Boundary Layer Components Research Articles

Plasma Facing Component Development: Boundary Layer Physics and Component Engineering

Tokamaks currently in operation deposit on the order of 1-30 MW/m2 onto plasma facing surfaces during normal operation and hundreds of MW/m2 for shorter periods of time (0.1–3 ms) during disruptions. Disruption deposited energies on future high-power tokamaks may be well in excess of 20 MJ/m2 Design of plasma facing components (PFCs) for such severe environments requires considerable advancements in materials development, armor tile bonding to actively cooled substrates, heat transfer, and many other areas of engineering concern. Considerable improvements in PFC performance, reliability and lifetime can also be accomplished through improved understanding and control of the edge plasma boundary layer. This paper covers both engineering and edge plasma physics issues that must be addressed in the development of reliable PFCs for ITER. Several specific examples are addressed since a complete treatment of all critical development issues would be lengthy. Topics covered include impurity generation and transport in the boundary layer plasma, materials response to intense pulsed disruption heat loads, runaway electron generation during disruptions, high heat flux performance and PFC fabrication issues. These topics are illustrative examples of the variety of complex issues that must be addressed in the development and design of PFCs.

Lava flow cooling estimated from Landsat Thematic Mapper infrared data: The Lonquimay Eruption (Chile, 1989)

Surface temperatures of a 1989 andesite lava flow at Volcán Lonquimay, Chile, derived from an analysis of Landsat Thematic Mapper (TM) infrared data, show a progressive cooling of crusted lava from 250°C to 170°C down a 1.5 km segment of the flow. These results are obtained by solving “dual‐band” equations for the two short‐wavelength infrared TM bands, assuming that the lava surface can be represented by two thermal components, exposed core and chilled crust, and unlike previous investigations, by predetermining the temperature of the hot component rather than the cool component. This approach is consistent with both observational data and theoretical models, and shows that any exposed core of the flow occupies tiny fractions, possibly less than 0.03%, of the surface area. As a result, the crust made by far the greatest contribution to radiative heat losses, estimated at between 1 and 3 MW per 30×30 m pixel, along most of the flow's length. Convective heat transfer into the air above the flow is about two thirds the corresponding radiative flux. These estimated surface heat losses suggest thicknesses of less than 1 m for a conductive thermal boundary layer component of the crust. Radiance values in the thermal infrared band 6 of the TM image are consistent with temperatures derived from the short‐wavelength infrared data and reveal the thermal manifestation of a topographic step beneath the flow.

Visualizing Interactions of Water Stress Responses with a Whole‐Plant Simulation Model

Simulation models provide a framework for visualizing how different physiological responses may be interacting when plants respond to water stress. The model McStress was used to evaluate data for rates of whole plant gas exchange of three species that showed contrasting responses to water stress under controlled environment conditions. Inputs to the model were systematically varied until the outputs matched the data. Excellent agreement was obtained. In analyzing how the model achieved the match, it became apparent that many of the differences among species could be explained by differences in leaf conductance under well‐irrigated conditions without invoking differences in stress response. The analysis showed both the boundary layer component and the stomatal component contributing to species differences in simulated leaf conductance, sometimes in opposite directions. Analysis of water use efficiency and carbon use efficiency data pointed up complex interacting effects of accelerated senescence on rates of photosynthesis and respiration that could not be discerned in the data. The relationship between root biomass and water uptake was analyzed by introducing the idea that only fine roots are capable of taking up water. The analysis could have been made even more realistic if the model had included gradients in water potential.

On Interaction Problem between Boundary Layer and Wave around Ship

In this paper an iterative method is proposed, combining an integral method based on 3-D boundary layer theory with Rankine-source method and considering the head loss due to viscosity in the equation of boundary condition on the free surface. The numerical calculation is carried out by using the Wigley models. The results of pressure distributions on the hull surface, wave profiles along the hull side, velocity distributions in the boundary layer and resistance components have been shown in comparison with measurements. They display good results to some extent. And the method has also been applied to the practical ship model Series 60 (Cd =0.6).

Biomass production and gas exchange of winter wheat as affected by flag leaf inoculations with Septoria nodorum

summaryInoculation of flan leaves of winter wheat with Septoria nodorum (Berk.) Berk was more effective in reducing final grain weight when inoculation was at anthesis than when it was at flag leaf emergence, either during or following leaf expansion; grain number was not significantly affected by the timing of inoculation. The greatest senescence was observed with late inoculations with correspondingly lower flag leaf weight at grain maturity. It is suggested that flag leaves become more susceptible to S. nodorum with increasing time after emergence. Inoculation did not result in any significant redistribution of assimilate from stems to ears as it did not affect stem weight. The reduction in photosynthesis at high irradiance was proportional to infection‐induced senescence. Change in the total resistance to the diffusive flow of carbon dioxide was controlled by the mesophyll resistance, i.e. that remaining following subtraction of boundary layer and stomatal components.

A study of wing-fuselage interaction

The problem addressed is that of the initial profile appropriate for the calculation of the boundary layer on the wing at a wing-body junction. The geometry considered is such that the fuselage boundary layer reaches the interaction region still attached and it is shown that when the wing has curvature the boundary-layer component of velocity normal to the wing is turned inviscidly through a right angle to provide a (in general) non-zero profile to initiate the wing calculation.

