Vibrations and Modal Analysis
Working with Rice professor Dr. Brake, Rice Eclipse has been performing vibrations research on our Titan test stand. The data collected will ensure our design will not fail due to catastrophic vibrations from loads during motor firing in addition to performing modal analysis on our structure so we can isolate stand vibrations from acoustic vibrations inside the combustion chamber. Modal analysis will allow us to optimize the performance of our motor by tweaking any irregularities inside the combustion chamber after examining the acoustic characteristics of our combustion chamber.
Using 16 channels of accelerometers, over 100 test points and Siemens software, we performed a rover hammer test. In a roving hammer test, an impact hammer with a high precision load cell is used to excite the structure over all the test points and data from the accelerometers is recorded. We are currently still analyzing the data we recorded but have thus far identified several modes for our Titan test stand.
When we first began testing our hybrid rockets, we used igniters donated to us by a hybrid rocket enthusiast. As testing progressed, a consensus was reached that we try to make our own igniters in pursuit of a complete understanding of rocket engine technology. After testing several unsuccessful ideas, we settled on using a rubber binding agent mixed with oxidizing agents and metals to produce a very combustible compound that begins burning with electrical current. While not fully integrated into our Mark I, Luna and Titan engine designs, with more rigorous testing we expect our homemade igniters to be a rousing success.
INJECTOR PLATE GEOMETRY
The injector plate is the piece of hardware that stands between the plumbing and the combustion chamber. It serves to atomize (turn into a very fine spay) any liquid that goes through it, in our case Nitrous Oxide, our oxidizer. We do this to increase the surface area of the oxidizer, allowing it to interact better with our fuel, and get a better, more complete burn. The simplest injector plate geometry, or arrangement and sizing of the holes on its face, is the showerhead, which simply uses small holes to atomize the liquid. This was our first design and it worked well, but we wanted to take it further. We have now created an impinging geometry injector plate. This uses the same small holes as before to atomize it, however rather than each hole going straight through the plate, pairs of holes are angled so that the streams hit each other, forming a fan and further atomizing the liquid. This is still being tested, but we wanted to continue to evolve, we are now designing an injector plate with a novel geometry we like to call, meta-impinging. This geometry takes the fans created by impinging two streams, and impinges them together to create a mist. We also have plans to test some more specific details such as the net direction of momentum and hole size.
HTPB Fuel Grain Composition
Computational Fluid Dynamics (CFD):
A thriving field within mechanical engineering, CFD uses sophisticated software and computing power to numerically solve the governing equations of complex fluid systems. This technology allows Eclipse members to simulate many of the important fluid flows experienced by a rocket, such as flow around the airframe or through the nozzle. Using ANSYS Fluent, members learn about critical elements of CFD such as mesh refinement, proper boundary conditions, and application of turbulence models. Outside of Eclipse, these topics can only be experienced at Rice through upper-level mechanical engineering courses. Thus, members are able to explore a subject which holds immense potential to drastically reduce costs in the aerospace industry by replacing expensive physical tests with computer simulations.
Many of Eclipse’s rocket motor components are machined in-house at Rice’s Oshman Engineering Design Kitchen (OEDK) by club members. Creating components from nozzles to injector plates, test structures to plumbing, many club members become talented operators of lathes and CNC mills (among other machines), learning to produce intricate rocket parts from raw stock. Under close supervision of the OEDK’s machine shop technician, and with guidance from experienced club members, even freshmen are encouraged to learn complex machining operations that they would otherwise not even sample until sophomore or junior year. These experiences also teach crucial engineering skills in designing for manufacturing, particularly in geometric dimensioning and tolerancing.