Analyse expérimentale et simulation CFD en vue de l'étude du refroidissement des aubes Rotor/Stator : cas d'une turbine à gaz

128 p. : ill. ; 30 cmLes performances aérothermiques d'un système de refroidissement interne du bord de fuite d'une aube de turbine à gaz sont évaluées expérimentalement et numériquement dans les conditions stationnaires et rotatives. La géométrie étudiée est un modèle à échelle 30 : 1 représentative d'une conduite sans et avec perturbateurs avec une ligne de 7 vannes élargies. Six géométries sont testées par le moyen de la technique TLC pour un nombre de Reynolds entre 10000-40000 et un nombre de Rotation jusqu'à 0.23. En outre, l'analyse CFD est basée sur ANSYS-Fluent et un modèle de turbulence k À- SST tout en considérant un écoulement d'air iso-thermique stationnaire à l'intérieur de la géométrie étudiée pour les conditions fixes et rotatives. Les résultats sont présentés sous forme de cartes 2D illustrant le coefficient d'échange thermique sur la surface en dépression, en plus de corrélations pour le nombre de Nusselt moyenné en fonction de Re, Pr, Ro et une fraction de la hauteur de l'aube. Les résultats obtenus sont d'un grand intérêt pour les concepteurs des systèmes de refroidissement pour les aubes de turbines à ga

Entwicklung einer Vorgehensweise zur Bestimmung und Verifikation von Wärmeübergangsparametern aus CFD Simulationen von Trockenkupplungssystemen = Development of an Estimation and Verification Approach for Heat Transfer Parameters of DryClutch Systems Obtained from CFD Simulations

Die Dimensionierung einer Kupplung für manuelle Schaltgetriebe ist stark von den Temperaturen im Friktionskontakt abhängig. Das richtige Verständnis für die Einstufung der Wärmeübertragungsmechanismen und der Randbedingungen ist eine Schlüsselstelle in der Ermittlung der Kupplungsgröße. Diese Arbeit widmet sich der Charakterisierung des Wärmeübergangs von Trockenkupplungssystemen, dem Prozess der Ergebnisvereinfachung und ?validierung, die von einer CFD Simulation generiert wurden

Thermal design of air-cooled axial flux permanent magnet machines

Accurate thermal analysis of axial flux permanent magnet (AFPM) machines is crucial in predicting maximum power output, and a number of heat transfer paths exist making it difficult to undertake a general analysis. Stator convective heat transfer is one of the most important and least investigated heat transfer mechanisms and therefore is the focus of the present work. Experimental measurements were undertaken using a thin-film electrical heating method based on a printed circuit board heater array, providing radially resolved steady state heat transfer data from an experimental rotor-stator system designed as a geometric mockup of a through-flow ventilated AFPM machine. Using a flat rotor, local Nusselt numbers Nu(r) = hR/k were measured across 0.6<r/R< 1, as a function of non-dimensional gap ratio 0.0106 < G < 0.0467 and rotational Reynolds number 3.7e4 < Re [Theta]1e6 where G = g/R and Re [Theta] = [omega]R2/[Nu]. Averaged results Nu were correlated with a power law and it was found that Nu [is approximately equal to] ARe0.7 [Theta] in the fully turbulent regime (Re [Theta] > 3e5), with A being a function of G. In the laminar regime, stator Nu was found to be similar to that of the free rotor. Transition at the stator occurred at Re [Theta] = 3e5 for all G and is particularly marked at G < 0.02. Increased Nusselt numbers at the periphery were always observed because of the ingress of ambient air along the stator due to the rotor pumping effect. A slotted rotor was also tested, and was found to improve stator heat transfer compared with a flat rotor. The measurements were compared with computational fluid dynamics simulations. These were found to give a conservative estimate of heat transfer, with inaccuracies near the edge (r/R > 0.85) and in the transitional flow regime. Predicted stator heat transfer was found to be relatively insensitive to the choice of turbulence model and the two-equation SST model was used for most of the simulations

