Fluids

Fluids

Divergence detected in AMG solver. VOF.

    • Anakin
      Subscriber

      Hi guys. I'm simulating air-water flow through a T pipe with 26mm inner diameter. The pipe was created in a 2D domain, there are two inlets (one for air and the other for water) and one outlet. The two inlets have velocity inlet conditions and the outlet has pressure outlet conditions. The pipe is filled with water and then water and air start to flow from the inlets with their respective inlet velocities. The time-step was calculated based on the CFL condition and the total flow time is 6 seconds. The simulation is presenting the following problems after the bubbles reach the outlet (which occurred approximately in 2,3 seconds):


      # Divergence detected in AMG for pressure correction: protective actions enabled!

      # Divergence detected in AMG for pressure correction, temporarily solve with BCGSTAB!


      Divergence detected in AMG solver: pressure correction# Divergence detected in AMG for pressure correction: protective actions enabled!

      # Divergence detected in AMG for pressure correction, temporarily solve with BCGSTAB!


      Divergence detected in AMG solver: pressure correction# Divergence detected in AMG for k: protective actions enabled!

      # Divergence detected in AMG for k, temporarily solve with BCGSTAB!


      Divergence detected in AMG solver: k# Divergence detected in AMG for omega: protective actions enabled!

      # Divergence detected in AMG for omega, temporarily solve with BCGSTAB!


      Divergence detected in AMG solver: omega

      Divergence detected in AMG solver: pressure correction

      Divergence detected in AMG solver: pressure correction

      Divergence detected in AMG solver: k

      Divergence detected in AMG solver: omega

      Divergence detected in AMG solver: pressure correction

      Divergence detected in AMG solver: pressure correction

      Divergence detected in AMG solver: k

      Divergence detected in AMG solver: omega

       reversed flow in 63 faces on pressure-outlet 9. 


      Divergence detected in AMG solver: pressure correction

      Divergence detected in AMG solver: pressure correction

      Divergence detected in AMG solver: k

      Divergence detected in AMG solver: omega

      Error at host: floating point exception


      Error at Node 0: floating point exception


      Error at Node 1: floating point exception


      Error at Node 2: floating point exception


      Error at Node 3: floating point exception


      Error: floating point exception

      Error Object: #f


      I checked the mesh quality and it looks good (min orthogonal quality = 0.73; max skewness = 0.53; max aspect ratio = 21.16). I tried to solve the problem by reducing the time step in half and decreasing the relaxation factors, but it didn't work. I don't know how to fix this problem, so I really need some help and I'm open to answering any questions. I'm going to list every piece of information I find relevant about the simulation.


      General:

      Parallel

      Solver type: Pressure-Based

      Time: Transient

      Planar 2D space

      Gravity on


      Models:

      Multiphase VOF with explicit formulation and Surface Tension Force Modeling (CSF)

      Default Courant number: 0,25

      Implicit Body Force

      Turbulence Model: SST k-omega


      Cell Zone Conditions:

      Specified Operating Density: 1.225 kg/m³ (air density)


      Boundary conditions:

      air inlet velocity = 0.936 m/s

      water inlet velocity = 0.37


      m/s

      outlet Gauge Pressure (pascal) = 0

      pipe wall: stationary, no slip


      Solution Methods:

      PISO Scheme

      Least Squares Cell Based Gradient

      PRESTO! Pressure

      volume fraction: Geo-Reconstruct

      Momentum, Turbulent Kinetic Energy and Specific Dissipation Rate = Second order upwind

      Transient Formulation = First order implicit


      Solution Controls: Default


      Residuals = 10e-5

      Standard initialization with default initial values

    • Keyur Kanade
      Ansys Employee
      I assume you have patched the volume before start of iterations.
      Please make sure that you reduce your timestep as 6 sec looks too large.
      Please search through forum and you will find many posts on VOF.
      Regards Keyur
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    • Anakin
      Subscriber
      Thank for your reply What do you mean by "patched the volume"? I think i did it, just want to be sure that we are talking about the same thing.
      The total flow time i'm going for is 6 sec, not my time step.
      Regards Anakin.
    • jao4817
      Subscriber
      Hello Anakin! Did you later find a solution. Im facing a similar problem and would appreciate any help greatly.
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