Due to their great potential for fuel saving, Contra-Rotating Open Rotors (CRORs) receive renewed interest by the airframers and the engine manufacturers. The inherent high efficiency of this propulsion system, however, is potentially offset by the level of noise emitted by the open blades. The acoustic impact on passengers and community may represent a major issue to their environmental acceptance. Fast and robust noise prediction tools are clearly required to support the development of quieter propellers and their integration in future civil aeronautical transport. The most common strategy for noise estimation consists in a two-step approach, based on the Lighthill analogy: unsteady near-field aerodynamic flow simulation to evaluate the noise sources, coupled to a far-field acoustic propagation code. Focus is given here on two structured grid flow solvers employed to investigate a scale-model of a 12×10 pusher CROR. The unsteady aerodynamic three-dimensional flow is indeed computed for typical cruise conditions using both the nonlinear harmonic method (NLH) of FINE™/Turbo software and elsA’s chorochronic technique. The evaluation of the far-field noise based on the aerodynamic fields is then carried out with the KIM code, Onera’s acoustic propagation code based on the Ffowcs-Williams and Hawkings (FW-H) formulation. The obtained results enable an analysis of the complex aerodynamic interactions between the two propellers that generate interaction tones in the acoustic signature of the propulsion system. A comparison in terms of numerical settings, computational costs and flow fields is performed between the two CFD methods, which show an excellent match of the predicted global performance of the propulsion system. Some differences in the predicted acoustic signatures are discussed in the paper.

An innovative computational approach, integrating mesh generation, CFD simultaneous analysis of noise source and propagation, with acoustic radiation, is presented and applied to the simulation of the Advanced Noise Control Fan (ANCF) developed by NASA Glenn Research Center. The tonal noise source and the sound propagation in the nacelle duct and in the nacelle near field are simultaneously predicted, starting from the engine geometry and parameters, with a single CFD analysis based on an efficient Nonlinear Harmonic (NLH) method. The sound radiation to the far field is computed with the Green’s function approach implemented in a BEM frequency domain solver of the convective Helmholtz equation. The present method provides to a gain of close to two orders of magnitude compared to standard approaches, based on full unsteady flow simulations, followed by a near-field FEM based approach and a BEM method for the far-field noise propagation. The final comparison between the numerical results and the measurements highlights the capability of the methodology to efficiently predict the unsteady flow field and the radiated sound field.

A centrifugal compressor volute should ideally collect the pressurized flow at the diffuser outlet and convey it to the outlet piping as efficiently as possible. The total pressure loss related to the conversion of a radial flow into an axial one, however, is often not negligible, especially for applications where severe dimensional constraints are given, such as in turbochargers applications. Having a reliable tool for the performance prediction of the volute, flexibly adaptable to external constraints, is then pivotal in the design phase of new prototypes. Within this context, a fully parametric tool has been developed. Based on few geometrical inputs, it allows an automatic generation of both the CAD model of the volute and the numerical setup for the CFD calculation. The shape of the volute cross-section can be fully customized and automatically adapted to the azimuthal distributions of the area and centroid radius given in input by the user. The volute tongue can be also freely modified in terms of shape, azimuthal position and width. An extensive parametric analysis was then carried out, aimed at investigating the influence of key design parameters needed to define the shape of the volute on the internal fluid dynamics. Particular attention was paid to the tongue modelling strategy and shape, being it the critical feature for the volute flow performance. As a result, some annotated indications are given to define the first layout of a volute when approaching a new design.