Surface correlations of hydrodynamic drag for transitionally rough engineering surfaces

Rough surfaces are usually characterised by a single equivalent sand-grain roughness height scale that typically needs to be determined from laboratory experiments. Recently, this method has been complemented by a direct numerical simulation approach, whereby representative surfaces can be scanned and the roughness effects computed over a range of Reynolds number. This development raises the prospect over the coming years of having enough data for different types of rough surfaces to be able to relate surface characteristics to roughness effects, such as the roughness function that quantifies the downward displacement of the logarithmic law of the wall. In the present contribution, we use simulation data for 17 irregular surfaces at the same friction Reynolds number, for which they are in the transitionally rough regime. All surfaces are scaled to the same physical roughness height. Mean streamwise velocity profiles show a wide range of roughness function values, while the velocity defect profiles show a good collapse. Profile peaks of the turbulent kinetic energy also vary depending on the surface. We then consider which surface properties are important and how new properties can be incorporated into an empirical model, the accuracy of which can then be tested. Optimised models with several roughness parameters are systematically developed for the roughness function and profile peak turbulent kinetic energy. In determining the roughness function, besides the known parameters of solidity (or frontal area ratio) and skewness, it is shown that the streamwise correlation length and the root-mean-square roughness height are also significant. The peak turbulent kinetic energy is determined by the skewness and root-mean-square roughness height, along with the mean forward-facing surface angle and spanwise effective slope. The results suggest feasibility of relating rough-wall flow properties (throughout the range from hydrodynamically smooth to fully rough) to surface parameters

Direct numerical simulation of turbulent flow over a rough surface based on a surface scan

Typical engineering rough surfaces show only limited resemblance to the artificially constructed rough surfaces that have been the basis of most previous fundamental research on turbulent flow over rough walls. In this article flow past an irregular rough surface is investigated, based on a scan of a rough graphite surface that serves as a typical example for an irregular rough surface found in engineering applications. The scanned map of surface height versus lateral coordinates is filtered in Fourier space to remove features on very small scales and to create a smoothly varying periodic representation of the surface. The surface is used as a no-slip boundary in direct numerical simulations of turbulent channel flow. For the resolution of the irregular boundary an iterative embedded boundary method is employed. The effects of the surface filtering on the turbulent flow are investigated by studying a series of surfaces with decreasing level of filtering. Mean flow, Reynolds stress and dispersive stress profiles show good agreement once a sufficiently large number of Fourier modes are retained. However, significant differences are observed if only the largest surface features are resolved. Strongly filtered surfaces give rise to a higher mean-flow velocity and to a higher variation of the streamwise velocity in the roughness layer compared with weakly filtered surfaces. In contrast, for the weakly filtered surfaces the mean flow is reversed over most of the lower part of the roughness sublayer and higher levels of dispersive shear stress are found

Flat-spectrum radio sources as likely counterparts of unidentified INTEGRAL sources (Research Note)

Many sources in the fourth INTEGRAL/IBIS catalogue are still unidentified, since they lack an optical counterpart. An important tool that can help in identifying/classifying these sources is the cross-correlation with radio catalogues, which are very sensitive and positionally accurate. Moreover, the radio properties of a source, such as the spectrum or morphology, could provide further insight into its nature. Flat-spectrum radio sources at high Galactic latitudes are likely to be AGN, possibly associated to a blazar or to the compact core of a radio galaxy. Here we present a small sample of 6 sources extracted from the fourth INTEGRAL/IBIS catalogue that are still unidentified/unclassified, but which are very likely associated with a bright, flat-spectrum radio object. To confirm the association and to study the source X-ray spectral parameters, we performed X-ray follow-up observations with Swift/XRT. We report the results obtained from this search and discuss the nature of each source. 5 of the 6 radio associations are also detected in X-rays; in 3 cases they are the only counterpart found. IGR J06073--0024 is a flat-spectrum radio quasar at z=1.08, IGR J14488--4008 is a newly discovered radio galaxy, while IGR J18129--0649 is an AGN of a still unknown type. The nature of IGR J07225--3810 and IGR J19386--4653 is less well defined, since in both cases we find another X-ray source in the INTEGRAL error circle; nevertheless, the flat-spectrum radio source, likely to be a radio loud AGN, remains a viable and more convincing association in both cases. Only for IGR J11544--7618 could we not find any convincing counterpart since the radio association is not an X-ray emitter.Comment: 7 pages, 7 figures, accepted for publication on Astronomy and Astrophysic

A temperate river estuary is a sink for methanotrophs adapted to extremes of pH, temperature and salinity

River Tyne (UK) estuarine sediments harbour a genetically and functionally diverse community of methane-oxidizing bacteria (methanotrophs), the composition and activity of which were directly influenced by imposed environmental conditions (pH, salinity, temperature) that extended far beyond those found in situ. In aerobic sediment slurries methane oxidation rates were monitored together with the diversity of a functional gene marker for methanotrophs (pmoA). Under near in situ conditions (4-30°C, pH 6-8, 1-15gl-1 NaCl), communities were enriched by sequences affiliated with Methylobacter and Methylomonas spp. and specifically a Methylobacter psychrophilus-related species at 4-21°C. More extreme conditions, namely high temperatures ≥40°C, high ≥9 and low ≤5 pH, and high salinities ≥35gl-1 selected for putative thermophiles (Methylocaldum), acidophiles (Methylosoma) and haloalkaliphiles (Methylomicrobium). The presence of these extreme methanotrophs (unlikely to be part of the active community in situ) indicates passive dispersal from surrounding environments into the estuary

