Analysis of Engine Noise, Acoustic Optimization of Fan Design, and Investigation of Optimal Take-Off Profiles for Certification Noise Reduction of Civil Supersonic Aircraft

Kurzfassung

A new generation of civil supersonic aircraft is being developed and may enter service as early as 2030. These aircraft are expected to have a bigger environmental impact than subsonic aircraft, as previous experience has shown. Besides the climate impact and en-route noise caused by the sonic boom, community noise has been a major challenge for supersonic transport. Research to quantify and minimize landing and take-off noise of a potential future supersonic fleet becomes necessary. The engine noise, which is dominant in supersonic aircraft during landing and take-off, must be predicted and reduced. To achieve both goals, empirical jet noise and analytical fan noise and noise propagation models are employed. They allow the prediction of realistic certification noise levels, which are vital to the process of setting new certification rules for supersonic aircraft. These predictions also help to reduce the certification noise levels through noise optimized design and operation by providing supporting data. Due to their mission specifics, civil supersonic aircraft are very different from subsonic aircraft in both design and operation. The design restrictions and low-speed characteristics of aircraft and engines, which impact landing and take-off noise are presented. The engine design is discussed and it is shown that trade-offs exist between fuel efficiency in cruise and engine noise on landing and take-off. Using a semi-analytical meanline approach to predicting fan aerodynamics and fan noise as well as analytical noise propagation models, an automatic design-to-noise process for the fan is developed and presented. Using this process, a noise optimized single-stage and a two-stage fan design for a supersonic airliner cruising at Mach 1.8 are designed. Then their acoustic and performance characteristics are studied, highlighting some advantages and disadvantages of each concept. Supersonic aircraft can easily take off without applying maximum thrust, so there are options to alter take-off procedures with the goal of reducing certification noise levels. Changes to the thrust application and speed management during take-off are investigated in a take-off profile variation study, using the supersonic airliner mentioned above. This allows to both evaluate the effectiveness and reasonable boundaries of these procedure variations and to predict minimum certification noise levels for the airliner. It is found that the airliner can meet Chapter 14 noise certification requirements with significant margins. The impact of using a single- or two-stage fan on those certification levels is investigated, and it is shown that on take-offs on which fan noise is dominant, significantly lower certification levels can be achieved by using the two-stage concept. Furthermore, a study is conducted on the effects of uncertainties in the airframe and liner modeling.