U.S. patent application number 13/183479 was filed with the patent office on 2012-01-26 for axial flow fun.
Invention is credited to Taku Iwase, Shigeyasu Tsubaki, Yusuke UCHIYAMA.
Application Number | 20120020780 13/183479 |
Document ID | / |
Family ID | 45493763 |
Filed Date | 2012-01-26 |
United States Patent
Application |
20120020780 |
Kind Code |
A1 |
UCHIYAMA; Yusuke ; et
al. |
January 26, 2012 |
AXIAL FLOW FUN
Abstract
The invention is directed to dual purposes of increasing air
volume and reducing noises of an inline axial flow fan. In the
inline axial flow fan including a first axial flow fan unit 100-1,
a first honeycomb 200-2, a second axial flow fan unit 100-2 and a
second honeycomb 200-2 which are arranged in the order starting
from an upstream side in an air flow direction, the first honeycomb
includes a stator vane configured to be warped in a "U" shape
against a rotation direction of the first axial flow fan unit,
while the second honeycomb includes a stator vane configured to
direct a trailing edge thereof in parallel to the air flow
direction.
Inventors: |
UCHIYAMA; Yusuke;
(Hitachinaka, JP) ; Iwase; Taku; (Mito, JP)
; Tsubaki; Shigeyasu; (Odawara, JP) |
Family ID: |
45493763 |
Appl. No.: |
13/183479 |
Filed: |
July 15, 2011 |
Current U.S.
Class: |
415/209.1 |
Current CPC
Class: |
F04D 29/541 20130101;
F04D 29/582 20130101; F04D 25/0613 20130101; H05K 7/20727 20130101;
H05K 7/20172 20130101 |
Class at
Publication: |
415/209.1 |
International
Class: |
F04D 29/54 20060101
F04D029/54 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 20, 2010 |
JP |
2010-163007 |
Claims
1. An axial flow fan comprising: a first axial flow fan unit
disposed on an upstream side with respect to an air flow; a first
honeycomb disposed downstream of the first axial flow fan unit; a
second axial flow fan unit disposed downstream of the second
honeycomb; and a second honeycomb disposed downstream of the second
axial flow fan unit, wherein a stator vane constituting the first
honeycomb is configured to be warped against a rotation direction
of the first axial flow fan unit, while a stator vane constituting
the second honeycomb is configured to direct a trailing edge
thereof in parallel to a direction of the air flow.
2. The axial flow fan according to claim 1, wherein the stator vane
constituting the first honeycomb is warped in a "U" shape.
3. The axial flow fan according to claim 1, wherein the stator vane
constituting the first honeycomb is divided into two parts.
4. An axial flow fan comprising: a first axial flow fan unit
disposed on an upstream side with respect to an air flow; a first
honeycomb disposed downstream of the first axial flow fan unit; a
second axial flow fan unit disposed downstream of the first
honeycomb; and a second honeycomb disposed downstream of the second
axial flow fan unit, the second axial flow fan unit rotating in a
different way from the first axial flow fan unit, wherein a stator
vane constituting the first honeycomb is configured to direct a
ventral side thereof against a rotation direction of the first
axial flow fan unit, while a stator vane constituting the second
honeycomb is configured to direct a trailing edge thereof in
parallel to a direction of the air flow.
5. The axial flow fan according to claim 1, comprising an inline
axial flow fan that uses the first and second axial flow fan units
and the first and second honeycombs as a cooling device for server
apparatuses.
6. The axial flow fan according to claim 2, comprising an inline
axial flow fan that uses the first and second axial flow fan units
and the first and second honeycombs as a cooling device for server
apparatuses.
7. The axial flow fan according to claim 3, comprising an inline
axial flow fan that uses the first and second axial flow fan units
and the first and second honeycombs as a cooling device for server
apparatuses.
