The dynamics of aircraft-propulsion flows is difficult to understand because of the intertwined interactions between the acoustics, combustion and hydrodynamics. The understanding, modeling and control of these flows are in constant development. In this talk, the multi-physics of such flows is tackled from angles that are different from the traditional paradigms.
The generation of sound at the combustor’s exit, which contributes to noise pollution, is investigated in the first part of the talk. The question that will be addressed is “Are there sources of sound due to combustion that have not been identified yet?” By considering a multi-component gas, such as that of a combustion chamber, a new supersonic-nozzle acoustic model is proposed. By drawing analogies from Quantum Mechanics, a solution is found. It is shown that differences in the gas composition generate indirect noise when accelerated through the nozzle, which may be louder than the sound generated by traditional mechanisms.
In the second part of the talk, the focus is on the sound waves that are reflected at the combustor’s exit back to the combustion chamber. These waves may cause thermoacoustic instabilities, which are one of the most intractable problems faced by gas-turbine and rocket-motor manufactures. This is due to the sheer number of parameters that come into play and influence the stability. Adjoint methods and inverse design have recently attracted attention in thermoacoustics because they offer accurate sensitivity information to this sheer number of parameters. With this information, the control, probabilistic sensitivities and physical understanding of thermacoustic instabilities, also in the presence of symmetry breaking, are enabled. Lyapunov analysis from chaos theory is applied to a turbulent reacting-flow simulation.
The methods presented in this talk are applied to modelling, control and optimization of reacting, multi-physical flows in propulsion systems.