Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Irregular – flanged or channel forming blade surface
Reexamination Certificate
1999-09-30
2001-10-02
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Irregular, flanged or channel forming blade surface
C416S23600R, C416SDIG002, C416S238000
Reexamination Certificate
active
06296446
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an axial blower used for a blower of an outdoor unit of an air conditioner or the like.
One example of a conventional axial blower of this type is shown in, for example, FIG.
10
. This axial blower
1
is provided with a plurality of vanes
3
formed integrally around a central hub
2
equidistantly in the circumferential direction thereof.
With reference to
FIGS. 10-12
, the cross-sectional shape of each vane
3
in the circumferential direction A-B at a portion having a radially arbitrary distance D from the center O of the hub
2
is formed into a thick stream-line shape
3
d
from the negative pressure surface-side leading edge portion
3
a
of the vane
3
to a vane surface
3
c
as shown in FIG.
11
.
The thick shape
3
d
advantageously allows an air flow F flowing from the negative pressure surface-side leading edge portion
3
a
of the vane
3
to travel along the positive and negative pressure sides of the vane surface
3
c
as indicated by arrows shown in
FIG. 12
, prevents the air flow F from separating from the vane surface
3
c
and makes small a trailing vortex Vf formed in the back of a vane trailing edge portion
3
b
thereby to reduce a blowing sound.
When the conventional axial blower
1
as mentioned above is incorporated, as a blower, into the outdoor unit of an air conditioner to increase the number of revolution of the blower per unit time (to be simply referred to as “the number of revolution” hereinafter) and to increase the quantity of blast, following disadvantages occur. That is, static pressure in the outdoor unit rises, the inflow angle of the air flow F with respect to the negative pressure surface-side leading edge portion
3
a
of each vane
3
varies and the separation of the air flow tends to occur on the vane surface
3
c
, thus increasing the blowing sound.
Further, it is easily be understood that the term “negative pressure side” used herein means an air-sucking side and the term “positive pressure side” used herein means an air-blowing side with respect to the vanes of the axial blower.
SUMMARY OF THE INVENTION
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide an inexpensive axial blower capable of suppressing the increase of blowing sound due to the separation of a flow generated on the negative pressure surface side of the vane and has excellent formability.
This and other objects can be achieved according to the present invention by providing an axial blower comprising:
a cylindrical hub;
a driving means for rotating the hub through a rotational shaft;
a plurality of vanes arranged to an outer peripheral surface of the hub in a circumferential direction thereof; and
a plurality of ribs, each having a stream-line shape, provided at a leading edge portion of a negative pressure surface-side of each of the vanes in a range from an end portion of the leading edge portion towards a trailing edge portion of the vane.
In a preferred embodiment, each of the stream-line ribs has a central axis along a blower rotational direction, the central axis passing a point of intersection of a circular arc having a center point of a circular arc portion on a vane outer periphery leading edge-side and the vane leading edge portion and being substantially in parallel to a tangent of the circular arc.
The plurality of stream-line ribs are arranged with equal distance from each other and the distance between the adjacent stream-line ribs is set at L/
12
with respect to a length L of the negative pressure surface-side leading edge portion along a radial direction of the axial blower. The stream-line ribs are formed integrally such that an outer surface of a cross section of each rib along the rotational direction of the axial blower forms a circular arc and a radius of a circular arc curve of the outer surface at a vane leading edge side is larger than a radius of a circular arc curve at a vane inner surface side.
The stream-line ribs have lengths k at a vane outer periphery side along the rotational direction of the air blower are set equal to one another. The lengths k of the stream-line ribs at the vane outer periphery side along the rotational direction of the axial blower are set to satisfy a relation of k:CL=1:9, where CL is a chord length of the vane outer periphery.
A height of the cross-section of each of the ribs along a thickness direction of each of the vanes is changed to be made gradually larger from the hub side towards the vane outer periphery direction in a manner reverse to that a thickness of a cross section of the vane leading edge portion is made gradually smaller from the hub side towards the direction of the vane outer periphery.
The plurality of stream-line ribs include a rib closest to the vane outer peripheral side having a height h, and a rib closest to the hub side of a stream-line rib closest to the vane outer periphery side having a height h
2
, the heights being set so as to satisfy an equation h
1
=2h
2
.
According to the present invention of the structures mentioned above, in the main aspect, the plural stream-line ribs at the negative pressure surface-side leading edge portion of each vane accelerate the transition of a laminar flow to a turbulent flow above a vane surface boundary layer of each vane. The flow above a turbulent flow boundary layer is less separated than that above the laminar boundary layer. Thus, it is possible to both enhance blast performance and reduce blowing noise.
In the other aspects of the embodiment, each of the stream-line ribs is arranged such that a central axis of the rib along a rotation direction of the blower passes a point of intersection of a circular arc about a center of a vane outer periphery leading edge-side circular arc portion and the vane leading edge and is parallel to a tangent of the circular arc. Accordingly, when an air-flow flowing from the negative pressure surface-side leading edge of each vane passes the stream-line ribs, the air-flow forms longitudinal vortex rows thereby to make the transition of a layer above the vane surface to a turbulent boundary layer. This action can make narrow the widths of the trailing vortexes which cause the blowing sound and can reduce the blowing sound.
The plural stream-line ribs are arranged equidistantly and the distance between the stream-line ribs is set at L/
12
with respect to a length L of the negative pressure surface-side leading edge portion along a radial direction of the blower. Accordingly, even if static pressure within the blower increases and the inflow angle of the air-flow at the negative pressure surface-side leading edge portion of each vane is changed, the blowing sound can be reduced.
Furthermore, if the radius of a circular arc curve thereof at a vane leading edge side becomes larger than that of a circular arc curve at a vane inner surface side on the circular arc cross section of each stream-line rib along the rotational direction of the blower, longitudinal vertexes generated when air flows pass through the stream-line ribs can be generated stably and the blowing sound reduction effect can be further improved.
Still furthermore, since, the lengths k of the stream-line ribs at the vane outer periphery side along the rotation direction of the air blower are set to satisfy k:CL=1:9 where CL is a chord length of the vane outer periphery, the blowing sound reduction effect can be maximized.
Still furthermore, since the thickness of the vane leading edge portion is changed so as to be gradually smaller from the hub side toward the vane outer periphery side, if the height h of each stream-line rib is changed so as to be gradually larger from the hub side towards the vane outer peripheral direction oppositely from the change of the vane thickness, and the height h
1
, of the stream-line rib at the vane outer periphery side and the height ha of the stream-line rib at the hub side are formed to satisfy the relationship of h
1
=2h
2
, then
Ishijima Mitsuyoshi
Koshitani Tetsuya
Shimizu Satoshi
Look Edward K.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Toshiba Carrier Corporation
Woo Richard
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