8. The axial flow fan according to claim 4, comprising an inline
axial flow fan that uses the first and second axial flow fan units
and the first and second honeycombs as a cooling device for server
apparatuses.
Description
CLAIM OF PRIORITY
[0001] The present application claims priority from Japanese patent
application serial no. 2010-163007 filed on Jul. 20, 2010, the
content of which is hereby incorporated by reference into this
application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an axial flow fan including
axial flow fan units serially arranged in a direction of rotary
shafts thereof.
[0004] 2. Description of Related Art
[0005] Home electric appliances and OA/IT apparatuses are equipped
with a cooling fan for cooling heat-generating electronic
components. More recently, the market has been meeting demands for
the downsizing and sophistication of these home electric appliances
and OA/IT apparatuses. Along with the downsizing and sophistication
efforts, the appliances and apparatuses tend to have an internal
structure more densely mounted with the electronic components. This
results in the increase in the amount of heat generation.
[0006] A compact, high volume axial flow fan is generally employed
as a cooling fan to deal with the increased amount of heat
generated by the electronic components.
[0007] However, in a case where the compact axial flow fan is
employed for cooling the electronic components, the fan must be
rotated at high speeds to provide a required volume of cooling air.
Unfortunately, this entails a problem of noise increase although
the air volume is increased by rotating the fan at high speeds.
[0008] On the other hand, a structure having the axial flow fan
units serially arranged in the direction of rotary shafts thereof
is adopted to deal with the increase in pressure loss as a
consequence of the high-density mounting of electronic
components.
[0009] As particularly exemplified by server apparatuses at data
centers, machines and equipment designed on the assumption of long
hours of continuous operation adopt a structure having a plurality
of axial flow fan units operatively arranged in series from the
standpoint of ensuring redundancy for preventing the total
breakdown of a cooling function associated with the failure of the
cooling fan.
[0010] In the structure wherein the axial flow fan units are
serially arranged and operated, therefore, emphasis is placed on a
technique for reducing noises during the operation of outputting
the increased volume of cooling air.
[0011] U.S. Pat. No. 4,167,861 discloses a structure wherein two
axial flow fan units are serially arranged in the direction of
rotary shafts thereof. Interposed between the upstream axial flow
fan unit and the downstream axial flow fan unit is a device
(hereinafter, referred to as "honeycomb") including a frame and
vanes. The frame is called a stator and includes an inside surface
and an outside surface. The vanes extend radially from the center
of the frame. This honeycomb removes a swirling flow produced in an
airflow by the axial flow fan unit, thus suppressing the noise
generation.
[0012] However, the honeycomb of the U.S. Pat. No. 4,167,861 does
not work on the air flow discharged from the downstream axial flow
fan unit, although working on the air flow discharged from the
axial flow fan unit disposed upstream thereof.
[0013] Therefore, the swirling flow in the air flow discharged from
the downstream axial flow fan unit cannot be removed although the
above-described honeycomb acts to remove the swirling flow from the
air flow discharged from the upstream axial flow fan unit. In view
of the whole body of the inline axial flow fan, therefore, the U.S.
Pat. No. 4,167,861 is not necessarily considered to provide an
effective solution to the above-described problem of noise
generation.
SUMMARY OF THE INVENTION
[0014] It is an object of the invention to provide an axial flow
fan adapted to increase the air volume and to reduce the noise of
inline axial flow fan units thereof.
[0015] The above object is accomplished in an axial flow fan
comprising: a first axial flow fan unit disposed on an upstream
side with respect to an air flow; a first honeycomb disposed
downstream of the first axial flow fan unit; a second axial flow
fan unit disposed downstream of the second honeycomb; and a second
honeycomb disposed downstream of the second axial flow fan unit,
wherein a stator vane constituting the first honeycomb is
configured to be warped against a rotation direction of the first
axial flow fan unit while a stator vane constituting the second
honeycomb is configured to direct a trailing edge thereof in
parallel to a direction of the air flow.
