Research Activities

High-speed flows over rough walls

Turbulent boundary layers in high-speed vehicles can be significantly affected by the presence of surface roughness. Although most flight systems are designed to have relatively smooth surfaces, roughness can still occur or develop for various reasons. For instance, surface topology may be altered by localized effects such as pitting, corrosion, spallation, or contamination deposits. Roughness can also extend across larger areas of the surface, especially where thermal protection systems (TPSs) are used. Tiled TPSs often exhibit seams at the interfaces between tiles, which interact with the incoming  turbulent boundary layer, strongly impacting both drag and heat transfer. Due to the complexities of supersonic and hypersonic flows compared to incompressible flows, the additional impact of surface roughness has rarely been studied. We explore the impact of surface roughness in high-speed boundary layers using high-fidelity simulations, which provide useful insights into critical aspects of flow dynamics.

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Supersonic flow control

Micro-ramps are passive control devices that can be used to counteract the detrimental effects caused by shock-waves/boundary layer interactions in many engineering flows, such as supersonic inlets and transonic wings.  In our studies, we use direct numerical simulations to unravel the complex flow organization around the micro-ramp, which includes the formation of lateral counter-rotating vortices merging into the micro-ramp wake and the formation of a fascinating train of vortex rings undergoing an azimuthal instability. These simulations help to clarify how such devices can be used to manipulate supersonic turbulent flows and control boundary layer separation.

Watch our Video awarded in the APS DFD Gallery of Fluid Motion 2022 

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Shock wave/boundary layer interaction

The interaction between shock waves and turbulent boundary layers represents a major challenge for modern aerospace research, given its occurrence in a broad range of engineering applications involving transonic, supersonic, and hypersonic systems. Shock Wave/Turbulent Boundary-Layer Interactions (SBLIs) must carefully be considered in the design process, since they have the potential of harmfully impact the performance of aerospace systems, by enhancing aerodynamic drag and heat transfer at the wall. In our studies, we use direct numerical simulations to reproduce SBLIs in different conditions and investigate various aspects of the phenomenon, such as the low-frequency unsteadiness that the system exhibits typically.

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Aeroacoustics of space lauchers

The lift-off of space launch vehicles generates strong acoustic waves that interact in a complex and potentially dangerous way with the launch facility and the launcher itself. Engineering tools developed in the past to predict strong acoustic radiation have limited validity and are not able to provide reliable predictions. It is thus fundamental to develop and validate advanced computational models able to capture the transient flow induced by the ignition of the motors. In our studies, we use high-fidelity 3D Large Eddy Simulations to predict the acoustic field produced by the lift-off of realistic space launchers, like Vega and Vega C. The results obtained demonstrate the capability to provide accurate numerical predictions compared to flight measurements of real configurations, despite the challenging scenario in terms of operating conditions and geometry.

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Supersonic and hypersonic boundary layers

The study of high-speed turbulent boundary layers is essential to determine the aerodynamic heating and drag on supersonic and hypersonic vehicles. The interest of the research community in this direction is fed by the technological advancements in the development of vehicles capable of sustained hypersonic flight in the atmosphere, sub-orbital flights, and planetary re-entry. In our studies, we investigate the structure of high-speed zero-pressure-gradient turbulent boundary layers using direct numerical simulation of the Navier–Stokes equations.

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Wind Energy applications

To reduce the cost of wind energy, diameters of wind turbines have exceeded 200 m. The relevant size suggests that for increasingly long and flexible blades, Fluid-Structure Interaction may play a significant role in the design of these colossal structures. Given the difficulties to measure the phenomena occurring, researchers advocate the development of high-fidelity numerical models exploiting Computational Fluid and Structural Dynamics. In our studies, we developed a novel aeroelastic model for wind turbines combining a 3D Large Eddy Simulation fluid solver with a modal beam-like structural solver. Additional studies improved also the description of the local aerodynamics of the blades’ airfoils, by implementing a semi-empirical model to consider hysteresis phenomena in the airloads along the blades.

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