EAGER: Improving the Aeroacoustic Properties of Hybrid Anechoic Wind Tunnels

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Wind tunnels are a fundamental part of the engineering and scientific process used to develop quieter and more efficient aircraft, wind turbines, and other systems. The hybrid anechoic wind tunnel, introduced some 13 years ago, provides a way to substantially increase the accuracy and scope of wind tunnel tests concerned with flow generated noise. This configuration, which has already been adopted by a number of research facilities across the world relies on “acoustic windows” – large panels of tensioned fabric that are transparent to sound but largely impervious to flow. Such windows have been made from commercially available Kevlar fabric which has many desirable characteristics for this purpose, but the fabric was designed for composites manufacture. A Kevlar fabric explicitly designed for wind tunnel applications promises additional benefits – an even quieter test environment and embedded instrumentation that can monitor the flow. Under this project, an interdisciplinary team of textiles, acoustics, and aerodynamics researchers will conduct a short-term research program to develop these materials. This innovative, potentially high payoff effort, promises to bring the advantages of hybrid anechoic testing to national scale facilities and greatly enhance the development quieter and more efficient vehicles and systems. This project will also be dedicated to research education at the postdoc, graduate and undergraduate levels. This research is based upon the observation that Kevlar fabric used as acoustic windows generates noise at high frequencies (10kHz) that potentially limits the application of this technology in the context of national scale wind tunnel facilities that perform applied model scale testing for vehicle development by industry and government. The hypothesis is that the noise is made by pores in the fabric that serve no useful aeroacoustic function. Adjusting the weave to eliminate the pores requires the multi-disciplinary collaboration needed to perform a systematic study of the optimum fabric design for aeroacoustic applications. The work is being performed by a team of researchers from Virginia Tech, Florida Atlantic University, and NC State. The NC State group will use a research loom fabricate the needed modified fabrics and also investigate the feasibility of embedding sensors. Wind tunnel experiments directed at documenting and understanding the aeroacoustic performance of the fabrics will be performed at Virginia Tech, which will also provide input on sensor choices and requirements. Theoretical modeling and understanding of the nature of the acoustic source will be performed at Florida Atlantic University. Together this effort is expected to generate robust recommendations for optimal acoustic window design and embedded sensors that can be adopted by current and planned hybrid anechoic wind tunnels.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.