Jimmy C. Tai

An Application of Response Surface Methodology to the Design of Tipjet Driven Stopped Rotor/Wing Concepts

Presented at the 1st AIAA Aircraft Engineering, Technology, and Operations Congress, Anaheim, CA, September 19-21, 1995.

Updates and Modeling Enhancements to the Assessment of NASA Environmentally Responsible Aviation Technologies and Vehicle Concepts

The National Aeronautics and Space Administration’s (NASA) Environmentally Responsible Aviation (ERA) project is conducting research at an integrated system level on promising concepts and technologies expected to mature in the N+2 time frame. It is essential for ERA to perform a systems level analysis of these concepts and technologies in order to estimate and track performance towards ERA’s goal of simultaneously achieving improvement in metrics for fuel burn reduction, noise margin, and LTO NOx emissions reduction. Previous vehicle modeling and technology assessment work conducted for the ERA project illustrated system level comparison of tube and wing versus hybrid wing body airframe configurations, as well as between ultra high bypass ratio direct drive and geared turbofan engines. Guidance drawn from these results has led to an updated list of ERA technologies of interest. Additionally, development of improved modeling capabilities and a better understanding of key technology impacts have been accordingly incorporated into an updated technology assessment. This assessment evaluates changes to the technology portfolio, incorporates updated technology assumptions, augmented vehicle and technology models, and includes for the first time LTO NOx estimates for advanced combustors. These new set of results allow for an understanding of the interdependencies between each of the ERA metrics and provide an update on ERA’s capability of achieving its goals.

Effects of Advanced Engine Technology on Open Rotor Cycle Selection and Performance

Recent increases in fuel prices and increased focus on aviations environmental impacts have reignited focus on the open rotor engine concept. This type of architecture was extensively investigated in previous decades but was not pursued through to commercialization due to relatively high noise levels and a sudden, sharp decrease in fuel prices. More recent increases in fuel prices and increased government pressure from taxing carbon-dioxide production mean the open rotor is once again being investigated as a viable concept. Advances in aero-acoustic design tools have allowed industry and academia to re-investigate the open rotor with an increased emphasis on noise reduction while retaining the fuel burn benefits due to the increased propulsive efficiency. Recent research with conceptual level multidisciplinary considerations of the open rotor has been performed (Bellocq et al., 2010, “Advanced Open Rotor Performance Modeling For Multidisciplinary Optimization Assessments,” Paper No. GT2010-2963), but there remains a need for a holistic approach that includes the coupled effects of the engine and airframe on fuel burn, emissions, and noise. Years of research at Georgia Institute of Technology have led to the development of the Environmental Design Space (EDS) (Kirby and Mavris, 2008, “The Environmental Design Space,” Proceedings of the 26th International Congress of the Aeronautical Sciences). EDS serves to capture interdependencies at the conceptual design level of fuel burn, emissions, and noise for conventional and advanced engine and airframe architectures. Recently, leveraging NASA environmentally responsible aviation (ERA) modeling efforts, EDS has been updated to include an open rotor model to capture, in an integrated fashion, the effects of an open rotor on conventional airframe designs. Due to the object oriented nature of EDS, the focus has been on designing modular elements that can be updated as research progresses. A power management scheme has also been developed with the future capability to trade between fuel efficiency and noise using the variable pitch propeller system. Since the original GE open rotor test was performed using a military core, there is interest in seeing the effect of modern core-engine technology on the integrated open rotor performance. This research applies the modular EDS open rotor model in an engine cycle study to investigate the sensitivity of thermal efficiency improvements on open rotor performance, including the effects on weight and vehicle performance. The results are that advances in the core cycle are necessary to enable future bypass ratio growth and the trades between core operating temperatures and size become more significant as bypass ratio continues to increase. A general benefit of a 30% reduction in block fuel is seen on a 737-800 sized aircraft.

Development of a Suite of Hybrid Electric Propulsion Modeling Elements Using NPSS

NASA is actively funding research into advanced, unconventional aircraft and engine architectures to achieve drastic reductions in vehicle fuel burn, noise, and emissions. One such concept is being explored by Boeing, General Electric, Virginia Tech, and Georgia Tech under the Subsonic Ultra Green Aircraft Research (SUGAR) project [1]. A major cornerstone of this research is evaluating the potential performance benefits that can be attributed to using hybrid electric propulsion. Hybrid electric propulsion in this context involves a non-Brayton power generation or storage source, such as a battery or a fuel cell, which can be used to provide additional propulsive energy to a conventional Brayton cycle powered turbofan engine. Employing additional power sources for thrust production increases the number of degrees of freedom both from a design and configuration standpoint and from an operational one. In order to assess and understand the myriad number of potential new configurations a modeling and simulation tool is needed; however, current state of the art propulsion modeling tools such as the Numerical Propulsion System Simulation (NPSS) are not natively capable of assessing novel hybrid electric configurations.This research addresses the gap between hybrid electric propulsion and conventional cycle analysis tools by developing a suite of native NPSS elements suitable for hybrid electric engine cycle design and analysis. Elements have been developed for a fuel cell, battery, motor, generator, and electrical distribution system. Both room temperature and cryogenically cooled superconducting variants are developed. The elements are designed such that they can be seamlessly integrated into existing NPSS cycle models to assess any system configuration or architecture the designer can envision.© 2014 ASME

