Dynamics of coherent structures in a plane mixing layer

An incompressible, time developing 3-D mixing layer with idealized initial conditions was simulated numerically. Consistent with the suggestions from experimental measurements, the braid region between the dominant spanwise vortices or rolls develops longitudinal vortices or ribs, which are aligned upstream and downstream of a roll and produce spanwise distortion of the rolls. The process by which this distortion occurs is explained by studying a variety of quantities of dynamic importance (e.g., production of enstrophy, vortex stretching). Other quantities of interest (dissipation, helicity density) are also computed and discussed. The currently available simulation only allows the study of the early evolution (before pairing) of the mixing layer. New simulations in progress will relieve this restriction

Evaluation of Noise Radiation Mechanisms in Turbulent Jets

Data from the direct numerical simulation (DNS) of a turbulent, compressible (Mach = 1.92) jet has been analyzed to investigate the process of sound generation. The overall goals are to understand how the different scales of turbulence contribute to the acoustic field, and to understand the role that linear instability waves play in the noise produced by supersonic turbulent jets. Lighthill’s acoustic analogy was used to predict the radiate sound from turbulent source terms computed from the DNS data. Preliminary computations (for the axisymmetric mode of the acoustic field) showgood agreement between the acoustic field determined from DNS and acoustic analogy. Further work is needed to refine the calculations and investigate the source terms. Work was also begun to test the validity of linear stability wave models of sound generation in supersonic jets. An adjoint-based method was developed to project the DNS data onto the most unstable linear stability mode at different streamwise positions. This will allow the evolution of the wave and its radiated acoustic field, determined by solving the linear equations, to be compared directly with the evolution of the near and far-field fluctuations in the DNS

Intranasal administration of RSV antigen-expressing MCMV elicits robust tissue-resident effector and effector memory CD8+ T cells in the lung

Cytomegalovirus vectors are promising delivery vehicles for vaccine strategies that aim to elicit effector CD8+ T cells. To determine how the route of immunization affects CD8+ T cell responses in the lungs of mice vaccinated with a murine cytomegalovirus vector expressing the respiratory syncytial virus matrix (M) protein, we infected CB6F1 mice via the intranasal or intraperitoneal route and evaluated the M-specific CD8+ T cell response at early and late time points. We found that intranasal vaccination generated robust and durable tissue-resident effector and effector memory CD8+ T cell populations that were undetectable after intraperitoneal vaccination. The generation of these antigen-experienced cells by intranasal vaccination resulted in earlier T cell responses, interferon gamma secretion, and viral clearance after respiratory syncytial virus challenge. Collectively, these findings validate a novel approach to vaccination that emphasizes the route of delivery as a key determinant of immune priming at the site of vulnerability

A complete X-ray spectral coverage of the 2010 May-June outbursts of Circinus X-1

Circinus X-1 is a neutron-star-accreting X-ray binary in a wide (P$_{\rm orb}$ = 16.6 d), eccentric orbit. After two years of relatively low X-ray luminosity, in May 2010 Circinus X-1 went into outburst, reaching 0.4 Crab flux. This outburst lasted for about two orbital cycles and was followed by another shorter and fainter outburst in June. We focus here on the broadband X-ray spectral evolution of the source as it spans about three order of magnitudes in flux. We attempt to relate luminosity, spectral shape, local absorption, and orbital phase. We use multiple Rossi-XTE/PCA (3.0--25 keV) and Swift/XRT (1.0--9.0 keV) observations and a 20 ks long Chandra/HETGS observation (1.0--9.0 keV), to comprehensively track the spectral evolution of the source during all the outbursting phases. These observations were taken every two/three days and cover about four orbital cycles. The PCA data mostly cover the major outburst, the XRT data monitor the declining phase of the major outburst and all the phases of the minor outburst, and Chandra data provide an essential snapshot of the end of this overall outbursting phase. The X-ray spectrum can be satisfactorily described by a thermal Comptonization model with variable neutral local absorption in all phases of the outburst. No other additive component is statistically required. The first outburst decays linearly, with an ankle in the light curve as the flux decreases below $\sim$\,5 $\times$ 10$^{-10}$ erg cm$^{-2}$ s$^{-1}$. At the same time, the source shows a clear spectral state transition from an optically thick to an optically thin state. While the characteristics of the first, bright, outburst can be interpreted within the disk-instability scenario, the following, minor, outburst shows peculiarities that cannot be easily reconciled in this framework.Comment: Accepted for publication in Astronomy and Astrophysic

