CN211648574U

CN211648574U - Centrifugal pump with cavitation erosion resistant blade

Info

Publication number: CN211648574U
Application number: CN201921406659.1U
Authority: CN
Inventors: 章子成; 郑晓周; 张文奇; 张毫杰
Original assignee: Zhejiang University of Technology ZJUT
Current assignee: Zhejiang University of Technology ZJUT
Priority date: 2019-08-28
Filing date: 2019-08-28
Publication date: 2020-10-09
Anticipated expiration: 2029-08-28

Abstract

A centrifugal pump with cavitation erosion resistant blades comprises a centrifugal pump body, wherein the centrifugal pump body comprises a volute, a connecting shaft, a motor and an impeller, the motor is fixed outside the casing, and the connecting shaft is supported on the volute and extends into the volute; the impeller comprises blades, a front cover plate and a rear cover plate, the blades are arranged on a connecting shaft between the front cover plate and the rear cover plate and are positioned in the volute, the motor is in shaft connection with the impeller through the connecting shaft, a non-smooth structure is arranged on the suction surface of each blade, which is close to the front cover plate, and the non-smooth structure is a plurality of bulges. The utility model has the advantages that: the non-smooth surface modification is carried out on the surface of the impeller blade, so that the cavitation erosion resistance is remarkably improved.

Description

Centrifugal pump with cavitation erosion resistant blade

Technical Field

The utility model relates to a centrifugal pump with anti cavitation erosion blade.

Background

The hollow corrosion phenomenon in the centrifugal pump is as follows: when cavitation occurs in the pump, the dense small-size cavitation bubbles are broken at the solid wall surface of the impeller and are in direct contact with the solid wall surface of the impeller, and the cavitation bubbles release high-strength pulse pressure when collapsing to continuously and repeatedly erode the wall surface of the impeller. Cavitation erosion is closely related to the evolution of cavitation bubbles, and the essential cause of cavitation erosion in centrifugal pumps is the result of the periodic collapse of a cavitation bubble population. Due to the transient and random nature of cavitation erosion, it is difficult to accurately predict cavitation erosion intensity and cavitation erosion area. For a centrifugal pump in work, the problem of cavitation damage caused by cavitation is difficult to completely overcome at present. In fact, the degree of cavitation damage of the cavitation bubbles to the wall surface of the centrifugal pump impeller is not only related to the material performance of the wall surface of the centrifugal pump impeller, but also depends on the geometric shape of the wall surface of the centrifugal pump impeller. Because the different geometric shapes of the solid surface of the impeller can influence the interaction form with the wall surface of the impeller when the cavitation collapse occurs, for example, the impact angle, the impact speed, the impact area distribution and the flow field change of the micro jet generated when the cavitation collapse occurs can influence the cavitation collapse.

The structure of the industrial machine under specific working conditions is improved by the bionics principle, the method is novel and effective in engineering modification, and the non-smooth surface structure is a bionic technology with wide application prospect. The utility model discloses the bionic non-smooth surface of application can improve centrifugal pump's performance effectively in the centrifugal pump, has a lot of designs to improve hydraulic element's such as impeller, spiral case structure to play the effect of suppression cavitation, but the utility model discloses with novel angle, provide one kind can reduce the structural design of the damage (cavitation) that the cavitation caused by a wide margin when the cavitation takes place, anti cavitation erosion blade surface non-smooth structure promptly.

Disclosure of Invention

To the above problem, the utility model provides a can improve the characteristics of flow field structure and improve the centrifugal pump that has anti cavitation erosion blade of the ability of the anti cavitation erosion damage of centrifugal pump.

The utility model discloses a centrifugal pump with cavitation erosion resistant blade, including the centrifugal pump body, the centrifugal pump body includes spiral case, connecting axle, motor and impeller, the motor be fixed in outside the casing, the connecting axle bearing in the spiral case and stretch into in the spiral case; the impeller include blade, front shroud and back shroud, the blade dress on the connecting axle between the front and back shroud and be located the spiral case, the motor pass through connecting axle and impeller coupling, its characterized in that: the suction surface of the blade close to the front cover plate is provided with a non-smooth structure, and the non-smooth structure is a plurality of bulges.

The bulges are arranged in rows, and each row of bulges extends from the center of the impeller to the edge of the impeller in a spiral shape.

The protrusions are spherical protrusions. Extracting the biological surface structure characteristic parameters of the shrimps, wherein the structural form of the skin of the shrimps is mainly expressed among the flowing concave-convex structures; and then, according to the skin structure, the structure conforms to the streamline characteristic structure, such as a spherical bulge structure, and the characteristic of the spherical bulge structure is relatively in accordance with the flowing form of the fluid.

