초록 ▼

A method and apparatus for reducing a selected tonal noise generated by a fan operating in a non-uniform flow by locating at least one obstruction in the non-uniform flow such that the at least one obstruction generates a noise that is out of phase with the selected tonal noise. The noise generated

A method and apparatus for reducing a selected tonal noise generated by a fan operating in a non-uniform flow by locating at least one obstruction in the non-uniform flow such that the at least one obstruction generates a noise that is out of phase with the selected tonal noise. The noise generated by the at least one obstruction interferes with the selected tonal noise, thus reducing the selected tonal noise. It is also contemplated to use additional obstructions to reduce other tonal noises generated by the fan.

대표청구항 ▼

1. An axial flow fan comprising: a rotor rotatable about an axis, the rotor having a number of blades and a radius, the number of blades generating a number of tonal noises when the rotor is rotating in a non-uniform flow, the number of tonal noises each having a phase and a magnitude; andat least o

1. An axial flow fan comprising: a rotor rotatable about an axis, the rotor having a number of blades and a radius, the number of blades generating a number of tonal noises when the rotor is rotating in a non-uniform flow, the number of tonal noises each having a phase and a magnitude; andat least one obstruction being positioned at a first distance radially away from the axis and at a second distance axially away from the rotor, the first distance being less than the radius,the at least one obstruction being positioned around the axis such that the at least one obstruction generates a second noise, when in the non-uniform flow, having a phase that is out of phase with the phase of one of the number of tonal noises,the second distance being selected such that a magnitude of the second noise is substantially equal to the magnitude of the one of the number of tonal noises,the at least one obstruction being shaped such that an interaction of the at least one obstruction with the rotor has a low harmonic content rate, andthe at least one obstruction being a sinusoidal obstruction forming a ring, the sinusoidal obstruction having a number of lobes. 2. The axial flow fan of claim 1, wherein the number of lobes of the sinusoidal obstruction is equal to the number of blades of the rotor. 3. The axial flow fan of claim 1, wherein the number of lobes of the sinusoidal obstruction is equal to an integer multiple of the number of blades of the rotor. 4. An axial flow fan comprising: a rotor rotatable about an axis, the rotor having a number of blades and a radius, the number of blades generating a number of tonal noises when the rotor is rotating in a non-uniform flow, the number of tonal noises each having a phase and a magnitude; andat least one obstruction being positioned at a first distance radially away from the axis and at a second distance axially away from the rotor, the first distance being less than the radius,the at least one obstruction being positioned around the axis such that the at least one obstruction generates a second noise, when in the non-uniform flow, having a phase that is out of phase with the phase of one of the number of tonal noises,the second distance being selected such that a magnitude of the second noise is substantially equal to the magnitude of the one of the number of tonal noises,the at least one obstruction being shaped such that an interaction of the at least one obstruction with the rotor has a low harmonic content rate, andthe at least one obstruction being generally trapezoidal in shape. 5. An axial flow fan comprising: a rotor rotatable about an axis, the rotor having a number of blades and a radius, the number of blades generating a number of tonal noises when the rotor is rotating in a non-uniform flow, the number of tonal noises each having a phase and a magnitude;at least one obstruction being positioned at a first distance radially away from the axis and at a second distance axially away from the rotor, the first distance being less than the radius,the at least one obstruction being positioned around the axis such that the at least one obstruction generates a second noise, when in the non-uniform flow, having a phase that is out of phase with the phase of one of the number of tonal noises,the second distance being selected such that a magnitude of the second noise is substantially equal to the magnitude of the one of the number of tonal noises, andthe at least one obstruction being shaped such that an interaction of the at least one obstruction with the rotor has a low harmonic content rate; andat least one other obstruction being positioned at a third distance radially away from the axis and at a fourth distance axially away from the rotor;the at least one other obstruction being positioned around the axis such that the at least one other obstruction generates a third noise, when in the non-uniform flow, having a phase that is out of phase with the phase of another of the number of tonal noises,the fourth distance being selected such that a magnitude of the third noise is substantially equal to the magnitude of the other of the number of tonal noises, andthe at least one other obstruction being shaped such that an interaction of the at least one other obstruction with the rotor has a low harmonic content rate. 6. An axial flow fan comprising: a rotor rotatable about an axis, the rotor having a number of blades, the number of blades generating a number of tonal noises when the rotor is rotating in a non-uniform flow, the number of tonal noises each having a phase and a magnitude;at least one first obstruction being positioned at a first distance radially away from the axis and at a second distance axially away from the rotor; andat least one second obstruction being positioned at a third distance radially away from the axis and at a fourth distance axially away from the rotor;the at least one first obstruction being positioned around the axis such that the at least one first obstruction generates a second noise, when in the non-uniform flow;the at least one second obstruction being positioned around the axis such that the at least one second obstruction generates a third noise, when in the non-uniform flow;the combination of the second and third noises resulting in a fourth noise having a phase that is out of phase with the phase of one of the number of tonal noises and a magnitude that is substantially equal to the magnitude of the one of the number of tonal noises. 