[0016] The above object is further accomplished in the axial flow
fan wherein the stator vane constituting the first honeycomb is
warped in a "U" shape.
[0017] The above object is further accomplished in the axial flow
fan wherein the stator vane constituting the first honeycomb is
divided into two parts.
[0018] The above object is further accomplished in an axial flow
fan comprising: a first axial flow fan unit disposed on an upstream
side with respect to an air flow; a first honeycomb disposed
downstream of the first axial flow fan unit; a second axial flow
fan unit disposed downstream of the first honeycomb; and a second
honeycomb disposed downstream of the second axial flow fan unit,
the second axial flow fan unit rotating in a different way from the
first axial flow fan unit, wherein a stator vane constituting the
first honeycomb is configured to direct a ventral side thereof
against a rotation direction of the first axial flow fan unit,
while a stator vane constituting the second honeycomb is configured
to direct a trailing edge thereof in parallel to a direction of the
air flow.
[0019] The above object is accomplished in the axial flow fan
comprising an inline axial flow fan wherein the first and second
axial flow fan units and the first and second honeycombs are used
as a device for cooling server apparatuses.
[0020] The invention can provide the axial flow fan adapted to
increase the air volume and to reduce the noise of the inline axial
flow fan units thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a schematic diagram showing a structure wherein
axial flow fan units and honeycombs are alternately arranged in
series;
[0022] FIG. 2 is a side view showing the axial flow fan unit;
[0023] FIG. 3 is a perspective view showing the axial flow fan
unit;
[0024] FIG. 4 is a side view showing the honeycomb unit;
[0025] FIG. 5 is a perspective view showing the honeycomb unit;
[0026] FIG. 6 represents a cylindrical plane containing an inline
axial flow fan according to a first embodiment of the
invention;
[0027] FIG. 7 is chart showing a relation between air inflow
velocity and air exit velocity for a rotor blade of the axial flow
fan;
[0028] FIG. 8 is a graph showing performance curve and resistance
curve of the axial flow fan;
[0029] FIG. 9 is a diagram showing air flow separation caused by
negative preswirl;
[0030] FIG. 10 represents a cylindrical plane containing an axial
flow fan according to a second embodiment of the invention;
[0031] FIG. 11 is a diagram showing a structure of an axial flow
fan including axial flow fan units and honeycombs according to a
third embodiment of the invention;
[0032] FIG. 12 represents a cylindrical plane containing the inline
axial flow fan according to the third embodiment of the
invention;
[0033] FIG. 13 is a diagram showing a structure of an axial flow
fan including axial flow fan units and honeycombs according to a
fourth embodiment of the invention;
[0034] FIG. 14 represents a cylindrical plane containing the inline
axial flow fan according to the fourth embodiment of the invention;
and
[0035] FIG. 15 is a schematic diagram showing a structure of a
blade server according to a fifth embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] A first embodiment of the invention will be described as
below with reference to the accompanying drawings. Referring to
FIG. 2 to FIG. 5, a brief description is made on an axial flow fan
unit and a honeycomb arranged in series.
[0037] FIG. 1 is a schematic diagram showing a structure wherein
the axial flow fan units and the honeycombs are alternately
arranged in series.
[0038] FIG. 2 is a side view showing the axial flow fan unit.
[0039] FIG. 3 is a perspective view showing the axial flow fan
unit.
[0040] FIG. 4 is a side view showing the honeycomb unit.
[0041] FIG. 5 is a perspective view showing the honeycomb unit.
[0042] Referring to FIG. 1, a first axial flow fan unit 1, a first
honeycomb 2, a second axial flow fan unit 3 and a second honeycomb
4 are arranged in series in the order starting from an upstream
side in an air flow direction indicated by the arrows. Namely, the
first axial flow fan unit is disposed on the upstream side while
the first honeycomb 2 is disposed downstream of the first axial
flow fan unit 1. The second axial flow fan unit 3 is disposed
downstream of this first honeycomb 2. The second honeycomb 4 is
disposed downstream of this second axial flow fan unit 3.
