A study of the turbulent wake of an airfoil in an air stream with a 90° curvature using hot-wire anemometry and large eddy simulation

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The broad aim of the work presented in this thesis is to investigate the wake of an airfoil under the combined effects of streamwise curvature and pressure gradient. This was accomplished by an experimental investigation using hot-wire anemometry and large eddy simulation (LES). The wake was generated by placing a NACA 0012 airfoil in a uniform stream of air, which is then subjected to an abrupt 90o curvature created by a duct bend. The experimental work was conducted in a subsonic open-return type wind tunnel. The test section measured 457 mm × 457 mm in cross-section and consisted of a 90o bend with radius-to-height ratio of 1.17. The symmetrical airfoil was of chord length (c) 150 mm, and its trailing edge was located one chord length upstream of the bend entry. The effects of airfoil angle of attack and mainstream velocity on the mean velocity and turbulence quantities of the near-wake were examined. In addition, the mean velocity and turbulence intensity profiles of the boundary layer on the upper surface of the airfoil were measured. In the numerical investigation, the three-dimensional, incompressible turbulent flow in the duct was computed using the finite volume method. The effect of modelling parameters, namely, grid resolution and sub-grid scale (SGS) model were studied. Three different sub-grid scale models were employed, namely, the classical Smagorinsky, its dynamic variant (DSMG) and the dynamic kinetic energy transport. The effect of grid resolution was assessed by conducting simulations with the DSMG model on three different grids. The first two grids incorporated the full spanwise extent of the duct (3c), and the third grid comprised a reduced spanwise segment (0.5c) with periodic conditions set in the spanwise direction. A bounded central differencing scheme was employed for the discretization of the convection terms. The temporal discretization was by a second-order implicit method that incorporated a forward difference approximation. The performance of LES in depicting the experimental flow was assessed and compared with the results predicted by the Reynolds Stress Model. The experimental profiles at zero angle of attack revealed the differing effects of curvature on the mean and turbulence quantities in the inner-side and outer-side of the wake. The spanwise distributions of mean velocity and turbulence intensity, in the near-wake, indicated variations with identifiable peaks and troughs which corresponded to the presence of streamwise vortices in the wake. The spanwise variations were larger on the inner side of the wake and significantly reduced on the outer side. The results showed that close to the trailing edge, the dominant effect on the wake was from the airfoil boundary layer, whereas one chord length downstream of the trailing edge, it was the effect of curvature and pressure gradient from the duct which was dominant. The results from the numerical study showed the advantages of LES over Reynolds-averaged Navier-Stokes methods in predicting separation on the convex wall of the bend on relatively coarse grids, but also shortcomings in the prediction of the wake parameters. The dynamic variants of the SGS models were more accurate in predicting the flow in the wake. On a considerably finer grid with near-wall airfoil grid spacings of Δx+ < 80, Δy+ < 0.5, and 20 < Δz+ < 50, LES resulted in much improved comparisons with the experimental data. The improved prediction of the wake parameters was attributed to the improved simulation of the boundary layers on the upper surface of the airfoil. However, the effect of the reduced spanwise extent resulted in a lack of prediction of separation on the convex wall of the duct

Feature Dimensionality Reduction via Homological Properties of Observability]{Feature Dimensionality Reduction via Homological Properties of Observability

Feature selection and its subsequent dimensionality reduction are significant problems in machine learning and it is at the core of several data science techniques. The 'shape' of data, or in other words its related topological properties, can provide crucial insights into the corresponding data types and sources and it enables the identification of general properties that facilitate its analysis and assessment. In this article, we discuss an information theoretic approach combined with data homological properties to assess dimensionality reduction, which can be applied to semantic feature selection

Supplemental: BPS Guidelines for Psychologists Working with Refugees and Asylum Seekers in the UK

These guidelines were developed by the British Psychological Society’s Presidential Taskforce on Refugees and Asylum Seekers. As a discipline and a profession, psychology has a wealth of knowledge, experience and talent to apply in this area to help improve the lives of refugees and asylum seekers who have fled their countries and are seeking safety. This guidance document is important, not only for frontline psychologists and others working in the field, but also for practitioners in related disciplines, including directors, managers and practitioners of organisations working with refugees and migrants, providing services to this population at home and abroad

