JP2010007632A - Vortex flow blower - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vortex flow blower reduced in noise. <P>SOLUTION: A vortex flow blower comprises a casing 12 provided with an arc-shaped still flow path 20, and an impeller 14 provided with a plurality of blades 17 corresponding to the still flow path 20, wherein the casing 12 is provided with an intake flow path 21 communicated with one end part of the still flow path 20, and a discharge flow path 22 communicated with the other end part. To an intake side conducting surface 25 forming one end surface of the still flow path 20 and a discharge side conducting surface 26 forming the other end surface of the still flow path 20, scattered reflection parts 30a and 30b are provided, respectively. The scattered reflection parts 30a and 30b scatter blower-related sound within the still flow path 20 to prevent the still flow path 20 from generating resonance phenomena. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a vortex blower that continuously feeds air by applying kinetic energy to the air by rotation of an impeller.

  The vortex blower, that is, the vortex blower, includes a casing in which an arcuate stationary flow path is formed, and an impeller provided with a plurality of blades, that is, blades at predetermined intervals in the circumferential direction corresponding to the stationary flow path. And the impeller is rotatably mounted on the casing. The casing is provided with a suction channel that communicates with one end of the static channel and a discharge channel that communicates with the other end of the static channel. When the impeller is rotated, the air flowing in from the suction passage is accelerated between the blades of the impeller from the inner periphery to the outer periphery, flows into the stationary passage, and guides the stationary passage in the circumferential direction. Then, the process of decelerating and increasing the pressure and the process of flowing again between the blades are repeated, and the inflowing air is pressurized by being repeatedly given kinetic energy by the impeller. The pressurized air is discharged to the outside through the discharge channel. The casing is provided with a partition partitioning the opposite ends of the stationary flow path so as to face the blade. The partition separates the opening on the impeller side of the suction flow path and the discharge flow path. And the discharge channel are not in direct communication.

  The vortex blower with such a structure is widely used as a relatively small-capacity air power source in general industrial machines because the pressure coefficient representing the work per unit impeller outer diameter is higher than that of a centrifugal blower and can be reduced in size and weight. Has been. As a usage form of the vortex blower, there are a case where positive pressure air discharged from the discharge passage is used and a case where negative pressure generated in the suction passage is used. For example, when vortex blowers are used to remove machine tool chips, positive pressure air is used. When vortex blowers are used to suck and convey workpieces, negative pressure air generated in the suction flow path is used. Is done.

As described in Patent Document 1, such a vortex blower has a shroud provided with an annular groove facing a stationary flow path, and the annular groove is circumferentially formed by a plurality of blades provided in the shroud. There is a type that is divided at predetermined intervals. Furthermore, as described in Patent Document 2, the vortex blower includes a type in which a stationary flow path is also formed on the inner surface of a casing cover attached to the casing via an impeller. As for the form of the blade, the blade is a straight type that extends straight in the radial direction of the impeller, and the blade inner surface is curved in the rotational direction and the tip surface of the blade is bent along the radial direction to form the blade in a three-dimensional shape. There is a curved type or the like.
Japanese Patent No. 2680136 JP-A-4-228899

  In the vortex blower, it is an important solution to suppress noise generation during driving. The noise of the vortex blower includes a flow noise having a relatively low frequency due to the turbulence of the flow and a wind noise caused by pressure fluctuation due to the interference between the impeller blade and the partition wall. The wind noise has a frequency characteristic composed of noise with a frequency obtained by multiplying the number of blades by the number of rotations and a high-order frequency that is an integral multiple of the frequency. The noise level is higher than that of the above-mentioned flow sound. In order to reduce the noise of the wind, it is necessary to reduce the wind noise. The wind noise generation mechanism has conventionally been thought to be due to fluctuations in power generated due to pressure interference between the blade and the partition wall, thereby generating sound.

  In order to reduce wind noise, various frictional sound absorbers using a sound absorbing material have been provided in the suction flow path and the discharge flow path so far, and are effective for reducing wind noise at a specific frequency. Resonant sound absorbers have been proposed for eddy current blowers. In the vortex blower described in Patent Document 2, wind noise is reduced by disposing a sound absorbing material on the inner surface of the opening and the partition wall on the impeller side of the suction flow channel and the discharge flow channel.

