Simulation of powder metal fabrication with high pressure gas atomization

A computational/analytical technique has been developed which models the physics of high pressure gas atomization. The technique uses an uncoupled approach, such that the gas flowfield is initially calculated with a commercially-available Navier-Stokes code. The liquid metal droplet breakup, dynamics, and thermodynamics, are then calculated using the pre-computed flowfield by a separate computer program written by the authors. The atomization code models the primary breakup of the liquid metal stream, tracks the droplets resulting from primary breakup through the flowfield until they undergo secondary breakup, and then tracks the subdroplets until they breakup, solidify, or leave the flowfield region of interest. The statistical properties of the metal powder produced are then computed from the characteristics of these droplets. Comparisons between experimental measurements and computations indicate that the Navier-Stokes code is predicting the gas flowfield well, and that the atomization code is properly modeling the physics of the droplet dynamics and breakup

Use of shear-stress-sensitive, temperature-insensitive liquid crystals for hypersonic boundary-layer transition detection

The use of shear-stress-sensitive, temperature-insensitive (SSS/TI) liquid crystals (LCs) has been evaluated as a boundary-layer transition detection technique for hypersonic flows. Experiments were conducted at Mach 8 in the Sandia National Laboratories Hypersonic Wind Tunnel using a flat plate model at near zero-degree angle of attack over the freestream unit Reynolds number range 1.2-5.8x10{sup 6}/ft. Standard 35mm color photography and Super VHS color video were used to record LC color changes due to varying surface shear stress during the transition process for a range of commercial SSS liquid crystals. Visual transition data were compared to an established method using calorimetric surface heat-transfer measurements to evaluate the LC technique. It is concluded that the use of SSS/TI LCs can be an inexpensive, safe, and easy to use boundary-layer transition detection method for hypersonic flows. However, a valid interpretation of the visual records requires careful attention to illumination intensity levels and uniformity, lighting and viewing angles, some prior understanding of the general character of the flow, and the selection of the appropriate liquid crystal for the particular flow conditions