Flow of a non-Newtonian Bingham plastic fluid over a rotating disk

Even though fluid mechanics is well developed as a science, there are many physical phenomena that we do not yet fully understand. One of these is the deformation rates and fluid stresses generated in a boundary layer for a non-Newtonian fluid. One such non-Newtonian fluid would be a waxy crude oil flowing in a centrifugal pump. This type of flow can be numerically modeled by a rotating disk system, in combination with an appropriate constitutive equation, such as the relation for a Bingham fluid. A Bingham fluid does not begin to flow until the stress magnitude exceeds the yield stress. However, experimental measurements are also required to serve as a database against which the results of the numerical simulation can be interpreted and validated. The purpose of the present research is to gain a better understanding of the behavior of a Bingham fluid in the laminar boundary layer on a rotating disk. For this project, two different techniques were employed: numerical simulation, and laboratory investigations using Particle Image Velocimetry (PIV) and flow visualization. Both methods were applied to the flow of a Bingham fluid over a rotating disk. In the numerical investigations, the flow was characterized by the dimensionless yield stress “Bingham number”, By, which is the ratio of the yield and viscous stresses. Using von Kármán’s similarity transformation, and introducing the rheological behavior of the fluid into the conservation equations, the corresponding nonlinear two-point boundary value problem was formulated. A solution to the problem under investigation was obtained by numerical integration of the set of Ordinary Differential Equations (ODEs) using a multiple shooting method. The influence of the Bingham number on the flow behavior was identified. It decreases the magnitude of the radial and axial velocity components, and increases the magnitude of the tangential velocity component, which has a pronounced effect on the moment coefficient, CM, and the volume flow rate, Q. In the laboratory investigations, since the waxy crude oils are naturally opaque, an ambitious experimental plan to create a transparent oil that was rheologically similar to the Amna waxy crude oil from Libya was developed. The simulant was used for flow visualization experiments, where a transparent fluid was required. To fulfill the demand of the PIV system for a higher degree of visibility, a second Bingham fluid was created and rheologically investigated. The PIV measurements were carried out for both filtered tap water and the Bingham fluid in the same rotating disk apparatus that was used for the flow visualization experiments. Both the axial and radial velocity components in the (r-z) plane were measured for various rotational speeds. Comparison between the numerical and experimental results for the axial and radial velocity profiles for water was found to be satisfactory. Significant discrepancies were found between numerical results and measured values for the Bingham fluid, especially at low rotational speeds, mostly relating to the formation of a yield surface within the tank. Even though the flow in a pump is in some ways different from that of a disk rotating in a tank, some insight about the behavior of the pump flow can be drawn. One conclusion is that the key difference between the flow of a Bingham fluid in rotating equipment from that of a Newtonian fluid such as water relates to the yield surface introduced by the yield stress of the material, which causes an adverse effect on the performance and efficiency of such equipment

Microfluidics and Nanofluidics Handbook

The Microfluidics and Nanofluidics Handbook: Two-Volume Set comprehensively captures the cross-disciplinary breadth of the fields of micro- and nanofluidics, which encompass the biological sciences, chemistry, physics and engineering applications. To fill the knowledge gap between engineering and the basic sciences, the editors pulled together key individuals, well known in their respective areas, to author chapters that help graduate students, scientists, and practicing engineers understand the overall area of microfluidics and nanofluidics. Topics covered include Finite Volume Method for Numerical Simulation Lattice Boltzmann Method and Its Applications in Microfluidics Microparticle and Nanoparticle Manipulation Methane Solubility Enhancement in Water Confined to Nanoscale Pores Volume Two: Fabrication, Implementation, and Applications focuses on topics related to experimental and numerical methods. It also covers fabrication and applications in a variety of areas, from aerospace to biological systems. Reflecting the inherent nature of microfluidics and nanofluidics, the book includes as much interdisciplinary knowledge as possible. It provides the fundamental science background for newcomers and advanced techniques and concepts for experienced researchers and professionals

