openPlume birth

Here I am: after a long flight from Paris, I arrive to Martinique, a beautiful French island in the middle of the Caribbean Sea. 3 Weeks are ahead of me with beaches, sea, nice food and rum... That was the best way for me to finish this 2015 year. A quite intensive year since I just survived my second summer in the quirky city of Bremen. Coming from Tunisia, I needed to connect to the sun that I rarely saw in north of Germany.

As my friends were driving me somewhere to the south part of the island, my mind drifted to reminisce these last 2 years. Joining OHB in 2013 happened just after an exhaustive experience at another satellite prime in Toulouse. I was wondering where I will end up next: born in Tunisia, studied and worked in Toulouse, now living in Bremen… It looks like I am keeping travelling north... Despite the fact that my Mediterranean body shivers to the idea of “winter is coming”, moving to Bremen turned my life upside down. In a good way.

In Martinique, in the middle of December, summer is there… the whole year: the sun always shines on the “Anse d’Arlet”. This is where my friend brought me to install me in “Gorgeous”, his magnificent boat that he was repairing. The bay is full of sailboats where all the neighbours know each other’s. It is not an official harbor but rather a wild peace of sea where the turtles swim next to colourful fishes from.

Gorgeous in Martinique

The nature surrounding the bay is of course gorgeous like the boat. However, the most striking fact I observed is the solidarity between these sailboat inhabitants. They are not sailors perse but they learn how to be one. They learn together how to repair boats, how to maintain them, how to sail… The knowledge is jointly shared.

One day, after having my breakfast (at 12:00), I lay down in the Hammock with my usual glass of Rum and my memory drifted again to recall the most amazing moment in 2015: that was the internship of Luka that ended in April. After 5 years in Toulouse, I thought that I learned everything I need about plume impingement. And here comes the Helium passivation. We are not used to model cold gas passivation device and the tools available at that time were not able to model a non-Laval shape. We knew at that time that openFOAM could help us but we were not sure about the stability of an open CFD tool.

And here comes Luka! Each time, he was confronted with a tedious task, he developed a python script to avoid it. “Need of a blockdict mesh file? Let me develop a script for that!” “Tedious task to have boundary conditions in openFOAM, let me develop a script for that!”

blockMeshDict_generator: first scripts of the future openPlume

And then, Python showed its strength: no need to compile and no need for thousands of code lines… Combining Python easiness and openFOAM flexibility, we managed in less than four month to model diverse passivation devices and to validate the method by modelling a N2 thruster that was used in the DLR Göttingen chamber.

Then, what was important is to make the method as generic as possible by modelling different types of geometry, of gases to be modelled. This way, when Luka leaves, I can continue developing the method and model another type of a venting device (propulsive vent) or using another gas (Xe).

When the internship finished, Luka generated 10 scripts so “short”, so “clean” and so “easy to read”. And the icing on the cake: a script called “extrapolation to the far field” was able to generate an output that could be read by the commercial tool we were using.

And then, the idea hit me (or what is probably the Rum?).

We are visualizing the CFD results from openFOAM with paraview … and we are already extrapolating the results to the far field: what is missing is just to load the geometry of the satellite and calculate the thermal fluxes and the forces and torques.

Easy as a Baba au rum cake.

And what made this scripts more appealing: is their transparency and their flexibility. How many time a commercial software was so obscure, so “black box”-y style… that I lost my temper? And even better, after Luka left, his scripts were a perfect mirror for his thoughts at that time.

That feeling of transparency was so enjoyable that it came back to me on this boat.

In the same time, I heard my friend talking to his boat neighbour about old sails that he wants to use to recover water from the rain (it was raining season there… 5 minutes rain for 12hours of sun…). And his neighbour was saying “of course! I will ask around for you”.

And then, it hit me again.

Cooperation and transparency.

If humans made it throughout the ages, it is not because we were able to destroy other species but rather because we were cooperating with each other’s. If the sailboat inhabitants are able to work together, why not us? In the space industry?

And if we manage to develop this numerical tool… Why not make it “open”? Why not share it with the community? I would love to enjoy the feeling of transparency with other users… Even more, may be other users could help me (us) out with other ideas, with other modifications?

Is the space industry able to accept this kind of crazy idea?

Distribute our own “open” plume software?

To be continued…