This work was concerned with the aerodynamic and acoustic performance of small axial flow refrigerator fans. Relevant literature focusing on the principles of fan noise generation and fan system elements that contribute to noise generation was identified and discussed. A plenum chamber test rig was designed and constructed following ISO 10302-1. A range of 200 mm diameter pressed aluminium Air-Drive fans, commonly used in commercial refrigerator systems, were evaluated using the test rig. It was found that the performance of these fans was highly dependent upon the impedance of the system in which they are installed. Indications of rotating stall under high load were observed and shown to significantly increase the noise output of the fan without greatly affecting the air moving capability. A series of novel colour map plots are presented, which allow for a visual interpretation of fan performance over a wide range of operating conditions. A fanpack developed by Wellington Drive Technologies Ltd was evaluated. This fanpack was found to generate significant tonal noise. The design of the fanpack was evaluated and improvements are suggested. Prototype fans were developed from the fanpack based on promising concepts presented in the literature. The performance of four prototype fans was evaluated. The results were disappointing, but proof of concept was demonstrated.

The purpose of this work was to investigate a permanent magnet synchronous machine which will be produced by an industry partner of the Institut für Stromrichtertechnik und Elektrische Antriebe (ISEA) an institute of the Rheinisch Westfälisch Technische Hochschule - Aachen, Germany (RWTH). The machine manufacturer noted certain abnormalities with the frequency spectrum produced by an electric machine that they were developing; this problem was brought to ISEA in order to be investigated. My work continues the work of my supervisor, Dipl.- Ing Matthias Bösing, and seeks to further examine the machine for a much wider range of operating points, determine the relationship between current amplitude, harmonics, control angle and rotor position on radial force components of the machine and therefore stresses on the stator; which are the primary causes of electrical machine noise. Rather than investigate acoustic issues in particular, the study was limited to the study of electromagnetically generated radial force ripple, which is the cause of stator deflection modes and therefore the emission of sound waves. The primary results of this thesis researched the operation of a permanent magnet synchronous machine and described its behavior with regards to force, torque, and force and torque ripple and their spectrums versus numerous parameters, including control angle, secant current and rotor position. Next, the work used provided data, literature and the simulation results for this thesis in order to deconstruct the operation regions of the particular machine and therefore link the causes of particular noise spectral components to the operation of the machine. From this it was possible to identify potential ways to eliminate these areas of noise. Following this, the thesis examined a particular abnormality in the torque and force waveforms produced by the machine and devised actions which could correct this abnormality. After identifying this asymmetry, the work explored how to choose an optimal control strategy for eliminating particular harmonics based on the simulated operating points and a desired command torque. Finally, the research built on the previous work by supplementing the method of current harmonic injection for eliminating radial force harmonics in this machine, with a method of determining an optimal operating point before the injection currents are calculated.