JPH045760Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field This invention relates to a stall prevention mechanism for an axial flow fan.

BACKGROUND ART A conventional example of a stall prevention mechanism for an axial fan is shown in FIGS. 3a and 3b. That is, in the casing 3 covered around the outer periphery of the axial fan rotor blade 1 fixed to the hub 2 that is rotated,
A recess is formed in the part of the casing facing the tip of the rotor blade from near the tip of the leading edge of the rotor blade 1 toward the upstream side to form a circulation passage 8, and a recess is formed in the portion of the casing facing the tip of the rotor blade 1, and a recess is formed in the portion of the casing facing the tip of the rotor blade 1 to form a circulation passage 8. A large number of rotation prevention vanes 5 are provided protrudingly, and a ring 7 is fixedly installed by connecting the inner peripheral sides of the prevention vanes to form a rear cavity 4 on the downstream side of the prevention vanes, and a front cavity on the upstream side. The axial fan rotor blade sends air in the direction of arrow A from its upstream side, and in the circulation flow path, the flow at the tip of the rotor blade 1 is controlled. Arrow B partially shown in dotted line
I try to circulate it in the direction of.

The effect of the conventional axial fan stall prevention mechanism described above is to stably generate a circulating flow in the circulating flow path, thereby preventing the low-energy flow accumulated at the tip of the rotor blade 1 in the vicinity of the fan stall point. This prevents deterioration of fan characteristics and stalls the fan by causing backflow.

Now, the results of an experiment on the stall prevention situation of an axial flow fan with a conventional stall prevention mechanism will be explained in Fig. 4.The results of a fan without the stall prevention mechanism are also shown. To explain the symbols first, Φ is the flow coefficient, Ψ is the pressure coefficient, Q is the fan flow rate, Δp is the fan pressure increase, D is the fan diameter, and u
is the fan circumferential speed and ρ is the airflow density, Φ=Q/(π/4)・D ²・u Ψ=Δp/(ρ/2)・u ² However, when expressed using this coefficient, the fan The influence of the rotational speed does not appear, and data obtained by changing the rotational speed can be conveniently illustrated as a single curve. According to the same figure, it is known that the performance curve 11 of the conventional fan without a stall prevention mechanism has the disadvantage that the pressure suddenly decreases at the stall point.
Other curve groups 12, 13, and 14 are performance curves related to the equipped fan, and when the fan rotation speed is increased sequentially from low speed, medium speed, and high speed, the characteristics of the stall improvement portion change to the curves 12, 13, and 14. It changes in the order of 14, and the stall prevention amount decreases as the speed increases.
In other words, there is a phenomenon where the stall speeds up, and the reason for this is not clear, but at low speeds the flow flows gently into the separator of the prevention mechanism installed and the desired purpose is achieved, but at high speeds the flow is turbulent. It is thought that the effect will be diminished as the
The issue that needs to be clarified is how much stall margin should be considered when planning the fan.

Problems to be Solved by the Invention This invention aims to eliminate the drawback of a sudden drop in pressure at the stall point, and also to make it possible to estimate the extent of the stall margin.

Means for Solving the Problem This invention is based on a casing covered around the outer periphery of a rotor blade of an axial flow fan, in which a portion of the casing opposite to the tip of the rotor blade is placed on the upstream side from near the leading edge tip of the rotor blade. A recess is formed to form a circulation flow path, and swirl removal vanes are arranged in the circulation flow path, one end of which terminates within the downstream casing, and are arranged in parallel in the circumferential direction.

Therefore, according to the configuration of this invention, the swirl removal vane eliminates the swirl of the circulating airflow in the circulation flow path, and then turns and guides the airflow in the axial direction.

Embodiment Next, an embodiment of this invention will be described with reference to the drawings. In FIGS. 1a, 1b and 1c, a casing 3 covered around the outer periphery of a rotor blade 1 of an axial flow fan is shown.
A recess is formed in the portion facing the tip of the rotor blade from near the leading edge tip of the rotor blade toward upstream to form a circulation flow path 8, A large number of swirl removal vanes 22 are arranged in parallel at a location closest to the tip of the rotor blade 1, and an annular ring 7 is fixed to a portion of the removal vane that does not contact the tip of the rotor blade 1 on the inner peripheral side. The removal vanes are connected to each other, and a front cavity 6 is formed upstream of the removal vanes.

Therefore, according to the embodiment described above, the row of swirl removal vanes 22 radially scoops the flow rotating in the same direction as the rotor blade 1 to remove the swirl flow,
The flow from which this swirling flow has been removed is
It is turned upstream in the direction of arrow C shown in dotted lines in FIG. 1a, and then passes through the front cavity 6 and joins the main stream (arrow A) again. In other words, the rotation prevention vane 5 of the conventional mechanism (Figures 3a and 3b)
However, the swirl removal vane 22 according to this invention performs swirl removal at the stage of radial flow, that is, the swirl removal vane 22 of this invention performs swirl removal at the stage of radial flow. The flow is rectified before it flows into the rear cavity 4.

Furthermore, when the experimental results of the axial flow fan equipped with the stall prevention mechanism according to this invention are shown in FIG. 2 in the same manner as in FIG. It is known that the stall prevention effect is significantly improved and stabilized, so you can feel confident taking this effect into consideration when planning the fan, regardless of whether the fan is large or small, or whether the rotation speed is high or low. Is possible.

Effects of the invention As mentioned above, this invention greatly improves the effect of preventing stalls, and also provides a stable effect, making planning easier and more reliable, making it extremely convenient for product manufacturing. It can be said that this is a great idea.

[Brief explanation of the drawing]

Fig. 1a is a vertical sectional side view of the main part showing an embodiment of this invention, Fig. 1b is a YY sectional view of the previous figure,
Figure 1c is a perspective view of the main parts showing the relationship between the stall removal vanes and the rotor blades, Figure 2 is a performance curve diagram of a fan without a prevention mechanism and a fan with a conventional mechanism, and Figure 3a is a diagram of the performance curves of a fan without a prevention mechanism and a fan with a conventional mechanism. , Fig. 3b is a cross-sectional view taken along the line X-X in the previous figure, and Fig. 4 is a longitudinal sectional side view of the main parts of an axial flow fan equipped with a conventional stall prevention mechanism. FIG. 3 is a performance curve diagram of the axial fan according to the invention. DESCRIPTION OF SYMBOLS 1... Moving blade, 3... Casing, 4... Rear cavity, 5... Rotation prevention vane, 6... Front cavity, 7... Annular ring, 8... Circulation channel, 11...
...Performance curve of a general fan, 12, 13, 14... Performance curve of a fan with a conventional mechanism (low speed, medium speed, high speed), 31... Performance curve of a fan according to this invention.

Claims (1)

[Scope of utility model registration request] Forming a recess from near the leading edge tip of the rotor blade toward the upstream side in a portion of the casing covered around the outer periphery of the rotor blade of the rotor blade facing the tip of the rotor blade to form a circulation flow path, A stall prevention mechanism for an axial fan, characterized in that swirl removal vanes are disposed in the circulation flow path, one end of which terminates within the downstream casing, and are arranged in parallel in the circumferential direction.