unexpected gusts of wind in gas flow simulation #81493

New Issue

jensdahlkunoy@gmail.com · 2020-10-06T21:35:31+02:00

2020-10-06 21:35:31 +02:00

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce RTX 2060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 451.48

Blender Version
Broken: version: 2.90.1, branch: master, commit date: 2020-09-23 06:43, hash: 3e85bb34d0
Worked: (newest version of Blender that worked as expected)

Short description of error
A simple setup with a steady jet is seeing unexpected strong gusts of wind.

Background
I use high initial gas velocities creatively as a rocket exhaust. High velocities give in this case a much better visual effect compared to slower. I want a relatively steady and centered gas jet. However the strong gusts from boundaries are severly disturbing rocket plume and the visual appearance.

Exact steps for others to reproduce the error

start blender
Change output properties to Frame end 300
scale default cube x2
apply all transform on cube.
add fluid domain to default cube
add border collision to bottom
Change gas bouyancy density to 0 and Heat to 0
change resolution divisions to 64
Change cache type to Modular
change frame end 300
Add 0.5m mesh plane
add fluid->inflow to mesh plane
set inflow initial temperature to 0
enable initial velocity to mesh plane
set initial z-velocity to -40m/s
bake fluid domain
Run animation and see how strong gusts of wind are disrupting the expected steady downward plume. There is no physical good reason why strong gusts of wind should occur. This is seen as a bug/instability.

I tried the following changes to improve convergence/accuracy/stability.

a. Cube fluid settings: CFL Number 0.5
b. Cube fluid settings: Timesteps Maximum time steps 20
c. Cube fluid settings: Timesteps Minimum time steps 4
d. Plane fluid settings: Sampling substeps 4
e. Plane fluid settings: Flow Source, set IsPlane to true

The strong gusts still occured with these changes.

Ideas for fixing

increase gas viscosity seen by the flow solver. Either
- Add a adjustment field for increasing uniform gas viscosity
- Add a simple turbulence model that increase gas visocity based on : https://en.wikipedia.org/wiki/Spalart%E2%80%93Allmaras_turbulence_model
review open boundary conditions to check they are meaningful in a scenario with a mix of inflow/outflow. Inflows in particular could potentially cause instability because inflow velocity and direction is hard to set meaningful.

Test File
gustofwind.blend

**System Information** Operating system: Windows-10-10.0.19041-SP0 64 Bits Graphics card: GeForce RTX 2060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 451.48 **Blender Version** Broken: version: 2.90.1, branch: master, commit date: 2020-09-23 06:43, hash: `3e85bb34d0` Worked: (newest version of Blender that worked as expected) **Short description of error** A simple setup with a steady jet is seeing unexpected strong gusts of wind. **Background** I use high initial gas velocities creatively as a rocket exhaust. High velocities give in this case a much better visual effect compared to slower. I want a relatively steady and centered gas jet. However the strong gusts from boundaries are severly disturbing rocket plume and the visual appearance. **Exact steps for others to reproduce the error** 1. start blender 2. Change output properties to Frame end 300 3. scale default cube x2 4. apply all transform on cube. 5. add fluid domain to default cube 6. add border collision to bottom 7. Change gas bouyancy density to 0 and Heat to 0 8. change resolution divisions to 64 9. Change cache type to Modular 10. change frame end 300 11. Add 0.5m mesh plane 12. add fluid->inflow to mesh plane 13. set inflow initial temperature to 0 14. enable initial velocity to mesh plane 15. set initial z-velocity to -40m/s 16. bake fluid domain 17. Run animation and see how strong gusts of wind are disrupting the expected steady downward plume. There is no physical good reason why strong gusts of wind should occur. This is seen as a bug/instability. I tried the following changes to improve convergence/accuracy/stability. a. Cube fluid settings: CFL Number 0.5 b. Cube fluid settings: Timesteps Maximum time steps 20 c. Cube fluid settings: Timesteps Minimum time steps 4 d. Plane fluid settings: Sampling substeps 4 e. Plane fluid settings: Flow Source, set IsPlane to true The strong gusts still occured with these changes. **Ideas for fixing** - increase gas viscosity seen by the flow solver. Either - Add a adjustment field for increasing uniform gas viscosity - Add a simple turbulence model that increase gas visocity based on : https://en.wikipedia.org/wiki/Spalart%E2%80%93Allmaras_turbulence_model - review open boundary conditions to check they are meaningful in a scenario with a mix of inflow/outflow. Inflows in particular could potentially cause instability because inflow velocity and direction is hard to set meaningful. Test File [gustofwind.blend](https://archive.blender.org/developer/F8965682/gustofwind.blend)

