An evaluative review of the VTOL technologies for unmanned and manned aerial vehicles

A review of installation effects of ultra-high bypass ratio engines

Off-Design Performance of Gas Turbines

Improving future low-noise aircraft technologies using experimental perception-based evaluation of synthetic flyovers.

Aircraft noise remains the key inhibitor of the growth of air transportation, but the focus of the noise mitigation strategies has changed. As the propulsor fan pressure ratio is decreased for improved fuel burn and lessened environmental impact, the propulsion system noise can be reduced near or even below the noise level of the airframe. Jet noise has become less of a concern, and during approach and landing, the acoustic signature is predominantly set by the airframe. Novel aircraft concepts and architectures, enabled by distributed, more integrated, and boundary-layer ingesting propulsion systems, pose new aeroacoustic problems which require innovative approaches and call for teaming and collaboration as the technological challenges cut across disciplines. One past example of such a collaborative research effort was the Silent Aircraft Initiative (SAI), aimed at the conceptual design of an aircraft imperceptible to the human ear outside the airport perimeter. The initiative brought together researchers from academia, industry, and government agencies. This chapter gives a brief summary of the Silent Aircraft Initiative, the SAX-40 aircraft design, and the noise reduction technologies which were pursued. A decade past SAI, novel aircraft architectures such as the D8 double bubble aircraft, the outcome of a joint effort between MIT, Aurora Flight Sciences and Pratt and Whitney, are being pursued in the quest of reducing the climate impact of aviation. With regulations continuing to reduce the allowable aviation noise emission levels, both new challenges and new opportunities are emerging. Electric, hybrid, and turbo-electric aircraft concepts are currently being investigated as potential game changers. Independent of the level of electrification, noise will remain a major issue as air transportation is growing and mobility might become a key driver. The chapter discusses a selection of enabling technologies and their implications on acoustics and noise and gives a perspective on future trends and new directions in aeroacoustics required to address the challenges.

/pdf/advanced-low-noise-aircraft-configurations-and-their-4dn2hje835.pdf

Advanced low-noise aircraft configurations and their assessment: past, present, and future

Today, main hub airports are already at their capacity limit and hence, smaller airports get more interesting to provide point-to-point connections. Unfortunately, the use of regional airports induces an increased environmental footprint for the population living around it. In an attempt to solve the related problems, unconventional aircraft and engine designs are required. The research project Coordinated Research Centre 880 aims at examing the fundamentals of a single-aisle aircraft powered by two geared ultra-high bypass turbofan engines mounted over the wing. Low direct operating costs, noise shielding due to the over-wing configuration, and short runway lengths are the main advantages of such an aircraft.
 Highlighting the performance, economical and noise benefits of a geared ultra-high bypass engine is the key aim of this paper. This assessment includes a correspondingly adjusted aircraft. Open literature values are applied to design the two investigated bypass ratios; an engine with a bypass ratio of 5 respectively 17. Furthermore, a variable bypass nozzle area for the ultra-high bypass ratio engine is analyzed. Finally, the three engines are evaluated based on aircraft direct operating costs and an initial engine noise assessment.
 This study concludes that increasing the bypass ratio from 5 to 17 drops the direct operating costs by 5.6% and
can reduce the sound at the source for a selected operating condition by up to 7dB. During the different flight phases the reduction in specific fuel consumption ranges between 18% to 40%. Applying a variable bypass nozzle leads to a further decrease by 0.6% for the direct operating costs. Opening the bypass nozzle during several flight phases stabilizes the fan shown by the surge margin increase. It is concluded that this unconventional aircraft configuration with ultra-high bypass ratio engines mounted over the wing has the potential to relieve main hub airports by also reducing the environmental impact.

https://journal.gpps.global/pdf-92455-40305?filename=Evaluation of ultra_high.pdf

Evaluation of Ultra-High Bypass Ratio Engines for an Over-Wing Aircraft Configuration

A geared turbofan with an increased bypass ratio promises reduced engine noise generation if compared to conventional turbofan engines with lower bypass ratios. As a result, the dominance of other ...

