Abstract. The disruptive potential of floating wind turbines has attracted the interest of both the industry and the scientific community. Lacking a rigid foundation, such machines are subject to large displacements whose impact on aerodynamic performance is not yet fully explored. In this work, the unsteady aerodynamic response to harmonic-surge motion of a scaled version of the DTU 10 MW turbine is investigated in detail. The imposed displacements have been chosen representative of typical platform motion. The results of different numerical models are validated against high-fidelity wind tunnel tests specifically focused on the aerodynamics. Also, a linear analytical model relying on the quasi-steady assumption is presented as a theoretical reference. The unsteady responses are shown to be dominated by the first surge harmonic, and a frequency domain characterization, mostly focused on the thrust oscillation, is conducted involving aerodynamic damping and mass parameters. A very good agreement among the codes, the experiments, and the quasi-steady theory has been found, clarifying some literature doubts. A convenient way to describe the unsteady results in a non-dimensional form is proposed, hopefully serving as a reference for future works.
The flow-field around a “common” European heavy truck, equipped with several different trailer devices, is investigated using steady and unsteady simulations.\ud
This work demonstrates how with simple devices added on the trailer it is possible to strongly decrease the aerodynamic drag over 10%, with an increase of overall dimensions below 1% without any change to the load capacity of the trailer.\ud
Several devices, installed on the trailer, are tested on a target vehicle and the shape of the “airbag”, the “fin”, the “boat tail” and the “front-rear trailer device” has been optimized to achieve the maximum in drag reduction in front wind. The performance of the optimized devices are tested also in cross wind conditions with the yaw angle varying from 0° to 30°.\ud
The truck equipped with the front-rear trailer device is also investigated using time variant simulation with yaw angle of 0°, 5°, 10°.\ud
Detached eddy simulation (DES) with one equation Spalart-Allmaras as turbulence model is used to perform the analysis of the unsteady flow; the two equation k-ω SST turbulence model is selected for the steady-state RANS simulations. The unsteady simulations are performed using computational meshes on the order of 40 million of elements while RANS simulation are done with mesh of 10 million of elements
Many studies have been carried out to optimize the aerodynamic performances of a single car or a single vehicle. In present days the traffic increases and sophisticated technologies are developing to guarantee the drivers safety, to minimize the fuel consumption and be more environmentally friendly. Within this research area a new technique that is being studied is Platooning: this means that different vehicles travel in a configuration that minimizes the aerodynamic drag and therefore the fuel consumption and the longitudinal space. In the present study platoons with different vehicles and configurations are taken into account, to analyze the influence of car shape and relative distance between the vehicles. The research has been carried out using CFD techniques to investigate the different flow fields around different platoons, while wind tunnel tests have been used to validate the results of the CFD simulations. The results show that vehicles with an estate back, like station wagons and sport utility vehicles, give a drag reduction up to more than 50% when running in platoon, while vehicles with a fast back, like sedan, that have better performances than sharp-back cars when running isolated, cannot reach the highest drag reduction obtained by the estate back cars. Trucks show negligible drag reduction when running in platoon with other cars, while the vehicles behind the truck experience a very low drag force. The distance between vehicles plays a very important role since smaller distances between the cars give lower aerodynamic forces, and may be minimized only by developing better technologies to control and maintain the position of the vehicle in the platoon without any risk for the passengers
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