Aerofoils--Noise

Broadband self-noise generated by rotating blades in a subsonic ducted propfan is studied for a hard walled cylindrical duct in a uniform flow. An expression for the induct sound power radiated by three self-noise mechanisms is derived: the Turbulent-Boundary-Layer-Trailing-Edge noise, the Laminar-Boundary-Layer-Vortex-Shedding noise and the Trailing-Edge-Bluntness noise. The present theory uses NASA's self-noise prediction methodology for an isolated airfoil. An efficient method of programming is presented which reduces the time of computation for multiple radial modes. The results obtained are presented, discussed and compared with Blade-Tip-Boundary-Layer fan noise predictions obtained using the SDPF code developed at FAU. The most important parameters which affect self-noise are found to be the angle of attack, the effective Mach number and the chord length of the blade. For high angles of attack, the TBL-TE noise gives significant amount of sound power especially at the low frequencies. For low effective Mach numbers and at certain angles of attack, the LBL-VS noise can have high power levels in the mid and high frequencies. Trailing edge bluntness noise appeared to give insignificant amounts of energy over the whole spectrum compared to the other self-noise mechanisms.

With the increase of air traffic and the introduction of larger aircraft and therefore larger engines, the noise generated by aircraft engines have become of greater importance. In order to address these problems, noise prediction codes must be developed in order to better understand the noise generating process. This thesis addresses important issues related to broadband self-noise from ducted fans based on the prediction model developed by Glegg and Jochault [1]. By addressing issues regarding the prediction of broadband self-noise from an isolated airfoil with the observer in the far field directly overhead (at 90° above), improvements can be made to Glegg and Jochault's approach for ducted fans. The prediction of broadband self-noise at 90° above a single airfoil is done by considering boundary layer parameters, the results obtained are compared with theoretical approaches, as well as experimental results obtained by Brooks [2] in order to verify its accuracy.