Method and apparatus for independently varying airflow and noise generation of a fan

A fan design method and fan structure is described, enabling independent control of the volume of airflow and the amount of noise produced. The noise produced is a close approximation to a pleasing red noise spectrum, and is generated solely by the interaction of the rotating fan blades with a petal assembly or a fan enclosure in several embodiments. A petal assembly may be positioned at varying spacings behind the rotating fan blades to control the level of noise production with minimal effect on the volume of airflow. Various aspects of the fan blade configuration, such as the blade pitch, camber, span, chord, etc., may be manipulated to control the ratio of airflow volume to the amount of noise produced.