Zonal LES for Axial Fan Broadband Noise Prediction, Part 1: Experimental Study

Broadband noise prediction is a major challenge in computational aeroacoustics for many industrial applications. A proper aeroacoustic simulation requires the use of highly accurate numerical approaches usually implying a high computational burden. Therefore they are not suitable to be implemented in optimization loops, even if they constitute a valuable support to address the performances of various designs. In order to reduce the computational time for such kind of simulations, strong approximations have to be introduced in the numerical models. Therefore the validation and benchmark of the simulation procedure with experimental data sets is an essential step in order to rely on numerical results. The object of this paper is to provide to the scientific community a reference test-case for turbomachinery noise, assessing the potentialities of a novel breakthrough approach for Computational Fluid Dynamics (CFD): the zonal Large Eddy Simulation (LES). Few experimental data are available in the literature concerning the aeroacoustic performance of axial fans, [1-3]. Therefore, to perform a proper validation of the numerical approach, in Part 1 of this paper a complete experimental characterization of the acoustic and aerodynamic field generated by a low noise axial fan is presented. On the other hand, in Part 2 [4], the numerical modelling of this test case and its validation is discussed. The test-case chosen is a 5-bladed axial fan in free field conditions with an outer diameter of 350 mm and nominal rotational velocity of 1400 rpm. The fan aerodynamics has been investigated by using the planar Particle Image Velocimetry technique (2D-PIV). The aeroacoustic measurements were performed in a fully anechoic chamber with multiple measurement high-sensitivity microphones placed around the fan.