# particle tracer - disappearing after time step 1

**URL:** https://discourse.paraview.org/t/particle-tracer-disappearing-after-time-step-1/16412
**Category:** ParaView Support
**Created:** [April 1, 2025, 2:07pm UTC](https://discourse.paraview.org/t/particle-tracer-disappearing-after-time-step-1/16412 "2025-04-01T14:07:39Z")
**Posts on this page:** 5
**Page:** 1

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### Author: ![Nikolas\_Kare](https://discourse.paraview.org/user_avatar/discourse.paraview.org/nikolas_kare/32/16253_2.png) [@Nikolas\_Kare](https://discourse.paraview.org/u/Nikolas_Kare)
#### Post date: [April 1, 2025, 2:07pm UTC](https://discourse.paraview.org/t/particle-tracer-disappearing-after-time-step-1/16412/1 "2025-04-01T14:07:39Z")

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Hello,

I’m using the _Particle Tracer_ filter to visualize particle age trajectories in a 3D unsteady CFD simulation.

I followed the steps from this video: [YouTube Tutorial](https://www.youtube.com/watch?v=Zmf8OE2N518&t=572s&ab_channel=TuxRiders).

The particles generate correctly at the first time step, but they disappear as the simulation progresses to the next step.

Has anyone encountered this issue? Any suggestions on how to resolve it?

Thanks!

 ![particles](https://discourse.paraview.org/uploads/default/original/3X/a/4/a4053b19ba6b521dee8fe4ece36684ea1455577c.jpeg)

I have uploaded the data here including the state file here:

> **[test\_case.zip](https://drive.google.com/file/d/1Eo8VpEKUYXtdVeJtgY4Gmg9kF8-A7POF/view?usp=sharing)**
>
> Google Drive file.

Kind regards,

Nikolas

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### Author: ![mwestphal](https://discourse.paraview.org/user_avatar/discourse.paraview.org/mwestphal/32/17_2.png) [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [April 3, 2025, 2:08pm UTC](https://discourse.paraview.org/t/particle-tracer-disappearing-after-time-step-1/16412/2 "2025-04-03T14:08:58Z")

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You need to reduce the magnitude of the velocity, your particles are going out of the domain right away.

Here is a fixed state file:

[state\_kw.pvsm](https://discourse.paraview.org/uploads/short-url/sCeH0dF6oM2YKKLlSwCbppBsPut.pvsm) (1.0 MB)

 ![image](https://discourse.paraview.org/uploads/default/original/3X/1/c/1c8c7e583fa4479c70f795df7c571000d8bf373b.png)

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### Author: ![Nikolas\_Kare](https://discourse.paraview.org/user_avatar/discourse.paraview.org/nikolas_kare/32/16253_2.png) [@Nikolas\_Kare](https://discourse.paraview.org/u/Nikolas_Kare)
#### Post date: [April 3, 2025, 2:40pm UTC](https://discourse.paraview.org/t/particle-tracer-disappearing-after-time-step-1/16412/3 "2025-04-03T14:40:52Z")

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Hi Mathieu,

Thank you! This actually worked!

Does this mean that the scaling factor of the velocity should correspond to the physical time-stepping between the flow shots? And second, when calculating the particle age, should the velocity scaling factor be added back?

Kind regards,

Nikolas

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### Author: ![mwestphal](https://discourse.paraview.org/user_avatar/discourse.paraview.org/mwestphal/32/17_2.png) [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [April 3, 2025, 2:46pm UTC](https://discourse.paraview.org/t/particle-tracer-disappearing-after-time-step-1/16412/4 "2025-04-03T14:46:34Z")

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> [@Nikolas\_Kare](#):
>
> Does this mean that the scaling factor of the velocity should correspond to the physical time-stepping between the flow shots?

The particles are just moved using the vector (interpolated on the particle location) from one timestep to the next, so that really depends on your units, which ParaView has no knowledge of.

> when calculating the particle age, should the velocity scaling factor be added back?

I dont think so, age should depend on time only, not on velocity.

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### Author: ![Nikolas\_Kare](https://discourse.paraview.org/user_avatar/discourse.paraview.org/nikolas_kare/32/16253_2.png) [@Nikolas\_Kare](https://discourse.paraview.org/u/Nikolas_Kare)
#### Post date: [April 4, 2025, 8:11am UTC](https://discourse.paraview.org/t/particle-tracer-disappearing-after-time-step-1/16412/5 "2025-04-04T08:11:01Z")

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Hi, Thanks for this. - Nikolas