Aeroacoustic wind tunnel design

Further progress in airframe noise research including noise prediction and noise reduction solutions depends on the availability of aeroacoustic wind tunnel test facilities with superior aerodynamic and acoustic quality. The demand for aeroacoustic wind tunnels with extremely low background noise and pressure fluctuations, yet with a relevant test section cross-section area and flow velocity, increased significantly over the last decade. In the future, this demand will continue to grow to cope with the challenging noise reduction objectives for aviation noise defined for the years to come. The present text is focused on the state-of-the-art aeroacoustic wind tunnels available today and their design. The design guidelines discussed here assume a classic aerodynamic wind tunnel as a baseline. Therefore, the present text is addressed to both those who are interested in the design of a completely new aeroacoustic wind tunnel as well as those interested in the acoustic upgrade of an existing aerodynamic wind tunnel. As a direct consequence of the multi-disciplinary nature of this complex task, and the multitude of solutions and design tools that are required to complete it, the approach followed here subdivides the design of the aeroacoustic wind tunnel into four main sections: wind tunnel airline circuit (includes the first and second airline cross legs), drive unit and anechoic plenum. While the design approach for the airline circuit and the drive unit is strongly based on coupled numerical solutions of CFD and acoustic solvers, the design of the acoustic plenum gives more emphasis to in situ observations and to experimental results. The main sections of the aeroacoustic wind tunnel and their best design are discussed separately in this contribution. © 2019, Deutsches Zentrum für Luft- und Raumfahrt e.V.