Projekt
Thermocapillary convection in materials processing.
ProjektbeskrivningIf surface tension depends on temperature, a fluid motion will be induced along a free surface with a temperature gradient. This is an important phenomenon in many materials processes, characterized by large temperature gradients, small volumes of liquid metal, and the presence of free surfaces. This convection is often crucial for the properties of the finished product. Examples of such processes are all the various techniques for crystal growth, and welding, where the flow in the weld pool determines the penetration of the liquid pool (i.e. `weldability`). Often it is technically important to avoid oscillatory flow, and thus it is important to understand the stability characteristics of thermocapillary convection in general. An experimental study of the transition from stationary to oscillatory motion in buoyant thermocapillary convection has been made. The instability was observed by flow visualizations and PIV measurements, and quantitative agreement was found with numerical calculations. The emphasis is on identifying instability mechanisms and to design e±cient active control strategies to suppress oscillations. Welding of the light metals Aluminum and Titanium today presents a number of practical difficulties. The flow in the melt during welding of Al and Ti alloys will be studied by numerical simulation, using tools and models developed in accompanying projects. This will be closely coupled to an experimental study of Al and Ti welding carried out by Torbjörn Carlberg, Sundsvall. The melt flow in stainless steel welding has also been simulated and compared to experiments performed at Nippon Steel, Futtsu,Japan. Another process where thermocapillary convection is crucial is float zone crystal growth. The stability of the flow in such processes are simulated numerically and comparisons are made with actual float zone experiments in space and on earth (Torbjörn Carlberg, Sundsvall). During the work described above, symbolic code generation tools (www.mech.kth.se/ gustava/femLego) have been used to a large extent. Cooperation with Torbjörn Carlberg, Sundsvall, Mårten Levenstam, CTH and Nippon Steel.
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