On applications of chimera grid schemes to store separation

A finite difference scheme which uses multiple overset meshes to simulate the aerodynamics of aircraft/store interaction and store separation is described. In this chimera, or multiple mesh, scheme, a complex configuration is mapped using a major grid about the main component of the configuration, and minor overset meshes are used to map each additional component such as a store. As a first step in modeling the aerodynamics of store separation, two dimensional inviscid flow calculations were carried out in which one of the minor meshes is allowed to move with respect to the major grid. Solutions of calibrated two dimensional problems indicate that allowing one mesh to move with respect to another does not adversely affect the time accuracy of an unsteady solution. Steady, inviscid three dimensional computations demonstrate the capability to simulate complex configurations, including closely packed multiple bodies

Experience with 3-D composite grids

Experience with the three-dimensional (3-D), chimera grid embedding scheme is described. Applications of the inviscid version to a multiple-body configuration, a wind/body/tail configuration, and an estimate of wind tunnel wall interference are described. Applications to viscous flows include a 3-D cavity and another multi-body configuration. A variety of grid generators is used, and several embedding strategies are described

A Monte Carlo study of the three-dimensional Coulomb frustrated Ising ferromagnet

We have investigated by Monte-Carlo simulation the phase diagram of a three-dimensional Ising model with nearest-neighbor ferromagnetic interactions and small, but long-range (Coulombic) antiferromagnetic interactions. We have developed an efficient cluster algorithm and used different lattice sizes and geometries, which allows us to obtain the main characteristics of the temperature-frustration phase diagram. Our finite-size scaling analysis confirms that the melting of the lamellar phases into the paramgnetic phase is driven first-order by the fluctuations. Transitions between ordered phases with different modulation patterns is observed in some regions of the diagram, in agreement with a recent mean-field analysis.Comment: 14 pages, 10 figures, submitted to Phys. Rev.

Flow characterisation for a validation study in high-speed aerodynamics

Validation studies are becoming increasingly relevant when investigating complex flow problems in high-speed aerodynamics. These investigations require calibration of numerical models with accurate data from the physical wind tunnel being studied. This paper presents the characterisation process for a joint experimental-computational study to investigate the streamwise corners of a Mach 2.5 channel flow. As well as checks of flow quality typically performed for phenomenological investigations, additional quantitative tests are conducted. The extra care to obtain high quality data and eliminate any systematic errors reveal useful information about the wind tunnel flow. Further important physical insights are gained from designing and conducting wind tunnel tests in conjunction with numerical simulations. Crucially, the close experimental-computational collaboration enabled the identification of secondary flows in the sidewall boundary-layers; these strongly influence the flow in the corner regions, the target of the validation study

Experimental validation of the quadratic constitutive relation in supersonic streamwise corner flows

The quadratic constitutive relation is a simple extension to the linear eddy-viscosity hypothesis and has shown some promise in improving the computation of flow along streamwise corner geometries. In order to further investigate these improvements, the quadratic model is validated by comparing RANS simulations of a Mach 2.5 wind tunnel flow with high-quality experimental velocity data. Careful set up and assessment of computations using detailed characterisation data of the overall flow field suggests a minimum expected discrepancy of approximately 3% for any experimental–computational velocity comparisons. The corner regions of the rectangular cross-section wind tunnel exhibit velocity differences of 7% between experimental data and computations with linear eddy-viscosity models, but these discrepancies are reduced to 4–5% when the quadratic constitutive relation is used. This improvement can be attributed to a better prediction of the corner boundary-layer structure, due to computations reproducing the stress-induced streamwise vortices which are known to exist in this flow field. However, the strength and position of these vortices do not correspond exactly with those in the measured flow. A further observation from this study is the appearance of additional, non-physical vortices when the value of the quadratic coefficient in the relation exceeds the recommended value of 0.3.This material is based upon work supported by the US Air Force Office of Scientific Research under award number FA9550–16–1–0430

The influence of nozzle geometry on corner flows in supersonic wind tunnels

In supersonic flows, the separation in streamwise corners is a significant and widely encountered problem which can not be reliably predicted with the numerical methods commonly used in industry. The few previous studies on this topic have suggested conflicting corner flow topologies. Experiments of supersonic flow are typically conducted in wind tunnels with rectangular cross-sections, which use either a symmetric (full) or asymmetric (half-liner) nozzle configuration. However, the effect of the nozzle arrangement on the corner flow itself is not known. This paper examines the influence of nozzle geometry on the corner regions of a Mach 2.5 flow using a joint experimental-computational approach. The full setup and half-liner configuration are shown to produce different corner flow structures. The corner regions of the full setup and top corners of the half-liner exhibit thin sidewall boundary layers and a single primary vortex on the floor or ceiling. Meanwhile, the bottom corners of the half-liner configuration contain thick sidewall boundary layers and a counter-rotating vortex pair. Considerable vertical velocities are measured within the sidewall boundary layers. These are directed towards the tunnel centre-height for the full setup and downwards with the half-liner. The differences in sidewall cross flows between the two nozzle arrangements are likely due to distinct pressure distributions in the nozzle, where the secondary flows are set up. Measurements suggest that these nozzle-dependent transverse flows are responsible for the differences in corner flowfield between the two configurations. The proposed mechanism also explains observed differences in corner flow topology between previous studies in the literature; nozzle geometry therefore appears to be the dominant influence on corner flows in supersonic wind tunnels

