Fluids

Fluids

How to resolve 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.

    • Karthik R
      Administrator
      Hello:
      If I understand your modeling approach right, you are solving the NS equations in the solid region as well. This will ask the solver to compute the velocity in the solid region too. In reality, the velocity of the solid region should be zero but your modeling approach will estimate some small finite velocity in this region. Is my understanding correct?
      Karthik
    • taosif_alam
      Subscriber
      Hi Karthik Yes, you are correct. Do you have any suggestion how to resolve this ? I have tried with increasing mushy zone constant values. But, makes the continuity residuals values very high and solution diverges eventually. Also, the direction of those small unwanted velocities are opposite to the general flow direction. Do you have any idea why the result is showing this? Your thought regarding this will be highly appreciated.
      Thanks.
    • Karthik R
      Administrator
      Hello:
      I'm not sure if there is a fool-proof solution for this. As I said, since you are solving the NS equations on the Solid side as well, you will have some unwanted velocity. If it is the properties of the solid (density and viscosity) that would help mimic the solid-like behavior. Just a curious thought - have you increased the viscosity of the solid to a very large number? This may cause additional stability issues.
      Karthik
    • taosif_alam
      Subscriber
      Hi, Karthik Thanks for your reply again. FYI, I have increased the viscosity of the solid phase 10^5 times higher than the liquid phase using UDF. The viscosity of the fluid is in the order of 10^-5 (in SI units)and viscosity of the solid taken as 1. And you are right, I was having stability issues for all other types of meshes except polyhedral meshes. If, I try to increase mushy zone constant more than 10^7 or 10^8, the continuity was diverging. What do you suggest regarding viscosity data should I use for solid and liquid phase ?
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