An open rotor has been considered as a process for converting
an unsteady velocity inflow into sound radiation. With the aid of
crude assumptions 'aero-acoustic transfer functions' have been
defined theoretically for both discrete frequency and broad band
noise. An experimental study of the validity of these transfer
functions has yielded results which show good agreement at discrete
frequencies though slightly less good for broad band noise.
Agreement in both cases holds over three or more decades of the
The experimental work involved has necessitated the development of a rotating hot wire anemometry system. A single hot wire probe
has been mounted in the nose-cone of the rotor and used to quantify
fluctuations in the airflow onto a single rotor blade for the transfer
function results. Further theoretical analysis has revealed that the
sound fieid can be expressed in terms of blade-to-blade correlations
in the airflow, and results from two probes rotating simultaneously
have been modelled mathematically and inserted in the theory.
Preliminary results show.encouraging agreement with experimental
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.