[0043] Referring to FIG. 2 and FIG. 3, the first and second axial
flow fan units 1, 3 are centrally formed with a boss 101,
respectively. A plurality of rotor blades 102 are provided on an
outer periphery of the boss 101. A motor 103 is coupled to the boss
101, which is brought into rotation by the motor 101 so as to
rotate the rotor blades 102. Support struts 105 support the motor
103 on a casing 104.
[0044] Referring to FIG. 4 and FIG. 5, the first and second
honeycombs 2, 4 each include an inside frame 201 and an outside
frame 202. The inside frame 201 and the outside frame 202 are
interconnected by a plurality of stator vanes 203 extending
radially from the inside frame 201.
[0045] According to the above-described patent literature 1, the
honeycomb 2 is interposed between the first axial flow fan unit 1
and the second axial flow fan unit 3 but the second honeycomb 4 on
the downstream side is not provided. In the structure of the patent
literature 1, therefore, a swirling flow can be removed from an air
flow discharged from the first axial flow fan unit 1 by the effect
of the honeycomb 2 but the swirling flow cannot be removed from the
air flow discharged from the second axial flow fan unit 3.
[0046] In this connection, the present inventors have achieved the
following embodiments by installing the second honeycomb 4
downstream of the second axial flow fan unit 3 and making various
studies on the configuration of the stator vanes of the second
honeycomb 4.
First Embodiment
[0047] FIG. 6 represents a cylindrical plane containing an inline
axial flow fan according to a first embodiment of the
invention.
[0048] Namely, FIG. 6 represents the cylindrical plane containing
fragmentary views of cross sections of the rotor blades 102 of the
first and second axial flow fan units 1, 3 and cross sections of
the stator vanes 203 of the first and second honeycombs 2, 4 shown
in FIG. 1.
[0049] In FIG. 6, as seen from an upstream side in an air flow
direction indicated by the arrows, a rotary rotor blade 102a of the
first rotary axial flow fan unit 1 (hereinafter, referred to as
"first rotor blade 102a") is disposed on the upstream side. A
stationary stator vane 203a of the first honeycomb 2 (hereinafter,
referred to as "first stator vane 203a") is disposed downstream of
this rotor blade 102a. A rotary rotor blade 102b of the second
axial flow fan unit 3 (hereinafter, referred to as "second rotor
blade 102b") is disposed downstream of this stator vane 203a. A
stationary stator vane 203b of the second honeycomb 4 (hereinafter,
referred to as "second stator vane 203b") is disposed downstream of
the rotating rotor blade 102b.
[0050] The first rotor blade 102a and the second rotor blade 102b
rotate in the same direction and have rotary shafts in aligned
relation. The first stator vane 203a is warped in a "U" shape
against a rotation direction of the rotor blade 102a and the rotor
blade 102b. The second stator vane 203b is configured to direct a
trailing edge thereof in parallel to the air flow direction.
[0051] These honeycombs 2, 4 allow the air flow to enter the rotor
blade 102a at a relative velocity 302a for a rotational field and
at an absolute velocity 303a for a static field. In the rotational
field commonly represented by the three-dimensional cylindrical
coordinate system, the relative velocity is given as a sum of a
circumferential velocity and the absolute velocity.
[0052] Passing through the rotor blade 102a, the air flow exits at
a relative velocity 302b for the rotational field and at an
absolute velocity 303b for the static field.
[0053] FIG. 7 is a chart showing a relation between air inflow
velocity and air exit velocity for the rotor blade of a common
axial flow fan.
[0054] Referring to FIG. 7, the air flow enters the rotor blade at
a relative inflow velocity 302(a) and a relative inflow angle
305(a) for the rotational field, and at an absolute inflow velocity
303(a) and an absolute inflow angle 304(a) for the static field.
