Numerical investigation of the refraction effects by jet flows in anechoic wind tunnels

In regard to the problem of aircraft noise mitigation, the present study focuses on the refraction effects to be possibly induced by anechoic facility jet flows on the measured acoustic signatures, during typical airframe noise experiments. To this end, Computational AeroAcoustics (CAA) calculations based on the solving of the Perturbed Euler Equations (PEE) are conducted, enabling the estimation of the refraction effects characterizing a typical open-jet, anechoic wind tunnel, namely the NASA Langley’s Quiet Flow Facility (QFF). Coming along with their validation against analytical results obtained through a Ray Tracing (RT) technique, the analysis of these CAA/PEE calculations highlights the refraction effects by the facility jet flow, delivering preliminary insights about what are the key parameters (jet height, jet curvature, jet spreading angle, shear layer thickness, etc.) to play a major role in these refraction phenomena.