In this article a combustor burning hydrogen and air in mild regime is numerically studied by means of computational fluid dynamic simulations. All the numerical results show a good agreement with experimental data. It is seen that the flow configuration is characterized by strong exhaust gas recirculation with high air preheating temperature. As a consequence, the reaction zone is found to be characteristically broad and the temperature and concentrations fields are sufficiently homogeneous and uniform, leading to a strong abatement of nitric oxide emissions. It is also observed that the reduction of thermal gradients is achieved mainly through the extension of combustion in the whole volume of the combustion chamber, so that a flame front no longer exists ('flameless oxidation'). The effect of preheating, further dilution provided by inner recirculation and of radiation model for the present hydrogen/air mild burner are analyzed.

The demand for quieter vehicles is pushing manufacturers of components for the automotive industry to seek for solutions to reduce the overall noise emissions. The cooling fan makes no exception: the aerodynamic interaction of the blades with the incoming flow generates turbulence and pressure fluctuations which ultimately translate into noise generation. A variety of expedients have been introduced to limit the produced noise, but no univocal solution has been found. In modern research, Computational Fluid Dynamics (CFD) has been successfully applied to blades and fans for both the flow and acoustic field derivation. By including the acoustic field, researchers have been able to predict the effect of changes in the blade geometry on the overall sound emission. This work reports a conjugate numerical-experimental study of a reference profile in different flow conditions, in order to validate the CFD acoustic prediction and to lay the basis for improved candidates able to lower the fan-generated noise.

Although noise from large fans has been extensively studied by the scientific community, few experimental studies have been performed on small-scale fans, where aerodynamic effects due to low Reynolds numbers needs be taken into account. For this reason, some preliminary experimental investigations have been carried out on cooling fans for automotive applications. The experimental campaign has been focused on the characterization of the flow outlet first, using a static Pitot on a 5.5-inch five-bladed fan, with and without its protective grid. After this preliminary phase, simultaneous measurements of velocity with hot-wire anemometry (HWA) and pressure fluctuations with microphones have been also carried out, the HWA probe being located downstream and two microphones positioned in the nearfield and far-field of the fan. The fan has been also studied at different working conditions, varying the rotational speed and applying specific fine grids at the intake, in order to well reproduce the presence of the cooler. Analyses in the time and frequency domain have been performed on the measured data, including cross-correlation between pressure and velocity signals, in order to find the main driving mechanisms that are related to the noise generation.

Electrical and fossil fuel powered vehicles require to reject some form of heat produced as a byproduct of their operating principle. This task is performed by radiators, typically equipped with axial flow fans to maximize the specific processed flow rate. These fans, as well as all the other fans that typically equip the vehicles (e.g., for HVAC purposes), are required to be very efficient and to produce a minimum level of noise. In this framework it is of crucial importance to adopt all the tools that can help in understanding the source of inefficiency and noise. This work presents the adoption of Computational Fluid Dynamics (CFD) as a possible tool for the investigation of the fluid dynamics of an axial flow fan. In order to let CFD become routinely employed, a sequence of validation steps is required by industries. In this work, two different CFD tools (ANSYS-CFX and OpenFOAM-v2006) are employed and the results of the investigation are compared to experimental data for assessing the reliability and the accuracy of each of these tools. Experimental data are obtained with two test benches: one build in compliance with ANSI/AMCA standards for airflow performance evaluation and one ad hoc developed for PIV measurements (i.e. flow field visualization). The capability of the CFD softwares of correctly replicating the fan performance and flow field even in this complex set-up (due to the loose constraints of the fluid flow) is shown both with steady and transient simulations.