Search

The 3D wind and turbulence characteristics of the atmospheric boundary layer experiment (3D Wind) was conducted to evaluate innovative remote sensing and in situ platforms for measurements of wind and turbulence regimes. The experiment is part of a planned series that focuses on quantifying wind and turbulence characteristics at the scales of modern wind turbines and wind farms and was conducted in northern Indiana in May 2012. 3D Wind had the following specific objectives: (i) intercomparison experiments evaluating wind speed profiles across the wind turbine rotor plane from traditional cup anemometers and wind vanes on a meteorological mast and from a tethered balloon, sonic anemometers (mast mounted and on an unmanned aerial vehicle), three vertical-pointing (continuous wave) lidars and a pulsed scanning lidar, and (ii) integrate these measurements and output from 3-km-resolution (over the inner domain) simulations with the Weather Research and Forecasting Model to develop a detailed depiction of the a...

Three recent microgravity experiments have been hampered by convection caused by unwanted voids and/or bubbles in the melt. We present a numerical study to delineate the ine uence of void-generated thermocapillary convectiononsolidie cationofadopedsinglecrystalfromitsdilutebinarymeltinmicrogravity.Adetailednumerical model for the Bridgman solidie cation process is developed. The e nite element numerical model solves the quasisteady Navier ‐Stokes equations, together with the conservation equations for transport of energy and species. The complicating effects of thermocapillary convection generated by the void and solutal rejection at the melt ‐solid interface are included. Through a quasi-steady analysis, it is shown that the convection generated by the void can affect radial segregation drastically, especially if the thermocapillary vortex penetrates the solutal boundary layer at the growth interface. From a transport point of view, three different regimes areidentie ed based on thedistance between the void and the growth interface. These range from a diffusion-controlled regime, where most of the radial nonuniformity in the interfacial composition is due to interface curvature with minimal e ow effects, to a fully mixed regime, where the penetration of the solutal boundary layer by the thermocapillary vortex tends to homogenize the interfacial compositions.

Shear cells have been used to measure diffusion coefficients for molten materials on earth as well as in space. The Diffuison Processes in Molten Semiconductors (DPIMS) project has previously flown a graphite shear cell on the reflight of the first Materials Science Laboratory (MSL-1R) spacelab mission with great success. These first-generation shear cells were however, very costly to fabricate. Therefore, an effort was undertaken to design a secondgeneration shear cell, which retained the important features of the first-generation shear cell, yet was much less costly to fabricate. Measurements of the new shear pin, which is broken to begin the diffusion experiment, indicate that a torque of 1.35 ± 0.29 N-m (1.00 ± 0.21 ft-lbf) is necessary to break the shear pin. Measurements of the new drive pin, which must not be broken, indicate that a torque of 3.50 ± 0.42 N-m (2.58 ± 0.31 ft-lbf) is necessary to break the drive pin. This factor of 2.6 difference between breaking the shear pin and breaking the drive pin retains a critical feature of the shear cell design.