JPH02298695A - Impeller - Google Patents

Abstract

PURPOSE:To suppress growth of a boundary layer on a vane surface and reduce noise due to outflow of convolution by allowing the max. warp position to be located nearer the front edge with a greater radial position, i.e. with nearer position to the tip, in the profile of each of aplurality of vanes fitted at the side face of a hub in approx. cylindrical form. CONSTITUTION:In an impeller fitted with a plurality of vanes 4 at the side face of a hub 3 in approx. cylindrical form, the max. warp position CX in the profile XX(A) of each vane 4 cut in a radial position near the hub 3 shall be located nearer the tail, while the max. warp position CY of the profile YY(B) cut in a radial position near the tip be situated around the center, and the whole construction shall be such as to be nearer the front edge as approaching the tip from the hub 3. Thereby the stream on the neg. pressure surface of the vane 4 shall be decompressing (accelerative) from the front edge till around the max. warp position, followed by pressure boosting (decelerative) thereafter, and the pressure distribution in the radial direction shall be such as to be high pressure distributed on the side nearer the tip than nearer the hub, which should preclude shift of the boundary layer toward the tip due to the centrifugal force.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an axial flow or mixed flow impeller used in small air conditioners and the like.

2. Description of the Related Art As shown in FIG. 3, a conventional impeller of this type has a structure in which a plurality of blades [2] are arranged around a substantially cylindrical hub l. This blade 2 is cut at an arbitrary radius position WW
Considering the cross-sectional shape of the blade, the cross-sectional shape of the blade, that is, the warp line of the blade is formed by one circular arc, as shown in Fig. 4, and the warp occurs exactly in the middle between the leading edge 2a and the trailing edge 2b. becomes the largest. The shape of this blade differs in the curvature of the circular arc depending on the radial position at which it is cut, but the fact that it is a circular arc does not change.

Traditionally, single-arc blades like the ones mentioned above have been widely used as the blades of this type of impeller.The reason why circular-arc blades have been widely used as blades for this type of impeller is that circular-arc blades are easier to handle in terms of design and manufacturing, and the use of non-arc blades improves performance. This is because it was thought that the amount of effort involved in development was small.

Problems to be Solved by the Invention However, the conventional impellers as described above are not fully satisfied in terms of performance, and improvements are required in terms of pressure characteristics and noise characteristics. In particular, with regard to noise, in recent years, there has been active progress in reducing the noise of household appliances, and there is also a strong demand for reducing the noise of the impeller itself.

In general, the main cause of noise generated from impellers is direct pressure fluctuations, and the factors that cause these pressure fluctuations include turbulence in the suction flow, shedding of vortices from the trailing edge, and turbulent boundary layer! Possible examples include IJH. Among these factors, vortex shedding and boundary layer separation can be considered as problems with the blade itself, but assuming there is no large flow separation near the design operating point, vortex shedding remains. Noise due to vortex shedding is proportional to the thickness of the boundary layer released when the flow velocity is the same, so in order to reduce the noise due to vortex shedding, it is necessary to reduce the thickness of the boundary layer.

Since the flow is pressed against the blade on the pressure surface of the blade, it is difficult for a boundary layer to develop, so here we will consider the flow on the negative pressure surface of the blade. Generally, the longer the chord length, the easier the boundary layer develops, so the boundary layer is thicker on the tip side of the blade than on the hub side. Furthermore, as shown in FIG. 5, the boundary layer that develops on the blade surface is directed toward the tip by centrifugal force from the hub side toward the tip, so that the boundary layer on the tip side becomes even thicker.

As described above, conventional impellers have a problem in that a region with a very thick boundary layer is formed on the tip side of the blade, and the release of vortices from this region becomes the main cause of noise.

The present invention solves such conventional problems, and aims to suppress the development of a boundary layer on the blade surface and reduce noise due to vortex shedding.