  In the vortex blower described in Patent Document 1, noise is reduced by providing a guide facing the suction channel and the opening of the discharge channel in the partition wall, and the guide on the suction channel side has a tip at the tip. The guide is inclined from the outer peripheral portion of the impeller so as to interfere with the blade, and the guide on the discharge channel side is inclined so that the tip thereof interferes with the blade from the inner peripheral portion of the impeller. Thereby, the flow of air entering the stationary flow path from the suction flow path and the flow of air from the stationary flow path toward the discharge flow path are smoothed to reduce noise generation. In this way, conventionally, the tip surface of the guide provided on the partition wall is inclined to increase the pressure fluctuation time generated by the interference between the blade and the partition wall, so that the pressure is gradually changed, or the generated frequency Measures have been taken to reduce the noise and silence of the vortex blower by attenuating the sound with a sound-absorbing material and a resonance type sound absorber for high noise, but there are limits to reducing the noise of the vortex blower there were. In particular, there is a problem that the dominant frequency of wind noise does not decrease.

  In order to investigate this reason, pure sound of a single frequency is caused to flow in the arc-shaped static flow path of the vortex blower, and the microphone is moved along the static flow path between the suction flow path side and the discharge flow path side and collected. A sound experiment was conducted. As a result, at a specific frequency, a waveform in which the top and bottom of the amplitude were uniform and the antinodes and nodes were clearly understood was detected. When a pure tone having a frequency different from that frequency was passed through the stationary flow path, the amplitude of the waveform was not aligned, and the antinode and node of the waveform could not be distinguished. As a result, it is considered that sound of a specific frequency is acoustically resonating with the stationary flow path.

  The casing is formed with a curved suction-side guide surface to smoothly guide the air flowing from the suction flow path to one end of the static flow path, and the air discharged from the other end of the static flow path to the discharge flow path is smooth. The discharge-side guide surfaces are curved so as to be guided to each other, and each guide surface forms an end face of an arcuate stationary flow path. Therefore, it is considered that the static flow path has a resonance frequency equivalent to an air column or pipe line provided with both end faces. The resonance frequency of the pipe appears to stop and vibrate when the sound traveling wave and the reflected wave from the end face of the pipe overlap in phase. It is a state waveform and is called a standing wave. Since the standing wave is a superposition of in-phase waves, the amplitude indicating the sound pressure is amplified more than the original waveform. In this way, it is considered that the sound is amplified when the sound generated in the pipe matches the standing wave that is the resonance frequency of the pipe. Since the suction flow path and the discharge flow path are respectively provided in the casing so as to face the guide surface serving as the reflection surface, the amplified sound is directly radiated to the outside.

  The frequency of the standing wave is considered to be one-dimensional sound field when the plane wave is perpendicular to the end face like a straight pipe with a straight channel, so the end face of the pipe is blocked. In this case, the frequency of the standing wave, that is, the resonance frequency is obtained by the following equation. That is, the frequency f of the standing wave is f = (2m−1) C / (4L) where C is the speed of sound and L is the length of the straight pipe. However, m is an integer.

  The stationary flow path of the vortex blower is a curved arc-shaped flow path and has a pipe shape. Sound is reflected on the curved surfaces that form both end faces of the static flow path, and it is fixed like a straight pipe. Waves are thought to exist. To design a vortex blower so that the dominant frequency of wind noise does not match the resonant frequency of the stationary flow path, the length of the stationary flow path determined by the impeller diameter and the rotation speed of the impeller that determines the frequency of the dominant sound The number of blades of the impeller is a variable. Therefore, if the impeller is always driven at a constant rotation speed, the frequency of wind noise can be shifted from the resonance frequency of the pipe.

  However, the frequency of the wind noise is not constant because the vortex blower is controlled so as to change the rotation speed for optimal operation. Moreover, since the operating principle of the vortex blower boosts the pressure using the shearing force of the fluid, the temperature of the fluid rises due to an increase in the frictional heat of the working fluid. As a result, the resonance frequency of the stationary flow path changes. For this reason, it is difficult to reduce the prevailing sound in all operating states in which the vortex blower is used by the sound absorber or the silencer.