After passing through the rotor blade, the air flow exits at a
relative exit velocity 302(b) and a relative exit angle 305(b) for
the rotational field and at an absolute exit velocity 303(b) and an
absolute exit angle 304(b) for the static field. The air flow is
varied in velocity as follows due to the effect of the rotor blade.
In the rotational field, a velocity variation is given by a
difference 306(b) between the relative inflow velocity 305(a) and
the relative exit velocity 305(b). In the static field, a velocity
variation is given by a difference 306(a) between the absolute exit
velocity 303(b) and the absolute inflow velocity 303(a).
P.sub.th=.rho.u(v.sub..theta.out-v.sub..theta.in)=.rho.u(w.sub..theta.in-
-w.sub..theta.out) Equation 1
[0055] The equation 1 represents the theoretical total pressure
rise of the air flow provided by the effect of the rotor blade. In
the equation, "P.sub.th" denotes a theoretical total pressure rise;
".rho." denotes an air density; "u" denotes a circumferential
velocity; "w.sub..theta.in" denotes a swirl component of the
relative inflow velocity; "w.sub..theta.out" denotes a swirl
component of the relative exit velocity; "v.sub..theta.in" denotes
a swirl component of the absolute inflow velocity; and
"v.sub..theta.out" denotes a swirl component of the absolute exit
velocity. The equation 1 means that the theoretical total pressure
rise of the air flow is proportional to the velocity variation of
the air flow caused by the effect of the rotor blade.
[0056] In the above-described first rotor blade 102a, a theoretical
total pressure rise corresponding to an inflow velocity and an exit
velocity of the air flow through the first rotor blade 102a of FIG.
6 can be calculated from the equation 1.
[0057] The air flow exiting from the first rotor blade 102a enters
the first stator vane 203a at the absolute velocity 303b for the
static field and exits from the stator vane at an absolute velocity
303c as decelerated by the effect of the first stator vane 203a. As
a consequence of the configuration of the first stator vane 203a
warped in the "U" shape against the rotation direction of the
second rotor blade 102b, the absolute velocity 303c contains a
swirl component, called a negative preswirl, in the opposite
direction to the rotation direction of the second rotor blade
102b.
.DELTA. P s = .rho. v 2 in - v 2 out 2 Equation 2 ##EQU00001##
[0058] The equation 2 represents the theoretical static pressure
rise in the air flow provided by a common effect of the stator
vane. In the equation, ".DELTA.P.sub.s" denotes a theoretical
static pressure rise; ".rho." denotes an air density; "v.sub.in"
denotes an absolute inflow velocity; and "v.sub.out" denotes an
absolute exit velocity. The equation 2 indicates that the absolute
velocity of the air flow is decreased by the effect of the stator
vane whereby the static pressure in the air flow is increased.
[0059] In the first stator vane 203a, a theoretical static pressure
rise corresponding to an inflow velocity and an exit velocity of
the air flow through the first stator vane 203a of FIG. 6 can be
calculated from the equation 2.
[0060] The air flow exiting from the first stator vane 203a enters
the second rotor blade 102b at a relative velocity 302c for the
rotational field and at the absolute velocity 303c for the static
field. The air flow passes through the second rotor blade 102b and
exits at a relative velocity 302d for the rotational field and at
an absolute velocity 303d for the static field. At this time, the
swirl component of the absolute inflow velocity in the equation 1
representing the theoretical total pressure rise of the air flow
has the negative sign. Therefore, the theoretical total pressure
rise is increased in value as compared with a case where the swirl
component of the absolute inflow velocity has the positive sign.
This effect permits the reduction of the circumferential velocity
when as much theoretical total pressure rise as that of a case
where the swirl component of the absolute inflow velocity has the
positive sign is imparted to the air flow.
