Aeroacoustic noise produced by an aerofoil.
Thesis DisciplineMechanical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis describes an investigation into the aeroacoustic noise produced by an aerofoil using experimental, computational and theoretical methods. Several different types of aeroacoustic noise generation mechanisms and the parameters which affect these mechanisms were identified and investigated. The aerofoils used' in this investigation all had chord lengths of 100mm and had a maximum thickness between 18mm and 30mm. Experimental testing was undertaken in the low noise wind tunnel in the Department of Mechanical Engineering at the University of Canterbury with the aerofoils mounted at the exit of the tunnel. Airflow speeds from 10m/s to 40m/s and a range of angles of incidence were investigated. A number of modifications were made to reduce the noise and improve the operation of the wind tunnel. Different methods of measuring the aeroacoustic noise produced by an aerofoil were also investigated. The theory of aeroacoustic noise generation is described and the effect of a scattering surface on the efficiency of these aeroacoustic noise sources was investigated. A number of different mechanisms by which an aerofoil produces aeroacoustic noise were identified. These mechanisms were divided into three main categories: (1) blunt trailing edge aerofoil noise (2) sharp trailing edge aerofoil noise and (3) stalled aerofoil noise. The effect of air temperature on the production of aeroacoustic noise was also investigated. It was found that in most instances air temperature would have little effect on aeroacoustic noise generation. An extensive study of the aeroacoustic noise produced by a number of different aerofoils was undertaken. Modelling of the airflow over the aerofoils was used to determine the mechanism by which aeroacoustic noise is produced. Several different aeroacoustic noise generation mechanisms were identified. Theoretical models were also used to model the aeroacoustic noise produced by the aerofoils. Several treatments to reduce the level of aeroacoustic noise produced by an aerofoil were investigated. The treatments reduced the aeroacoustic noise produced by an aerofoil with varying degrees of success. A method for measuring the aeroacoustic noise produced by car roof racks mounted on the roof of a vehicle using a relatively small wind tunnel was established. The noise level produced by a roof rack installed 011 the roof of a vehicle measured using this technique compared favourably with measurements made on a full vehicle in a large wind tunnel. The method shows promise as a low cost method of accurately measuring the aeroacoustic noise produced by roof racks installed on a vehicle roof.