  Based on the elucidation of the mechanism of noise generation described above, the present invention has been found to be able to reduce the noise of a vortex blower by preventing the occurrence of a resonance phenomenon of a stationary flow path due to wind noise. Is.

  An object of the present invention is to provide a vortex blower that can reduce noise.

  The vortex blower of the present invention includes a casing provided with an arc-shaped stationary flow path, and an impeller driven by an electric motor provided with a plurality of blades at predetermined intervals in the circumferential direction corresponding to the stationary flow path. A suction flow path that is provided in communication with one end of the stationary flow path in the casing and that guides air from the outside to the stationary flow path; and A discharge channel that is provided in communication with the other end and guides pressurized air from the stationary channel to the outside, and forms one end surface of the stationary channel and air from the suction channel to the stationary channel A diffuse reflection portion provided on at least one of a suction side guide surface that guides air and a discharge side guide surface that forms the other end face of the static flow path and guides air from the static flow path to the discharge flow path; It is characterized by having.

  The vortex blower of the present invention is characterized in that the irregular reflection portions are provided on both the suction side guide surface and the discharge side guide surface. In the vortex blower of the present invention, the irregular reflection portion is a protrusion that protrudes toward the center of the flow path and extends in the air flow direction. The vortex blower according to the present invention is characterized in that the height of the protrusion is gradually lower from the center in the longitudinal direction of the protrusion toward both ends. The vortex blower of the present invention is characterized in that the side surface of the protrusion is curved in a concave shape.

  According to the present invention, since the irregular reflection part is provided on the guide surface that forms the end face of the static flow path, the wind noise that travels to the end face of the static flow path due to the fluctuation of the force generated by the interference between the blade and the partition wall hits the irregular reflection part. It is diffusely reflected and reflected in the stationary flow path in a state that is different in phase from the wind noise. As a result, even if a wind noise with a frequency that matches the resonance frequency of the stationary flow path is generated, the resonance phenomenon in the stationary flow path is prevented and the generation of dominant noise is prevented, thereby reducing the noise of the vortex blower. Can do.

  By providing the irregular reflection part on either the discharge-side guide surface or the suction-side guide surface, noise caused by wind noise can be reduced, but by providing irregular reflection parts on both guide surfaces, the noise reduction effect can be achieved. Can be increased. The pressurized air flows spirally in the static flow path and the impeller, and the flow velocity at the center of the flow path is low, so that it protrudes toward the center of the flow path and extends in the air flow direction. By forming the irregular reflection portion, it is possible to reduce the generation of noise while reducing the pressure loss in the flow path due to the irregular reflection portion. Noise is reduced while reducing the pressure loss in the flow path by gradually lowering the height of the protrusion from the central part of the protrusion in the longitudinal direction toward both ends, or by curving the side surface of the protrusion concavely. Can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 is a partially cutaway perspective view showing a vortex blower according to an embodiment of the present invention, FIG. 2 is a longitudinal sectional view showing a part of the vortex blower shown in FIG. 1, and FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. 2, FIG. 4 (A) is a front view showing the inner surface of the impeller, FIG. 4 (B) is a front view showing a modification of the impeller, and FIG. 4A is a sectional view taken along line 5A-5A in FIG. 4A, FIG. 5B is a sectional view taken along line 5B-5B in FIG. 4B, and FIG. It is sectional drawing shown.

  As shown in FIG. 1, this vortex blower has an electric motor 11 attached to a pedestal 10, and a casing 12 is assembled to the electric motor 11. As the electric motor 11, an induction motor is used, and the rotation speed is controlled by an inverter. As shown in FIG. 1 and FIG. 2, the casing 12 includes a disk portion 12 a on which the rotating shaft 13 of the electric motor 11 is rotatably mounted, a bending portion 12 b integrally provided outside the disk portion 12 a, and a bending portion. And a cylindrical portion 12c provided integrally on the outside of 12b. An impeller 14 is attached to the rotating shaft 13, and the impeller 14 is rotationally driven by the electric motor 11. The impeller 14 has a shroud 15 provided with a disk portion 15a fixed to the rotating shaft 13 and a curved portion 15b facing the curved portion 12b. An annular groove 16 is formed on the inner surface of the curved portion 15b. . The annular groove 16 is partitioned by a plurality of blades or blades 17 provided at predetermined intervals in the circumferential direction in the curved portion 15 b of the shroud 15, and a centrifugal groove 18 is formed between the blades 17. A casing cover 19 is attached to the cylindrical portion 12 c of the casing 12, and the impeller 14 is covered with the casing cover 19.