L'.sub.A=L.sub.A+60 log.sub.10(N'/N) Equation 3
[0061] The equation 3 represents the variation of noise level
associated with the variation of motor revolving speed. In the
equation, "N" denotes a pre-variation revolving speed; "N'" denotes
a post-variation revolving speed; "L.sub.A" denotes a pre-variation
noise level; and "L'.sub.A" denotes a post-variation noise
level.
[0062] If the motor revolving speed is reduced by reducing the
circumferential velocity of the second rotor blade 102b, the noise
level is lowered as indicated by the equation 3.
[0063] The air flow exiting from the second rotor blade 102b enters
the second stator vane 203b at the absolute velocity 303d for the
static field and exits therefrom at an absolute velocity 303e as
decelerated by the effect of the second stator vane 203b. At this
time, the air flow obtains as much theoretical total pressure rise
as determined by the equation 2.
[0064] FIG. 8 is a graph showing performance curve and resistance
curve of the axial flow fan.
[0065] Referring to FIG. 8, the air volume of the axial flow fan is
generally determined by an operating point defined by intersection
of a characteristic curve 401 representing a relation between air
volume and pressure loss in an operating environment of the axial
flow fan and a characteristic curve 402 representing a relation
between air volume and pressure specific to the axial flow fan.
Therefore, the fact that the static pressure rise is obtained due
to the effect of the second stator vane indicates that the above
characteristic curve of air volume versus pressure is converted to
a characteristic curve 403 of air volume versus pressure. As a
result, the operating point is shifted toward larger air volume.
Namely, the air volume is increased.
[0066] In this embodiment, if the first axial fan unit 1 shown in
FIG. 1 fails, the first axial flow fan unit 1 makes an obstacle. At
this time, the second axial flow fan unit 2 is operated at the
maximum revolving speed.
[0067] As shown in FIG. 6, the negative preswirl is applied to the
second rotor blade 102b by the effect of the first stator vane
203a, whereby the air flow can obtain a greater theoretical total
pressure rise than in a case where the negative preswirl, expressed
by the equation 1, is not applied to the second rotor blade.
Further, the effect of the second stator vane 203b provides a
larger air volume than in a case where the second honeycomb 4 of
FIG. 1 is omitted. That is, in the event of a failure of the first
axial flow fan unit 1, the drop of air volume can be reduced.
[0068] According to this embodiment as described above, the first
stator vane 203a and the second stator vane 203b have different
configurations so that the axial flow fan can achieve not only the
reduced noise level and the increased air volume but also the
effect to suppress the failure induced degradation of
performance.
[0069] Now, description is made on a case where the first axial
flow fan unit 1 and the second axial flow fan unit 2, described
with reference to FIG. 1 illustrating the first embodiment of the
invention, rotate in different directions.
[0070] A set of two axial flow fan units arranged in tandem and
rotated in the different directions is generally called a duplicate
contra-rotating fan. In this duplicate contra-rotating fan, an air
flow through an axial flow fan unit on the upstream side in the air
flow direction contains a swirling flow, which acts as the negative
preswirl to the downstream fan unit. Hence, the pressure rise
increased by the negative preswirl, as described in the first
embodiment, can always be prospected.
[0071] However, if inflow condition for the air into the upstream
axial flow fan unit varies due to the change in the operating
environment or the like so that the negative preswirl to the
downstream axial flow fan unit is increased too much, an air flow
along a dorsal side of the blade becomes unable to withstand such a
large pressure rise and sustains flow separation. This results in
pressure loss.
Second Embodiment
[0072] According to a second embodiment, therefore, there are
provided the first rotary rotor blade 102a and a second rotary
rotor blade 102c. In the structure wherein the second rotor blade
102c rotates in the different direction, the first stationary
stator vane 203a is configured to direct a dorsal side thereof
against the rotation direction of the first rotor blade 102a, while
the second stationary stator vane 203b is configured to direct the
trailing edge thereof in parallel to the air flow direction.
