Gas turbine compressor and turbine blade tip clearance (i.e., the radial distance between the blade tip of an axial compressor or turbine and the containment structure) is a major contributing factor to gas path sealing, and can significantly affect engine efficiency and operational temperature. This paper details the creation of a generic but realistic high pressure turbine tip clearance model that may be used to facilitate active tip clearance control system research. This model uses a first principles approach to approximate thermal and mechanical deformations of the turbine system, taking into account the rotor, shroud, and blade tip components. Validation of the tip clearance model shows that the results are realistic and reflect values found in literature. In addition, this model has been integrated with a gas turbine engine simulation, creating a platform to explore engine performance as tip clearance is adjusted. Results from the integrated model explore the effects of tip clearance on engine operation and highlight advantages of tip clearance management.
The performance of propulsion engine systems is sensitive to weight and volume considerations. This can severely constrain the configuration and complexity of the control system hardware. Distributed Engine Control technology is a response to these concerns by providing more flexibility in designing the control system, and by extension, more functionality leading to higher performing engine systems. Consequently, there can be a weight benefit to mounting modular electronic hardware on the engine core casing in a high temperature environment. This paper attempts to quantify the in-flight temperature constraints for engine casing mounted electronics. In addition, an attempt is made at studying heat soak back effects. The Commercial Modular Aero Propulsion System Simulation 40k (C-MAPSS40k) software is leveraged with real flight data as the inputs to the simulation. A two-dimensional (2-D) heat transfer model is integrated with the engine simulation to approximate the temperature along the length of the engine casing. This modification to the existing C-MAPSS40k software will provide tools and methodologies to develop a better understanding of the requirements for the embedded electronics hardware in future engine systems. Results of the simulations are presented and their implications on temperature constraints for engine casing mounted electronics is discussed. F American Institute of Aeronautics and Astronautics 3 technology are high temperature electronics embedded on the engine core that allow transducer elements to act as intelligent modular devices with digital data interfaces (smart nodes). More information about the concept of DEC technology is provided in Ref. 1.In the near term, DEC technology provides aerodynamic and thermodynamic engine system benefits, but it also improves engine life cycle cost and can reduce the total system weight 1 . For example, DEC hardware can be more easily located or configured to reduce engine drag by shrinking the size of the FADEC mounted to the fan casing; high temperature electronics can improve heat quality for more efficient cooling while they are also located more easily on the engine; and reusable modular components can reduce design and manufacturing costs. In the long term, assuming the continued advancements in electronics, tremendous new control-based capabilities will be introduced that make significant contributions to engine performance, efficiency, and safety. For example, embedded signal processing can extract new information from each existing sensor location while more rapid control design can improve the accuracy and capabilities of the supervisory system control. Additional benefits to the DEC approach are discussed in Refs. 1, 2, 3, 4, and 5.The temperature environment on the engine will always be a concern even with high temperature electronics capability for embedded devices. For example, the state of the art materials technology for internal gas path components in the engine is approaching 1500 o C 6 , however, no known electronics technology can reli...
NASA is investing in Electrified AircraftPropulsion (EAP) research as part of an effort to assist industry in meeting the future needs of a global aviation market. The integration of electric machines into traditional turbine-based propulsion provides opportunities to change system architectures effecting radical improvements in propulsive efficiency. However, less consideration has been afforded to the utilization of these electrical machines to improve the thermal efficiency and performance of the gas turbine engine. Noting this deficit, a novel operability concept is proposed and is referred to as Turbine Electrified Energy Management (TEEM). The concept is a transient control technology that supplements the main fuel control for the suppression of the natural off-design dynamics associated with changes in engine operating state. Here the electric machines, used as engine actuators during the transient, add or extract torque from the engine shafts to maintain the speed-flow characteristics of steadystate design operation. This greatly reduces the need to maintain transient stall margin stack in the compressors, among other potential benefits. This paper demonstrates the feasibility of the concept in dynamic simulation using a Numerical Propulsion System Simulation (NPSS) engine model of a NASA hybrid electric propulsion concept known as the Parallel Hybrid Electric Turbofan (hFan).
In the pursuit of Electrified Aircraft Propulsion (EAP), much of the attention is on the development of hybrid electric concept vehicles and their propulsion systems from a steady-state performance perspective. While it is steady-state performance that largely determines the efficiency of civil air transports, engine operability and transient performance define constraints for the steady-state design that impact efficiency and system viability. Neglecting dynamics and control technologies can result in an over-designed, sub-optimal propulsion system or a concept that is not feasible. Thus, dynamic system studies were conducted on the propulsion system of the conceptual aircraft design known as the Singleaisle Turboelectric AiRCraft with Aft Boundary Layer propulsor (STARC-ABL). This paper describes the development of a controller to verify the baseline concept's feasibility from an operability perspective. Further, studies were conducted to identify excessive stability margin in the baseline design that could be traded for potential benefits in efficiency through an engine re-design. This study revealed the potential to reduce the high pressure compressor (HPC) stall margin by 3%. Finally, a study was conducted to investigate the potential benefit of adding energy storage to the STARC-ABL concept that further improves operability and enables more gains in engine efficiency and performance. The energy storage provided an additional 0.5% stall margin can be removed from the HPC.
NASA and a variety of aerospace industry stakeholders are investing in conceptual studies of electrified aircraft, including parallel hybrid electric aircraft such as the Subsonic Ultra Green Aircraft Research (SUGAR) Volt. At this point, little of the work published in the literature has examined the transient behavior of the turbomachinery in these systems. This paper describes a control system built around the hFan, the parallel hybrid electric turbofan engine designed for the SUGAR Volt concept aircraft. This control system is used to show that the hFan, running with its baseline concept of operations, is capable of transient operation throughout the envelope. The design parameters of this controller are varied to assess the amount of operability margin built into the engine design, and whether this margin can be reduced to enable more aggressive designs, that may feature better fuel economy. Further, studies are performed as parameters for the hFan electric motor are varied to determine how the motor impacts the engine's need for transient operability margin. The studies suggest that the engine may be redesigned with as much as a 3% reduction in high pressure compressor stall margin. It was also demonstrated that appropriate design and control of the electric motor may be able to buy an additional 0.5% stall margin reduction or a turbine inlet temperature reduction of 35 ˚R, as tested at the sea-level static condition.
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