A Multidisciplinary Design Optimization Approach to Sizing Stopped Rotor Configurations Utilizing Reaction Drive and Circulation Control

Presented at the 5th AIAA/NASA/USAF/ISSMO Symposium on Multidisciplinary Analysis and Optimization, Panama City, FL, September 7-9, 1994.

Cycle Design Exploration Using Multi-Design Point Approach

The focus of this study is to compare the aerothermodynamic cycle design space of a gas turbine engine generated using two on-design approaches. The traditional approach uses a single design point (SDP) for on-design cycle analysis, where off-design cycle analysis must be performed at other operating conditions of interest. A multi-design point (MDP) method performs on-design cycle analysis at all operating conditions where performance requirements are specified. Effects on the topography of the cycle design space as well as the feasibility of the space are examined. The impacts that performance requirements and cycle assumptions have on the bounds and topography of the feasible space are investigated. The deficiencies of a SDP method in determining an optimum gas turbine engine will be shown for a given set of requirements. Analysis will demonstrate that the MDP method, unlike the SDP method, always obtains a properly sized engine for a set of given requirements and cycle design variables, resulting in an increased feasible region of the aerothermodynamic cycle design space from which the optimum performance engine can be obtained.Copyright

Multi-Design Point Cycle Design Incorporation into the Environmental Design Space

A multi-point design cycle analysis methodology has been developed and implemented into the Environmental Design Space to ensure the proper matching of engine and aircraft. The method ensures the feasibility of the engine designs throughout the cycle design space by adjusting the design to simultaneously meet performance requirements and constraints at different operating conditions. EDS incorporates NPSS for the cycle analysis and utilizes its solver to find the solution of a system of nonlinear equations established by the user and the NPSS auto solver to that meets all requirements and constraints.

Elements of an Emerging Virtual Stochastic Life Cycle Design Environment

Presented at the 4th World Aviation Congress and Exposition, San Francisco, CA, October 19-21, 1999.

Surrogate Modeling for Simultaneous Engine Cycle and Technology Optimization for Next Generation Subsonic Aircraft

This paper presents an engine sizing and cycle selection study of ultra high bypass ratio engines applied to a subsonic commercial aircraft in the N+2 (2025) timeframe. NASA has created the Environmentally Responsible Aviation (ERA) project to serve as a technology transition bridge between fundamental research (TRL 1–4) and potential commercial application (TRL 7). Specifically, ERA is focused on subsonic transport technologies that could reach TRL 6 by 2020 and can be integrated into an advanced vehicle concept to simultaneously meet the ERA project metrics for noise, emissions, and fuel burn. An important variable in exploring the technology trade space is the selection of the optimal engine cycle for use on the advanced aircraft. Previous literature demonstrated the cycle optimization using a design of experiments (DOE) to explore the engine cycle design space for a pre-defined technology package. However, since the optimal engine cycle is dependent upon the specific technology package, this process would have to be repeated to ensure optimal performance for each technology package. With more than 80 technologies to be analyzed, the combinatorial space of technology packages is enormous. As a result, executing a DOE to find the optimum engine cycle for each technology package is infeasible. To address this issue, it is proposed to use surrogate models that encompass the engine cycle and technology design space to enable fast and accurate optimization of the engine cycle for any given technology package.This paper describes the generation and analysis of surrogate models used for technology assessment and cycle optimization of an ultra high bypass geared turbofan engine architecture. The first study in the paper shows that a single surrogate model can be used to accurately simulate both a technology and cycle design space. To demonstrate the proposed surrogate modeling approach, the cycle design space for three different technology packages was analyzed. This study demonstrated that when an optimal cycle is found within the constrained interior of a design space, the surrogate modeling approach is quite accurate. The study also established that the surrogate models can also be used to assess potential cycles at the boundaries or even outside of the region for which they were trained.© 2012 ASME

A Gas Turbine Engine Model of Transient Operation Across the Flight Envelope

This paper introduces a method to create engine transient models that retain the fidelity and non-linearity of complex models as well as simplicity and speed of lower fidelity linearized models. The method is based on the design of experiments (DOE) and neural network methodology to create an analytic non-linear model of engine transient operation which has the potential to be used in on-board and off-board applications. The feed forward neural net models were created for a high fidelity model of high bypass turbofan engine (truth model). The performance of the neural net models was verified against the truth model. The verification results showed good agreement between the output of the neural net models and the truth model. Initial investigations also showed a significant reduction in the model execution time.Copyright