The Effect of Acoustic Noise on Aero-Optical Measurements in Wind Tunnels

Both ground and flight test data show that optical wavefront measurements can detect and be influenced by acoustic noise, where the optical aberrations originate from density variations associated with the sound waves. This finding has implications regarding the potential effect of background acoustic noise on optical measurements during wind-tunnel testing. In this article, results are presented for optical wavefront measurements through the empty test section of a subsonic wind tunnel, with emphasis on how optical data can be affected by acoustic noise from the main fan. A predictive model employing an acoustic mode-marching method is shown to provide good comparison with measured optical data.