Noise reduction apparatus and jet fan
According to one embodiment, a noise reduction apparatus includes a speaker, a generator and a controller. The speaker outputs control sound. The generator generates self-excited sound. The controller controls a phase and an amplitude of the control sound to reduce noise generated from a noise source, based on the control sound and the self-excited sound that is synchronized with the control sound.
1. A noise reduction apparatus, comprising:
a speaker that outputs control sound;
a generator that generates self-excited sound; and
a controller that controls a phase and an amplitude of the control sound to reduce noise generated from a noise source, based on the control sound and the self-excited sound that is synchronized with the control sound by a lock-in phenomenon.
2. The apparatus according to claim 1 , wherein the noise is generated by rotation of a rotor blade, and
wherein the generator has a shape of a generation structure of the self-excited sound which is determined based on a flow velocity caused by rotation of the rotor blade, a rotation velocity of the rotor blade, and a number of blades of the rotor blade.
3. The apparatus according to claim 2 , wherein the generator has a cavity structure, and
the speaker is arranged at the noise source side relative to the generator.
4. The apparatus according to claim 3 , wherein the cavity structure is adjusted to satisfy
k/d=B/ 60,
wherein d is a length of the cavity structure parallel to an air supply direction, B is a number of blades of the rotor bade, and k is a constant number based on the flow velocity and the rotation velocity.
5. The apparatus according to claim 2 , wherein
the generator has an edge structure, and
the generator is arranged at the noise source side relative to the speaker.
6. The apparatus according to claim 5 , wherein the edged structure is adjusted to satisfy
k/ 2 d=B/ 60,
wherein d is a distance between a distal end of the edge structure and a member present on an extension of the distal end, B is a number of blades of the rotor bade, and k is a constant number based on the flow velocity and the rotation velocity.
7. The apparatus according to claim 1 , wherein a plurality of pairs of the generator and the speaker are arranged along a circumferential direction of an inner wall of a duct including the noise source, and in front of or behind the noise source in a tube axis direction of the duct.
8. A jet fan, comprising:
a tubular housing;
a rotor blade arranged in the tubular housing and including a plurality of blades;
a stator blade straightening airflow generated by rotation of the rotor blade; and
a plurality of noise reduction apparatuses arranged in a circumferential direction of an inner wall of the housing and in front of or behind the rotor blade in a tube axis direction of the tubular housing,
at least one of the plurality of noise reduction apparatuses comprising:
a speaker that outputs control sound;
a generator that generates self-excited sound; and
a controller that controls a phase and an amplitude of the control sound to reduce noise generated from a noise source, based on the control sound and the self-excited sound that is synchronized with the control sound by a lock-in phenomenon.