When good bugs go bad: Epidemiology and antimicrobial resistance profiles of Corynebacterium striatum, an emerging multidrug-resistant, opportunistic pathogen

ABSTRACT Infections with Corynebacterium striatum have been described in the literature over the last 2 decades, with the majority being bacteremia, central line infections, and occasionally, endocarditis. In recent years, the frequency of C. striatum infections appears to be increasing; a factor likely contributing to this is the increased ease and accuracy of the identification of Corynebacterium spp., including C. striatum , from clinical cultures. The objective of this study was to retrospectively characterize C. striatum isolates recovered from specimens submitted as part of routine patient care at a 1,250-bed, tertiary-care academic medical center. Multiple strain types were recovered, as demonstrated by repetitive-sequence-based PCR. Most of the strains of C. striatum characterized were resistant to antimicrobials commonly used to treat Gram-positive organisms, such as penicillin, ceftriaxone, meropenem, clindamycin, and tetracycline. The MIC 50 for ceftaroline was &gt;32 μg/ml. Although there are no interpretive criteria for susceptibility with telavancin, it appeared to have potent in vitro efficacy against this species, with MIC 50 and MIC 90 values of 0.064 and 0.125 μg/ml, respectively. Finally, as previously reported in case studies, we demonstrated rapid in vitro development of daptomycin resistance in 100% of the isolates tested ( n = 50), indicating that caution should be exhibited when using daptomycin for the treatment of C. striatum infections. C. striatum is an emerging, multidrug-resistant pathogen that can be associated with a variety of infection types. </jats:p

Technical and Environmental Analysis of Methanol Synthesis from Solid Recovered Fuel and Lignite

The purpose of this work was to perform a technical and environmental analysis of methanol production from solid recovered fuel (SRF) and lignite feedstocks. The main driver was to ensure that while pursuing the dual goal of improving security of supply within the EU and reducing carbon dioxide emissions from the power and transport sector, other environmental issues were not engineered into the system, and to provide recommendations to improve the process sustainability. The technical analysis was carried out using the inhouse ECLIPSE software and SimaPro was used for the environmental assessment. Data for the modelling was supplied by project partners, supply companies, databases, and literature where necessary. The results showed that increased SRF in the feedstock mix, decreased the environmental impact of methanol production, however, the environmental impact was greater than the natural gas reformer used for benchmarking. The sensitivity study considered off-gas thermal recovery and carbon capture, which for the 80% SRF, the impact was less than the natural gas reformer. It was concluded that SRF mixed with lignite to produce methanol could achieve the dual goal, providing off-gas recovery and carbon capture was employed. Other recommendations include considering onsite renewable electricity generation for process electricity.The authors kindly acknowledge the financial support of the European Project LIG2LIQ (RFCS-01-2017 GA796585) co-funded by the European Commission managed Research Fund for Coal and Steel (RFCS)

Methanol Production from Solid Recovered Fuel and Lignite: Techno-Economic and Environmental Assessment

The main purpose of this work is to examine the techno-economics and environmental assessment of the Solid Recovered Fuel and Lignite to methanol pathway. Methanol is produced by gasifying the solid fuels to carbon monoxide and hydrogen and then reacting to produce methanol under pressure during the methanol synthesis process. The data obtained from the partners is used to adapt this study for the liquid fuel synthesis application. The in-house personal computer-based process simulation package, ECLIPSE, is used to perform process modelling and the techno-economic assessment of methanol production. The @Risk 8.2© software is used to estimate the cost contingency of the project. The SimaPro © software package was used to carry out the Life Cycle Assessment (LCA). The gasifier plant contributes significantly to the capital costs. The results show that increased Solid Recovered Fuel (SRF) in the feedstock mix has favourable economics due to the negative SRF charges resulting in a lower break-even selling price (BESP) than feedstock mixes with higher ratios of Lignite. Plant availability, capital investment and the time value of money are the factors that have the greatest impact on BESP. Increasing the SRF in the feedstock mix decreases the Global Warming impact of the methanol production compared to higher proportions of Lignite. However, the resultant impact is much greater than that of a natural gas reformer. Furthermore, the employment of off-gas recovery and carbon capture can further reduce both the Global Warming impact and the overall Single Score of the process, making it favourably comparable to the natural gas water gas shift configurations.The authors kindly acknowledge the financial support of the European Project LIG2LIQ (RFCS-01-2017 GA796585) co-funded by the European Commission managed Research Fund for Coal and Steel (RFCS)

Reynolds number dependence of the near-wall flow over irregular rough surfaces

The database contains representations of the two surfaces studied, a graphite and a gritblasted surface, and the corresponding time-averaged velocity data for Reynolds numbers Re� = 90; 120; 180; 240; 360; 540, and 720