Experimental Investigations on Noise Shielding: Dependency on Reference Noise Source and Testing Environment

Abstract

This paper presents the experimental results of a study conducted at DLR, ONERA and NASA on the shielding of sound by an NACA 0012 airfoil. The work presented was done in the context of the AVT-233 working group of the Science and Technology Organization (STO) of NATO. The experiments were conducted in the DLR Acoustic Wind Tunnel Braunschweig (AWB), the ONERA F2 tunnel and the NASA Quiet Flow Facility (QFF), with the goal of investigating facility-to-facility effects on the collected data. Two impulsive source concepts were used in the course of these experiments, DLR’s laser sound source and ONERA’s electric discharge source (SPARC). The collected data reveal that the different tunnel environments do not strongly affect the results obtained with either source. The laser sound source is found to deliver consistent results in all three wind tunnels, for the 7, 14 and 28 kHz octave bands at M=0.0 and M=0.16. In the highest octave band considered (56 kHz), the results are found to be very sensitive to the choice of operating parameters. The SPARC source also delivered consistent results in the low frequency range, in both the F2 tunnel and the AWB, for both Mach numbers tested. This joint effort has led to the development of a highly valuable database for the validation of shielding prediction tools.