Directed percolation in aerodynamics: resolving laminar separation bubble on airfoils

In nature, phase transitions prevail amongst inherently different systems, while frequently showing a universal behavior at their critical point. As a fundamental phenomenon of fluid mechanics, recent studies suggested laminar-turbulent transition belonging to the universality class of directed percolation. Beyond, no indication was yet found that directed percolation is encountered in technical relevant fluid mechanics. Here, we present first evidence that the onset of a laminar separation bubble on an airfoil can be well characterized employing the directed percolation model on high fidelity particle image velocimetry data. In an extensive analysis, we show that the obtained critical exponents are robust against parameter fluctuations, namely threshold of turbulence intensity that distinguishes between ambient flow and laminar separation bubble. Our findings indicate a comprehensive significance of percolation models in fluid mechanics beyond fundamental flow phenomena, in particular, it enables the precise determination of the transition point of the laminar separation bubble. This opens a broad variety of new fields of application, ranging from experimental airfoil aerodynamics to computational fluid dynamics.Comment: 8 pages, 11 figure

A Portable TV-Holography (ESPI) System for QNDE

Quantitative nondestructive evaluation of structures is achieved by this remote sensing technique which measures the deformation vector components of a surface in all 3 dimensions. Traditional techniques involve predominantly the application of strain gauges for the two in-plane deformation vector components. This technique unfortunately only reveals the in-plane deformation between two distinct points where the strain gauge is glued onto the surface. Interferometric techniques on the other hand are most common to measure the out-of-plane deformation component. Conventional film or thermoplastic holography is one of the most sensitive among those techniques measuring out-of-plane deformations in the micron and submicron range. One major disadvantage of this technique is the low time-resolution due to the fact that it involves the processing of photographic or thermoplastic film.</p

Remote surface damage detection on rotor blades of operating wind turbines by means of infrared thermography

Wind turbines are constantly exposed to wind gusts, dirt particles and precipitation. Depending on the site, surface defects on rotor blades emerge from the first day of operation on. While erosion increases quickly with time, even small surface defects can affect the performance of the wind turbine. Consequently, there is demand for an easily applicable remote monitoring method for rotor blades that is capable of detecting surface defects at an early stage. In this work it is investigated if infrared thermography (IRT) can meet these requirements by visualizing differences in the thermal transport and the corresponding surface temperature of the wall-bounded flow.Firstly, a validation of the IRT method compared to stereoscopic particle image velocimetry measurements is performed comparing both types of experimental results for the boundary layer of a flat plate. Then, the main characteristics of the flow in the wake of generic surface defects on different types of lifting surfaces are studied both experimentally and numerically: temperature gradients behind protruding surface defects on a flat plate and a DU 91-W2-250 profile are studied by means of IRT. The same is done with the wall shear stress from Reynolds-averaged Navier–Stokes simulations of a wind turbine blade. It is consistently observed, both in the experiments and the simulations, that turbulent wedges are formed on the flow downstream of generic surface defects. These wedges provide valuable information about the kind of defects that generate them. At last, experimental and numerical performance measures are taken into account for evaluating the aerodynamic impact of surface defects on rotor blades. We conclude that the IRT method is a suitable remote monitoring technique for detecting surface defects on wind turbines at an early stage.</p

Measurement of polarization transfer in the quasi-elastic 40Ca(e⃗,e′p⃗)^{40}{\rm Ca}(\vec{e},e' \vec{p}) process

Polarization transfer to a bound proton in polarized electron knock-out reactions, $\mathrm{A}(\vec{e},e^{\prime}\vec{p})$, is a powerful tool to look for in-medium modification of the bound proton. It requires comparison to calculations which consider the many-body effects accompanying the quasi-free process. We report here measured components $P_x^{\prime}$, $P_z^{\prime}$, and their ratio $P_x^{\prime}/P_z^{\prime}$, of polarization transfer to protons bound in $^{40}\mathrm{Ca}$, which is described well by the shell model and for which reliable calculations are available. While the calculations capture the essence of the data, our statistical precision allows us to observe deviations which cannot be explained by simple scaling, including by varying the proton electromagnetic form factor ratio $G_E/G_M$. We further explore the deviations of the ratio of the polarization transfer components from that of a free proton, $(P_x^{\prime}/P_z^{\prime})_{\rm A}/(P_x^{\prime}/P_z^{\prime})_{\rm H}$, and its dependence on the bound-proton virtuality

Six sequence variants on chromosome 9p21.3 are associated with a positive family history of myocardial infarction: a multicenter registry

<p>Abstract</p> <p>Background</p> <p>Recent genome-wide association studies have identified several genetic loci linked to coronary artery disease (CAD) and myocardial infarction (MI). The 9p21.3 locus was verified by numerous replication studies to be the first common locus for CAD and MI. In the present study, we investigated whether six single nucleotide polymorphisms (SNP) rs1333049, rs1333040, rs10757274, rs2383206, rs10757278, and rs2383207 representing the 9p21.3 locus were associated with the incidence of an acute MI in patients with the main focus on the familial aggregation of the disease.</p> <p>Methods</p> <p>The overall cohort consisted of 976 unrelated male patients presenting with an acute coronary syndrome (ACS) with ST-elevated (STEMI) as well as non-ST-elevated myocardial infarction (NSTEMI). Genotyping data of the investigated SNPs were generated and statistically analyzed in comparison to previously published findings of matchable control cohorts.</p> <p>Results</p> <p>Statistical evaluation confirmed a highly significant association of all analyzed SNP's with the occurrence of MI (p < 0.0001; OR: 1.621-2.039). When only MI patients with a positive family disposition were comprised in the analysis a much stronger association of the accordant risk alleles with incident disease was found with odds ratios up to 2.769.</p> <p>Conclusions</p> <p>The findings in the present study confirmed a strong association of the 9p21.3 locus with MI particularly in patients with a positive family history thereby, emphasizing the pathogenic relevance of this locus as a common genetic cardiovascular risk factor.</p

Instandhaltung und Ökologie. Rahmenbedingungen, Aufgaben, Lösungen. Tagungsband zum 7. Instandhaltungsforum

Die Beiträge berichten über rechtliche Rahmenbedingungen für die Ökologie in der Instandhaltung, sowie spezielle Aufgaben des Umweltschutzes in der Instandhaltung und zeigen Lösungsansätze für ökologische Maßnahmen