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akash.iitb August 23, 2010 23:53

Dynamic Mesh moving interface help

I am trying to apply dynamic mesh in Fluent for the first time thereby seeking help.

Project - The overall problem concerns multiphase wax deposition modeling in subsea pipeline where the pipe diameter shrinks because of wax clogging. This is oil and gas company project.

Background - Hence, as a basic preliminary model consisting of single phase, it consists of a fluid and solid region , solid being the wall + wax deposit, I have developed a small computational domain where i have incorporated hydrodynamics, heat and species transport.

Current problem help - I want to move the solid-liquid interface at some specific rate (for the simplest model case say by 10 mm in all in 500 time steps - my geometry domain height is 40 mm). So, how should i set up my dynamic mesh for moving this solid-fluid interface?

My attempt -
I created a pretty simple UDF which asks to move the solid-fluid interface y position by 0.5 mm each time step. I applied the deforming dynamic mesh zone to interface using layering scheme. Length scales were chosen equal to half the adjacent cell sizes ( 0.5 mm on fluid and 0.1 mm on solid zone side)
But as i progress through 20 odd time steps (0.0005 second per step), i get the negative cell volume error. I see from the mesh that once my interface cells reach the first fluid zone cell, the program gives negative cell volume error. I believe there is something fundamentally wrong - probably in UDF itself or dynamic mesh setup. So, please help. I have not worked with UDFs before.

Based on what little i know and what i have tried, these are some queries -

  • What kind of dynamic mesh UDF should i write for deforming interface - CG motion , grid motion, geom ? Can someone please share a similar UDF if possible to help me start.
  • I have read that for linear moving boundary, layering scheme is applicable. What other options - remeshing and smoothing should i use?
  • Any recommended settings for shrink factor, collapse factor, minimum and maximum length scales?
I have seen quite a lot of people have already worked on dynamic mesh in this forum and hence they know a lot to help me solve this simple problem. I will really appreciate the help.

Thanks in advance,
Akash Gupta

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