Near-wall dynamics of laminar separation bubbles at low turbulence intensities

The experiments are conducted at Rec=6⋅10^4 and 8⋅10^4 and an angle of attack of AoA=6°. The applied heating power at the lower Rec is 1764 W/m2 and 2545 W/m2 at the higher. SPOD analysis of the thermal fluctuations displays the footprints of the Kelvin-Helmholtz instabilities with temporary high levels of span-wise coherence. Instantaneous thermal snapshots display the propagation of simultaneously emerging V-shaped footprints in the stream-wise direction. Examples are shown in the paper. Some of the snapshots depict span-wise coherent footprints, which can only be assumed to be caused by Kelvin-Helmholtz vortices, in the same region as the V-shaped footprints, which implies that these are two distinct phenomena. Quasi-simultaneous PIV and TSP measurements confirm the assumption

Laminar separation bubble analysis by means of single–shot lifetime temperature sensitive paint in a water towing tank

A laminar separation bubble (LSB) is studied on an SD7003 foil in a water towing tank at a Reynolds number of 6 · 104 and an angle of attack of 6◦ by means of the temperature sensitive paint single-shot lifetime method in order to resolve the footprints and dynamics of vortical structures at low inflow turbulence levels. A heat flux is created by applying a carbon based heating layer on the suction side of the foil. The influence of the surface heating on the transition behaviour is analyzed using 2D2C-PIV and found to be negligible. The results demonstrate the capability of the single-shot lifetime method to quantify salient time-averaged flow characteristics, as well as to resolve and characterize the footprints of the dominant coherent structures

Different duration strategies of perioperative antibiotic prophylaxis in adult patients undergoing cardiac surgery:an observational study

Background: All international guidelines recommend perioperative antibiotic prophylaxis (PAB) should be routinely administered to patients undergoing cardiac surgery. However, the duration of PAB is heterogeneous and controversial. Methods: Between 01.01.2011 and 31.12.2011, 1096 consecutive cardiac surgery patients were assigned to one of two groups receiving PAB with a second-generation cephalosporin for either 56 h (group I) or 32 h (group II). Patients' characteristics, intraoperative data, and the in-hospital follow-up were analysed. Primary endpoint was the incidence of surgical site infection (deep and superficial sternal wound-, and vein harvesting site infection; DSWI/SSWI/VHSI). Secondary endpoints were the incidence of respiratory-, and urinary tract infection, as well as the mortality rate. Results: 615/1096 patients (56,1%) were enrolled (group I: n = 283 versus group II: n = 332). There were no significant differences with regard to patient characteristics, comorbidities, and procedure-related variables. No statistically significant differences were demonstrated concerning primary and secondary endpoints. The incidence of DSWI/SSWI/VHSI were 4/283 (1,4%), 5/283 (1,7%), and 1/283 (0,3%) in group I versus 6/332 (1,8%), 9/332 (2,7%), and 3/332 (0,9%) in group II (p = 0,76/0,59/0,63). In univariate analyses female gender, age, peripheral arterial obstructive disease, operating-time, ICU-duration, transfusion, and respiratory insufficiency were determinants for nosocomial infections (all Conclusions: Reducing the duration of PAB from 56 h to 32 h in adult cardiac surgery patients was not associated with an increase of nosocomial infection rate, but contributes to reduce antibiotic resistance and health care costs

Experimental evidence of near-wall reverse flow events in a zero pressure gradient turbulent boundary layer

This study reports on experimentally observed rare near-wall reverse flow events in a fully developed turbulent flat plate boundary layer at zero pressure gradient with Reynolds numbers between Re_\theta \approx 2500 and Re_\theta \approx 8000 (Re_\tau = 800-2400). The reverse flow events are captured using high magnification particle image velocimetry sequences with record lengths varying from 50 000 to 126 000 samples. Time resolved particle image sequences allow singular reverse flow events to be followed over several time steps whereas long records of nearly statistically independent samples provide a variety of single snapshots at a higher spatial resolution. The probability of occurrence lies in the order of 0.012-0.018% which matches predictions from direct numerical simulations (DNS). The typical size of the reverse flow bubble is about 30 wall units in length and 5 wall units in height which agrees well with similar observations made in existing DNS data

