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Tai, Jimmy C. M.

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    CFD Study of an Over-Wing Nacelle Configuration
    (Georgia Institute of Technology, 2018-10-05) Berguin, Steven H. ; Renganathan, Sudharshan Ashwin ; Ahuja, Jai ; Chen, Mengzhen ; Perron, Christian ; Tai, Jimmy C. M. ; Mavris, Dimitri N.
    Engine bypass ratio (BPR) has grown significantly over the years, due to a desire for increased efficiency, and the large fan diameters that have resulted are forcing the engines so close to the wing that there is no room left for them to grow any larger due to ground clearance constraints. As BPR increases even further in the future, conventional Under-Wing Nacelle (UWN) installations will therefore no longer be possible without drastic modification of the wing and landing gear. Over-Wing nacelle concepts solve this problem by offering a convenient installation for high BPR turbofans and, additionally, offer the potential to mitigate community noise through engine noise shielding using the wing as a shield. However, OWN has historically warranted concern about unacceptably high drag levels at transonic speeds and the purpose of this research was to determine whether or not drag can be improved enough to take advantage of the aforementioned cross-disciplinary benefits. To do so, three studies were conducted: study 1 conducted a simple nacelle sweep in order to identify and visualize the physical mechanisms driving the configuration, study 2 then conducted a sensitivity analysis in order to understand important design variables and, finally, study 3 performed single point optimization for a trailing edge OWN concept. Overall, results suggests that OWN drag can be improved to levels commensurate with its Under-Wing Nacelle (UWN) counterpart. However, limitations of the analysis tools employed for this research (in the area of shape optimization) were insufficient to outperform the UWN baseline. Such limitations were successfully overcome by modern OWN concepts, such as the Honda Business Jet and the military Lockheed HWB for air mobility missions. Overall, it is therefore the authors' opinion that either leading-edge or trailing-edge mounted OWN configurations are concepts worth investigating further for civil transport applications.
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    Modeling Airlift Operations for Humanitarian Aid and Disaster Relief to Support Acquisition Decision-Making
    (Georgia Institute of Technology, 2018-06) Weit, Colby J. ; Chetcuti, Steven ; Chan, Cherlyn ; Muehlberg, Marc ; Wei, Lansing ; Gilani, Hassan ; Schwartz, Katherine G. ; Sudol, Alicia M. ; Tai, Jimmy C. M. ; Mavris, Dimitri N.
    In a fiscally constrained environment, it is crucial that both equipment manufacturers and defence invest in technology that shows marked operational improvement. A priori identification of cost-benefit at the early acquisition stage is often limited and incomplete, leading to poor value propositions. This conundrum motivates the need to develop a method to evaluate technologies such as levels of autonomy, stealth capability, improved engines, etc. and make tradeoffs against operational measures of performance and effectiveness (MOP/Es) rather than solely against vehicle performance characteristics. The objective of this study is to create an environment in which those trades against MOEs could be performed rapidly to inform technology investment and acquisition decision-making. This environment is built on top of representative models of a discrete event simulation of disaster relief airlift operations to compare technology modifications or vehicle acquisition options rapidly against operational measures of effectiveness.
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    Sensitivity Analysis of Aero-Propulsive Coupling for Over-Wing-Nacelle Concepts
    (Georgia Institute of Technology, 2018) Berguin, Steven H. ; Renganathan, Sudharshan Ashwin ; Ahuja, Jai ; Chen, Mengzhen ; Tai, Jimmy C. M. ; Mavris, Dimitri N.
    A sensitivity analysis is performed to quantify the relative impact of perturbing a set of design variables representing an airplane configuration with Over-Wing Nacelles (OWN), operating at transonic cruise. The goal is to study the impact of perturbing the engine's XYZ position and power setting on installation drag, engine inlet pressure recovery, and lift curve characteristics. High- fidelity Reynolds Averaged Navier-Stokes (RANS) simulations of the Common Research Model (CRM) modified with powered, over-wing nacelles are performed and dominant main effects and interactions are identified. The most dominant effect was by far the engine's X position, but it was also found that podded OWN configurations exhibit statistically significant, aero-propulsive coupling. Specifically, certain engine locations cause changes in the flow-field that deteriorate inlet pressure recovery and, vice versa, a change in engine boundary conditions can affect installation drag. It is therefore recommended to simulate OWN concepts using a coupled MDA or MDAO approach to capture interdependencies between aerodynamics and propulsion.
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    Boeing propulsion sub-systems: NPSS/WATE parametric model, stage-stack & mean-line, and transient analyses
    (Georgia Institute of Technology, 2012-12-31) Mavris, Dimitri N. ; Tai, Jimmy C. M. ; Schutte, Jeff ; Denney, Russell ; Kestner, Brian