jensdahlkunoy@gmail.com commented

2020-10-06 21:35:31 +02:00

Added subscriber: @jdk

Germano Cavalcante commented

2020-10-07 20:25:05 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2020-10-07 20:25:05 +02:00

Thanks for the report,

I believe that the problem would be more easily reproducible with a simple .blend file.

If there are many steps to reproduce the problem, it is recommendable to attach a .blend file saved right before the bug occurs, so only a few steps are needed to trigger the bug.

Can you provide this?

Thanks for the report, I believe that the problem would be more easily reproducible with a simple .blend file. If there are many steps to reproduce the problem, it is recommendable to attach a .blend file saved right before the bug occurs, so only a few steps are needed to trigger the bug. Can you provide this?

Philipp Oeser commented

2020-10-07 20:36:04 +02:00

Changed status from 'Needs Triage' to: 'Needs User Info'

jensdahlkunoy@gmail.com commented

2020-10-07 22:40:11 +02:00

Here is the blend file.
gustofwind.blend

You need to rebake or download files here (640MB)
https://drive.google.com/drive/folders/1XpdRR4ok14nvS95BHZwpkGio8twAYiD4?usp=sharing

The gust happens around frame 120

Let me know if I can help more.

Here is the blend file. [gustofwind.blend](https://archive.blender.org/developer/F8965682/gustofwind.blend) You need to rebake or download files here (640MB) https://drive.google.com/drive/folders/1XpdRR4ok14nvS95BHZwpkGio8twAYiD4?usp=sharing The gust happens around frame 120 Let me know if I can help more.

Ankit Meel commented

2020-10-18 21:46:42 +02:00

Changed status from 'Needs User Info' to: 'Needs Triage'

Pratik Borhade commented

2021-06-02 11:56:59 +02:00

Added subscriber: @PratikPB2123

Jesse Yurkovich commented

2021-06-21 08:33:08 +02:00

Added subscriber: @deadpin

Jesse Yurkovich commented

2021-06-21 08:33:08 +02:00

Changed status from 'Needs Triage' to: 'Needs User Info'

Jesse Yurkovich commented

2021-06-21 08:33:08 +02:00

Hi @jdk, I was able to bake all 300 frames from your example file using 2.93.0 today and things seem fine. I did not observe any strong gusts of wind, just a relatively constant stream of smoke downwards. Can you try reproducing your problem using 2.93.0 or later? If it's still a problem, can you post a screenshot of the frame that exhibits the problem as well as the frame just before perhaps (or whatever might show the difference)?

jensdahlkunoy@gmail.com commented

2021-06-21 18:44:10 +02:00

Hi @deadpin,
I cannot recreate the issue of sudden gust either. So I guess it has been fixed somehow. Problem solved I guess.

Hi @deadpin, I cannot recreate the issue of sudden gust either. So I guess it has been fixed somehow. Problem solved I guess.

Jesse Yurkovich commented

2021-06-21 20:35:37 +02:00

Changed status from 'Needs User Info' to: 'Resolved'

Jesse Yurkovich closed this issue

2021-06-21 20:35:37 +02:00

Jesse Yurkovich self-assigned this 2021-06-21 20:35:37 +02:00

Jesse Yurkovich commented

2021-06-21 20:35:37 +02:00

Thanks for checking. If you encounter a similar problem please feel free to create a new report on the issue.

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unexpected gusts of wind in gas flow simulation #81493