  As shown in FIGS. 1 to 3, an arcuate stationary flow path 20 is formed on the inner surface of the curved portion 12 b of the casing 12. A suction flow path 21 is provided in the casing 12 in communication with one end portion of the static flow path 20, and a discharge flow path 22 is provided in the casing 12 in communication with the other end portion of the static flow path 20. As shown in FIG. 3, the suction channel 21 has a communication opening 21 a that communicates with one end of the stationary channel 20, and the discharge channel 22 communicates with the other end of the stationary channel 20. A partition wall 23 that partitions the suction flow path 21 and the discharge flow path 22 is provided between the communication openings 21a and 22a.

  The suction passage 21 extends along the electric motor 11 so as to be substantially parallel to the rotary shaft 13, and as shown in FIG. 1, a suction pipe for connecting a suction pipe (not shown) to the tip of the suction passage 21. An opening 21b is provided, and air is supplied from the outside to the suction flow path 21 through the suction pipe. The discharge flow path 22 extends substantially along the electric motor 11 in parallel with the suction flow path 21, and a discharge port for connecting a discharge pipe (not shown) is provided at the tip. As shown in FIG. 1, a silencer 24 is incorporated in the suction passage 21, and a silencer (not shown) is also incorporated in the discharge passage 22.

  As shown in FIGS. 4A and 5A, the blade 17 is a curved type that is curved so that the front side in the rotational direction of the impeller 14 becomes a concave surface 17a. 4 (A), it is bent so as to protrude toward the front side in the rotational direction from the radial center portion 17b toward both ends in the radial direction. When the impeller 14 is rotationally driven by the electric motor 11, the air that is guided by the suction flow path 21 and flows into the impeller 14 from the stationary flow path 20 passes through the centrifugal groove 18 between the blades 17 of the impeller 14 from the inner periphery. The speed is increased toward the outer periphery and flows into the stationary flow path 20, and the process of decelerating and increasing the pressure while being guided in the circumferential direction in the stationary flow path 20 and the process of flowing into the centrifugal groove 18 again are repeated. . In this manner, while air flows spirally in the vortex blower, kinetic energy is repeatedly applied by the impeller 14 and pressurized. The pressurized air is guided to the outside through the discharge flow path 22. 2 and 3, the air flow in the impeller 14 is indicated by a solid line, and the air flow in the stationary flow path 20 is indicated by a broken line. As shown in FIGS. 4A and 5A, when the blade 17 is a curved type, the impeller 14 has rotational directionality so that the concave surface side of the blade 17 faces forward in the rotational direction. Driven by rotation.

  4 (B) and 5 (B) show an impeller 14 provided with straight blades 17, and each blade 17 extends straight in the radial direction. The impeller 14 provided with this type of blade 17 has a symmetrical shape in the rotational direction and is provided with the blade 17. Therefore, when the motor 11 is reversed, the suction flow path 21 becomes the discharge flow path, and the discharge flow The path 22 becomes a suction flow path. FIG. 5C shows a modification of the straight blade 17, and an inclined surface 17 c is provided on the back side in the rotational direction of the blade 17. Thus, as the impeller 14 of the vortex blower shown in FIGS. 1 and 2, any of the above-described types can be applied.

  6 is an enlarged sectional view taken along line 6-6 in FIG. 3, FIG. 7A is a sectional view taken along line 7A-7A in FIG. 6, and FIG. 7B is a sectional view taken along line 7B-7B in FIG. FIG. 7C is a cross-sectional view taken along line 7C-7C in FIG.

  As shown in FIGS. 6 and 7, the suction flow path 21 and the discharge flow path 22 are substantially perpendicular to the stationary flow path 20. Therefore, air flows from the suction flow channel 21 to the stationary flow channel 20 in a substantially perpendicular direction, and in order to smoothly guide the posture of the air flowing from the suction flow channel 21 to the stationary flow channel 20, The casing 12 is provided with a suction-side guide surface 25 that is curved into a spherical inner surface shape. Similarly, in order to smoothly guide the posture of the air discharged from the stationary flow path 20 to the discharge flow path 22, the casing 12 is provided with a discharge-side guide surface 26 that is curved into a spherical inner surface shape.