Modification of the SSG/LRR-omega RSM for adverse pressure gradients using turbulent boundary layer experiments at high Re

A modification of the SSG/LRR-omega model for turbulent boundary layers in adverse pressure gradient is presented. The modification is based on a new wall law for the mean velocity at adverse pressure gradient. The wall law is found from two new joint DLR/UniBw experiments and from the analysis of a data base from the literature. The mean velocity profile in the inner layer is found to consist of a log-law region, which is thinner than its zero pressure gradient counterpart, and a half-power law region above the log law. An empirical correlation for the wall-distance of the transition from the log-law to the half-power law is presented. Then a modification of the omega-equation to account for a half-power law behaviour of the mean velocity is described. The modified SSG/LRR-omega model is then applied to the two joint DLR/UniBw experiments. The modification leads to a reduction of the mean velocity in the inner part of the boundary layer and makes the model more susceptible for flow separation, which is in good agreement with the experimental data

Comparative genomics and transcriptomics of lineages I, II, and III strains of Listeria monocytogenes

BACKGROUND: Listeria monocytogenes is a food-borne pathogen that causes infections with a high-mortality rate and has served as an invaluable model for intracellular parasitism. Here, we report complete genome sequences for two L. monocytogenes strains belonging to serotype 4a (L99) and 4b (CLIP80459), and transcriptomes of representative strains from lineages I, II, and III, thereby permitting in-depth comparison of genome- and transcriptome -based data from three lineages of L. monocytogenes. Lineage III, represented by the 4a L99 genome is known to contain strains less virulent for humans. RESULTS: The genome analysis of the weakly pathogenic L99 serotype 4a provides extensive evidence of virulence gene decay, including loss of several important surface proteins. The 4b CLIP80459 genome, unlike the previously sequenced 4b F2365 genome harbours an intact inlB invasion gene. These lineage I strains are characterized by the lack of prophage genes, as they share only a single prophage locus with other L. monocytogenes genomes 1/2a EGD-e and 4a L99. Comparative transcriptome analysis during intracellular growth uncovered adaptive expression level differences in lineages I, II and III of Listeria, notable amongst which was a strong intracellular induction of flagellar genes in strain 4a L99 compared to the other lineages. Furthermore, extensive differences between strains are manifest at levels of metabolic flux control and phosphorylated sugar uptake. Intriguingly, prophage gene expression was found to be a hallmark of intracellular gene expression. Deletion mutants in the single shared prophage locus of lineage II strain EGD-e 1/2a, the lma operon, revealed severe attenuation of virulence in a murine infection model. CONCLUSION: Comparative genomics and transcriptome analysis of L. monocytogenes strains from three lineages implicate prophage genes in intracellular adaptation and indicate that gene loss and decay may have led to the emergence of attenuated lineages

Multi-PIV Measurements of an Adverse Pressure Gradient Turbulent Boundary Layer

We report on a multi-national measurement campaign aimed at providing highly resolved flow field data of a turbulent boundary layer subjected to an adverse pressure gradient (APG). In the case of APGs the structure and dynamics of large scale turbulent flow structures along with their significance on the statistical properties of the flow is not well understood. Hence the fundamental aim was to resolve and characterise the large-scale coherent structures in an APG boundary layer flow. In addition to large-field-of-view PIV measurements using 16 sCMOS cameras along a 3.5m length, stereoscopic PIV measurements were performed at specific locations in order to also resolve the span-wise velocity statistics. Long-distance, high-speed micro-PIV measurements provided near wall statistics at selected locations including the time-resolved wall shear stress. The measurements were performed in the boundary layer wind tunnel of the Laboratoire de Mécanique de Lille (LML) and funded by EuHIT (www.euhit.org)