Longitudinal combustion instabilities
Acoustic perturbations travel in flow direction inside the combustion chamber where they get reflected at walls and turbine stages. The reflected waves travel upstream and regenerate perturbations of the flame which again excites acoustics to travel downstream. This is continously feeding energy to the acoustic field and establishes a self-excited feedback loop. Watch an example of longitudinal modes impacting the flame of an afterburner.
Transverse combustion instabilities
One of the most famous examples of transverse modes is the F1-engine of the Saturn V. Back in the 1960’s, more than 1200 full-scale tests with varying injector designs have been performed in order to stabilize the combustion process. Still, transverse modes develop in modern combustion devices and little is known. During my thesis I worked on the numerical simulation of transverse instabilities in order to better understand the physical mechansisms.
A. Ghani, T. Poinsot, L. Gicquel & G. Staffelbach
LES of longitudinal and transverse self-excited combustion instabilities in a bluff-body stabilized turbulent premixed flame
Combustion and Flame (2015), vol. 162 (11), pp. 4075-4083
Here you can watch my numerical simulations of transverse modes during action for an afterburner.
Annular combustion instabilities in a pressurized model combustor
An exciting test rig has been developed by Nicholas Worth and James Dawon at NTNU Trondheim. A full-annular combustion chamber terminated by a choked nozzle is feed by 12 burners with a perfectly-premixed methan/air mixture. Based on the experimental configuration, I have set up the LES computation during my time at IMFT (ERC Advanced Grant of Thierry Poinsot and Laurent Selle).
I continued the collaboration with NTNU and IMFT since my arrival at TU Munich. Currently we are using one LES sector (1/12 from the full geometry) coupled with 11 low-order models of the remaining configuration. The full LES computation serves as a reference case for validation of the low-order tool calles taX. It is an in-house tool of the Thermo-Fluid Dynamics Group guided by Wolfgang Polifke at TUM.