  The discharge-side guide surface 26 is provided with an irregular reflection portion 30 a that irregularly reflects a traveling wave of wind noise generated by pressure fluctuation caused by pressure interference between the blade 17 and the partition wall 23. The irregular reflection portion 30a is formed by a protrusion 31 protruding toward the center of the discharge side guide surface 26. The protrusion 31 extends from the end of the discharge side guide surface 26 on the stationary flow path 20 side to the communication opening 22a. It extends along the flow direction of the air to the inside of the discharge flow path 22 through. As shown in FIG. 7 (A), the apex portion that is the peak of the protrusion 31, that is, the tip portion 32, is the portion corresponding to the center portion of the stationary flow path 20, that is, the longitudinal center portion of the tip portion. It is highest from surface 26. As shown in FIGS. 7B and 7C, the height of the protrusion 31 gradually decreases from the central portion in the longitudinal direction toward both ends.

  As shown in FIG. 3, the air flow in the vortex blower advances spirally in the stationary flow path 20 and the impeller 14, so that the protrusion 31 is directed toward the center of the discharge-side guide surface 26. Even if it protrudes, it does not become resistance with respect to the flow of air, but pressure loss can be made small. Furthermore, both side surfaces 33 of the protrusion 31 are formed to be curved in a concave shape, and an increase in air resistance can be suppressed.

  As shown in FIG. 6, the suction side guide surface 25 is also provided with an irregular reflection portion 30b, and the irregular reflection portion 30b is formed by a protrusion 31 having the same shape as the irregular reflection portion 30a.

  As described above, the protrusions 31 as the irregular reflection portions 30a and 30b gradually change in height along the air flow direction and the side surfaces 33 are concavely curved or inclined surfaces. The traveling wave is irregularly reflected by each part of the protrusion 31 and the reflection condition changes, and the phase of the traveling wave and the reflected wave is shifted, and the occurrence of the resonance phenomenon in the stationary flow path 20 is prevented. In order for the vortex blower to change the discharge air volume, the rotational speed of the electric motor 11 is inverter-controlled. For this reason, it is inevitable that the impeller 14 is rotationally driven at a rotation speed at which a wind noise that matches the resonance frequency of the stationary flow path 20 is generated. Occurrence is prevented. Thereby, the noise of the vortex blower can be reduced regardless of the rotational speed of the impeller 14. Generation of noise can be suppressed by providing an irregular reflection portion on one of the suction-side guide surface 25 and the discharge-side guide surface 26, but the suppression effect can be further enhanced by providing both. In FIG. 6, a solid line arrow with a symbol S indicates a traveling wave of wind noise, and a broken line arrow with a symbol R indicates a reflected wave.

  FIG. 8 is a cross-sectional view showing a modified example of the irregular reflection portions 30a and 30b, and shows a cross-sectional shape of the same portion as the portion shown in FIG. The protrusion 31 forming the irregular reflection portions 30a and 30b has a recess 34 formed at the tip 32, the recess 34 extends in the air flow direction, and the depth of the recess 34 increases toward both longitudinal ends of the protrusion 31. It is shallow. By forming the concave portion 34 in the tip portion 32, the reflection condition by irregularly reflecting the traveling wave can be made more complicated and diversified. The diffuse reflection effect can also be obtained by making the both side surfaces 33 of the protrusion 31 into a flat inclined surface without curving into a concave shape, but the concave shape makes noise while reducing the pressure loss in the flow path. Can be reduced.

  FIG. 9 is a schematic view showing a state of a sound collection experiment for a vortex blower as a comparative example, and FIG. 9 shows an inner surface of the casing 12. The suction side guide surface and the discharge side guide surface forming the end surface of the stationary flow path 20 are spherically shaped on the back side of the partition wall 23 of the casing 12 shown in FIG. It is not done. Under such a state where a pure sound of a single frequency is passed from the speaker to the stationary flow path 20 of the vortex blower, the microphone is connected to the stationary flow path 20 as indicated by a thick line between the suction port side and the discharge port side. The sound was collected by moving along.

