Analyse expérimentale et numérique de l'écoulement dans le canal d'entrée d'un modèle de turbine bulbe

Ce travail de maitrise s’inscrit dans le cadre des activités de recherche du Laboratoire de Machines Hydraulique de l’Université Laval et a pour objectif la caractérisation de l’écoulement dans le canal d’entrée d’un modèle de turbine hydraulique de type bulbe. La représentation des champs de vitesses moyennes et des fluctuations sous différentes conditions d’opérations ont été obtenues en utilisant un système de mesure LDV. Un débalancement du débit et des structures tourbillonnaires dans le canal d’entrée ont été mises en évidence. La conception d’une géométrie d’obstacle provoquant une non-uniformité dans le canal d’entrée a été développée en tenant compte des prédictions de simulations numériques. Des simulations numériques de la machine complète en régime stationnaire et instationnaire selon deux configurations géométriques ont été menées pour déterminer l’influence des conditions d’entrée de l’écoulement sur les performances de la machine. Des comparaisons entre les quantités expérimentales et numériques ont été réalisées.This work is part of the research activities of the Hydraulic Machines Laboratory of the Laval University and its objective is to contribute to the characterisation of the intake flow in a model of a bulb turbine. The representation of the mean velocity fields and the turbulent fluctuations under predefined operating conditions were obtained by the use of a LDV measurement system. Mass-flow imbalance and vortices in the intake channel were identified. The conception of an obstacle geometry causing a non-uniformity in the intake channel has been developed taking in consideration the predictions of numerical simulation. Numerical simulations of the complete machine for both steady and unsteady case were performed with and without obstacle in the intake channel. The objective of this process was to evaluate the influence of the intake flow condition on the turbine performances. Moreover, comparisons between experimental and numerical quantities were made

High-temperature nano-impact testing of a hard-coating system

Forging and cutting tools for high-temperature applications are often protected using hard nanostructured ceramic coatings. While a moderate amount of knowledge exists for material properties at room temperatures, significantly less is known about the system constituents at the elevated temperatures generated during service. For rational engineering design of such systems, it is therefore important to have methodologies for testing these materials to understand their properties under such conditions (i.e. high strain rate, temperature, or impact). In this work, we present our first results using a newly developed Alemnis piezo actuated nanoindenter device which utilizes dynamic indentation testing at frequencies approaching 10 kHz. A sinusoidal displacement amplitude input is provided, while a stage heater allows for sample temperatures exceeding 500 °C. Thermal drift can be minimized through high frequency, and therefore low contact time, impacts. We investigated a thin (4.65 μm) physical vapor deposited chromium nitride (CrN) ceramic coating, which had been deposited onto plasma nitrided tool steel. Forces of approximately 400 mN were applied sinusoidally at 500 Hz using a 5 μm diameter diamond flat-punch at room temperature, 200°C, 300°C, 400°C and 500°C. It was found that increasing the number of impacts led to plastic deformation and fatiguing of the hard ceramic coating. At 300°C a transition to increased material flow and consequently larger crater size, and crack initiation and propagation in the ceramic, was observed. These ceramic deformation results are understood using high-resolution scanning electron microscopy (HR-SEM), elastic simulations, and large scale batch processing of force-deformation data which are generated during high-frequency measurement and collected at a sampling rate of 50 kHz. The results are further put into context by understanding recently measured small-scale high-temperature fracture toughness and yield strength properties of thin CrN films. The presented results are the first for in situ high-temperature nano-impact testing, and will be useful for hard coatings industries involving high service temperatures and high impact strain rates, such as for forging processes

An in‐situ indentation system for high dynamic nanomechanical measurements

Nanoindentation is typically confined to quasi-static strain rates of testing. This poster presents the development of an in-situ indenter designed to measure the response of materials at high strain rates and high oscillation frequencies at the nanoscale. This builds up on the previous work that was the first to report on in-situ nanoindentation in a SEM in 2004 which eventually resulted in the founding of the company Alemnis AG, today one of the key players in in-situ high temperature and high dynamic nanoindentation. The motivation for variable strain rate studies is that this allows analysis of activation parameters of the physical deformation processes. Once the activation parameters are known, the deformation mechanism(s) can be determined and materials science approaches to improve materials performance can be developed. Ultra-high frequency nanoindentation enables high strain rate studies and high cycle fatigue tests that can be performed within reasonably short timespan. Compared to other actuation principles, piezo actuators offers very fast response time and high force density and are compatible with vacuum environments. At the technological heart of this innovation is a transducer called “SmarTip” consisting of a diamond tip mounted on miniaturized and embedded three-axis piezo-actuators and sensors. The SmarTip allows a full range displacement of 1μm along the three axes and to measure forces up to 1N. The theoretical bandwidths are up to 10kHz and 40kHz for lateral and axial displacements respectively. We aim to reach strain rates as high as 105s-1 meaning that the speed of displacement must reach 60mm/s for a displacement of 600nm. With such high ambitions, several parameters have to be taken into consideration such as resonant frequencies of the indenter, self-heating and cabling inducing spurious capacitance. This poster will report on these design aspects, instrumentation and technique development in addition to presenting initial data on high strain rate and high cycle fatigue tests at the micron scale. It is hoped that the multi-axis capabilities of the SmarTip will result in additional breakthroughs for applications on nano-tribology, fretting and more generally on the translation of dynamic mechanical analysis (DMA) to the micro/nanoscale. Acknowledgments Research work partially co-funded by the Commission for Technology and Innovation (CTI), the State Secretariat for Education, Research and the Innovation Eurostars program and project UHV

Suspected Case of Drug-Induced Acute Respiratory Distress Syndrome following Trimethoprim-Sulfamethoxazole Treatment

In this article, we reported the case of a child patient who was admitted to our PICU for severe acute respiratory distress syndrome (ARDS) while being treated with trimethoprim-sulfamethoxazole (TMP-SMX) for osteomyelitis. Based on the timing of exposure, lack of alternative explanations, and clinical course similar to previously described cases, we suspect that TMP-SMX may have triggered ARDS. Despite meeting criteria for extracorporeal membrane oxygenation cannulation, conservative management and lung recruitment with high-frequency percussive ventilation could avoid the latter

Sodium thiosulfate, a source of hydrogen sulfide, stimulates endothelial cell proliferation and neovascularization

Therapies to accelerate vascular repair are currently lacking. Pre-clinical studies suggest that hydrogen sulfide (H2S), an endogenous gasotransmitter, promotes angiogenesis. Here, we hypothesized that sodium thiosulfate (STS), a clinically relevant source of H2S, would stimulate angiogenesis and vascular repair. STS stimulated neovascularization in WT and LDLR receptor knockout mice following hindlimb ischemia as evidenced by increased leg perfusion assessed by laser Doppler imaging, and capillary density in the gastrocnemius muscle. STS also promoted VEGF-dependent angiogenesis in matrigel plugs in vivo and in the chorioallantoic membrane of chick embryos. In vitro, STS and NaHS stimulated human umbilical vein endothelial cell (HUVEC) migration and proliferation. Seahorse experiments further revealed that STS inhibited mitochondrial respiration and promoted glycolysis in HUVEC. The effect of STS on migration and proliferation was glycolysis-dependent. STS probably acts through metabolic reprogramming of endothelial cells toward a more proliferative glycolytic state. These findings may hold broad clinical implications for patients suffering from vascular occlusive diseases