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Computation of cOmpouNd rotorCraft latEral RoTor nOise

Periodic Reporting for period 1 - CONCERTO (Computation of cOmpouNd rotorCraft latEral RoTor nOise)

Reporting period: 2018-03-01 to 2019-08-31

Growing demand for air travel raises new environmental and socio-economic challenges. Research and Innovation (R&I) has been and remains core to European competitiveness and sustainable value creation. The investment made by European Union and its Aeronautics Sector has made the industry competitive, allowing it to drive the innovation agenda in many areas. The Horizon 2020 program will be decisive for delivering the innovations defining this century’s flying fleet and its environmental footprint. As Public Private Partnership, Clean Sky 2 (CS2) represents a strategic input to the H2020 objectives, by boosting private investments in R&I, making the best use of public research funding and delivering higher TRL outputs based on full scale demonstrator of novel architectures.
In this framework, the CS2 Fast Rotorcraft Platform, led by Airbus Helicopters (AH), aims at demonstrating that compound rotorcrafts implementing cutting-edge technologies open up to new mobility roles that neither conventional helicopters nor fixed wing aircraft can currently cover in a sustainable way. The resulting rotorcraft, named RACER, will take advantage of the configuration adopted by the AH X3 rotorcraft characterized by two lateral rotors placed under the main rotor. This configuration will bring technological, economical and environmental benefits such as the possibility to combine the high cruise speed, low fuel consumption and gas emission, low community noise impact, and productivity for operators. However, this noise issue remains a major challenge and is one of the most important factors to be considered to ensure that this rotorcraft can be used in urbanized areas to address new mobility roles.
Many progresses were made during the last decades concerning the prediction and the definition of Low Noise Procedures (LNP) on classical helicopters. LNP allow lowering the ground noise level related to helicopters mission through the management of their trajectories. Nevertheless, due to the specific architecture of the RACER, lessons from past studies could not directly be applied. New LNP have to be defined and a novel modelling approach is needed to predict the noise emitted by this rotorcraft.
The main objective of the CONCERTO project (Computation of cOmpouNd rotorCraft latEral RoTor nOise), involving ONERA and DLR, is to develop a new computational tool enabling, in multiple operating conditions, the noise prediction of lateral rotors installed on the RACER demonstrator, and equip Airbus Helicopters with this necessary tool to significantly improve the noise performance of this rotorcraft. This tool, enabling both fast prediction and high fidelity approaches, will include 3 modules: aerodynamics, free field acoustic and scattering effects. All three modules will be implemented in a chaining process based on a seamless workflow and software environment that will be created during the project. The overall tool will be validated and applied to a subset of the RACER flight domain. This project will go beyond the state of the art (investigating unsteady flight cases, capturing quadrupole noise sources, solving efficiently the multifrequency problem of combined main rotor and lateral rotors, etc.), and will fully address user needs. It will contribute to the maturation and future commercialization of a new aircraft vehicle satisfying new mobility roles, thus contributing to the competitiveness of the European aeronautic industry.
During the first period of the CONCERTO project, several tools have been set-up to ensure an efficient management; including a Data Management Plan, a Plan for Exploitation and Dissemination of the Results, servers for data exchange, documents template and monitoring tables. From a more technical point of view, a first release of the computational chain has been created and delivered to Airbus Helicopters. Using this tool, AH is now able to perform aeroacoustic predictions of RACER’s lateral rotors. The noise source can be obtained thanks to either using the PUMA code for fast predictions or the CFD Tau code for high fidelity computations. For the time being, acoustic waves propagate in free-field i-e without the effect of the fuselage and the wings. The tool has been delivered together with user-manuals and good practices that will provide valuable support and help AH in the use of the computational chain.
The state of art at the beginning of the CONCERTO project regarding the noise prediction of the RACER’s lateral rotors corresponds to what has been done in the CS2 NACOR project. In this project ONERA and DLR realize global aeroacoustic predictions of the RACER. The methodology proposed by ONERA which is the basis for the activities in CONCERTO to predict lateral rotors noise is the following:
• the aerodynamic code PUMA computes the noise source by taking into account interactions with the main rotor’s downwash and the wings’ wake using a perturbation field computed separately by a CFD code (ONERA’s elsA code or DLR’s Tau code),
• using those noise sources, the direct acoustic field and the incident field on to the rotorcraft are computed by the KIM code,
• the acoustic field scattered by the RACER’s solid surfaces is obtained thanks to a Boundary Element Method. The total acoustic field at observer locations is finally computed as the addition of the scattered and direct acoustic fields.
The CONCERTO project will go beyond this approach, and significant improvements have already been achieved during the first period of the project. First of all, the previously described methodology is now fully integrated in a computational process chain, allowing easier and faster predictions. Also, DLR has developed a Reduced Order Model (ROM) strategy to provide perturbation fields derived from CFD. Using CFD simulations for a few, carefully selected, flight conditions as input, the ROM will provide perturbation data for PUMA for a wide range of flight conditions without additional time consuming CFD simulations. Other improvements are under developments and will soon be integrated:
• noise predictions during a maneuver,
• inclusion of the main rotor in the PUMA simulations,
• development of analytical models to capture propeller interactions with wings and main rotor in PUMA calculations,
• fast predictions of the acoustic scattered field using simplified approaches.

Several impacts have been identified, at the environmental, industrial and societal levels:
• by mitigating the noise footprint of a compound helicopter,
• by strengthening the European Competitiveness of the aeronautical industry,
• by increasing the range and speed for rescue and emergency and passenger transport.
These impacts are related to the fact that this project will provide AH with the tools for designing the best possible compound rotorcraft in terms of noise emission in a shorter period of time. This is actually the case, since Airbus Helicopters’ engineers are now able to perform their own noise prediction using the first release of the CONCERTO chain. Another expected impact is the enhancement of research and innovation capacity. Compound helicopters, like the unique RACER configuration, are an actual challenge for the aeronautical research community. The work already done so far, and all the improvements to be achieved in the CONCERTO project will definitely help in the prediction of aerodynamics and acoustics installation effects of next generation aircraft.