Fluids

Fluids

Unwanted velocity flow created at the edge of the melting temperature line

    • taosif_alam
      Subscriber

      I am simulating the temperature and velocity distribution of a laser powder bed fusion process with a moving laser heat source. I have attached the temperature distribution and velocity vector figures (full view and zoomed view). Only half domain is simulated due to symmetric nature of the moving laser. The top surface is a powder region and laser heat source moves over it. At the top surface, it has only convection and radiation heat loss boundary condition. The top surface also have Marangoni stress boundary condition the surface tension gradient is negative. This means that the velocity flow direction will be opposite to the direction of the temperature gradient. The picture of temperature gradient vector directions is also attached which shows they are directed inward towards the high temperature region. As the laser scans through the top surface, the powder region melts and creates a melt pool which is bounded by the liquidus line. The melting and solidification modelling done with enthalpy porosity method inherent in ANSYS Fluent. The A_mush value is taken 10^7 as suggested by the literature. The powder region has very low thermal conductivity and once it melts the its thermal conductivity switches to thermal conductivity of the bulk material which is much higher that that of powder region. The density of the bulk material and powder region is assumed to be same and Bousinessq approximation is also considered. The velocity directions seen from the picture, is directed outwards from the center of the laser active region. But, just across the edge of the liquidus and solidus line we can see very small velocity flow which is directed inwards and marked by the dotted line. This inward velocity is unwanted as the temperature gradient is also inward there. Can anyone please give me any reason, what is the cause of the inward velocities at the edge of the liquidus temperature line? Also, there are some velocity flow in the solid powder region which is also unwanted. Can someone please suggest me how can I get rid of those. Please note, that the mesh is poly-hexcore and mininum size is 3.5 um. For solving the problem, the continuity, momentum and energy equations are iterated until residuals become 10^-6 for each time step.

    • Karthik R
      Administrator
      Hello We are answering your question here. Please respond to the thread below.
      How to resolve unwanted velocity flow created at the edge of the melting temperature line ÔÇö Ansys Learning Forum
      To avoid any further confusion, I'm going to close this thread.
      Karthik
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