[0001] The present invention relates to a guide vane for an axial fan.
[0002] When a gas passes through a fan the gas is deflected by the impeller rotor blades
and a pressure increase is obtained across the impeller. However, the deflection means
that the gas flow velocity has a rotation component after passage through the impeller.
This rotation component forms a rotation energy which is often lost in the continued
gas transport downstream the fan.
[0003] It is known, e.g. through SE-B-94040, to arrange a ring of guide vanes downstream
the impeller to make use of this rotation energy and then raise the pressure increase
of the fan as well as its efficiency. The rotation energy of the gas flow after the
impeller is thus converted into a static pressure increase on passing over the guide
vanes. This conversion is not free of losses, and to minimize the losses it is essential
that the inlet angle of the guide vanes substantially coincides with the direction
of gas flow leaving the impeller. If the inlet side of the guide vanes is not adapted
to the direction of the impinging gas, a strong release of the flow is obtained at
the guide vane, with large energy losses and acompanying decrease of the fan efficiency
as a result. The guide vanes are also implemented so that the gas on the outlet side
is given a substantially axial direction.
[0004] It has been found that the magnitude of the rotation component varies in radial direction,
which means that the angle which the flow direction forms with the central axis varies
with the radius. The flow is very complex, and secondary effects result in that the
rotation after the fan blades will be larger at the root and top of the blades. At
the root of blades, i.e. att the point of attachment of the blades to the hub, the
gas flow is given an increased rotation by back flow in gaps and by the rotation of
the hub, and at the top of the blades there is an increased rotation as a result of
back flow which lowers the axial component. In addition, it should be noted that the
exterior limiting surface, e.g. the wall of a flow duct or the like, does not only
retard the tangential movement component but also the axial one. Taken together this
gives the unexpected radial variation of the flow direction illustrated in Figure
1.
[0005] Figure 1 thus illustrates the result of measurements made with an axial fan. As will
be seen, the flow direction angle towards the central axis is greater at the top and
root of the blade, and the angle passes through a minimum value therebetween. The
exact appearance of the graph is affected by such parameters as the blade angles on
the impeller and the selected operating point in the corresponding fan diagram (pressure
flow diagram), but the shape of the graph is qualitively the same, with a minimum
between the positions of the blade root and top.
[0006] In attempts to adapt the inlet angle of the guide vane to the rotation component,
which varies radially, guide vanes have been produced with varying curvature, which
requires a very complicated manufacturing technique, however.
[0007] Guide vanes have also been made with an oblique edge between the inner and outer
longitudinal edges of the guide vane, so that the arcuate length of the guide vane
along the inner edge is longer than the arcuate length along the radially outer edge.
For a constant curvature of the guide vane there is thus obtained a greater inlet
angle at the radially inward portion of the guide vane than at its radially outward
portion.
[0008] The object of the present invention is to provide a new guide vane, starting from
the above-mentioned knowledge of the radial variation of the rotation, which vane
is adapted on its inlet side to the direction of the impinging gas in a considerably
improved way along the entire radial extension of the guide vane, while the guide
vane is simple and cheap to manufacture.
[0009] This object is achieved with a guide vane of the kind described in the introduction
and with the characterizing features stated in claim 1.
[0010] By giving the edge of the vane portion facing towards the axial rotor a configuration
substantially following the variation of the rotation illustrated in Figure 1, the
vane can be produced with single curvature and simultaneously obtains excellent adaption
of the inlet angle to the direction of the impinging gas at every point.
[0011] With the guide vane in accordance with the invention, improvements of the fan efficiency
up to 20% can be obtained compared with guide vanes generally available on the market.
[0012] In accordance with an advantageous embodiment of the inventive guide vane, the inlet
angle ₁ at the radially inward portion or root portion meets the condition:
preferably
according to another advantageous embodiment of the inventive guide vane having a
constant radius of curvature, the ratio between the radius of curvature R and the
length L₁ of the radially inward edge of the guide vane meets the condition:
preferably
[0013] Optimization of the guide vane configuration to the selected operating point in the
area in the pressure-flow diagram which is of interest is thus enabled.
[0014] According to a still further advantageous embodiment of the inventive guide vane,
the relationship between the length L₁ of the radially inward edge of the guide vane
and the length L₂ of the guide vane at the level of the concaveness meets the condition:
and the concaveness level is given by the condition:
preferably
where H denotes the height for the concaveness position from the radially inward edge
and H₂ the total height of the guide vane.
