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Numerical aero-acoustic assessment of installed Counter Rotating Open Rotor (CROR) power plant

European Union
Complete with results
Geo-spatial type
Total project cost
€200 000
EU Contribution
€150 000
Project Acronym
STRIA Roadmaps
Vehicle design and manufacturing (VDM)
Transport mode
Airborne icon
Transport policies
Environmental/Emissions aspects,
Transport sectors
Passenger transport,
Freight transport


Call for proposal
Link to CORDIS

The inherently high propulsive efficiency of advanced propellers and Counter-Rotating Open Rotors (CROR) have a great potential for fuel savings, but the level of noise emitted by the open blades represent a major obstacle to their environmental acceptance. Consequently, the design of a low noise, fuel efficient open rotor powerplant is one of the major objectives in the CleanSky JTI.

Within the virtual prototype design environment, the availability of highly efficient calculation procedures of noise sources and their propagation are essential to achieve the set objectives. While the CAA approach for the acoustic far-field noise propagation was well established, the critical issue remains the delivery of fast and accurate unsteady CFD-solutions for prediction of the noise sources. The NAA-CROR proposal responded to this objective, through an advanced new approach for the CFD determination of the noise sources. The NAA-CROR project relied on the nonlinear harmonic method (NLH) which allows a gain in CPU performance for CROR’s compared to current CFD sliding grid or Chimera methodologies, of two to three orders of magnitude. This method, defined in the frequency domain, has been largely validated and successfully applied on multistage turbines and compressors at many companies. Its extension to propeller and CROR configurations has recently been achieved.

The present project proposed the further extension of this approach, focused on the ability to capture installation effects for CROR configurations. The near-field and far-field noise was evaluated with an acoustic propagation module solving the Ffwocs Williams and Hawkings (FW-H) equations. The acoustic module was fully integrated with the NLH code, allowing a turnaround time for a complete CFD-CAA simulation of a few hours on a low number of processors.


Parent Programmes
Institution Type
Public institution
Institution Name
European Commission
Type of funding
Public (EU)
Specific funding programme
JTI-CS - Joint Technology Initiatives - Clean Sky
Other Programme
JTI-CS-2010-3-SFWA-02-008 Numerical and experimental aero-acoustic assessment of installed Counter Rotating Open Rotors (CROR) power plant


Executive Summary:

During the course of this project, several improvements of the CFD/CAA system were pursued to ensure a professional, user-friendly and quality assured software environment applied to open rotors. The Non-Linear Harmonic (NLH) method, implemented in NUMECA software, is applied, providing a highly efficient method for a simultaneous prediction of the unsteady aerodynamics and the near-field acoustics of Counter-Rotating Open Rotors (CROR). Far-field acoustic propagation method (computed with a Ffowcs-Williams and Hawking solver) is also applied to NLH results. Several aspects of the software have been enhanced with respect to the meshing tool (AutoGrid5™), the CFD solver in FINE™/Turbo, the acoustic solver FINE™/Acoustics and its integration with FINE™/Turbo.

The numerical CFD/CAA approach has then been extensively applied to several CROR configurations (cruise, take-off, with/out incidence, with/out pylon, and with/out imposed transition). Both pre-test and post-test simulations have been run. When available, the results have been compared to those of other partners or to wind tunnel test data. The performed calculations prove that the NLH method is capable of accurately predicting CROR configurations at a very low computational cost (when compared to full unsteady calculations).


Lead Organisation
Numerical Mechanics Applications International Sa
Organisation website
EU Contribution
€150 000
Partner Organisations
EU Contribution


Technology Theme
Aircraft propulsion
Counter Rotating Open Rotor Engine
Development phase

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