Edge Temperature Research Articles

Effect of leading edge bluntness on the interaction of ramp induced shock wave with laminar boundary layer at hypersonic speed

Present investigations deal with ramp induced shock wave and boundary layer interaction (R-SWBLI) in the presence of leading edge bluntness. A second order accurate finite-volume compressible flow solver is employed to assess the effectiveness of leading edge bluntness in reducing the separation bubble size. Boundary layer edge Mach number and temperature, sonic height, boundary layer thicknesses, skin friction coefficient and pressure difference are considered for this assessment. Present studies reveal the existence of two critical radii of leading edge bluntness associated with R-SWBLI. Increase in separation bubble size has been observed with increase in leading edge radius until the first critical radius called as ‘inversion radius’ which corresponds to maximum extent of separation. Swallowing of the entropy layer by the boundary layer is seen to increase the separation zone size while the separation bubble length decreases when the boundary layer is immersed within the entropy layer. The inversion radius is shown to be associated with equal thicknesses of the entropy and boundary layers. Increase in leading edge radius beyond the second critical radius, called as ‘equivalent radius’, is found to decrease the size of separation zone in comparison with that of the sharp leading edge case. This reduction is attributed mainly to the existence of a wide over pressure region. Physics-driven predictive strategies, to determine the critical radii for given geometry and freestream conditions, are derived successfully from the present numerical simulations. Current studies on a 50mm long plate with 15° compression ramp for Mach number 6 and wall temperature of 300K show that the inversion radius lies between 0.3 and 0. 6mm while the equivalent radius lies between 1 and 1.2mm.

Microstability analysis of pellet fuelled discharges in MAST

Reactor grade plasmas are likely to be fuelled by pellet injection. This technique transiently perturbs the profiles, driving the density profile hollow and flattening the edge temperature profile. After the pellet perturbation, the density and temperature profiles relax towards their quasi-steady-state shape. Microinstabilities influence plasma confinement and will play a role in determining the evolution of the profiles in pellet fuelled plasmas. In this paper we present the microstability analysis of pellet fuelled H-mode MAST plasmas. Taking advantage of the unique capabilities of the MAST Thomson scattering system and the possibility of synchronizing the eight lasers with the pellet injection, we were able to measure the evolution of the post-pellet electron density and temperature profiles with high temporal and spatial resolution. These profiles, together with ion temperature profiles measured using a charge exchange diagnostic, were used to produce equilibria suitable for microstability analysis of the equilibrium changes induced by pellet injection. This analysis, carried out using the local gyrokinetic code GS2, reveals that the microstability properties are extremely sensitive to the rapid and large transient excursions of the density and temperature profiles, which also change collisionality and βe significantly in the region most strongly affected by the pellet ablation.

Mechanical properties and fracture dynamics of silicene membranes.

As graphene has become one of the most important materials, there is renewed interest in other similar structures. One example is silicene, the silicon analogue of graphene. It shares some of the remarkable graphene properties, such as the Dirac cone, but presents some distinct ones, such as a pronounced structural buckling. We have investigated, through density functional based tight-binding (DFTB), as well as reactive molecular dynamics (using ReaxFF), the mechanical properties of suspended single-layer silicene. We calculated the elastic constants, analyzed the fracture patterns and edge reconstructions. We also addressed the stress distributions, unbuckling mechanisms and the fracture dependence on the temperature. We analysed the differences due to distinct edge morphologies, namely zigzag and armchair.

Experimental Study and Modelling of Plastic Deformation of Cemented Carbide Tools in Turning

The plastic deformation of coated cemented carbide cutting tools was investigated. Testing methods were developed for the experimental determination of the high-temperature strength of cemented carbide (compressive strength, creep resistance). CVD-coated cemented carbide inserts were tested in continuous turning of quenched and tempered steel (AISI 4340). Cutting forces and edge temperature distributions were measured in 2D orthogonal turning. Normal stress distributions on the tool surface were estimated from measured cutting forces and tool-chip contact lengths. These data, together with measured high-temperature strength data for the cemented carbide, were introduced into a finite element model (ANSYS). The agreement between the predicted deformation and the experimental results was acceptable. The difference between the simulated and measured flank width on deformed cutting edges was approximately 15%. It has been demonstrated that numerical methods (FE) provide an opportunity to describe the effect of cutting conditions and tool material properties on tool behaviour quantitatively and in a systematic manner.