[0015] The inlet angle of the guide vane at the vane top must be related, e.g. to the inlet
angle at the guide vane root, and according to another advantageous embodiment of
the inventive guide vane this relationship is given by the condition:
where L₃ and L₁ denote the lengths of the radially outer and inner edges of the guide
vane.
[0016] If the above indicated limits of the different parameters determining the configuration
of the guide vane are exceeded, disturbances of different kinds occur, e.g. separation
of the gas flow from the guide vane with energy losses as a result.
[0017] Embodiments of the guide vane in accordance with the invention, selected as examples,
will now be described in more detail in connection with figures 2-5.
[0018] Figure 1 illustrates the radial variation of the angle between the flow direction
and the central axis from the blade root to the blade top.
[0019] Figure 2 illustrates an axial fan with guide vanes arranged downstream in accordance
with the invention.
[0020] Figure 3 illustrates a preferred embodiment of the inventive guide vane extended
in a plane.
[0021] Figure 4 illustrates the guide vane of Figure 3 with constant curvature, and
Figure 5 illustrates an alternative embodiment of the guide vane in accordance
with the invention, also extended in a plane.
[0022] In Figure 2 there is illustrated an axial fan 2, installed in a duct 4, with the
air flow direction indicated by the arrow q. Downstream the fan and at a given distance
from it a ring of guide vanes 6 is mounted, the radial extension of the guide vanes
substantially corresponding to that of the fan blades 8. As will be particularly seen
from the vane 6', the vanes have a substantially axial outlet angle while the inlet
angle forms a given angle to the central axis of the fan.
[0023] In Figure 3 there is illustrated a preferred embodiment of a guide vane 6, extended
in a plane. The end portion of the guide vane 6 which is intended to face towards
the fan has an edge 10 with a parabola like shape so that between the inner and outer
longitudinal edges 12 and 14 of the guide vane 6 there is obtained a concaveness with
a shorter lenth L₂ along the vane than said edges L₁ and L₃. The vane 6 has a stright
trailing edge 16.
[0024] The height of the concaveness from the inner longitudinal edge 12 is denoted by H₁
and the total height of the vane by H₂. The position of the concaveness is determined
by the condition:
preferably
[0025] When the guide vane of Figure 3 is given a constant curvature with a radius of curvature
according to Figure 4, there is obtained a greater inlet angle in relation to the
central axis at the inner portion of the guide vane, which will be at the level of
the blade root, that at the outer portion of the vane 6, which will be at the level
of the vane top, since the inner longitudinal edge 12 is longer than the outer longitudinal
edge 14, see Figure 3. In the intermediate concaveness portion, the inlet angle will
be still less, and thus there is achieved in a simple way a radial variation in the
inlet angle which agrees with the radial variation of the gas flow rotation component,
as discussed above.
[0026] For
there are obtained the ratios between the inlet angles at the outer and inner portions
of the vane, which are well suited to practical applications.
[0027] The lengths L₁ and L₂ meet the condition:
[0028] To enable optimization of the guide vane at different operating points in the pressure-flow
diagram, i.e. both for large flow and high pressure, the radius of curvature R, see
Figure 4, and L₁ must meet the condition:
preferably
[0029] The ratio between the radii R₁ and R₂ from the central axis 18 of the fan to the
inner edge 12 of the guide vane and the outer edge 14, respectively, meets the condition:
preferably
[0030] The vane will thus be useful for practically all axial fans used in practice.
[0031] In addition, R₁ corresponds to the radius of the impeller hub, while the radius R₂
corresponds to the radius in the flow duct 4 in question, which also substantially
agrees with the radius of the blade wheel, cf. Figure 2.
[0032] In Figure 5 there is illustrated an alternative embodiment of a guide vane in accordance
with the invention, the edge intended to face towards the fan being formed by a polygonal
train of three sides 20, 22, 24. The side 22 will then form the intermediate concaveness
portion. It should be noted that the concaveness portion 22 is displaced closer to
the outer edge 14, compared with the inner edge 12. This vane is also curved with
a constant radius of curvature, as illustrated in Figure 4. This is a simple guide
vane configuration, which gives a considerable increase in efficiency compared with
previous embodiments with a monotonously extending oblique edge, as indicated by the
dashed line 26 in the figure.
