Ph.D. Proposal
Edan Baltman
(Advisor: Prof. Dimitri Mavris)
"An Improved Methodology for Quantifying the Trade-off between Fuel Efficiency and LTO Noise for a Commercial Supersonic Transport by Optimization of the Fan Design"
Wednesday, October 16
12:00 p.m.
Weber, Collaborative Visualization Environment (CoVE)
Abstract
Commercial supersonic air travel offers the promise of reduced travel time, but to date, there have only been two commercial supersonic aircraft. There is renewed interest today in supersonic air travel; however, there is also a need to improve fuel efficiency (or fuel burn) and landing and takeoff (LTO) noise relative to past commercial supersonic aircraft. Fuel efficiency and LTO noise cannot be simultaneously optimized due to a fundamental conflict between design features favoring high-speed vs. low-speed flight; this results in a trade-off that is important to quantify to balance the economic and environmental impacts of high poor fuel efficiency with the noise impacts on communities around airports. Given the higher speeds of supersonic aircraft, the trade-off between fuel efficiency and LTO noise for commercial supersonic aircraft (the Trade-off) is likely more severe than for subsonic aircraft. Given a lack of historical data on which to base the Trade-off, before any commercial supersonic aircraft can be realized, it is necessary to synthesize the Trade-off in an explicit, consistent, and replicable manner to enable informed decision-making by regulatory organizations, the aviation industry, and impacted communities as to how to balance the two objectives.
The problem of quantifying the Trade-off is a multi-objective optimization problem. The solution of a multi-objective optimization problem depends, in part, on the design variables that are optimized and the models used to predict the objectives as a function of the design variables. In past work on the Trade-off the only propulsion design variables considered were the engine cycle variables and engine size (i.e., design airflow or thrust). One important cycle variable is the fan pressure ratio, as this plays a strong role in determining the specific thrust, bypass ratio, and jet velocity. For fuel efficiency, supersonic aircraft tend to favor high-specific thrust (i.e., low bypass ratio) engines because they can achieve comparable efficiency in supersonic flight to high-bypass ratio engines in subsonic flight but with much smaller size, weight, and drag for the thrust required. From a noise perspective, high-specific thrust engines have high jet velocities and jet noise, and as such, the selection of fan pressure ratio has played an important role in the Trade-off. However, jet noise is not the only source of noise.
Fan noise can be dominant during the approach when the engine is throttled back and, while not dominant during takeoff, contributes to the overall takeoff noise level. Fan noise is affected by design variables of the fan beyond pressure ratio, such as the blade speed, the number of blades, and the spacing between blade rows. These variables also affect the efficiency and weight of the fan, which impacts the overall aircraft's fuel efficiency, indicating that there exists an interdependency between fan efficiency, fan weight, and fan noise. However, the importance of this fan-level interdependency to the aircraft-level trade-off between fuel efficiency and LTO noise has not been investigated. Past work on the Trade-off typically makes fixed assumptions about the number of blades and rotor-stator spacing and correlates blade speed with pressure ratio. This work proposes to investigate how to quantify the impact that not optimizing fan design variables has relative to optimizing fan design variables on the Trade-off. The results of this research are intended to establish an improved methodology for quantifying the Trade-off.
Committee
- Prof. Dimitri Mavris – School of Aerospace Engineering (advisor)
- Prof. Jerry Seitzman – School of Aerospace Engineering
- Prof. Jechiel Jagoda – School of Aerospace Engineering
- Dr. Jimmy Tai – School of Aerospace Engineering
- Dr. Sriram Rallabhandi – NASA Ames