[0073] Referring to FIG. 10, the operation of this embodiment is
described as below.
[0074] FIG. 10 represents a cylindrical plane containing an axial
flow fan according to the second embodiment of the invention.
[0075] Referring to FIG. 10, the air flow through the first stator
vane 203a has the absolute velocity 303c for the static field. The
airflow enters the second rotor blade 102c at the relative velocity
302d for the rotational field and at the absolute velocity 303d for
the static field. At this time when the air flow enters the second
rotor blade 102c, the first stator vane 203a acts to prevent an
excessive increase of the negative preswirl. Hence, the pressure
loss caused by the air flow separation is prevented while the
theoretical total pressure rise expected from the equation 1 may
preferably be achieved. As illustrated by the first embodiment, the
air flow through the second rotor blade 102c is increased in the
static pressure by the effect of the second stationary stator vane
203b.
[0076] As described above, this embodiment affords an effect to
suppress the loss encountered by the axial flow fan or more
particularly the duplicate contra-rotating fan by virtue of the
structure wherein the stator vane 203a of the first honeycomb 2 and
the stator vane 203b of the second honeycomb 4 have different
configurations from those of the stator vane 203a of the first
honeycomb 2 and the stator vane 203b of the second honeycomb 4
shown in FIG. 1.
Third Embodiment
[0077] A third embodiment of the invention is described with
reference to FIG. 11.
[0078] FIG. 11 is a diagram showing a structure of an axial flow
fan including axial flow fan units and honeycombs according to a
third embodiment of the invention.
[0079] Referring to FIG. 11, the embodiment has the structure
including the first axial flow fan unit 1, the first honeycomb 2, a
second honeycomb 2a, the second axial flow fan unit 3 and a third
honeycomb 4 which are arranged in the order starting from the
upstream side in the air flow direction indicated by the
arrows.
[0080] FIG. 12 represents a cylindrical plane containing the inline
axial flow fan according to the third embodiment of the
invention.
[0081] Referring to FIG. 12, this embodiment has the structure
wherein the first stationary stator vane 203a is warped at a
leading edge thereof against the rotation direction of the first
rotary rotor blade 102a, wherein the second stationary stator vane
203b is warped at a trailing edge thereof against the rotation
direction of the first rotor blade, and wherein the third
stationary stator vane 203c is configured to direct a trailing edge
thereof in parallel to the air flow direction.
[0082] In other words, the first stator vane 203a and the second
stator vane 203b are two parts that form the first stator vane 203a
described in the first embodiment shown in FIG. 6. If the "U"
shaped stator vane 203a is to be formed in an integral mold, the
molded product may have such a configuration as not to be demolded.
In this embodiment, therefore, the stator vane is formed of two
separate parts, such as to facilitate the molding process.
[0083] Next, the operation of this embodiment is described with
reference to FIG. 12.
[0084] The air flow through the first rotor blade 102a enters the
first stator vane 203a at an absolute velocity 301b for the static
field. The air flow passing through the first stator vane 203a via
the static field enters the second stator vane 203b at the absolute
velocity 303c, the swirl component of which is reduced in the
static field. The air flow through the second stator vane 203b has
the absolute velocity 303d, which contains the negative preswirl
against the second rotary rotor blade 102b. When the negative
preswirl is applied to the air flow entering the second rotor blade
102b, the swirling flow of the air flow is reduced by the effect of
the first stator vane 203a. Thus is obtained an effect to suppress
the production of flow separation from the air flow passing through
the second stator vane 203b. As a result, the loss caused by the
air flow separation can be reduced or preferably eliminated.
[0085] As described above, this embodiment has the structure
wherein the stator vane 203a of the first honeycomb 2 and the
stator vane 203b of the second honeycomb 2a, shown in FIG. 11, have
the different configurations. Therefore, the embodiment can afford
the effect to suppress the loss caused by the flow separation from
the air flow, the flow separation occurring when the negative
preswirl is applied to the air flow into the second axial flow fan
unit 3 by means of the honeycomb.
