Fluid mechanics and fluid-structure interactions

Research focus

The Peer review has evaluated this group as Average

Research in this area is mainly focused on the fluid-dynamic aspects related to Civil, Environmental and Industrial applications. A major feature of the fluid-dynamic conditions in civil and environmental engineering applications is the asymmetrical confinement of the flow, typically observed for free surface flows. The fluid-structure interaction between base shape structures, like circular and rectangular cylinders and sphere, which is extensively studied in unbounded or symmetrically bounded flow conditions, is characterized by several aspects that are still not completely understood and are significant for practical application. Notably, when a river bridge is partially or completely submerged by the flow during an extreme event, the hydraulic loading on the bridge deck can effectively be modeled upon considering the interaction between the free-surface flow field and a rectangular cylinder. Magnitude of mean force coefficients highlights the differences between unbounded or symmetrical bounded flow conditions phenomena and the field scenario, where the presence of the free surface and the channel floor significantly affects the process. Other complex phenomena of interest concerning infrastructures include the dynamics of the flow around piers and abutments in rivers and offshore platform, the pressure fluctuation over bottom sills and movement of tethered bodies within a free-surface stream. A fertile field for fluid mechanics related research is that concerning industrial applications of (generally transient) pipe flows. A recent relevant body of activity deals with applications related to the mechanics of control valves. The research is concerned with several geometrical configurations of ball valves and resistors. The analysis of the performance of existing valves and the cavitation attitudes of different valve configurations is conducive to developing a model of the mechanism of energy dissipation in a variety of flow and geometrical conditions. Due to the complexity of the investigated processes, the problems are tackled in terms of both numerical modeling and laboratory scale experiments. Main axes of the research therefore include the development of advanced methods for fluid-dynamic measurements based on image analysis technologies and direct assessment and modeling of fluid-structure interactions. Particle Image Velocimetry (PIV) is currently one of the most used techniques for measurements of the velocity distributions in complex flow fields. The DIIAR has a long tradition in development and testing of image techniques for fluid-dynamic measurements, specifically targeted to civil and environmental applications. Starting from the common application of the PIV methodology, proper techniques have been developed and adapted to solve the specific problems tackled. These methods allow two-dimensional measurements with a temporal resolution (frame-rate) of up to 200Hz, an acquisition time up to 30 seconds and good reliability for laboratory and outdoor measurement. Due to the intrinsic relevant to these issues, the years between 2003 and 2006 have therefore witnessed major emphasis on the study of flow field structures generated by the interaction between river structures (bridges and sills) and free-surface flows and snowdrift phenomena. The fluid-structure interaction was mainly focused on the relationship between fluid-dynamic loading on structures and the flow distortions that these structures cause on the fluid flow field. Aspects related to the ensuing energy losses are also investigated. The research is concerned with a variety of geometrical configurations (confined and unconfined flows, single and multiple cylinders), kinematical conditions (steady and oscillatory flows) and dynamical conditions (Reynolds numbers ranging from laminar flows for direct numerical simulations to fully turbulent flows for LES models and laboratory experiments). Major emphasis was on the analysis of the larger vortical structures that are primarily responsible for the loadings on submerged objects. The identification of the physical properties of coherent structures within the flow field is also a key point for the understanding of local scour phenomena: the flow fields are highly variable in time and space so that the interaction between the solid and the fluid phase can not be analyzed on the basis of universal statistics for stationary developed boundary layers. Average and instantaneous drag and lift coefficients and velocity flow field around the structures are modeled, and the dominant frequencies of loading and vortex shedding are studied. These processes are then modeled and verified in terms of energy losses by applying the momentum equation. International collaborative research is active, as testified by joint publications appearing on several international journals.

Dipartimento di afferenza

Dipartimento di Ingegneria Idraulica, Ambientale, Infrastrutture Viarie, Rilevamento (DIIAR)

Docenti afferenti

Full Professors
Francesco Ballio
Enrco Larcan
Silvio Franzetti
Associate Professors
Stefano Mambretti
Stefano Malavasi
Assistant Professors
Diego Berzi