Flow Field and Acoustic Predictions for Three-Stream Jets

Computational fluid dynamics was used to analyze a three-stream nozzle parametric design space. The study varied bypass-to-core area ratio, tertiary-to-core area ratio and jet operating conditions. The flowfield solutions from the Reynolds-Averaged Navier-Stokes (RANS) code Overflow 2.2e were used to pre-screen experimental models for a future test in the Aero-Acoustic Propulsion Laboratory (AAPL) at the NASA Glenn Research Center (GRC). Flowfield solutions were considered in conjunction with the jet-noise-prediction code JeNo to screen the design concepts. A two-stream versus three-stream computation based on equal mass flow rates showed a reduction in peak turbulent kinetic energy (TKE) for the three-stream jet relative to that for the two-stream jet which resulted in reduced acoustic emission. Additional three-stream solutions were analyzed for salient flowfield features expected to impact farfield noise. As tertiary power settings were increased there was a corresponding near nozzle increase in shear rate that resulted in an increase in high frequency noise and a reduction in peak TKE. As tertiary-to-core area ratio was increased the tertiary potential core elongated and the peak TKE was reduced. The most noticeable change occurred as secondary-to-core area ratio was increased thickening the secondary potential core, elongating the primary potential core and reducing peak TKE. As forward flight Mach number was increased the jet plume region decreased and reduced peak TKE

Posebnosti bogoslužja na spomendane

This work was supported by the Ministry of Education, Youth and Sports CZ (no. LD14009, no. SV/FVZ201201, no. SVV260062), COST CM1103, MH CZ - DRO (UHHK, 00179906), The Alzheimer’s Society, The Barcopel Foundation and the MSD Scottish Life Sciences fund.The amyloid-β peptide (Aβ) has been associated with Alzheimer’s disease (AD) for decades. The original amyloid cascade hypothesis declared that the insoluble extracellular plaques were responsible for Aβ toxicity. Later, this hypothesis has been updated and soluble intracellular Aβ forms and their effects within the cell have come into focus. Mitochondrial dysfunction plays an important role in the pathophysiology of AD. Aβ was detected inside mitochondria and several mitochondrial proteins were found to interact directly with Aβ. Such interactions can affect a protein’s function and cause damage to the mitochondria and finally to the whole cell. This review summarizes the current knowledge of mitochondrial proteins directly interacting with Aβ and discusses their significance for the development of therapeutics in the treatment of AD.PostprintPeer reviewe

Design, synthesis and in vitro evaluation of benzothiazole-based ureas as potential ABAD/17β-HSD10 modulators for Alzheimer’s disease treatment

This work was supported by the Ministry of Health of the Czech Republic (no. NV15-28967A), Charles University in Prague (no. GAUK B-CH/992214, SVV 260 291) and the Alzheimer’s Society (specifically The Barcopel Foundation). This research is part-funded by the MSD Scottish Life Sciences fund.Amyloid-beta peptide (Aβ) has been recognized to interact with numerous proteins, which may lead to pathological changes in cell metabolism of Alzheimer’s disease (AD) patients. One such known metabolic enzyme is mitochondrial amyloid-binding alcohol dehydrogenase (ABAD), also known as 17β-hydroxysteroid dehydrogenase type 10 (17β-HSD10). Altered enzyme function caused by the Aβ-ABAD interaction, was previously shown to cause mitochondrial distress and a consequent cytotoxic effect, therefore providing a feasible target in AD drug development. Based on previous frentizole derivatives studies, we report two novel series of benzothiazolyl ureas along with novel insights into the structure and activity relationships for inhibition of ABAD. Two compounds ( 37 , 39 ) were identified as potent ABAD inhibitors, where compound 39 exhibited comparable cytotoxicity with the frentizole standard; however, one-fold higher cytotoxicity than the parent riluzole standard. The calculated and experimental physical chemical properties of the most potent compounds showed promising features for blood-brain barrier penetration.PostprintPeer reviewe

Development and Use of Engineering Standards for Computational Fluid Dynamics for Complex Aerospace Systems

Computational fluid dynamics (CFD) and other advanced modeling and simulation (M&S) methods are increasingly relied on for predictive performance, reliability and safety of engineering systems. Analysts, designers, decision makers, and project managers, who must depend on simulation, need practical techniques and methods for assessing simulation credibility. The AIAA Guide for Verification and Validation of Computational Fluid Dynamics Simulations (AIAA G-077-1998 (2002)), originally published in 1998, was the first engineering standards document available to the engineering community for verification and validation (V&V) of simulations. Much progress has been made in these areas since 1998. The AIAA Committee on Standards for CFD is currently updating this Guide to incorporate in it the important developments that have taken place in V&V concepts, methods, and practices, particularly with regard to the broader context of predictive capability and uncertainty quantification (UQ) methods and approaches. This paper will provide an overview of the changes and extensions currently underway to update the AIAA Guide. Specifically, a framework for predictive capability will be described for incorporating a wide range of error and uncertainty sources identified during the modeling, verification, and validation processes, with the goal of estimating the total prediction uncertainty of the simulation. The Guide's goal is to provide a foundation for understanding and addressing major issues and concepts in predictive CFD. However, this Guide will not recommend specific approaches in these areas as the field is rapidly evolving. It is hoped that the guidelines provided in this paper, and explained in more detail in the Guide, will aid in the research, development, and use of CFD in engineering decision-making