  FIG. 10 is a waveform diagram showing the results of a sound collection experiment for the comparative example shown in FIG. As shown in FIG. 10, in the eddy current blower as a comparative example, when a pure tone having a specific frequency was passed, a waveform in which the amplitudes were aligned and the belly and the node were clearly understood was detected. As described above, when the sound from the microphone matches the standing wave of the resonance frequency of the stationary flow path 20, the noise is amplified and radiated to the outside. On the other hand, if the irregular reflection portions 30a and 30b are provided on the suction-side and discharge-side guide surfaces 25 and 26 that form the end face of the static flow path 20, such a resonance phenomenon occurs even when sound of the same frequency is sent from the microphone. No generation was seen and no dominant frequency was generated.

  FIG. 11 is a characteristic diagram showing performance curves measured for the vortex blower of the present invention and the vortex blower as a comparative example having the casing shown in FIG. When a noise measuring device was arranged around each of the vortex blowers and noises of various frequencies were measured, as shown in FIG. 11, the vortex blower of the present invention is reduced in noise by the turbulent reflection portion as compared with the comparative example. It was confirmed.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiments of the invention. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say. For example, as described in Patent Document 2, the present invention can also be applied to a vortex blower in which stationary flow paths are formed on both sides in the axial direction of the blade. Further, as shown by a two-dot chain line in FIG. 6, a guide 23a covering the front of each communication opening 21a, 22a may be provided in the partition wall 23, and the leading end surface of the guide 23a is as described in Patent Document 1. It may be inclined to.

It is a partially cutaway perspective view showing an eddy current blower according to an embodiment of the present invention. It is a longitudinal cross-sectional view which shows a part of eddy current blower shown by FIG. FIG. 3 is a sectional view taken along line 3-3 in FIG. 2. (A) is a front view which shows the inner surface of an impeller, (B) is a front view which shows the modification of an impeller. 4A is a cross-sectional view taken along line 5A-5A in FIG. 4A, FIG. 4B is a cross-sectional view taken along line 5B-5B in FIG. 4B, and FIG. It is. FIG. 6 is an enlarged sectional view taken along line 6-6 in FIG. (A) is the 7A-7A sectional view taken on the line in FIG. 6, (B) is the 7B-7B sectional view in FIG. 6, (C) is the 7C-7C sectional view in FIG. It is sectional drawing which shows the modification of a irregular reflection part. It is a schematic diagram which shows the mode of the sound collection experiment about the eddy current blower which is a comparative example. It is a waveform diagram which shows the result of the sound collection experiment about the comparative example shown in FIG. It is a characteristic view which shows the performance curve measured about the eddy current blower of this invention, and the eddy current blower of a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Electric motor 12 Casing 13 Rotating shaft 14 Impeller 15 Shroud 16 Annular groove 17 Blade 20 Static flow path 21 Suction flow path 22 Discharge flow path 23 Partition 25 Suction side guide surface 26 Discharge side guide surface 30a, 30b Random reflection part 31 Protrusion 32 Projection End 33 Side 34 Recess

Claims (5)

An eddy current blower having a casing provided with an arc-shaped stationary flow path, and an impeller provided with a plurality of blades at predetermined intervals in the circumferential direction corresponding to the stationary flow path and driven by an electric motor. And
A suction channel that is provided in communication with one end of the stationary channel in the casing and guides air from outside to the stationary channel;
A discharge channel provided in communication with the other end of the stationary channel in the casing and guiding pressurized air from the stationary channel to the outside;
A suction-side guide surface that forms one end face of the static flow path and guides air from the suction flow path to the static flow path, and another end face of the static flow path that forms the discharge flow from the static flow path An eddy current blower comprising: a turbulent reflection portion provided on at least one of a discharge side guide surface that guides air to a path.   The vortex blower according to claim 1, wherein the turbulent reflection portion is provided on both the suction side guide surface and the discharge side guide surface.   3. The vortex blower according to claim 1, wherein the irregular reflection portion is a protrusion that protrudes toward the center of the flow path and extends in the air flow direction. 4.   4. The vortex blower according to claim 3, wherein the height of the protrusion gradually decreases from a central portion in the longitudinal direction of the protrusion toward both ends. 5.   5. The eddy current blower according to claim 3, wherein a side surface of the protrusion is curved in a concave shape.

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