JPH04334797A - Diffuser for centrifugal pump - Google Patents

Abstract

PURPOSE:To reduce peeling-off from a guide vane at a low-flow range for highly reliable pump operation. CONSTITUTION:A guide vane inlet part 4 is provided with a projecting part 8 where a vane width 6 on the negative-pressure side is larger than a vane width 7 on the pressure side of the guide vane to a vane thickness center line 5 of the guide vane 2, and a communicating hole 12 communicating with a guide vane pressure surface 11 is provided at the guide vane negative-pressure surface 10 of a recessed part 9 on an final point of the projecting part. It is thus possible to reduce peeling-off flow from the guide vane inlet at the low-flow range, and prevent a head-discharge curve from becoming flat for highly reliable pump operation control.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a centrifugal pump, and more particularly to a diffuser for a centrifugal pump suitable for a high-pressure pump such as a boiler feed pump.

0002

[Prior Art] In a centrifugal pump, in order to sufficiently restore the static pressure of the flow coming out of the impeller and increase the efficiency of the pump, a diffuser with guide vanes is used in the diffuser section after the flow comes out of the impeller. A centrifugal pump with an attached centrifugal pump is used (Japanese Utility Model Publication No. 147803/1983).

Conventional centrifugal pumps with diffusers operate in a wide flow rate range from large flow rates to small flow rates in a shut-off state. Therefore, in a low flow rate range away from the design point, the inflow angle of the flow from the impeller into the guide vane becomes smaller than the inlet angle of the guide vane, and the flow separates from the negative pressure surface of the guide vane. The size of this separation area increases as the flow rate decreases.

[0004] Therefore, due to the separation loss caused by this separation flow, sufficient static pressure recovery cannot be obtained in the diffuser section, and as shown in FIG. 2, a characteristic occurs in which the head curve becomes flat 11 in the low flow area 12. . For this reason, the flow rate cannot be properly controlled by controlling the rotational speed of the pump, resulting in a loss of operational reliability.

[0005] In order to prevent the above-mentioned separation flow in the low flow rate region, as described in Japanese Utility Model Application Publication No. 59-192699, a through hole passing through the pressure surface and the negative pressure surface of the guide vane is provided, and the pressure surface The structure reduces the separation of the guide vane from the suction surface by causing a flow from the through hole of the suction surface along the suction surface due to the pressure difference between the suction surface and the suction surface, and the inflow angle of the flow and the guide vane that cause separation. In order to prevent separation due to mismatch of blade entrance angles, a structure that makes the guide vanes variable as disclosed in Japanese Utility Model Application No. 54-147803, and furthermore,
As described in Japanese Patent No. 9-231199, a structure in which the blade inlet angle is made different between the shroud side and the hub side has been devised.

[0006]

[Problem to be Solved by the Invention] However, in the prior art, a through hole passing through the pressure surface and the negative pressure surface of the guide vane is provided,
In the case of a structure in which the flow along the suction surface is caused by the pressure difference between the pressure surface and the suction surface to reduce separation of the guide vane from the suction surface, the through hole is designed to prevent separation flow due to the strength constraints of the guide vane. It is not provided at the tip of the guide vane inlet where it is most likely to occur, and therefore the effect of reducing separation flow is small. Also,
Those with variable guide vanes not only have a complicated structure and high price, but also have problems with the strength of the casing because the casing is provided with a movable mechanism.

[0007]Furthermore, a guide vane having a three-dimensional shape in which the entrance angle of the guide vane is twisted differently on the shroud side and the hub side has the problem that not only is the cost high, but the strength of the blade is reduced.

[0008] The object of the present invention is to:
By reducing the separation from the negative pressure surface of the guide vane, the lift curve caused by the separation is prevented from becoming flat, and highly reliable pump operation control is performed in the entire flow rate operation range.

[0009]

[Means for Solving the Problems] The above object is to provide a convex portion at the inlet of the guide vane with a thickness larger on the suction side than on the pressure side with respect to the blade thickness center line of the guide vane.
Moreover, this is achieved by providing a communication hole communicating with the guide vane pressure surface on the guide vane negative pressure surface of the concave portion at the end point of the convex portion.

