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.
The evolution of minimally invasive tissue sampling in postmortem examination: a narrative review
GLOBAL HEALTH ACTION
Authors: Paganelli, Christina R.; Goco, Norman J.; McClure, Elizabeth M.; Banke, Kathryn K.; Blau, Dianna M.; Breiman, Robert F.; Menendez, Clara; Rakislova, Natalia; Bassat, Quique
Abstract
Background Because of low acceptance rates and limited capacity, complete diagnostic autopsies (CDAs) are seldom conducted in low- and middle-income countries (LMICs). There have been growing investments in less-invasive postmortem examination methodologies, including needle-based autopsy, known as minimally invasive autopsy or minimally invasive tissue sampling (MITS). MITS has been shown to be a feasible and informative alternative to CDA for cause of death investigation and mortality surveillance purposes. Objective The aim of this narrative review is to describe historical use and evolution of needle-based postmortem procedures as a tool to ascertain the cause of death, especially in LMICs. Methods Key word searches were conducted in PubMed and EBSCO in 2018 and 2019. Abstracts were reviewed against inclusion and exclusion criteria. Full publications were reviewed for those abstracts meeting inclusion criteria and a start set was established. A snowball search methodology was used and references for all publications meeting inclusion criteria were manually reviewed until saturation was reached. Results A total of 1,177 publications were initially screened. Following an iterative review of references, 79 publications were included in this review. Twenty-nine studies, published between 1955 and 2019, included MITS as part of postmortem examination. Of the publications included, 76% (60/79) have publication dates after 2010. More than 60% of all publications included addressed MITS in LMICs, and a total of nine publications compared MITS with CDA. Conclusions Although there is evidence of less-invasive postmortem sampling starting in the 1800s, more structured needle-based postmortem examination publications started to appear in the mid-twentieth century. Early studies were mostly conducted in high-income countries but starting in 2010 the number of publications began to increase, and a growing number of studies were conducted in LMICs. Initial studies in LMICs were disease-specific but since 2015 have evolved to include more expansive postmortem examination.