Predicting drag and heat transfer in flows over complex surfaces is a considerable challenge. The importance of understanding how rough, compliant, lubricated, and porous surfaces interact with turbulent and separated flows has increased due to its relevance in urban, environmental and energy-intensive industrial applications. This mini-symposium will gather presentations that have advanced our understanding of flows over various complex surfaces, using new modeling approaches, high-performance computing, and innovative experiments.

Countless materials that flow like fluids also exhibit more complex rheological behaviour. In geophysical, industrial and household settings, numerous - perhaps most - fluids display some mix of viscous, elastic, plastic, non-linear or transient responses to forcing: these responses can be highly complex, often occurring as a result of the mechanics of an underlying small-scale structure in the material. While fluid-mechanical modelling of non-Newtonian fluids has a long history, recent years have seen numerous advances in this field, both in terms of rheometry and our understanding of different rheological models, and expertise in numerical and theoretical modelling of complex fluid flow problems. This minisymposium aims to celebrate and draw together the increasingly broad wealth of research in complex fluid mechanics, drawing in work on ‘classical’ viscoelastic and viscoplastic fluids with studies of suspension dynamics, granular mechanics and multi-scale rheology.

Flapping wings, buildings swaying in wind, and other bodies subjected to oscillatory motions (or time-varying inflow velocities) operate under complex unsteady flow conditions. Those are characterized by flow separation, the repeated formation and shedding of vortices and their subsequent interaction; all of which makes it increasingly hard to predict associated force responses. Over the past decades, advances in time-resolved imaging techniques and high-order numerical simulations have helped to extend the boundaries of our understanding of canonical unsteady separating flows. In this mini-symposium, we would like to address more specifically cases where the generated unsteady flows mediate interaction between neighbouring bodies. It involves wake-wing, wing-wing, wing-wall or wing-body interactions, and constructive/destructive interference between the unsteady flow fields around multiple bodies.