Among all aquatic species, mantas and rays swim by flapping their pectoral fins; this motion is similar to other fishes in terms of efficiency, but it gives better maneuverability and agility in turning. The fin's motion is featured by a traveling wave going opposite to the forward motion, producing a force thanks to momentum conservation. This article aims at understanding the swimming dynamics of rays, focusing on energy efficiency. A computational fluid dynamics (CFD) model of the swimming motion of a cownose ray has been implemented in openfoam, simulating the acceleration of the fish from still to the steady-state velocity using an overset mesh. In this analysis, the one degree-of-freedom dynamics of forward swimming is solved together with the fluid velocity and pressure. The effect of frequency and wavelength of fin motion on thrust, power, and velocity has been investigated and an analysis of the vortices in the wake showed has been performed. The energy efficiency of a self-propelled body has been defined in a novel way and it has been calculated for different motion conditions. The results showed that batoid fishes swim with high energy efficiency and that they are a promising source of inspiration for biomimetic autonomous underwater vehicles.

High-sided vehicles experience sudden changes in aerodynamic forces when passing through the wake of towers of bridges under crosswind. This may lead, in the worst case, to vehicle rollover or undesired lane changes, thus representing a critical concern for running safety. Computational fluid dynamics (CFD) is used to simulate and investigate the aerodynamic forces acting on a heavy goods vehicle (HGV) during the overtaking maneuver of a bridge tower when the vehicle is passing through the wake of the pylon generated by lateral wind. Dynamic mesh techniques are adopted to simulate the relative velocity between the vehicle and the infrastructure. Such an approach can be used to design lateral shields to be installed on existing infrastructure, reducing the risk of a wind-induced accident involving overturning of the HGV. The validation of the moving mesh strategies is performed comparing numerical and wind tunnel test results in terms of aerodynamic forces and moments acting on a stationary vehicle for different exposure angles.

In this study the pure effect of raindrops on dynamic stall of a pitching airfoil has been investigated. The simulation was performed at Reynolds number of $${10}^{6}$$10 6 with raindrop diameter equal to $${10}^{-5}\text{m}$$10 - 5 m . A couple of multiphase models based on Eulerian and Lagrangian frames of reference have been implemented to simulate the raindrops. In the first step the accuracy of each multiphase model has been appraised. As a result, the Lagrangian multiphase model, which is called Discrete Phase Model, has been proven to be of better accuracy. It has been concluded that in general raindrops has negative effects on the lift coefficient of the pitching airfoil. In addition, a lead in aerodynamic phenomena has been observed due to the presence of water drops. This phenomenon has also been observed in the formation and separation of Leading Edge and Trailing Edge vortices which come to existence in advance of the dry case. Finally, it has been illustrated that the main effect of raindrops is on the phase of force oscillation rather than the force amplitude.

This works focuses on a series of experimental tests carried out to investigate overpressures in tunnels due to train crossings. Although the above-mentioned topic is well known and also defined in European standards, in the literature full-scale data are lacking, which are useful to validate the numerical codes required in the certification process and are used in train structural dimensioning. In this respect, an extensive full-scale experimental campaign was planned for observing as many test conditions as possible, such as single passages of different trains, two train crossing, different tests speed, and different tunnel characteristics. In detail, the understanding of the pressure wave generation and transmission is deeply enhanced by studying the pressure evolution both on board and at trackside, considering both single train passages or two trains crossings and having the possibility to compare aerodynamic loads on sealed and unsealed trains. Furthermore, the position of sensors, the speed of the train, and the initial conditions within the tunnel have been proven to be fundamental parameters for properly estimating the pressure loads on trains.