What is Ulula?

Ulula is an ultra-lightweight 2D hydrodynamics code for teaching and experimentation. Written in Python, it is designed to be compact and easy to comprehend while not compromising on performance. Ulula solves the Eulerian fluid equations on a grid using the Godunov method. The name is a play on words: Euler’s name contains the German word for owl, Eule. Ulula means owl in Latin, the language in which Euler wrote most of his papers.

The main motivation behind Ulula is to create a laboratory for important algorithms used in numerical hydrodynamics. In full-blown production codes, these algorithms tend to be obscured by layers of technical code for parallelization, adaptive meshes, and so on. The brevity of the Ulula solver makes it easy to identify, switch, and modify the main components such as reconstruction, slope limiter, Riemann solver, and timestepping.

Given its simplicity, Ulula is not meant to compete with more complex codes such as Pyro. Similarly, Ulula is not intended for scientific production runs because it is not parallelized and uses a fixed-size 2D grid. On the other hand, the code performs fairly well because all array operations are implemented using numpy. As a result, many of the test problems run in less than a minute on a modern laptop.

Documentation & reference

The Online Documentation contains all further information, including how to get the code, a quickstart guide for running it, and a series of pre-implemented hydro tests. If you wish to cite Ulula, you can refer to the ASCL entry. The algorithms are described in the hydrodynamics class notes for the ASTR 670 course.

Please feel free to get in touch if you have any questions or if you would like to develop Ulula!