Sviluppo di un sistema per la riproduzione degli scarichi di modelli di vetture da corsa per galleria del vento

The goal of the aerodynamic development of a racing car is to reach higher and higher performance levels. An accurate representation of the aerodynamics of the car in the wind tunnel is a fundamental condition to succeed in this task. Any detail of both the wind tunnel facility and the wind tunnel model can contribute to make the simulation as faithful as possible to the reality. Among all aspects, the presence of the exhaust flows surely influences the flow field around the car. Hence, the aim of this study, performed in collaboration with Dallara, was to develop a system for the reproduction of the exhausts of race car models for wind tunnels. After a general introduction regarding wind tunnels in Chapter 1, with particular attention to the Dallara wind tunnel, the issues related to the reproduction of the exhaust flows in a closed-circuit wind tunnel are discussed in Chapter 2. Due to the necessity of using a cold airflow, an analysis of the theoretical background inherent the similitude between the hot exhaust of the real car and the cold exhaust of the wind tunnel model has been conducted. In addition, the target mass flow rate of the exhaust system is set according to some preliminary calculations. In Chapter 3, the previous exhaust system of Dallara is analysed. An Airmover (also called Air Amplifier) is installed in the exhaust pipe of the wind tunnel model: by exploiting the Coandă effect, it generates the required mass flow rate by amplifying up to 20 times a small amount of compressed air (supplied by a compressor external to the wind tunnel test section). However, several limitations have been encountered: thus in Chapter 4 new components have been proposed, tested and implemented. A more performant type of Airmover has been investigated, a proportional valve piloted by a PID controller has been installed for each Airmover and polyurethane flexible hoses have been installed in the compressed air line. In Chapter 5, the new system has been set up and verified during a wind tunnel test session performed with the model of a Le Mans Prototype racing car. At the same time, the effects of the exhaust flows on the aerodynamics of the car were analysed. Finally, in Chapter 6 additional tests at a dedicated bench have been carried out, in order to analyse the behaviour of the system for different layout and geometries of the exhaust pipes of the wind tunnel model.