Simple pipe flow

[rakue]

Hello,
I have just started using this great simulation toolbox.
As a test case I am currently trying to simulate a simple laminar pipe flow of a viscous fluid.
However, the simulation “explodes” after a short simulation time, regardless of the combination of viscosity and time step I use.
Can someone please help me to find out the fundamental error in my approach?

The pipe in my setup has a length of 1000 mm (Z direction), an inner diameter of 100 mm, and a wall thickness of 10 mm.

I have placed an emitter at the inlet of the pipe (0.1 m/s) and particles reaching the exit should be reused.

The direction of gravity is in negative Z direction so that the pipe should be filled evenly.
The viscosity is 0.1 (Pa s)

I expect to see the typical parabolic velocity profile and a pressure gradient along the axis of the pipe.

Attached is my short scene file:

{
"Configuration":
{
"particleRadius": 0.002,
"numberOfStepsPerRenderUpdate": 1,
"density0": 1000,
"simulationMethod": 4,
"gravitation": [0,0,-9.81],
"cflMethod": 1,
"cflFactor": 0.5,
"cflMaxTimeStepSize": 0.005,
"cflMinTimeStepSize": 0.0001,
"timeStepSize": 0.0002,
"maxIterations": 100,
"maxError": 0.05,
"maxIterationsV": 100,
"maxErrorV": 0.1,
"stiffness": 50000,
"exponent": 7,
"velocityUpdateMethod": 0,
"enableDivergenceSolver": true,
"particleAttributes": "velocity",
"boundaryHandlingMethod": 2
},
"Materials": [
{
"id": "Fluid",
"colorField": "velocity",
"colorMapType": 1,
"renderMinValue": 0.0,
"renderMaxValue": 0.4,
"viscosity": 0.01,
"viscosityBoundary": 0.01,
"viscosityMethod": 6,
"maxEmitterParticles": 200000,
"emitterReuseParticles": true,
"emitterBoxMin": [-0.1,-0.1,-0.1],
"emitterBoxMax": [0.1,0.1,1.0]
}
],
"RigidBodies": [
{
"id":4,
"geometryFile": "../models/Pipe_L1000_Di100.obj",
"translation": [0, 0, 0],
"scale":[1.0,1.0,1.0],
"rotationAxis": [1, 0, 0],
"rotationAngle": 0,
"color": [0.2, 0.2, 0.2, 0.2],
"isDynamic": false,
"isWall": true,
"mapInvert": false,
"mapThickness": 0.0,
"mapResolution": [20,20,100]
}
],
"Emitters": [
{
"id":"Fluid",
"width": 24,
"translation": [0.0,0.0,0.05],
"rotationAxis": [0, 1, 0],
"rotationAngle": -1.5708,
"velocity": 0.1,
"type": 1
}
]
}

Simulations with this setup will "explode" ...

Any assistance is appreciated.
Thanks in advance.

[rakue]

Pipe_L1000_Di100.zip
Added geometry ...

[anserko]

hello
I have a similar problem, I was wonderring whether you managed to resolve yours

[rakueEP]

No, unfortunetly not.
For me it's still an unresolved problem and any help is apreciated.

[janbender]

I just tested the scenario and in the beginning it works fine. Then after a while the emitter fights against gravity since the whole fluid body is pushing down while the emitter wants to push the particles up.