gerris software package provides Fluid Flow Solver, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install gerris
gerris is installed in your system.
Make ensure the gerris package were installed using the commands given below,
$ sudo dpkg-query -l | grep gerris *
You will get with gerris package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Science |
| Package | gerris |
| Version | 20131206+dfsg-12 |
| Description | Fluid Flow Solver |
| Sub Section | Science |