Aerospace Engineering Brown Bag Lecture Series, Ben Breer and Keshav Ramanathan

The October 22 AE Brown Bag Presentation featured Ben Breer and Keshav Ramanathan.
Ben Breer presented, "Mode Identification and Prediction of Thermoacoustic Instabilities"
Combustion instabilities are one of the most significant issues plaguing a wide array of combustors, from large, ground-based gas turbines to liquid bipropellant rocket engines. Large-amplitude, high-frequency instabilities can result in high cycle fatigue (HCF) of the combustor hardware, leading to reduced combustor lifetime. Additionally, high frequency acoustic modes are narrowly spaced apart, making it difficult to simultaneously identify multiple modes. Therefore, determining the range of operating conditions which reduce or eliminate combustion instabilities is of great interest to the combustion community. Thermoacoustic instabilities were generated on a lean, premixed methane/air, can-annular combustor rig by varying the pilot and equivalence ratios, among other parameters. The thermoacoustic profile inside the chamber was reconstructed as a function of equivalence and pilot ratio to identify the modes present at each operating condition. The mode shapes in the axial and azimuthal directions were simultaneously identified by employing a least squares routine and solving the three-dimensional wave equation using pressure oscillations measured from multiple high temperature pressure transducers.
Prediction of thermoacoustic modes requires considering the stochastic behavior of heat release and mode development. Using hydrodynamics, a two-mode system of non-linear, coupled, stochastic PDEs were numerically solved, thereby generating a data set from which combustion parameters (e.g., mode net growth rate) could be determined using an analytical functional form for the amplitude development. Current work focuses on employing an iterative routine to back-solve for the combustion parameters (operating conditions) which yield combustion processes void of instabilities.
Keshav Ramanathan presented, "Iterative Inhibit Switch Design Process for the GT-2 CubeSat Mission"
GT-2 is a CubeSat currently under development in the Space Systems Design Laboratory, with an expected launch of April 2022. GT-2 is built off lessons learned from the previously designed CubeSat, GT-1, and with modifications to fit new design requirements for this mission. One aspect of the structural design that required a redesign was regarding the inhibit switches. There were numerous design decisions and changes made to update the GT-1 structure for these inhibits, including switching between inhibit types, placement of the inhibits, and changes to the CubeSat walls with the inhibits. This presentation will cover this iterative design process, go over lessons learned, and additionally cover future work for the structure of GT-2 before launch.

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