Modelling and prediction of non-linear scale-up from an Ultra Scale-Down membrane device to process scale tangential flow filtration

Ultra scale-down (USD) tools have demonstrated the huge potential for accelerated process development by significantly reducing the material requirements and providing better solutions, as part of the Quality by Design initiative. Key benefits of using USD techniques include the relatively small quantities of feedstock and minimal capital equipment needed to generate large volumes of statistically significant process data in a short period, leading to significant time and cost savings during process development. However, the use of small scale devices such as the stirred cell filtration units have been primarily limited to preliminary testing and initial screening due to their geometric and flow dissimilarities to tangential flow filtration at scale. As a result, process development and optimisation trials are generally carried out using the smallest c commercially available TFF cassettes, the use of which are primarily limited by time and material constraints that are invariably present at the early stages of process development. Therefore, the central focus of this work was to develop a USD methodology and model to accurately predict the performance of large scale tangential flow filtration (TFF) using a USD membrane filtration device. // The commercial package COMSOL was used to carry out computational fluid dynamics (CFD) modelling and simulation of the fluid flow dynamics in Pellicon TFF cassettes with different feed screens and a USD membrane device, in order to develop average wall shear rate correlations and channel pressure drops expressed as functions of the respective hydrodynamic conditions across scales. In addition, the impact of non-TFF related factors such as the system and cassette-specific hydraulic resistances on TFF performance was characterised using semi-empirical models. Finally, a scale-up methodology and mathematical model to predict the large scale performance using USD data was developed by combining the various resistances, channel pressure drop correlations and an empirical USD-derived model that characterises the specific feed-membrane interactions. The CFD simulations were independently verified using 2D particle imaging velocimetry to compare experimental data to the CFD simulated data. // 100-fold scale-up experiments were carried out based on equivalent averaged wall shear rates (w) as the geometry-independent parameter. Permeate flux excursions were carried out to validate the USD methodology and prediction model, by comparing USD model predictions against the large scale experimental data. Different membranes, feed screens (A, C and V) and feedstock, ranging from simple proteins like Bovine Serum Albumin (BSA) to more complex, multicomponent feed such as Escherichia coli homogenate, were used. Predicted flux and transmission results were in good agreement with the large scale experimental data, showing less than 5% difference across scales, demonstrating the robustness of the non-linear scale-up model. // Following the successful validation of the scale-up methodology and prediction model, other potential applications of the USD membrane device such as the optimisation of TFF microfiltration was demonstrated using Saccharomyces cerevisae and Chlorella sorokiniana. Fed-batch concentration experiments using Saccharomyces cerevisae were done to compare the volumetric throughput limits. The USD-predicted capacity limit of 49.2 L/m2 was very similar to the experimental large scale capacity value of 52.0 L/m2, and considered fully scalable within experimental errors. Finally, fouling studies were performed using Chlorella sorokiniana and the USD device to investigate the impact of media type and growth conditions on the filtration performance. The results indicated a strong correlation between soluble fouling species, such as exopolysaccharides and carbohydrates, rather than the algal biomass. A novel, dynamic flux control methodology was developed based on empirically determined critical fluxes expressed as a function of cell concentration. The dynamic control strategy was successfully verified by performing a 50-fold concentration experiment using a hollow fibre module and the USD device. An improvement of greater than 50% in average throughput was achieved using the 3-step flux cascade compared to the traditional flux-time/capacity optimised fluxes, with no observable increase in TMP throughout. // The work presented here demonstrates the potential of ultra scale-down tools coupled with a mathematical modelling approach to establish a predictable scale-up performance, which can be used to rapidly develop and optimise tangential flow filtration processes, regardless of differences in geometry, flow configuration and system setup