Search

The complex, multi-faceted physics of laser-based additive metals processing tends to demand high-fidelity models and costly simulation tools to provide predictions accurate enough to aid in selecting process parameters. Of particular difficulty is the accurate determination of melt pool shape and size, which are useful for predicting lack-of-fusion, as this typically requires an adequate treatment of thermal and fluid flow. In this article we describe a novel numerical simulation tool which aims to achieve a balance between accuracy and cost. This is accomplished by making simplifying assumptions regarding the behavior of the gas-liquid interface for processes with a moderate energy density, such as Laser Engineered Net Shaping (LENS). The details of the implementation, which is based on the solver simpleFoam of the well-known software suite OpenFOAM, are given here and the tool is verified and validated for a LENS process involving Ti-6Al-4V. The results indicate that the new tool predicts width and height of a deposited track to engineering accuracy levels.

Understanding the endwall flow phenomena surrounding low-pressure turbine blades is key to improving performance, as these flow features contribute significantly to loss generation at low Reynolds number cruise. It is well documented that a horseshoe vortex system forms at the junction of the endwall and turbine blade. The vortices develop and gain significant strength in the passage and contribute to total pressure losses. During low Reynolds number conditions, the flow through a low-pressure turbine passage can be greatly impacted by a number of factors, including Reynolds number and incoming turbulence. The focus of this paper is on significant changes to the endwall flow field observed in experimental measurements and an accompanying implicit large-eddy simulation of the flow through a linear cascade of high-lift front-loaded low-pressure turbine blades at low Reynolds number. Results show a significant effect on both the time-averaged endwall flow topology and the unsteady vortical flow characteristics when the Reynolds number based on inlet conditions was decreased to 30,000. Various techniques, such as spectral proper orthogonal decomposition, were used to analyze and compare both high-speed particle image velocimetry measurements and numerical results in order to extract the dominant structures and their unsteady behavior. The total pressure loss development through the passage was assessed in order to better understand how the observed changes in endwall flow structures contribute to the overall losses.

The AIAA Fluid Dynamics Technical Committee formed a working group in 2010 to explore how to include computational fluid dynamics (CFD) in undergraduate education. The following article is the best practices guide resulting from that working group, and is intended to guide the development of CFD instructional content in undergraduate aerospace and mechanical engineering curricula. The article addresses a growing need for new engineers to become ‘intelligent users’ of CFD: that is, to be able to obtain a solution of a flow, and to critically assess the quality of the result. The article distils the concepts of CFD into curricular elements, and establishes reasonable expected outcomes for undergraduate-level instruction of these concepts. It then provides numerous case studies of existing CFD courses, presented in a hierarchy of various ‘profiles’ – from CFD light to CFD heavy – for inclusion in courses with lecture, laboratory or design formats. Specific needs of mechanical engineering programmes are also discussed. Hardware, software, and textbook resources are also briefly reviewed.