Using LES to Study Reacting Flows and Instabilities in Annular Combustion Chambers

Great prominence is put on the design of aeronautical gas turbines due to increasingly stringent regulations and the need to tackle rising fuel prices. This drive towards innovation has resulted sometimes in new concepts being prone to combustion instabilities. In the particular field of annular combustion chambers, these instabilities often take the form of azimuthal modes. To predict these modes, one must compute the full combustion chamber, which remained out of reach until very recently and the development of massively parallel computers. Since one of the most limiting factors in performing Large Eddy Simulation (LES) of real combustors is estimating the adequate grid, the effects of mesh resolution are investigated by computing full annular LES of a realistic helicopter combustion chamber on three grids, respectively made of 38, 93 and 336 million elements. Results are compared in terms of mean and fluctuating fields. LES captures self-established azimuthal modes. The presence and structure of the modes is discussed. This study therefore highlights the potential of LES for studying combustion instabilities in annular gas turbine combustors

Trust in financial services: Retrospect and prospect

Fostering and maintaining high levels of trust in the financial services sector is seen as crucial because of the characteristics of many financial service and in order to promote consumer engagement in the sector. In this article, we report evidence from a body of work and other commentary to provide an insight into trends in consumer trust in the sector as a whole, in comparison with other organisations and how different types of financial services provider have performed relative to each other. We show that the financial services sector as a whole is trusted more than some comparator institutions, and that aggregate levels of trust in the sector have fluctuated a relatively small amount subsequent to the financial crisis. However, important differences between provider types are apparent and these differences have become more profound in the recent past. We provide suggestions as to how trust in the sector may be improved and provider an analysis of current initiatives to improve trust levels in the sector in general and in banking in particular

Performance of wall-modeled LES with boundary-layer-conforming grids for external aerodynamics

We investigate the error scaling and computational cost of wall-modeled large-eddy simulation (WMLES) for external aerodynamic applications. The NASA Juncture Flow is used as representative of an aircraft with trailing-edge smooth-body separation. Two gridding strategies are examined: i) constant-size grid, in which the near-wall grid size has a constant value and ii) boundary-layer-conforming grid (BL-conforming grid), in which the grid size varies to accommodate the growth of the boundary-layer thickness. Our results are accompanied by a theoretical analysis of the cost and expected error scaling for the mean pressure coefficient ($C_p$) and mean velocity profiles. The prediction of $C_p$ is within less than $5\%$ error for all the grids studied, even when the boundary layers are marginally resolved. The high accuracy in the prediction of $C_p$ is attributed to the outer-layer nature of the mean pressure in attached flows. The errors in the predicted mean velocity profiles exhibit a large variability depending on the location considered, namely, fuselage, wing-body juncture, or separated trailing-edge. WMLES performs as expected in regions where the flow resembles a zero-pressure-gradient turbulent boundary layer such as the fuselage ($<5\%$ error). However, there is a decline in accuracy of WMLES predictions of mean velocities in the vicinity of wing-body junctions and, more acutely, in separated zones. The impact of the propagation of errors from the underresolved wing leading-edge is also investigated. It is shown that BL-conforming grids enable a higher accuracy in wing-body junctions and separated regions due to the more effective distribution of grid points, which in turn diminishes the streamwise propagation of errors.Comment: arXiv admin note: text overlap with arXiv:2101.0033