Optimal control of system governed by nonlinear volterra integral and fractional derivative equations

AbstractThis work presents a novel formulation for the numerical solution of optimal control problems related to nonlinear Volterra fractional integral equations systems. A spectral approach is implemented based on the new polynomials known as Chelyshkov polynomials. First, the properties of these polynomials are studied to solve the aforementioned problems. The operational matrices and the Galerkin method are used to discretize the continuous optimal control problems. Thereafter, some necessary conditions are defined according to which the optimal solutions of discrete problems converge to the optimal solution of the continuous ones. The applicability of the proposed approach has been illustrated through several examples. In addition, a comparison is made with other methods for showing the accuracy of the proposed one, resulting also in an improved efficiency

Comparison of flow and dispersion properties of free and wall turbulent jets for source dynamics characterisation

The objective of this paper is to provide an investigation, using large eddy simulations, into the dispersion of aircraft jets in co-flowing take-off conditions. Before carrying out such study, simple turbulent plane free and wall jet simulations are carried out to validate the computational models and to assess the impact of the presence of the solid boundary on the flow and dispersion properties. The current study represents a step towards a better understanding of the source dynamics behind an airplane jet engine during the take-off and landing phases. The information provided from these simulations can be used for future improvements of existing dispersion models

Displaced Voices: A Journal of Migration, Archives and Cultural Heritage, Volume 3 Issue 1 (Spring 2023)

Twentieth Century Histories of Civic Society’s Responses to Crises of Displacement: A Special Issue to mark the 70th Anniversary of Refugee Council Displaced Voices is a biannual digital magazine produced twice a year by the Living Refugee Archive team at the University of East London. Displaced Voices aims to provide a digital platform for activists, archivists, researchers, practitioners and academics to contribute to issues pertaining to refugee and migration history; refugee and migrant rights; social justice; cultural heritage and archives. We welcome a range of contributions to the magazine including articles of between 1000-2000 words; reports on fieldwork in archival collections; book recommendations and reviews; and more creative pieces including (but not limited too) cartoons; photography; and poetry. We would also welcome news on activities; publication of reports, projects; letters and news from your own networks. We welcome submissions from all writers whether you are a student, practitioner, activist or established academic. The Displaced Voices online magazine is born out of the collaborative and intersectional work that we have been undertaking through our work with the refugee and migration archives housed at the University of East London. Our work to date has explored the intersections of refugee and migration studies with narrative and life history research linked to oral history methods and archival approaches to the preservation, documentation and accessibility of archival resources recording the refugee experience. This magazine is a collaborative project between the Living Refugee Archive at the University of East London; the Oral History Society Migration Special Interest Group and the International Association for the Study of Forced Migration Working Group on the History of Forced Migration and Refugees. Thematically we are looking to engage with articles that explore the intersection of refugee and forced migration studies; history and cultural heritage studies; narrative research; oral history and archival science

2nd Workshop on Energy for Sustainable Science at Research Infrastructures

Liam will provide an overview of the current state of data center technology including practical guidance on how best to operate what you already have and how differently you should build new capacity based on recent changes in technology and knowledge. The way data centers are built and operated has changed fundamentally in the last 5 years which has resulted in substantial changes to the construction and operational costs for those able to take advantage of these changes. This is particularly true for high performance compute type facilities where many of the expensive traditional elements may be discarded by the well-informed operator. The presentation will discuss key changes in data center technology and practices such as IT environmental controls and answer the question, do you need to go to Iceland to get rid of mechanical cooling? The discussion will include practical measures for operators to implement as well as identifying the relevant standards and free guidance such as the EU Code of Conduct for Data Centers Energy Efficiency

Guidance for clinicians when working with refugees and asylum seekers

The contribution and role of psychologists, psychiatrists or mental health practitioners in working alongside forced migrants may take many forms. The guidance on which this paper is based, came about when several members of the British Psychological Society (including those with lived experience and insight and those who had set up services); became aware of the need for good practice guidance for clinicians working with refugees, asylum seekers including forced migrants across Britain. These guidelines cover a range of areas where clinicians work with individuals in clinical contexts, schools, nurseries, colleges and within community organisations