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Divergence detected in AMG solver. VOF.

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Old   May 7, 2021, 01:02
Default Divergence detected in AMG solver. VOF.
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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. I'm conducting a mesh independence test with four meshes. The time-step for each mesh was calculated based on the CFL condition and the total flow time for each one was 6 seconds. The first three simulations had no problems but the fourth one is presenting the following problems after the bubbles reach the outlet (which occurred approximately in 2,3 seconds):

# Divergence detected in AMG for x-momentum: protective actions enabled!
# Divergence detected in AMG for x-momentum, temporarily solve with BCGSTAB!

Divergence detected in AMG solver: x-momentum# Divergence detected in AMG for y-momentum: protective actions enabled!
# Divergence detected in AMG for y-momentum, temporarily solve with BCGSTAB!

Divergence detected in AMG solver: y-momentum# 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: x-momentum
Divergence detected in AMG solver: y-momentum
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: x-momentum
Divergence detected in AMG solver: y-momentum
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 118 faces on pressure-outlet 9.

Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
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 = 0.68; max skewness = 0.60; max aspect ratio = 10.07). 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/m (air density)

Boundary conditions:
air inlet velocity = 0.123 m/s
water inlet velocity = 0.6 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
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Old   May 17, 2021, 15:07
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Maharshtra
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You got the solution of this problem ?
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Old   August 31, 2021, 20:42
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Hi Harshad Bhalerao,

I still dont know the answer. It has been months since i posted this and nobody posted a reply.
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