# Always stuck at Floating point exception Fluent

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• Last Post 16 January 2018
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Ido Yudhatama posted this 10 January 2018

Hello, I am using ANSYS 18.2 Student Version for my Final Project now

I try to simulate erosion rate in pipe elbow with multiphase flow interaction (air and water using VoF method with k epsilon turbulent model).

I always get stuck at calculation, search for solutions from various discussion forum and tried the solution like they said ''check your boundary conditions or mesh", "change solution method and control", but get zero result, still stuck at this problem.

I think I have good mesh skewness (0.15), right model and right boundary conditions

And i still don't have any idea why my calculation convergence at the beginning calculation and become diverging at time step 19

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Raef.Kobeissi posted this 10 January 2018

Hi, In order to help you we need more information about your case. The boundary conditions used, the schemes used etc... Regards

Raef Kobeissi

Ido Yudhatama posted this 11 January 2018

Hi Raef,  this is the problem description

The configuration consists of a 60 mm diameter pipe with the 90-degree bend (long elbow). Fluid (air and water annular flow horizontal pattern) flows in the pipe with entrained solid particles at 49 m/s normal velocity and the outlet is assumed to be pressure outlet boundary. Turbulent and transient conditions. Solid particles (sand) with 2650 kg/m3 density release from the inlet pipe with initial velocity same as phase 1 (air) 49 m/s. Mass flow rate 0.0084 kg/s.

For fluid flow consist of air with initial velocity 49 m/s and water 0.183 m/s. Center of inlet is the area of air initial velocity. Particle interacts with the continuous phase.

To solve this, I make detail configuration like this:

Type: Pressure-based

Velocity Formulation: Absolute

Time: Transient

VOF multiphase model

N of Eulerian Phase: 2

Formulation: Explicit

Interface Modelling: Sharp

k-epsilon realizable turbulence model

Phase 1: air

Phase 2: water

Surface tension: 0.072 constant

Inert particle: sand

Boundary Conditions:

Gas Inlet (velocity-inlet type)

V: 49 m/s

Initial Pressure: 0

TKE: 1.14

Epsilon: 1725

Phase 2 fraction: 0

DPM: escape

Water Inlet (velocity-inlet type)

V: 0.183 m/s

Initial Pressure: 0

TKE: 0.000167

Epsilon: 0.003047

Phase 2 fraction: 1

Outlet (outflow)

Flow Rate Weighting: 1

DPM: escape

Wall:

Stationary wall, no slip, standard wall roughness

DPM: reflect

Solution Methods:

Pressure-Velocity Coupled

Pressure: PRESTO!

Momentum: Second Order Upwind

Volume Fraction: Compressive

TKE: First Order Upwind

Turbulent Dissipation Rate: First Order Upwind

Transient Formulation: First Order Implicit

Solution Control:

Flow Courant: 100

Eexplicit RF

Momentum: 0.3

Pressure: 0.3

Under RF

Density: 1

Body Forces: 0.5

TKE: 0.6

TDR: 0.6

Turbulent Viscosity: 0.5

Discrete Phase: 0.9

Hybrid Initialization

Time step size: 0.001

N of time step: 1000

Raef.Kobeissi posted this 11 January 2018

Hello, Did you try to solve the case first without enabling DPM? Also, I am assuming you have 2 inlet surfaces? Can you show me the setup of your DPM? Your Coursnt number is high, did you try refucing your time step?

Raef Kobeissi

Ido Yudhatama posted this 11 January 2018

Never try without enabling DPM before. Yes, I have 2 inlet surface like your tutorial on youtube about slug flow using multiphase VOF. I tried to reduce until 50 for courant number but still get the same result. Never tried to reduce below 0.001 s time step before.

Below setup of my DPM and injection

Raef.Kobeissi posted this 12 January 2018

Can you please attach the case file Cheers

Raef Kobeissi

Ido Yudhatama posted this 13 January 2018

You mean .wbjp file?

Raef.Kobeissi posted this 13 January 2018

Yes please Cheers

Raef Kobeissi

Ido Yudhatama posted this 13 January 2018

Here's the link

https://drive.google.com/open?id=18HGzISvF3Nay5iHjfnUk97GfF4fPMoBW

I uploaded to drive include the folder

Ido Yudhatama posted this 16 January 2018

I think I have found the solution. I input the wrong equation discrete phase reflection conditions.

Thanks for your helping Raef

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