# Compressible solver: Negative initial temperature error at low temperatures (216-223K)

**URL:** <https://www.simscale.com/forum/t/compressible-solver-negative-initial-temperature-error-at-low-temperatures-216-223k/101152>\
**Category:** Fluid Flow / CFD\
**Created:** [June 26, 2026, 6:06am UTC](https://www.simscale.com/forum/t/compressible-solver-negative-initial-temperature-error-at-low-temperatures-216-223k/101152 "2026-06-26T06:06:06Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![BraylovesF1](https://www.simscale.com/forum/letter_avatar/braylovesf1/32/6_22734026db12803ebb3e059622ac3534.png) [@BraylovesF1](https://www.simscale.com/forum/u/BraylovesF1)\
**Post date:** [June 26, 2026, 6:06am UTC](https://www.simscale.com/forum/t/compressible-solver-negative-initial-temperature-error-at-low-temperatures-216-223k/101152/1 "2026-06-26T06:06:06Z")

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Using the compressible solver at steady state with k-omega SST turbulence model. I am simulating external flow over a delta wing at high altitude conditions.

I have tried setting initial conditions, subdomain, and velocity inlet temperature to both 216K and 223K, but get the same FOAM FATAL ERROR: Negative initial temperature T0: -26.3 (at 216K) and T0: -14.3 (at 223K). The error occurs at the very first time step.

Interestingly the negative T0 value scales with the temperature — lower temperatures produce more negative T0 values, suggesting a fixed offset is being subtracted somewhere internally.

All temperature values are set in Kelvin. Pressure is set to 7,170 Pa (60,000ft altitude) and velocity inlet is 280 m/s.

Is there a minimum temperature limit in the compressible solver, or a known unit conversion issue at low temperatures?

Thank you for any responses.

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**Author:** ![RicardoParis](https://www.simscale.com/forum/user_avatar/www.simscale.com/ricardoparis/32/30222_2.png) [@RicardoParis](https://www.simscale.com/forum/u/RicardoParis)\
**Post date:** [June 26, 2026, 1:25pm UTC](https://www.simscale.com/forum/t/compressible-solver-negative-initial-temperature-error-at-low-temperatures-216-223k/101152/3 "2026-06-26T13:25:44Z")

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Hi @BraylovesF1,

The limitation isn’t necessarily with temperature, but more so with velocity. The ‘compressible’ solver is pressure-based, which means that it can become unstable at speeds of approximately 0.7 Mach and greater.

It can be that you can stabilize the run with velocity ramping (like in **[this tutorial](https://www.simscale.com/docs/tutorials/tutorial-compressible-flow-simulation-around-a-wing/#:~:text=as%20pictured%20below%3A-,Figure%2019,-%3A%20Configuring%20a%20table)**), but it can also be the case that you won’t be able to run it with the compressible solver.

A solver that handles that speed range better is “Multi-purpose” with compressibility enabled, so that would be my initial suggestion. Multi-purpose can go transonic/supersonic.

Cheers

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<div class="post-metadata">

**Author:** ![BraylovesF1](https://www.simscale.com/forum/letter_avatar/braylovesf1/32/6_22734026db12803ebb3e059622ac3534.png) [@BraylovesF1](https://www.simscale.com/forum/u/BraylovesF1)\
**Post date:** [June 26, 2026, 2:04pm UTC](https://www.simscale.com/forum/t/compressible-solver-negative-initial-temperature-error-at-low-temperatures-216-223k/101152/4 "2026-06-26T14:04:45Z")

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Thank you so much, really appreciate your response!