Analyses of Effects of Cutting Parameters on Cutting Edge Temperature Using Inverse Heat Conduction Technique

During machining energy is transformed into heat due to plastic deformation of the workpiece surface and friction between tool and workpiece. High temperatures are generated in the region of the cutting edge, which have a very important influence on wear rate of the cutting tool and on tool life. This work proposes the estimation of heat flux at the chip-tool interface using inverse techniques. Factors which influence the temperature distribution at the AISI M32C high speed steel tool rake face during machining of a ABNT 12L14 steel workpiece were also investigated. The temperature distribution was predicted using finite volume elements. A transient 3D numerical code using irregular and nonstaggered mesh was developed to solve the nonlinear heat diffusion equation. To validate the software, experimental tests were made. The inverse problem was solved using the function specification method. Heat fluxes at the tool-workpiece interface were estimated using inverse problems techniques and experimental temperatures. Tests were performed to study the effect of cutting parameters on cutting edge temperature. The results were compared with those of the tool-work thermocouple technique and a fair agreement was obtained.

Estimation of Cutting Conditions in Precision Micromachining of CuNi Alloys of Varying Composition

A non-dimensional model is developed that relates cutting edge temperatures to process inputs (speed and feed) and outputs (cutting and thrust forces) as well as tool and work thermal properties in micromachining with diamond tools. The temperature estimates are used to determine activation energy for thermally activated chemical wear of a PCD tool milling Monel 400 (Cu 32, Ni 65 wt%). Activation energy estimates are from 15 to 60kJ/ mole, depending on systematic uncertainties, such as diamond thermal conductivity, that still need to be addressed.

Characterization of temperature profiles in the outer region of RFX-mod

The onset of helical states has been shown to strongly affect the transport properties and the plasma performance of both the core region (|R − R0|/a ≲ 0.5) and the plasma edge (|R − R0|/a ≳ 0.95) in the RFX-mod reversed field pinch experiment. Both regions have been widely investigated and a strong effort is still dedicated to deepening the comprehension of the phenomena affecting them. Conversely, the region bounded between the plasma core and the plasma edge (0.6 ≲ |R − R0|/a ≲ 0.95) has been poorly analyzed, despite the large plasma volume enclosed in this domain. Improvements in RFX-mod global plasma performance are thus closely linked to the identification of the physical mechanisms occurring in this region, referred to as the outer region. A specifically conceived method of analysis, which gathers together data from a Thomson scattering system and two edge temperature diagnostics, allows the study of the entire temperature profile of RFX-mod. A statistical analysis performed on a large discharge database shows that the temperature profile in the central region of the plasma column is mainly established by the plasma current and the degree of stochasticity of the magnetic field. On the other hand, the temperature profile in the outer plasma region is found to vary with electron density and plasma equilibrium.

Generation of a fully valley-polarized current in bulk graphene

The generation of a fully valley-polarized current (FVPC) in bulk graphene is a fundamental goal in valleytronics. To this end, we investigate valley-dependent transport through a strained graphene modulated by a finite magnetic superlattice. It is found that this device allows a coexistence of insulating transmission gap of one valley and metallic resonant band of the other. Accordingly, a substantial bulk FVPC appears in a wide range of edge orientation and temperature, which can be effectively tuned by structural parameters. A valley-resolved Hall configuration is designed to measure the valley polarization degree of the filtered current.

Investigation of mechanisms for He-I emission radial profile broadening in a weakly ionized cylindrical helium plasma with recombining edge

Spatially resolved spectroscopic measurements of He-I line emission are used to study the causes of emission profile broadening radially across the cylinder of a weakly ionized helium plasma. The plasma consists of an ionizing core (r < 2 cm) surrounded by a recombining edge (r > 2 cm) plasma. The brightness profiles of low-n EUV He-I resonance lines are shown to be strongly radially broadened due to opacity. The brightness profiles of high-n visible lines are also found to be strongly radially broadened, but dominantly due to edge recombination. Visible low-n lines are less strongly radially broadened, apparently by a combination of both recombination and EUV opacity. The low-n visible He-I line ratio method with central opacity correction is found to calculate central electron density and temperature well, with poor agreement at the edge, as expected for recombining plasma. In the recombining edge, high-n Boltzmann analysis is found to accurately measure the cold (Te < 0.2 eV) edge temperature. Near the core, however, high-n Boltzmann analysis can be complicated by electron-impact excitation, giving incorrect (Te≈ 0.1 eV) apparent temperatures. Probe measurements were not able to capture the cold edge temperature accurately, probably due to large potential fluctuations, even when using fast triple probe measurements. Fast spectroscopic measurements show that this discrepancy is not explained by recombining plasma alternating with ionizing plasma in the edge region.

