their broadband attenuation characteristics, positions them as promising candidates for reducing noise pollution in aircraft engines.
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    Stepwise gradient acoustic liners for engine noise reduction applications
    (Wichita State University, 2023-07) Lomte, Amulya; Sharma, Bhisham N.
    Aircraft noise has been a persistent issue to the communities around the globe. Conventional acoustic liners used to attenuate aircraft engine noise are only effective over a narrow frequency range and considered poor broadband sound absorbers. Metal foams, on the other hand, have a greater potential to replace these conventional liners with their multifunctional properties. Our initial study with metal foams with increasing relative density, compression ratios, and decreasing pore sizes showed that the acoustic properties—the sound absorption coefficient and sound transmission loss—improved over a broad frequency range. Further, we studied stepwise relative density gradient aluminum foams with increasing and decreasing order of compression ratios along the thickness. Our results showed that these configurations have a greater potential to offer lightweight alternatives to uniform foams with better acoustic performance, and with the ability to be tailored acoustic performance over the frequency range of interest. Although metal foams offer multifunctional properties, maintaining consistency in the fabrication process with repeatability is still a challenge. The factors of randomness and irregularity cannot be fully ignored yet as the acoustic properties are affected significantly with changes in microgeometry. Alongside, the advancements in additive manufacturing technologies have pushed the boundaries on realizing the true potential of manufacturing complex micro- and nano-geometries for various applications. Here, we focus on Stereolithography technique, understand the material behavior of the clear resin, and use hybrid modeling methods to extract the sound absorption properties. Our results show a significant difference in its acoustic behavior when compared to the experiments. We also realize that not all the acoustic energy dissipation is being captured; hence, we propose using a correction factor to be able to understand and predict the true nature of additively manufactured porous absorbers with uniform and stepwise relative density gradients along the thickness.
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