The 2014–2016 JET results are reviewed in the light of their significance for optimising the ITER research plan for the active and non-active operation. More than 60 h of plasma operation with ITER first wall materials successfully took place since its installation in 2011. New multi-machine scaling of the type I-ELM divertor energy flux density to ITER is supported by first principle modelling. ITER relevant disruption experiments and first principle modelling are reported with a set of three disruption mitigation valves mimicking the ITER setup. Insights of the L–H power threshold in Deuterium and Hydrogen are given, stressing the importance of the magnetic configurations and the recent measurements of fine-scale structures in the edge radial electric. Dimensionless scans of the core and pedestal confinement provide new information to elucidate the importance of the first wall material on the fusion performance. H-mode plasmas at ITER triangularity (H = 1 at βN ~ 1.8 and n/nGW ~ 0.6) have been sustained at 2 MA during 5 s. The ITER neutronics codes have been validated on high performance experiments. Prospects for the coming D–T campaign and 14 MeV neutron calibration strategy are reviewed.
Since the installation of an ITER-like wall, the JET programme has focused on the consolidation of ITER design choices and the preparation for ITER operation, with a specific emphasis given to the bulk tungsten melt experiment, which has been crucial for the final decision on the material choice for the day-one tungsten divertor in ITER. Integrated scenarios have been progressed with the re-establishment of long-pulse, high-confinement H-modes by optimizing the magnetic configuration and the use of ICRH to avoid tungsten impurity accumulation. Stationary discharges with detached divertor conditions and small edge localized modes have been demonstrated by nitrogen seeding. The differences in confinement and pedestal behaviour before and after the ITER-like wall installation have been better characterized towards the development of high fusion yield scenarios in DT. Post-mortem analyses of the plasma-facing components have confirmed the previously reported low fuel retention obtained by gas balance and shown that the pattern of deposition within the divertor has changed significantly with respect to the JET carbon wall campaigns due to the absence of thermally activated chemical erosion of beryllium in contrast to carbon. Transport to remote areas is almost absent and two orders of magnitude less material is found in the divertor.
The buoyancy-affected flow in rotating disk cavities, such as occurs in compressor disk stacks, is known to be complex and difficult to predict. In the present work, large eddy simulation (LES) and unsteady Reynolds-averaged Navier-Stokes (RANS)
The influence of high mainstream turbulence on turbulent boundary layer flow and heat transfer is experimentally investigated for length Reynolds numbers between 4 × 104 and 1.5 × 106. The high mainstream turbulence is produced by a round tube grid with uniform jet injection. Injected air is blown in either an upwind or downwind direction at a controllable flow rate. A flat plate test section instrumented with foil thermocouples is located downstream from the jet grid. The turbulence intensity decay and length scale growth along the test plate, the mean velocity and temperature profiles across the boundary layer, and surface heat transfer distribution are measured. The results show that the grid with downwind injection produces a slightly higher turbulence intensity and a smaller length scale than the grid with upwind injection. A higher turbulence intensity and a smaller length scale further enhance the surface heat transfer coefficient. The jet-induced high turbulence does not alter the downstream velocity and temperature profiles in their logarithmic regions, but the wake regions are lower than the zero turbulence profiles. The Reynolds analogy factor, the augmented friction factor, and the augmented Stanton number are higher than those from existing correlations when the jet grid turbulence intensity is greater than 6 percent.
High loads and bearing life requirements make journal bearings the preferred choice for use in high power, epicyclic gearboxes in jet engines. In contrast to conventional, nonorbiting journal bearings in epicyclic star gearboxes, the kinematic conditions in epicyclic planetary arrangements are much more complex. With the planet gears rotating about their own axis and orbiting around the sun gear, centrifugal forces generated by both motions interact with each other and affect the external flow behavior of the oil exiting the journal bearing. This paper presents a literature and state-of-the-art knowledge review to identify existing work performed on cases similar to external journal bearing oil flow. In order to numerically investigate external journal bearing oil flow, an approach to decompose an actual journal bearing into simplified models is proposed. Later, these can be extended in a step-wise manner to allow key underlying physical phenomena to be identified. Preliminary modeling considerations will also be presented. This includes assessing different geometrical inlet conditions with the aim of minimizing computational requirements and different numerical models for near-wall treatment. The correct choice of near-wall treatment models is particularly crucial as it determines the bearing's internal and external thermal behavior and properties. The findings and conclusions are used to create a three dimensional (3D), twocomponent computational fluid dynamic (CFD) sector model with rotationally periodic boundaries of the most simplistic approximation of an actual journal bearing: a non-orbiting representation, rotating about its own axis, with a circumferentially constant, i.e. concentric, lubricating gap. The inlet boundary conditions for simulating the external oil flow are generated by partly simulating the internal oil flow within the lubricating gap. In order to track the phase interface between the oil and the air surrounding the bearing, the Volume of Fluid (VoF) method is used. The quality of the CFD simulations of the domain of interest is not only dependent on the accuracy of the inlet conditions, but is also dependent on the computational mesh type, cell count, cell shape and numerical methods used. External journal bearing oil flow was simulated with a number of different mesh densities and the effect on the flow field behavior will be discussed. Two different operating temperatures, representing low and high viscosity oil, were used and their effect on the flow field behavior will also be assessed.In order to achieve the future objective of creating a design tool for routine use, key areas will be identified in which further progress is required. This includes the need to progressively increase the model fidelity to eventually simulate an orbiting journal bearing in planetary configuration with an eccentric, i.e. convergent-divergent, lubricating gap.
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