How far can we push linear flow modelling?

Abstract: Linear flow modelling has been historically used to understand transition to turbulence for a range of flows, leading to both qualitative and quantitative predictions of flow behaviour. Application of linear theory in turbulent flows is somewhat more recent and less rigorously justified — its validity is usually discussed in terms of direct comparison with experiments and simulations. Surprisingly, models based on the linearised Navier-Stokes equations perform remarkably well for a range of turbulent flows, and are able to capture many features of coherent structures in subsonic jets, wakes, and boundary layers. Shock-containing flows, however, violate some of the most essential assumptions of linear modelling. Shocks introduce strong non-linearities in the flow, and flow disturbances may reach amplitudes beyond what linear theory may consider plausible. In this talk, we will look at a range of shock-containing flows and evaluate what kinds of information linear models can provide. We will see that, even in conditions where very strong shocks are present, the models can still predict many flow features of interest, which can be directly validated against optical measurements.

Bio: Petronio Nogueira is a Senior Lecturer at the Shock-Lab, Monash University, Australia. He specialises in linear modelling of turbulent flows, aiming to clarify the dynamics of coherent structures that impact the different components of jet noise, both in the subsonic and supersonic regimes. His recent works have helped to answer questions like what triggers resonance in shock-containing jets, what kinds of coherent structures are present in turbulent jets, and how shocks interact with vortices to generate broadband noise. He holds a Discovery Early Career Researcher Award from the Australian Research Council, and is currently supervising five PhD candidates working on different aspects of jet noise.