[0086] Another advantageous effect of this embodiment is that the
first stator vane 203a and the second stator vane 203b can be
relatively easily formed by molding, as described above.
Fourth Embodiment
[0087] A fourth embodiment of the invention is described with
reference to FIG. 13.
[0088] FIG. 13 is a diagram showing a structure of an axial flow
fan including axial flow fan units and honeycombs according to a
fourth embodiment of the invention.
[0089] Referring to FIG. 13, the embodiment has the structure
including the first honeycomb 2, the first axial flow fan unit 1,
the second honeycomb 4, the second axial flow fan unit 3 and a
third honeycomb 5 which are arranged in the order starting from an
upstream side in the air flow direction indicated by the
arrows.
[0090] As shown in FIG. 14 representing a cylindrical plane
containing the structure shown in FIG. 13, the first stationary
stator vane 203a is configured to be warped at a trailing edge
thereof in the rotation direction of the first rotary rotor blade
102a. The second stationary stator vane 203b is configured to be
warped in a "U" shape against the rotation direction of the second
rotary rotor blade 102b. The third stationary stator vane 203c is
configured to direct a trailing edge thereof in parallel to the air
flow direction.
[0091] Next, the operation of this embodiment is described with
reference to FIG. 14.
[0092] The air flow passes through the first stator vane 203a to
obtain the absolute velocity 303b for the static field before
entering the first rotor blade 102a. Since an operating environment
assumed in a design phase differs from an actual operating
environment, the loss may be caused by the air flow separation
which may occur depending upon the air inflow condition varied due
to the change in the operating environment. A function of the first
stator vane 203a is to reduce or preferably to eliminate this
loss.
[0093] As described above, this embodiment has the structure
wherein the stator vane 203a of the first honeycomb 2, the stator
vane 203b of the second honeycomb 2a and the stator vane 203c of
the third honeycomb 5, shown in FIG. 13, have the different
configurations. Therefore, the embodiment can afford the effect to
prevent the loss resulting from the air inflow condition varied due
to the change in the operating environment.
Fifth Embodiment
[0094] A fifth embodiment of the invention is described with
reference to FIG. 15.
[0095] FIG. 15 is a schematic diagram showing a structure of a
blade server according to the fifth embodiment of the
invention.
[0096] Referring to FIG. 15, a blade server 500 includes a casing
501, server blades 502 arranged in the casing, and cooling fan
modules 503 for cooling the server blades.
[0097] According to the invention, the structure of the first
embodiment, for example, may be adopted to form the cooling fan
module 503 so that a blade server can attain high air volume and
low noise by virtue of the effects of the first embodiment. It is
also possible to provide the cooling fan module excellent in
redundancy in the event of a failure.
[0098] The applications of the cooling fan module according to the
embodiment include, but are not limited to the blade server, all
kinds of server apparatuses such as rack mount servers and PC
servers.
[0099] According to the invention as described above, a notable
noise reduction can be achieved because the effect of the first
honeycomb permits the second axial flow fan unit to be reduced in
the revolving speed. In addition, the cooling fan module is
increased in the air volume because the static pressure is
increased due to the effects of the first honeycomb and the second
honeycomb.
[0100] In addition, if the first axial flow fan unit should fail,
the drop of cooling capacity can be reduced because the second
honeycomb is provided.
[0101] On the other hand, the first honeycomb acts to prevent the
air flow separation occurring in the second axial flow fan unit,
thereby suppressing the generation of loss. Furthermore, the first
honeycomb also acts to reduce the loss resulting from the varied
inflow condition of the air into the first axial flow fan unit.
[0102] In addition, the provision of the axial flow fan featuring
the low noise and high air volume makes it possible to fabricate a
cooling fan module for server that is excellent in redundancy in
the event of a failure.
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