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

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 is well established, the critical issue remains the delivery of fast and accurate unsteady CFD-solutions for prediction of the noise sources. The present NAA-CROR proposal responds to this objective, through an advanced new approach for the CFD determination of the noise sources. The NAA-CROR project will rely 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 proposes the further extension of this approach, focused on the ability to capture installation effects for CROR configurations. The near-field and far-field noise will be evaluated with an acoustic propagation module solving the Ffwocs Williams and Hawkings (FW-H) equations. The acoustic module is 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.""