Role of plasma response in displacements of the tokamak edge due to applied non-axisymmetric fields

Linear, two-fluid, resistive modelling of the plasma response to applied non-axisymmetric fields shows significant displacement of edge temperature and density profiles. The calculated displacements, often of 2 cm or more in H-mode pedestals with parameters appropriate to DIII-D, are due to the helical distortions resulting from stable edge modes being driven to finite amplitude by the applied fields. In many cases, these displacements are greater in magnitude, and different in phase, than the distortions of the separatrix manifolds predicted from vacuum modelling. Comparison of these results with experimental measurements from Thomson scattering and soft x-ray imaging finds good quantitative agreement. In these experiments, the phase of the applied non-axisymmetric magnetic field was flipped or rotated in order to probe the non-axisymmetric features of the response. The poloidal structures measured by x-ray imaging show clear indications of a helical response, as opposed to simply a change in the axisymmetric transport. Inclusion of two-fluid effects and rotation are found to be important in obtaining quantitative agreement with Thomson scattering data. Modelling shows screening of islands in the H-mode pedestal, but island penetration near the top of the pedestal where the electron rotation vanishes in plasmas with co-current rotation. Enhanced transport due to these islands may provide a mechanism for maintaining the pedestal width below the stability threshold of edge-localized modes. For typical DIII-D parameters, it is shown that the linear approximation is often near or beyond the limit of validity in the H-mode edge; however, the general agreement with experimental measurements indicates that these linear results nevertheless maintain good predictive value for profile displacements.

Spectroscopic Measurement of Neutral Particle Influx Ratio on EAST

The spectra of HeI (587.6 nm), Hα (656.28 nm) and Dα (656.1 nm) of the helium discharges as well as the normal deuterium discharges have been measured with two optical spectroscopic multi-channel analysis (OMA) systems on the experimental advanced superconducting tokamak (EAST). The influx ratio of the sum of H and D to He spectral lines and the influx ratio of H to D are given. In this way the ratio of hydrogen/deuterium ion (S/XB)H/D to (S/XB)He as well as (S/XB)H/D is not very sensitive to the variation in the edge density and temperature. The low-density helium discharges are operated in order to reduce the recycling hydrogen fluxes; however, the effect is not obvious. The possible reason is that the number of helium discharges is not enough and the content of hydrogen in the wall is still very abundant, which is caused by frequent wall conditionings and the vacuum leakage. The H/(H+D) ratio decreases quickly after one lithium coating and reduces to less than 10% using several accumulated lithium wall conditioning. It is found that the deposited He atoms on the carbon wall will remain at a low level after several D2 discharges.

Effects of Tool Edge Geometry on Cutting Temperature in Continuous Cutting of Case Hardened Steel

This study was conducted to investigate the effects of tool edge geometry on cutting temperature in the continuous cutting of case hardened steel. The tool edge temperature was measured using a two-color pyrometer with an optical fiber. The tool flank temperature increased with the negative land angle. When the flank wear VB was 0.05 mm, the tool flank temperature was only a little higher than with a new insert. However, when the flank wear VB was 0.1 mm, the tool flank temperature was dramatically higher. A horned insert resulted in higher tool flank temperature than when an insert without a horned edge was used. The tendency was remarkable at larger negative land angles and wider flank wear widths. Tool flank temperature increased with an increase in the nose radius of inserts. When comparing inserts with the same nose radius, the insert with the wiper edge caused higher tool flank temperatures than did the insert without the wiper edge.

On the accretion disc and evolutionary stage of β Lyrae

We modeled the V-band light curve of beta Lyrae with two stellar components plus an optically thick accretion disc around the gainer assuming a semidetached configuration. We present the results of this calculation, giving physical parameters for the stars and the disc, along with general system dimensions. We discuss the evolutionary stage of the system finding the best match with one of the evolutionary models of Van Rensbergen et al. According to this model, the system is found at age 2.30E7 years, in the phase of rapid mass transfer, the second one in the life of this binary, in a Case-B mass-exchange stage with dM/dt = 1.58E-5 Msun/year. This result, along with the reported rate of orbital period change and observational evidence of mass loss, suggests that the mass transfer in beta Lyrae, is quasi-conservative. The best model indicates that beta Lyrae finished a relatively large mass loss episode 31400 years ago. The light curve model that best fit the observations has inclination angle i = 81 degree, M1 = 13.2 Msun, M2 = 3.0 Msun, R1 = 6.0 Rsun and R2 = 15.2 Rsun. The disc contributes 22% to the total V-band light curve at quadrature, has a radius of 28.3 Rsun and the outer edge thickness is 11.2 Rsun. The light curve model is significantly better with two bright regions in the disc rim with temperatures 10% and 20% higher than the disc outer edge temperature. We compare our results with earlier studies of this interacting binary.

