This paper presents the work of an R&D project which aims to augment IDIADA’s capabilities in the prediction of aerodynamically generated passby noise via CFD simulations. The project focuses on the noise generated by the A-pillar and the side view mirror of IDIADA’s iShare concept car and combines numerical and experimental investigations. The objective is to develop and validate the numerical aeroacoustics methodology, as well as to develop an experimental methodology that makes use of IDIADA’s semi-anechoic chamber. The main numerical methodology used was based on the surface integral formulation of Ffowcs Williams-Hawkings, this is an acoustic analogy which splits up the problem to the local noise generation first and to the propagation of the acoustic wave second. For the local noise generation two approaches were used, a compressible and an incompressible one. The latter assumes that the acoustic field has a negligible effect on the hydrodynamic flow field, which simplifies the physics involved. The technique uses the theory of Acoustic Perturbation Equations to model the acoustic field that is generated by the flow of an incompressible fluid. The solver used was STAR-CCM+. Parallel to the numerical methodology development the project developed an experimental methodology. This involved the design of a nozzle that could channel the available flow of the semi-anechoic chamber into a high velocity jet that could be directed towards the A-pillar or the side view mirror of a vehicle, thus focusing the noise generation in these features. Finally, the numerical tests were compared to the experiments for validation. The paper will present the numerical and experimental SPL measurements in an array of microphones placed 0.6m away from the left hand side of the iShare, as well as, CFD visualisations of the flow field generated and of the noise sources. The numerical results follow the trends of the experimental results, but for certain frequency octaves there was a small deviation in the predicted SPL. Overall the agreement was satisfactory. This work has shown the potential of the methodologies used to solve aeroacoustics problems and the limitations of what can be tested in IDIADA’s semi-anechoic chamber and of the numerical methods. The paper will elaborate in detail on these findings. This is a new field for IDIADA, and it offers a new aeroacoustic validation case for numerical codes to be compared against.

Dr. CHARALAMPOS TSIMIS, Applus IDIADA, SPAIN Mr. Xavier Montane, Applus IDIADA, SPAIN