[0033] It will be obvious that a number of curve shapes are possible for the edge facing
towards the fan, these shapes having a concaveness as described above. In practical
application the curve shape giving an optimum result is of course selected.
1. Guide vane (6,6') for an axial fan (2), characterized in that in the portion facing towards the fan a concaveness is formed between the radially
outward and inward portions of the guide vane (14 and 12, respectively), such that
the arc length in a plane parallel to the axis of the fan along the single curved
guide vane at the level of the deepest part of the concaveness (L₂) is shorter than
the arc lengths in said plane at said outward and inward portions (L₃ and L₁, respectively).
2. Guide vane as claimed in claim 1, characterized in that the edge (10) of the end portion facing towards the fan has a continous concave
shape.
3. Guide vane as claimed in claim 2, characterized in that the edge (10) has a parabola-like shape.
4. Guide vane as claimed in claim 1, characterized in that the edge of the end portion facing towards the fan has the shape of a polygonal
train (20,22,24).
5. Guide vane as claimed in claim 4, characterized in that the edge of the end portion facing towards the fan has the form of a trilateral
polygonal train (20,22,24).
6. Guide vane as claimed in anyone of claims 2-5,
characterized in that the ratio between the length (L₁) of the radially inward edge of the guide
vane and the length (L₂) of the guide vane at the level of the web meets the condition:
7. Guide vane as claimed in any one of claims 1-6,
characterized in that the inlet angle (α) at the root portion of the guide vane meets the condition
preferably
8. Guide vane as claimed in any one of claims 1-7, characterized in that the single-curved guide vane has a constant radius of curvature (R).
9. Guide vane as claimed in claim 8,
characterized in that the ratio between the radius of curvature (R) and the length (L₁) of the radially
inward edge of the guide vane meets the condition
preferably
10. Guide vane as claimed in any one of claims 2-9,
characterized in that the ratio between the height (H₁) of the position of the web from the radially
inward edge and the total height (H₂) of the guide vane meets the condition:
preferably
11. Guide vane as claimed in any one of claims 2-10,
characterized in that the ratio between the lengths (L₃) and (L₁) of the radially outward and inward
edges respectively of the guide vane meets the condition:
12. Guide vane as claimed in any one of claims 1-11,
characterized in that the ratio between the radii (R₁) and (R₂) from the fan axis to the outer and
inner edges of the guide vane meets the condition:
preferably
1. Leitschaufel (6,6') für ein Axialgebläserad (2), dadurch gekennzeichnet, das in dem
dem Gebläserad zugewanden Abschnitt eine Konkavität zwischen dem radial äußeren und
dem radial inneren Abschnitt der Leitschaufel (14 bzw. 12) ausgebildet ist, so daß
die Bogenlänge in einer Ebene parallel zu der Achse des Gehläserades entlang der konstant
gekrümmten Leitschaufel in Höhe des tiefsten Teiles der Konkavität (L₂) kürzer ist
als die Bogenlängen in einer solchen Ebene an dem äußeren und dem inneren Abschnitt
(L₃ bzw, L₁).
2. Leitschaufel nach Anspruch 1, dadurch gekennzeichnet, daß die Kante (10) des dem Gebläserad
zugewanden Endabschnittes eine kontinuierlich konkave Form aufweist.
3. Leitschaufel nach Anspruch 2, dadurch gekennzeichnet, daß die Kante (10) eine parabolartige
Form hat.
4. Leitschaufel nach Anspruch 1, dadurch gekennzeichnet, daß die Kante des dem Gebläserad
zugewanden Endabschnittes die Form eines Polygonzuges (20,22,24) aufweist.
5. Leitschaufel nach Anspruch 4, dadurch gekennzeichnet, daß die Kante des dem Gebläserad
zugewanden Endabschnittes die Form eines dreiseitigen Polygonzuges (20,22,24) aufweist.
6. Leitschaufel nach einem der Ansprüche 2-5, dadurch gekennzeichnet, daß das Verhältnis
zwischen der Länge (L₁) der radial inneren Kante der Leitschaufel und der Länge (L₂)
der Leitschaufel in Höhe des Halses die Bedingung erfüllt:
7. Leitschaufel nach einem der Ansprüche 1-6, dadurch gekennzeichnet, daß der Eintrittswinkel
(α) an dem Fußabschnitt der Leitschaufel die Bedingung erfüllt:
vorzugsweise
8. Leitschaufel nach einem der Ansprüche 1-7, dadurch gekennzeichnet, daß die einzelgekrümmte
Leitschaufel einen konstanten Krümmungsradius (R) aufweist.