0010

[Operation] In a low flow rate region, the inflow angle of the flow becomes smaller than the vane inlet angle of the guide vane. For this reason, the flow tends to separate from the suction side of the guide vane, but at the inlet of the guide vane where separation is likely, the blade thickness on the suction side with respect to the blade center line of the guide vane should be A convex portion larger than the blade thickness is provided, and a communication hole communicating with the guide vane pressure surface is provided on the guide vane negative pressure surface of the concave portion at the end of the convex portion. Therefore, if the inflow angle of the flow becomes small in the low flow rate region and the flow tends to separate from the negative pressure surface of the guide vane, the flow on the negative pressure surface of the guide vane should be arranged along the flow direction in the low flow rate region. The flow flows along the convex part without separation, and the concave part at the end of the convex part has a communication hole that communicates with the pressure surface, so the pressure difference between the pressure surface and the negative pressure surface causes the flow to flow on the negative pressure side. Since a flow is generated from the hole along the shape of the suction surface, the flow flows along the blade surface without separation or stagnation even in this recess, so that the separation flow from the suction surface at the blade inlet can be significantly reduced.

Therefore, it is possible to prevent the lift curve from becoming flat due to separation loss of the separated flow from the guide vanes, and highly reliable pump operation control can be performed in the entire flow rate operation range.

0012

[Embodiment] An embodiment of the present invention will be explained below with reference to FIG. In a diffuser 3 having a plurality of guide vanes 2 arranged after exiting the impeller 1, the vane inlet portion 4 of the guide vanes has a vane thickness t1 on the suction side of the guide vanes with respect to the vane thickness center line 5 of the guide vanes. A convex portion 6 is provided which is larger than the blade thickness t2 on the pressure surface side, and a communication hole 10 communicating with the guide vane pressure surface 9 is provided on the guide vane negative pressure surface 8 of the concave portion 7 at the end point of the convex portion.
has been established.

Next, its operation will be explained. At the design flow rate, the flow leaving the impeller and entering the diffuser is a uniform flow along the guide vanes 2. However, as the flow rate decreases, the flow exiting the impeller becomes inward, and the flow entering the guide vane inlet 4 becomes smaller than the guide vane entrance angle. Therefore, the flow tends to separate from the negative pressure surface 8 of the guide vane, but at the guide vane inlet 4, the flow flowing into the guide vane is separated from the negative pressure surface 8 of the guide vane, which is formed to match the flow direction of the low flow rate region. Since it flows along the convex portion 6, it does not peel off. Further, in the concave portion 7 at the end point of the convex portion 6, a communication hole 10 is provided that communicates the guide vane pressure surface 9 with the guide vane negative pressure surface 8.
Since the flow along the guide vane negative pressure surface 8 is generated from the recess 7 where flow separation or stagnation is likely to occur due to the pressure difference, separation does not occur from the recess 7 either.

[0014]

Effects of the Invention According to the present invention, it is possible to prevent separation of the guide vane from the negative pressure surface in the low flow rate range, and to significantly reduce separation loss, so that the head curve is not flat in the full flow rate operation range but is rightward. Since the flow rate can be lowered, highly reliable pump operation control can be performed in the entire flow rate operation range.

[Brief explanation of drawings]

FIG. 1 is a front view of a diffuser section of the present invention.

FIG. 2 is a head characteristic diagram of a conventional centrifugal pump diffuser.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Impeller, 2... Guide vane, 3... Diffuser, 4... Inlet part of guide vane, 5... Blade thickness center line, 6... Blade thickness on suction side, 7... Blade thickness on pressure side, 8 ... Convex portion, 9... Concave portion, 10... Guide vane negative pressure surface.

Claims (1)

[Claims] 1. A convex portion is provided at the guide vane inlet, with respect to the blade thickness center line of the guide vane, the thickness of the blade on the negative pressure side of the guide vane being larger than the thickness of the blade on the pressure side of the guide vane,
A diffuser for a centrifugal pump, characterized in that a communication hole communicating with the guide vane pressure surface is provided on the guide vane negative pressure surface of the concave portion at the end point of the convex portion.