Aeroacoustic measurements of airframe components: in an open-jet, a hard-wall and a hybrid wind tunnel test section

Abstract

Aircraft noise is a major source of environmental noise that negatively affects human health. Stakeholders and policymakers are nowadays increasingly confronted with protests from residents exposed to high aircraft noise levels, forcing them to change their noise policies. A solution to the aircraft noise problem is the further development and validation of more accurate noise prediction tools and noise reduction technologies. These tools and technologies are crucial to aircraft manufacturers because they help reduce uncertainties arising during the design process of a new aircraft. Wind tunnel measurements play an essential role in the development of noise prediction tools and noise reduction technologies because they provide valuable physics-based data in a controlled environment in a cost-efficient way. This data is then be used to develop or validate new (semi-)analytical noise prediction models or extend existing semi-empirical noise prediction models for new or even disruptive aircraft designs. Moreover, computational aeroacoustic (CAA) simulation tools still rely heavily on wind tunnel data for validation.Aeroacoustic measurements in wind tunnels nowadays commonly use the microphone phased array technique for the localization and quantification of sound sources. However, this type of measurement is subject to considerable uncertainty. This is mainly due to a lack of: (1) an understanding of how the wind tunnel affects the aeroacoustic measurements, (2) a general framework to correct aeroacoustic measurement to a standard free-field condition and (3) an identification and reduction of systematic errors. The work in this thesis aims at understanding and reducing the uncertainty in wind tunnel testing, thereby facilitating the development of more accurate noise prediction tools and noise reduction technologies.A literature review of the theoretical principles and basic concepts of aerodynamic noise is first presented, and airframe noise prediction models are described. Aeroacoustic measurements in wind tunnels are discussed, and a review of comparability studies found v xi keuze te maken in het selecteren van een windtunnel testsectieconfiguratie voor een specifiek doeleind. Ten slotte zullen de meetgegevens beschikbaar worden gesteld in een open database voor validatiedoeleinden, waarbij een vergelijking met metingen in andere windtunnelfaciliteiten kan worden gedaan. Met name de datsets van de NACA-63018 en 30P30N zijn beschikbaar als maatstaaf in de Hybrid Anechoic Wind Tunnel Workshop. Bovendien kunnen de 30P30N gegevens worden gebruikt in de workshop Bechmark for Airframe Noise Computations om numerieke simulaties te valideren.