9. Leitschaufel nach Anspruch 8, dadurch gekennzeichnet, daß das Verhältnis zwischen
dem Krümmungsradius (R) und der Länge (L₁) der radial inneren Kante der Leitschaufel
die Bedingung erfüllt:
vorzugsweise
10. Leitschaufel nach einem der Ansprüche 2-9, dadurch gekennzeichnet, daß das Verhältnis
zwischen der Höhe (H₁) der Stelle des Halses von dar radial inneren Kante zu der Gesamthöhe
(H₂) der Leitschaufel die Bedingung erfüllt:
vorzugsweise
11. Leitschaufel nach einem der Ansprüche 2-10, dadurch gekennzeichnet, daß das Verhältnis
zwischen den Längen (L₃) und (L₁) der radial äußeren bzw. inneren Kante der Leitschaufel
die Bedingung erfüllt:
12. Leitschaufel nach einem der Ansprüche 1-11, dadurch gekennzeichnet, daß das Verhältnis
zwischen den Radien (R₁) und (R₂) von der Gebläseradachse zu der äußern bzw. inneren
Kante der Leitschaufel die Bedingung erfüllt:
vorzugsweise
1. Aube directrice (6, 6') pour ventilateur axial (2) caractérisée en ce que la partie
dirigée vers le ventilateur est formée d'une concavité située entre les parties radialement
extérieure et intérieure de l'aube directrice (14 et 12 respectivement) de telle sorte
que la longueur d'arc dans un plan parallèle à l'axe du ventilateur le long de la
vanne directrice à incurvation unique au niveau de la partie la plus profonde de la
concavité (L₂) est plus courte que la longueur d'arc située dans ledit plan au niveau
desdites parties extérieure et intérieure (L₃ et L₁, respectivement).
2. Aube directrice selon la revendication 1, caractérisée en ce que le bord (10) de la
partie formant extrémité dirigée vers le ventilateur a une forme concave continue.
3. Aube directrice selon la revendication 2 caractérisée en ce que le bord (10) a une
forme analogue à une parabole.
4. Aube directrice selon la revendication 1, caractérisée en ce que le bord de la partie
formant extrémité dirigée vers le ventilateur a la forme d'une traînée polygonale
(20, 22, 24).
5. Aube directrice selon la revendication 4, caractérisée en ce que le bord de la partie
formant extrémité dirigée vers le ventilateur a la forme d'une traînée polygonale
à trois côtés (20, 22, 24).
6. Aube directrice selon l'une quelconque des revendications 2 à 5, caractérisée en ce
que le rapport entre la longueur (L₁) du bord radialement intérieur de l'aube directrice
et la longueur (L₂) de l'aube directrice au niveau de l'âme satisfait la condition:
7. Aube directrice selon l'une quelconque des revendications 1 à 6, caractérisée en ce
que l'angle d'entrée (α) au niveau de la partie formant racine de l'aube directrice
satisfait à la condition:
et de préférence
8. Aube directrice selon l'une quelconque des revendications 1 à 7, caractérisée en ce
que l'aube directrice ayant une courbure unique a un rayon de courbure constant (R).
9. Aube directrice selon la revendication 8, caractérisée en ce que le rapport entre
le rayon de courbure (R) et la longueur (L₁) du bord radialement intérieur de l'aube
directrice satisfait la condition suivante
et de préférence
10. Aube directrice selon l'une quelconque des revendications 2 à 9, caractérisée en ce
que le rapport entre la hauteur (H₁) de la position de l'âme à partir du bord radialement
intérieur et la hauteur totale (H₂) de l'aube directrice satisfait la condition suivante:
et de préférence
11. Aube directrice selon l'une quelconque des revendications 2 à 10, caractérisée en
ce que le rapport entre les longueurs (L₃) et (L₁) des bords radialement extérieur
et intérieur respectivement de l'aube directrice satisfait la condition:
12. Aube directrice selon l'une quelconque des revendications 1 à 11, caractérisée en
ce que le rapport entre les rayon (R₁) et (R₂) à partir de l'axe du ventilateur vers
les bords extérieur et intérieur de l'aube directrice satisfait la condition suivante:
et de préférence