The Ignus II engine is a 3D printed, pressure fed, liquid bipropellant rocket engine that runs on refined kerosene called Jet-A (the jet fuel used by commercial airlines and other planes) and liquid oxygen. For our engine to operate as designed, fuel and oxidizer must pass through complicated internal geometries and be delivered to the combustion chamber at precise pressures and flow rates.
Calculating these pressures with a traditional pen-and-paper method requires many assumptions, which can lead to mistakes or extensive testing programs which is difficult for a student org to obtain. CFD, or Computational Fluid Dynamics software, has made solutions to these complex problems much more attainable and has allowed engineers to have a good idea about how their designs will perform before progressing to the manufacturing or testing stages.
However, these programs can require enormous computational resources that a student organization seldom has access to and sometimes took days to yield results. Before Nimbix, we relied on the computers available to our team on campus. While this allowed us to run basic CFD testing on our parts, it was hard to trust their results. Between Nimbix and ANSYS, our team has been able to run high-fidelity simulations rapidly and adjust our designs based on their results. For a student team with limited time and funding, ANSYS products on the Nimbix platform have proved invaluable.
Uploading simulation geometry or ANSYS workbench files is quick and easy and allows you to jump right into your simulation. The simulations we ran were done on virtual desktops that allow you to select the amount of computing resources you want to devote to your simulation. After getting into the virtual desktop, the experience is exactly the same as using ANSYS on your personal desktop. There was very little learning curve on the Nimbix platform, which allowed us to quickly become accustomed to the software.
One example of how we leveraged ANSYS Fluent running on Nimbix was in determining the required fuel inlet pressure of our regenerative cooling channels to provide the appropriate fuel flow rates into the combustion chamber. To keep the combustion chamber from melting, fuel is passed through tiny channels in the wall of the engine, where it absorbs heat before being injected into the engine and burned. The pressure losses in the cooling channels determine what we have to pressurize the tanks on our rocket too, which ultimately affects the thickness of the tanks and thus the overall mass of the rocket. Nimbix was extremely helpful in ensuring that our propellant tanks are rated to the proper pressures.
ANSYS Fluent was also used to analyze fluid flow in our fuel injector, which has the critical task of delivering fuel and oxidizer at the right ratio and distribution to maintain efficient and uniform combustion. In Ignus II, four ring manifolds, two each devoted to kerosene and liquid oxygen, take in the propellants and spray them into the combustion chamber as small jets. Once inside the chamber, these jets collide with one another and blow apart into tiny droplets, which can efficiently mix and be burned. ANSYS Fluent on Nimbix allowed us to ensure that the propellants flowed as designed within our injector so that the engine would perform as expected.
These simulations allowed us to have greater faith in our design before doing any potentially destructive and expensive testing. Before Nimbix, we likely would have had to wait days to get results, which would then need to be analyzed and used to guide our design. The Nimbix platform allowed us the confidence in our engine before we manufactured it and led us to an optimized design that functioned as expected on the first iteration. All of this simulation work paid off when our engine performed as expected this past June, at the inaugural hotfire of this engine and SEDS UCSD’s mobile engine test stand, Colossus!
SEDS UCSD, the UC San Diego chapter of the Students for the Exploration and Development of Space, is an organization made up of passionate students dedicated to cutting edge collegiate engineering projects relating to aerospace and rocketry. SEDS at UCSD made extensive use of the Nimbix platform for our projects.