7. The axial flow fan of claim 6, wherein at least one of the at least one first obstruction and the at least one second obstruction is shaped such that an interaction of the at least one of the at least one first obstruction and the at least one second obstruction with the rotor has a low harmonic content rate. 8. The axial flow fan of claim 6, wherein the at least one first obstruction and the at least one second obstruction are shaped such that an interaction of the at least one first obstruction and the at least one second obstruction with the rotor has a low harmonic content rate. 9. The axial flow fan of claim 6, further comprising: at least one third obstruction being positioned at a fifth distance radially away from the axis and at a sixth distance axially away from the rotor; andat least one fourth obstruction being positioned at a seventh distance radially away from the axis and at an eighth distance axially away from the rotor;the at least one third obstruction being positioned around the axis such that the at least one third obstruction generates a fifth noise, when in the non-uniform flow;the at least one fourth obstruction being positioned around the axis such that the at least one fourth obstruction generates a sixth noise, when in the non-uniform flow;the combination of the fifth and sixth noises resulting in a seventh noise having a phase that is out of phase with the phase of another one of the number of tonal noises and a magnitude that is substantially equal to the magnitude of the other of the number of tonal noises. 10. A fan comprising: a rotor rotatable about an axis, the rotor having a number of blades and a radius, the number of blades generating a number of tonal noises, the number of tonal noises each having a phase and a magnitude;a housing housing the rotor, the housing defining an outlet of the fan, the outlet being generally tangential to the rotor; andat least one obstruction being positioned relative to the rotor such that the at least one obstruction is disposed in an air flow caused by the rotor when the rotor rotates, the at least one obstruction being disposed at a distance radially away from the axis that is less than the radius of the rotor,the at least one obstruction being positioned in the air flow such that the at least one obstruction generates a second noise, having a phase that is out of phase with the phase of one of the number of tonal noises, anda distance between the at least one obstruction and the rotor being selected such that a magnitude of the second noise is substantially equal to the magnitude of the one of the number of tonal noises. 11. The fan of claim 10, wherein the at least one obstruction is disposed about the axis, the distance between the at least one obstruction and the rotor is a first distance axially away from the rotor, and the distance radially away from the axis is a second distance radially away from the axis. 12. The fan of claim 11, further comprising: at least one other obstruction being positioned at a third distance radially away from the axis and at a fourth distance axially away from the rotor;the at least one other obstruction being positioned around the axis such that the at least one other obstruction generates a third noise having a phase that is out of phase with the phase of another of the number of tonal noises,the fourth distance being selected such that a magnitude of the third noise is substantially equal to the magnitude of the other of the number of tonal noises. 13. The fan of claim 10, wherein the at least one obstruction is shaped such that an interaction of the at least one obstruction with the rotor has a low harmonic content rate. 14. The fan of claim 10, wherein the at least one obstruction is a number of equally spaced obstructions disposed in a circle. 15. The fan of claim 14, wherein the number of obstructions is equal to one of: the number of blades of the rotor, andan integer multiple of the number of blades of the rotor. 16. The fan of claim 14, wherein the number of obstructions is equal to one of: the number of blades of the rotor minus one,the number of blades of the rotor plus one,an integer multiple of the number of blades of the rotor minus one, andan integer multiple of the number of blades of the rotor plus one. 17. The fan of claim 10, wherein the at least one obstruction is positioned upstream of the rotor. 18. The fan of claim 17, further comprising a duct assembly connected to the housing about the axis for receiving air going to the rotor; wherein the at least one obstruction is disposed in the duct assembly. 19. The fan of claim 10, wherein the fan is a centrifugal fan. 20. The fan of claim 10, wherein the at least one obstruction is an obstruction forming a ring, the obstruction having a number of lobes; and wherein the number of lobes is equal to one of: the number of blades of the rotor, andan integer multiple of the number of blades of the rotor. 21. The fan of claim 10, wherein the at least one obstruction is an obstruction forming a ring, the obstruction having a number of lobes; and wherein the number of lobes is equal to one of: the number of blades of the rotor minus one,the number of blades of the rotor plus one,an integer multiple of the number of blades of the rotor minus one, andan integer multiple of the number of blades of the rotor plus one.