A review of selected experimental investigations of Curle's theory

Abstract

Curle published an article, widely known as Curle's theory, in which he sought to extend the theory of Sir James Lighthill on aerodynamic noise generation to include the effects of rigid boundaries. His theory has been accepted as mathematically correct and has been widely referenced, but it remains without experimental verification. A review of five selected articles published over a span of 35 years reporting experimental investigations of Curle's theory will be presented. The review will show that, in cases where the source is compact, Curle's theory predicts radiated sound power about 5 dB too high, while in non-compact cases Curle's theory predicts radiated sound power about 5 dB too low. These observations are readily explained and the explanation suggests why Curle's theory has not been experimentally verified but, more importantly, what may require further consideration. In the cases investigated Curle's failure to consider source structure is shown to be responsible for the observed disparities. The disparate results may be explained if in the case of non-compact wave numbers the dominant noise source is a surface source distribution proportional to the square of the dimensionless wave number, while at compact wave numbers the latter source tends to insignificance and a less efficient leading edge dipole independent of the dimensionless wave number is then dominant.