Fan assembly and method for reducing fan noise

Details Fan assembly and method for reducing fan noise Fan assembly and method for reducing fan noise

1994-03-09

1995-02-14

Look, Edward K.

Rotary kinetic fluid motors or pumps

Method of operation

415102, 415119, 416200R, 416203, F04D 2966

Patent

active

053889568

ABSTRACT:
A fan assembly has a fan motor and first and second generally identical and spaced apart fans each rotationally attached to the fan motor to turn at the same rotational speed. Each fan has an equal number of generally identical fan blades and produces noise including a tone having a frequency equal to its rotational speed times its number of fan blades. The fan blades of one fan are angularly offset at a relative phase angle with respect to the fan blades of the second fan such that the tones of each fan generally cancel each other out. An equation is provided for a ducted fan assembly relating the relative phase angle to the rotational speed of the fans, the number of fan blades of each fan, the geometry of the duct, and the speed of sound in air within the duct.

REFERENCES:
patent: 3856431 (1974-12-01), Tucker
patent: 4746266 (1988-05-01), Kirchner et al.
patent: 4887940 (1989-12-01), Todoroki et al.
patent: 5221185 (1989-06-01), Pla et al.
"Active Control of Sound", by P. A. Nelson et al., Institute of Sound and Vibration Research, The University, Southampton,, U.K., Academic Press, 1992, pp. 122-126.
Applicant's attached statement entitled "Microwave Oven Fan Assembly", offered for sale more than one year prior to filing date.

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