A comparison between off and on-body control surfaces for the FW-H equation: Application to a non-compact landing gear wheel
JOURNAL OF SOUND AND VIBRATION
Authors: Hajczak, Antoine; Sanders, Laurent; Vuillot, Francois; Druault, Philippe
Abstract
This work is a contribution to the ongoing debate about the role of quadrupoles in low Mach number flows, studied through the use of solid and permeable surface Ffowcs-Williams & Hawkings (FW-H) integrals for landing gear numerical noise predictions. It rests upon the key idea that the dominance of surface sources over volume sources can only be guaranteed when the compact-source condition is met. We propose here to express this property as a condition on the smallness of the product between the Mach and Strouhal numbers, or formally as MSt < 1. We consider a canonical isolated wheel, that basically consists in a shallow circular cavity inscribed in a coin-like cylinder, thus presenting few different length scales, as compared to a full landing gear assembly. Zonal Detached Eddy Simulations are performed on several gradually refined grids to assess the grid convergence of the numerical result. In particular, important computational effort is put into the accurate resolution of acoustic waves up to Strouhal numbers such that MSt > 1. Overall, determining the real significance of quadrupoles was challenging as numerical errors or misleading effects such as near-field terms, surface discretization, or source domain truncation biased the initial permeable surface results. Even when these sources of bias are removed, non-negligible differences are found between the solid and permeable noise spectra at non-compact St values, while both formulations are equivalent at lower Strouhal numbers. The analysis of these differences is extended to the determination of their impact on frequency-domain noise maps obtained with the DAMAS algorithm fed with far field signals computed with both FW-H approaches. A tentative interpretation of the wheel noise sources is finally proposed, highlighting the dominant role of the scattering of aerodynamic sources by the cavity downstream edge at low Strouhal numbers, while wake sources dominate at higher Strouhal numbers. (C) 2020 Elsevier Ltd. All rights reserved.
Understanding the Audience Turn in Journalism: From Quality Discourse to Innovation Discourse as Anchoring Practices 1995-2020
JOURNALISM STUDIES
Authors: Meijer, Irene Costera
Abstract
Paying close attention to news users has become fully integrated in professional journalism. Even though this practice may still meet with resistance, becoming more audience responsive is no longer automatically condemned as the highway to popularization and sensationalism. What has changed in journalism's ecosystem to account for this turnaround? This paper explains how journalists' attitude towards audiences changed from keeping them at a distance to constantly monitoring their movements. It is based on longitudinal participatory observation of key moments (editorial meetings, public debates) in Dutch journalism, as well as on informal talks and formal interviews with more than one hundred journalists and editors during the last twenty years. It traces four tipping points between 1995 and 2020 regarding the audience turn in commercial news and public service journalism: (1) Quality news as "not having to reckon with your audience". (2) Increasing professional awareness of "informed citizenship" as quality journalism's remit; (3) digitalization of journalism; and (4) increasing relevance of "audience engagement". Ann Swidler's concept of "anchoring practice" (2001) will be used as a lens to understand the gradual shift from quality discourse to innovation discourse as anchoring practices in journalism and journalism studies.