System Noise Assessment of a Tube-and-Wing Aircraft with Geared Turbofan Engines

This paper discusses characteristic multi-disciplinary issues related to quiet short take-off and landing for civil transport aircraft with a typical short to medium range mission. The work reported here is focussing on the noise aspects and is embedded in the collaborative research centre CRC880 in Braunschweig, Germany. This long term aircraft Research initiative focusses on a new transport aircraft segment for operation on airports with shorter
runway length in commercial air transport. This calls for a community-friendly aircraft designed for operations much closer to the home of its passengers than today. This Scenario sets challenging, seemingly contradictory aircraft technology requirements, namely those for extreme lift augmentation at low noise. The Research Centre CRC880 has therefore devised a range of technology projects that aim at significant noise reductions and at the generation of e�cffient and flexible high lift. The research also addresses 
flight Dynamics of aircraft at takeoff and landing. It is envisaged that in general significant noise reduction -compared to a reference turbofan driven aircraft of year 2000 technology- necessarily requires component noise
reduction in combination with a low noise a/c concept. Results are presented from all the acoustics related projects of CRC880 which cover the aeroacoustic simulation of the source noise reduction by flow permeable materials, the characterization, development, manufacturing and operation of (porous) materials especially tailored to aeroacoustics, new UHBR
turbofan arrangements for minimum exterior noise due to acoustic shielding as well as the
prediction of jet noise vibration excitation of cabin noise by UHBR engines compared to conventional turbofans at cruise.

Aircraft and technology for low noise short take-off and landing

Noise from civil air traffic affects millions of people worldwide. Aircraft noise management should be addressed by different principal elements, such as noise reduction at the
source and noise abatement operational procedures. To date, usually conventional noise metrics are applied towards the acoustical optimization while noise effects are usually only indirectly accounted for. The objective of this contribution is the optimization of conventional and novel aircraft concepts with respect to their evoked aircraft noise annoyance. The optimization will be based on the perceived sound and the associated annoyance. To do so, virtual aircraft flyovers are auralized based on noise level predictions, i.e. they are artificially made audible. The auralization is accomplished by parametric sound synthe-
sis and a 3D spatial audio technique. Short-term noise annoyance is measured through controlled listening experiments in which participants rate the level of annoyance for each auralized 
flyover. The aircraft design and the flight path are evaluated according to the associated annoyance. The subsequent ranking can be compared to a conventional ranking based on standard noise metrics. The results of such a study will help to identify parameters describing aircraft and flight path parameters that have an impact on noise annoyance. Consequently, these parameters can then be selected for further optimization to reach even
lower levels of noise annoyance and not simply reduce standard noise metrics. Ultimately, the main goal of the research is optimizing the noise annoyance of (novel) aircraft along tailored flight paths. This contribution documents the status quo of the joint DLR and Empa activities, i.e., the structure of a pilot study. First results that were obtained while developing the methodology and the test cases within the pilot study are presented.

Simulation process for perception-based noise optimization of conventional and novel aircraft concepts

The number of flight movements is further increasing in the future and some major airports are already at their capacity limit. Therefore, it becomes beneficial for short range aircraft to operate on regional airports as well. Short range aircraft with conventional high-lift systems, however, are not able to safely operate on the comparatively short runways of regional airports. Instead, new aircraft concepts are required that are equipped with an active high-lift system. Such an active high-lift system offers high lift coefficients and thus the ability for short take-off and landing. In order to ensure a sustainable growth in aviation, such new aircraft concepts also have to offer reduced fuel consumption and low noise on the ground.

The Coordinated Research Center (SFB) 880 focuses on such an active high-lift system. This active high-lift system is comprised of a flexible leading edge device, referred to as Droop nose, and an internally blown flap at the trailing edge, referred to as Coanda flap. Within the SFB880, the active high-lift system is applied to several aircraft concepts. These aircraft concepts are equipped with different propulsion systems, that is, turbofan engines of different bypass ratio or a turbine-driven propeller engine. 

In this study, the noise prediction methodology for the noise assessment within the SFB880 is summarized and applied to the aircraft concepts. The assessment includes the noise at the three noise certification points as well as along a line of observers. The study also includes a preliminary uncertainty assessment in order to evaluate the reliability of the predicted noise on the ground. The results show that the SFB vehicles can provide significant noise reduction compared to a reference aircraft with a conventional high-lift system and turbofan engine. Most noise reduction can be achieved with the aircraft that is equipped with the ultra-high bypass ratio turbofan engine.

Jason Blinstrub

Papers

Evaluation of Ultra-High Bypass Ratio Engines for an Over-Wing Aircraft Configuration

System Noise Assessment of a Tube-and-Wing Aircraft with Geared Turbofan Engines

Aircraft and technology for low noise short take-off and landing

Simulation process for perception-based noise optimization of conventional and novel aircraft concepts

Assessment of the Noise Immission along Approach and Departure Flightpaths for Different SFB 880 Vehicle Concepts