Abstract
It has been known for many years that the broadband noise of rotating machinery is dependent on the condition of the boundary layers on the lifting surfaces. Designs with high efficiencies and clean flow have mainly produced low noise levels. These units have generally used high technology blading, with low inlet velocities and minimal separated flow.
In the application of machines in industry, however, many are subject to inlet flow distortion and turbulence. These produce changes to the flow pattern around the blades which may have a relatively insignificant effect on the aerodynamics of the machine but almost completely destroy its acoustic performance.
The design method described by Hay, Metcalfe and Reizes (
Thus low-response blading can be used for those installations whose flow conditions cannot be improved.
This method is further developed in this paper using some correlations from McKenzie's work (
The application of the method to the design of a low noise fan in the presence of a ±10 per cent perturbation on inlet velocity is given in way of illustration of the approach.
In Part 2 of this paper (to be published later) it is hoped to demonstrate the validity of the design philosophy presented here with test results from fans designed according to this philosophy.
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