Means for Solving the Problems In order to solve the above problems, an impeller of the present invention includes a plurality of blades on the side surface of a substantially cylindrical hub, and the shape of the blades is such that the blades are cut at a certain radial position. In the cross-sectional shape of the blade in this case, the ratio of the maximum warp position from the leading edge differs depending on the radial position, and the larger the radius, the closer the maximum warp position is to the leading edge.

Effect of the Invention With the above-described configuration, the shape of the warp line of the blade differs depending on the radial position, so that the flow on the blade surface is improved.

In other words, the flow on the suction surface generally has a pressure that gradually decreases from the leading edge of the blade and rises from around the point of maximum warping. The closer the wing is to the side, the closer to the leading edge the maximum deflection position is, so the pressure on the wing surface recovers faster.

Therefore, when looking at the pressure distribution on the blade surface in the radial direction, the distribution increases from the hub side toward the tip side. Therefore, the phenomenon in which the boundary layer on the blade surface flows toward the tip side is suppressed, the development of the boundary layer on the tip side is weakened, and a noise reduction effect is obtained.

Example Embodiments of the present invention will be described below based on the accompanying drawings.

In Fig. 1, 3 is the hub, and 4 is a blade. Fig. 2 (A) and (B) show a cross section XX of the blade 4 taken at a radial position close to the hub and a cross section YY taken at a radial position close to the tip. show.

In Figure 2, 4Xa and 4Ya are leading edges, 4Xb and 4Y
b is the trailing edge. Maximum warp Cx for each cross-sectional shape.

The position of cy is located near the rear edge in cross section XX, approximately near the center in cross section YY, and is formed so as to become closer to the front edge as it goes from the hub to the tip as a whole.

The flow on the suction surface of the blade decreases in pressure (increases) from the leading edge to the vicinity of the maximum warp position, and increases in pressure (decelerates) thereafter.

Now, considering the pressure difference on the blade surface in the radial direction (comparison between points P and Q) shown by the ZZ line in Fig. 1, as shown in Fig. 2, the pressure difference at point Q in the pressure increase region It can be seen that the pressure is higher at point P than at point P. As described above, the maximum warp position of the blade warp line moves closer to the leading edge as it goes from the hub to the tip, so the pressure distribution in the radial direction is higher on the tip than on the hub side.

Therefore, since a centripetal force acts inward from the outer circumference of the blade, the boundary layer on the blade surface is prevented from flowing toward the tip side. As a result, the very thick region of boundary layer that existed near the trailing edge on the tip side is eliminated, reducing noise due to vortex shedding.

Effects of the Invention As described above, according to the impeller of the present invention, the maximum warp position of the blade warp line is distributed from the hub side to the tip side, changing from the trailing edge to the leading edge. The pressure distribution in the radial direction is higher on the chimney side. Therefore, a centripetal pressure distribution occurs on the blade surface from the tip side toward the hub side, and the movement of the boundary layer, which would have been swept toward the tip side by centrifugal force, is suppressed.

Therefore, the extremely thick region of the boundary layer that had been occurring at the trailing edge of the blade on the tip side is eliminated, and the effect of suppressing noise due to vortex shedding therefrom is achieved.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an impeller according to an embodiment of the present invention, FIG. 2 (A) is a cross-sectional view of the impeller blade taken along the XX line,
Figure 2 (B) is a cross-sectional view of the impeller blade taken along the YY line, Figure 3 is a plan view of a conventional impeller of this type, and Figure 4 is a sectional view of the blade of the same impeller taken at an arbitrary radial position. FIG. 5 is an explanatory diagram showing the flow on the blade surface of the same impeller. 3...Hub, 4...Blade. Name of agent: Patent attorney Shigetaka Awano (1 person)

Claims (1)

[Claims] A plurality of blades are provided on the side surface of a substantially cylindrical hub, and the shape of the blade is such that, in the cross-sectional shape of the blade when the blade is cut at a certain radial position, the ratio of the maximum warp position from the leading edge is the radius. The impeller is configured such that the position of maximum warpage varies depending on the position, and as the radius increases, the position of maximum warp is located closer to the leading edge.