Some Effects of Surface Heating and Topography on the Regional Severe Storm Environment. Part I: Three-Dimensional Simulations

Model experiments have isolated several effects of surface heating and topography which may act in concert to focus the potential for severe thunderstorms in certain areas downstream of dry elevated terrain. These effects are examined primarily in results from 12 h and 36 h three-dimensional model simulations of the 9–11 April 1979 (SESAME I) case, but are also found in simulations of the 9–10 May 1979 (SESAME IV) case. The experiments are performed using the Pennsylvania State University mesoscale model, which includes a sophisticated boundary-layer component with horizontally varying surface characteristics and cloud effects on the surface radiation budget. Comparisons of simulations with and without surface fluxes of heat and moisture confirm that differential surface heating, topography, and differential advection may combine to produce a stabilizing effect. In certain synoptic situations, air strongly heated over the arid Mexican plateau rides over moist potentially cooler air downstream, thereby forming a strong restraining inversion or “lid” over Texas. This elevated mixed layer inversion prevents the occurrence of thunderstorms over a large area; instead, storms are focused in the region where a southeasterly low-level flow underruns the northern and western boundary of the inversion. Model trajectories also support the hypothesis that this lateral boundary of the lid, a baroclinic zone approximately between 800 and 500 mb, is formed by confluence between the Mexican airstream and a subsided polar airstream which has traversed the upper-level trough approaching from the western United States. Model experiments also reveal that the strength of the low-level flow toward the severe storm region may itself be enhanced by effects related to surface heating and topography. First, the lee trough which forms with flow aloft across the southern Rockies and Mexican plateau intensifies as a result of daytime surface heating. This effect, which is related to differential heating and differential mixing of momentum, is significant in that the low-level flow east of the lee trough from the Gulf of Mexico toward the severe storm region is also strengthened by several meters per second. Secondly, transverse circulations associated with jet streaks, which were crucial in inducing low-level flow in both the SESAME I and IV cases, were also found to intensify in the presence of surface heating.

The pressure field along the western margin of the North Atlantic

The surface elevation field over a shelf‐slope region is subject to a parabolic differential equation, the timelike coordinate being longshore distance in the direction of propagation of vorticity waves. Two source terms in this equation contain long‐isobath and cross‐isobath density gradients. In the absence of long‐isobath variations the particular solution of the equation containing the cross‐isobath density gradient source term describes a steric setup distribution, which represents a plausible extension of the dynamic height method to shallow water. When long‐isobath variations of density are also present, the steric setup solution is complemented by a residual field, which is essentially a diffusive smoothing out of the steric setup distribution. The steric setup distribution calculated for the shelf‐slope region of the Northwest Atlantic from Cape Hatteras to the Grand Banks shows two major features: a mound of water associated with the St. Lawrence outflow and a rapid drop at the shelf break associated with an upper slope mean current having a surface velocity of the order of 20 cm s−1. The effects of the St. Lawrence outflow are felt mainly over the Scotian Shelf and in the Gulf of Maine. The shelf break current is apparently a boundary layer component of the cyclonic gyre between the Gulf Stream and the North American mainland.

On the Mean Circulation in the Mid-Atlantic Bight

Abstract Two possible mechanisms which may drive the observed mean alongshelf flow in the Mid-Atlantic Bight are described. Runoff from concentrated sources could conceivably force this flow; however, the one-layer homogeneous model results of Csanady (1978) and Beardsley and Hart (1978) imply that the observed shelf flow is not driven by runoff alone. On the other hand. the Semtner and Mintz (1977) numerical model of the North Atlantic strongly suggests that the shelf circulation is just a boundary layer component of the ocean circulation and thus driven by the large-scale wind stress and heat flux distributions. This model result supports Csanady's (1978) conclusion that the physical mechanism which creates the alongshelf pressure gradient thought to drive the alongshelf flow must be of oceanic origin.

Leaf Area and CO2‐exchange Rate as Determinants of the Rate of Vegetative Growth in Soybean Plants1

The purpose of this experiment was to examine the interrelationships between CO2‐exchange rate (CER) and certain growth analysis variables in soybean [Glycine max (L.) Merr.] plants.Soybean plants representing 16 cultivars were grown in a controlled environment chamber. At 22 and 29 days after planting, leaf area and dry weights of the leaves, supporting tissue, and roots were measured for each plant. From these data, the rate of vegetative growth (GR) was determined for each cultivar as well as leaf area growth rate (LAGR), specific leaf weight (SLW), and other growth analysis variables.At 28 days after planting, the CER per unit leaf area of the terminal leaflet of the second trifoliolate leaf was measured. The resistance to CO2 diffusion was partitioned into boundary layer, stomatal, and mesophyll components. Gas exchange was measured independently for each leaf surface.Growth rate was negatively related to CER and SLW and positively related to LAGR. Furthermore, CER was positively and negatively related to SLW and LAGR, respectively. As the leaves increased in SLW and CER across the cultivars, their rate of area expansion decreased. Since GR was positively correlated with LAGR and negatively correlated with CER, it appears that increases in CER did not compensate for decreases in LAGR; consequently, differences in GR among the cultivars were detected.