Using a direct-adjoint framework for the analysis of turbomachinery aeroacoustics

New efficiency and emission standards in contemporary aero-engine design are increasingly introducing the need for the understanding of fundamental flow processes and their optimisation. Here, a newly developed high-order, time-domain, direct-adjoint framework for the analysis and optimisation of turbomachinery aeroacoustics will be presented, and two classes of representative problems considered. First, self-excited instabilities and the resulting acoustic fields on an isolated compressor bladerow at off-design conditions are characterised by means of a direct-adjoint meanflow global stability analysis, with wavemaker regions calculated to identify self-reinforcing feedback mechanisms that perpetuate these features. An extension to multiple identical blade passages is then demonstrated by reinterpreting the periodic meanflow within each passage as a block-circulant system. A Bloch-wave decomposition of this system yields independent and computationally tractable subproblems, by means of which new flow structures are identified. To conclude, a time-domain, unsteady adjoint sliding plane treatment is introduced, and its utility highlighted, by considering the unsteady rotor-stator interaction problem from the adjoint sensitivity perspective.