ENGINEERING AND CFD
CARo – Computational Aeroacoustics of Rotors
Principal Investigator:
Manuel Keßler
Affiliation:
Institute of Aerodynamics and Gasdynamics, University of Stuttgart
Local Project ID:
GCS-CARo
HPC Platform used:
Hazeln Hen of HLRS
Date published:
The helicopter and aeroacoustics group at IAG simulates the complex aerodynamics and aeromechanics of rotorcraft since the early 90s. Aeroacoustics have been added a couple of years later, with simulation technology nowadays utilising highly resolved CFD solutions, postprocessed for noise exposure at arbitrary observer points by means of the Ffowcs Williams-Hawkings approach.
© IAG, University of Stuttgart
Due to the extremely high demand of computational resources for acoustic simulations, those activities were forked off in 2017 from our long-running HELISIM project. Two years later, aerodynamics and aeroacoustics were re-united to simplify administrative burden, so this report constitutes the end of the separate CARo project.
During CARo, the noise emission of Contra-Rotating Open Rotors (CROR) have been investigated, especially in the installed case on an airliner tail, and predictive capability has been explored on the advanced compound configuration RACER from Airbus Helicopters, which is due for first flight in 2022.
mp4 video © IAG, University of Stuttgart
Other results obtained within CARo were the detailed investigation of noise characteristics in different flight situations on more conventional helicopters, like the H145 in horizontal flight.
The spectra show the variation from mostly tonal noise with distinctive peaks during take-off (pls. see image below, left hand side) to broadband dominated sound in a horizontal flyover situation (right). Although some discrepancies exist, especially to higher frequencies, the agreement between flight test and simulation is sufficiently good to serve as an indicator of fundamental noise source mechanisms as well as their relative importance, depending on flight condition and emission direction. At the aircraft level, more silent rotors may be developed using this knowledge. From an operational point of view, the information obtained allows a flight path planning taking “quiet zones” into account, for example to avoid residential areas nearby.
© IAG, University of Stuttgart
The simulation technology developed and advanced in the helicopter group of IAG thus helps to further investigate the sound mechanisms of different rotorcraft and thus allows to diminish the noise impact on the community. Especially with regard to upcoming eVTOL concepts for Urban Air Mobility, so-called air taxis, which operate mostly close to inhabited areas, this capability is extremely important to assess different technologies under consideration at early design stages, before actual aircraft are built and further changes get extremely expensive in terms of money and delays.
References
- Patrick P Kranzinger, Manuel Keßler, and Ewald Krämer. Examination of the influence of empiric parameters on the aero-acoustic results of the free wake code FIRST. In 43rd European Rotorcraft Forum, Milan, Italy, 2017.
- Constantin Öhrle, Felix Frey, Jakob Thiemeier, Manuel Keßler, and Ewald Krämer. Coupled and trimmed aerodynamic and aeroacoustic simulations for Airbus helicopters’ compound helicopter RACER. In AHS Specialists’ Conference on Aeromechanics Design for Transformative Vertical Flight, San Francisco, CA. American Helicopter Society, 2018.
- Lukas Dürrwächter, Manuel Keßler, and Ewald Krämer. Numerical assessment of CROR noise shielding with a coupled Möhring analogy and BEM approach. In 24th AIAA/CEAS Aeroacoustics Conference, Atlanta, Georgia. AIAA Paper 2018-2822, June 2018.
- Johannes Kleinert, Lukas Dürrwächter, Manuel Keßler, and Ewald Krämer. Aeroacoustics of high-fidelity URANS simulations of a model contra-rotating open rotor with mounting pylon. In 24th AIAA/CEAS Aeroacoustics Conference, Atlanta, Georgia. AIAA Paper 2018-4082, June 2018.
- Manuel Keßler. Progress in helicopter noise prediction. In Andreas Dillmann, Gerd Heller, Ewald Krämer, Claus Wagner, Cameron Tropea, and Suad Jakirlic, editors, New Results in Numerical and Experimental Fluid Mechanics XII: Contributions to the 21th STAB/DGLR Symposium Darmstadt, Germany, 2018, Notes on Numerical Fluid Mechanics and Multidisciplinary Design. Springer International Publishing, 2019.
- Lukas Dürrwächter, Manuel Keßler, and Ewald Krämer. Numerical assessment of open-rotor noise shielding with a coupled approach. AIAA Journal, 57(5):1930– 1940, 2019.
- Constantin Öhrle, Felix Frey, Jakob Thiemeier, Manuel Keßler, and Ewald Krämer. Coupled and trimmed aerodynamic and aeroacoustic simulations for Airbus Helicopters’ compound helicopter RACER. Journal of the American Helicopter Society, 64(3):1–14, 2019.
- Manuel Keßler. Expanding helicopter noise simulation scope, based on high-fidelity CFD. In 75th VFS Annual Forum, Philadelphia, PA, 2019.
Scientific Contact:
Dr. Manuel Keßler, Dipl.-Phys.
Institut für Aerodynamik und Gasdynamik (IAG)
Universität Stuttgart
Pfaffenwaldring 21, D-70550 Stuttgart (Germany)
e-mail: kessler [@] iag.uni-stuttgart.de
Website: Helicopter and Aero Acoustics Group, IAG, University of Stuttgart
Local project ID: GCS-CARo
March 2021