Laser-based Acoustic Sensing for Noise Measurement in Wind Tunnel

Aeroacoustic testing of rotors and propellers in wind tunnels fulfills an important role in the design and evaluation of future concepts as well as existing technologies. Laser-based sensors for standoff measurement of aeroacoustic perturbations are required in order to overcome the limitations of traditional microphones that are mounted on struts. AeroMancer Technologies proposes to develop a Laser Rayleigh Aeroacoustic Density Sensor (LRADS) for the measurement of acoustic density perturbations using Rayleigh scattering of laser radiation by air molecules. The relative acoustic density perturbations are directly proportional to the ratio of fluctuations of the intensity of the light received by the detector to the mean light intensity. While wind tunnel pressure and velocity measurements will be contaminated by periodic fluctuations from air turbulence, especially below 1KHz where acoustic measurements are desired, density measurements will not be affected as the turbulence is incompressible. In Phase I, AeroMancer will refine the instrument requirements and develop a simulation of its performance; build and test a breadboard instrument for validating the performance simulation; and develop the preliminary design of the system. AeroMancer will also study the potential for developing a miniature in situ version of the instrument for obtaining higher sensitivity and higher frequency response.