On the identification of instabilities with neural networks on JET

JET plasmas are affected by various instabilities, which can be particularly dangerous in high performance discharges. An identification method, based on the use of advanced neural networks, called Recurrent Neural Networks (RNNs), has been applied to ELMs. The potential of the recurrent networks to identify the dynamics of the instabilities has been first tested using synthetic data. The networks have then been applied to JET experimental signals. An appropriate selection of the networks topology allows identifying quite well the time evolution of the edge temperature and of the magnetic fields, considered the best indicators of the ELMs. A quite limited number of periodic oscillations are used to train the networks, which then manage to follow quite well the dynamics of the instabilities, in a recurrent configuration on one of the inputs. The time evolution of the aforementioned signals, also during intervals not used in the training and never seen by the networks, are properly reproduced. A careful analysis of the various terms in the RNNs has the potential to give clear indications about the nature of these instabilities and their dynamical behaviour.

Elastic–plastic stresses in rotating connection disk under temperature rise and transmitted torque

A connection disk rotating at constant speed under temperature rise and transmitted torque at the inner and outer clamped edges is modeled using a nonlinear elastic–plastic stress–strain relation, and the elastic–plastic effective stress in Von Mises yield criterion is obtained efficiently by the finite difference method with a closed-form initial predicted value. Effects of rotational speed, edge temperature rises, transmitted torque and their couplings on the elastic–plastic stresses of the connection disk are studied. It is seen that the effective stress increases generally with the edge temperature rises, and the outer edge temperature rise increases the maximum effective stress more remarkably than the inner edge one; the maximum elastic–plastic effective stress occurs at either the inner edge or outer edge.

Postbuckling behavior of functionally graded cylindrical panels with tangential edge constraints and resting on elastic foundations

This paper presents an analytical approach to investigate the effects of tangential edge constraints on the buckling and postbuckling behavior of functionally graded flat and cylindrical panels subjected to thermal, mechanical and thermomechanical loads and resting on elastic foundations. Material properties are assumed to be temperature independent, and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of constituents. Governing equations are derived basing on the classical shell theory incorporating von Karman–Donnell type nonlinearity, initial geometrical imperfection and Pasternak type elastic foundations. Approximate solutions are assumed and Galerkin procedure are applied to obtain explicit expressions of buckling loads and load–deflection relations. The effects of in-plane edge restraint, elastic foundation, temperature and imperfection on the nonlinear response of the panels are graphically analyzed.

Numerical investigation of Scrape Off Layer anomalous particle transport for MAST parameters

Numerical simulations of L-mode plasma turbulence in the Scrape Off Layer of MAST are presented. Relevant features of the boundary plasma, such as the thickness of the density layer or the statistics of the fluctuations are related to the edge density and temperature, plasma current and parallel connection length. It is found that the density profile is weakly affected by the edge density, it broadens when the current or the temperature are decreased while the connection length has the opposite effect. The statistics of the turbulence is relatively insensitive to variations of all the edge parameters and show a certain degree of universality. Effective transport coefficients are calculated for several plasma conditions and display a strong nonlinear dependence on the parameters and on the radial variable. Finally, it is shown how the perpendicular particle fluxes in the Scrape Off Layer are related to the edge parameters.

Numerical sensitivity analysis of divertor heat flux and edge temperature at DIII-D under the influence of resonant magnetic perturbations

The impact of resonant magnetic perturbations on the edge plasma is investigated with the EMC3-EIRENE code. Earlier simulations have shown discrepancies to experimental observations regarding splitting of the divertor heat flux and reduction of the edge temperature. We demonstrate that the latter discrepancy is related to a possible overestimation of the classical parallel electron heat conductivity at low collisionalities. Furthermore, the heat flux splitting pattern can be modified through the application of an RMP screening model, while other model advancements – such as neutral gas pumping and re-fuelling, an ‘ad hoc’ flux limit or impurity radiation – seem to have no impact on the splitting pattern. A broadening and shape change of the toroidally averaged divertor heat flux is analyzed.

0638 水平な上向き加熱二次元平板上の自然対流境界層流れの剥離の数値解析(OS6-7 噴流,後流およびはく離流れ現象の探求と先端的応用,OS6 噴流,後流およびはく離流れ現象の探求と先端的応用)

Fluid flow and heat transfer of natural convection over a horizontal heated two-dimensional plate is investigated by means of DNS. Special attention is focused on development and separation of natural convection boundary layer flow. The Rayleigh and the Prandtl numbers are 108 and 0.71. Stimulating the thermal instability, a spanwise sinusoidal disturbance is added on surface temperature of the plate edge as a boundary condition. A stable pair of counter-rotating longitudinal vortices appears when the spanwise wavelength of the disturbance is in a range of 0.06 ? D ? 0.09. Between the vortices, the flow separates without a definite recirculation bubble downstream. Intensity of circumferential velocity of the vortices takes its maximum just downstream of the separation point and the value is 8% of the natural convection velocity.

Analysis of Cutting Behavior during Tapping and Measurement of Tool Edge Temperature Measured by a Two-Color Pyrometer

Analysis of Cutting Behavior during Tapping and Measurement of Tool Edge Temperature Measured by a Two-Color Pyrometer