# Plane Poiseuille flow

**URL:** <https://discourse.channelflow.ch/t/plane-poiseuille-flow/193>\
**Category:** Usage\
**Created:** [April 2, 2025, 3:45am UTC](https://discourse.channelflow.ch/t/plane-poiseuille-flow/193 "2025-04-02T03:45:17Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![crc150](https://avatars.discourse-cdn.com/v4/letter/c/f07891/32.png) [@crc150](https://discourse.channelflow.ch/u/crc150)\
**Post date:** [April 2, 2025, 3:45am UTC](https://discourse.channelflow.ch/t/plane-poiseuille-flow/193/1 "2025-04-02T03:45:17Z")

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Hello, I am currently trying to run pressure driven (-dPds) Poiseuille flows, in the installation, it says :

The following example simulates a pressure driven (-dPds) Poiseuille flow (-Uwall 0) at the Reynolds number 1000 using a 1st order forward-backward euler scheme as initial time stepping algorithm (-is).

`simulateflow -R 1000 -Uwall 0 -` `dPds -0.002 ` `-is SBDF1 newfield.nc`

I am a bit confused of the `-dPds -0.002 as I would expect that by fixing the Reynolds the code would already know the required pressure drop. ```

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**Author:** ![jc.ring](https://avatars.discourse-cdn.com/v4/letter/j/58956e/32.png) [@jc.ring](https://discourse.channelflow.ch/u/jc.ring)\
**Post date:** [January 20, 2026, 12:26am UTC](https://discourse.channelflow.ch/t/plane-poiseuille-flow/193/2 "2026-01-20T00:26:25Z")

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Hello,  
ChannelFlow uses an influence-matrix method to accurately solve the Helmholtz equations. Because the domain is periodic, the pressure is defined only up to an additive constant, and the pressure gradient must therefore be constrained. This can be achieved either by prescribing the mean bulk velocity or by fixing the mean pressure gradient; both choices are equivalent.

For reference you can check :

- [Spectral methods in fluid dynamics - NASA Technical Reports Server (NTRS)](https://ntrs.nasa.gov/citations/19860017078)
- Spectral Methods for Incompressible Viscous Flow from Peyret (2002)
- [https://www.mdpi.com/2227-7390/13/16/2549](https://www.mdpi.com/2227-7390/13/16/2549)