The spherical bulges are distributed in rows along the length direction of the blade, and the spherical pits in each row are arranged at equal intervals. Considering that centrifugal pump cavitation firstly occurs at the impeller inlet, the suction surface of the blade is close to the front cover plate, and the molded line of the front edge of the blade and the shape of the suction surface have great influence on the centrifugal pump cavitation performance. The back ridge structure of the peeled shrimp is simplified into a spherical convex structure by the bionic principle, and the spherical convex structure is added to the suction surface position of the centrifugal pump impeller close to the front cover plate.

Cavitation damage is the main reason causing the centrifugal pump impeller wall to lose efficacy, when the pump cavity grows gradually, with the liquid flow entering high pressure area after, the cavity receives the effect of surrounding high pressure liquid and begins to collapse. When the cavitation bubbles are broken at the solid wall surface of the centrifugal pump, high-pressure water around the cavitation bubbles fills the broken cavitation bubbles at high speed to form high-speed micro jet flow and shock waves, so that cavitation erosion damage is caused to the solid wall surface of the centrifugal pump. When the centrifugal pump is in a cavitation damage state for a long time, the metal wall surface of the blade firstly has cavitation pinholes, a large amount of bubbles are repeatedly and continuously collapsed, so that the walls of the cavitation pinholes are continuously peeled off, and the cavitation pinholes are gradually enlarged to form cavitation pits after a period of time. The utility model discloses a better cavitation erosion damage performance that improves the centrifugal pump establishes bionical non-smooth surface structure in centrifugal pump impeller suction surface department through bionical principle, and this structure is a circular structure. Because the surface of the non-smooth blade is provided with the convex structure and does not accord with the flow state characteristic of the fluid, vortex is easily generated at the concave pit, energy is consumed, the conversion of pressure energy to speed energy is influenced, and the lift and the efficiency are reduced. But the non-smooth surface is well fitted with the flow curve of the liquid flow, and no overlarge bending angle exists, so that the lift and the efficiency of the vane are closer to those of a smooth vane, and the decline of the external characteristics is extremely small.

The utility model has the advantages that: the non-smooth surface modification is carried out on the surface of the impeller blade, so that the cavitation erosion resistance is obviously improved; the bionic non-smooth surface structure with proper structure and size is arranged on the suction surface of the centrifugal pump where cavitation and cavitation are most likely to occur, and a method combining numerical simulation and experimental verification is adopted, so that the characteristics of the non-smooth surface structure in improving the flow field structure and the capability of improving the cavitation erosion resistance of the centrifugal pump are verified, further development of the cavitation and cavitation performance of the centrifugal pump is certainly promoted, and the method has important theoretical significance and engineering practical value.

Drawings

FIG. 1 is a block diagram of the present invention;

FIG. 2a is a cloud of the distribution of void volumes of a conventional blade at the suction side of the blade;

FIG. 2b is a cloud of the vacuole volume of the vane of the present invention distributed at the suction surface of the vane;

FIG. 3a is a velocity vector diagram at smooth blade and dimple;

FIG. 3b is a velocity vector diagram of the blade and the pit of the present invention;

FIG. 3c is an enlarged view of the vector diagram at the pocket of the suction side of the blade of FIG. 3 b;

fig. 4 is an overall structural view of the centrifugal pump.

Detailed Description

The present invention will be further described with reference to the accompanying drawings.

With reference to the accompanying drawings:

embodiment 1 the utility model discloses a centrifugal pump with anti cavitation erosion blade, including the centrifugal pump body, the centrifugal pump body includes spiral case 2, connecting axle 3, motor 4 and impeller 5, motor 4 be fixed in outside the casing, connecting axle 3 support in spiral case 2 and stretch into in the spiral case; the impeller 5 comprises a blade 1, a front cover plate 6 and a rear cover plate 7, the blade is arranged on a connecting shaft between the front cover plate and the rear cover plate and is positioned in the volute, the motor is in shaft connection with the impeller through the connecting shaft, a non-smooth structure 11 is arranged on the suction surface of the blade 1 close to the front cover plate, and the non-smooth structure is a plurality of bulges.

The bulges are arranged in rows, each row of bulges extends from the center of the impeller to the edge of the impeller in a spiral shape, and the rotating directions of the bulges in each row are consistent.

Example 2 in conjunction with fig. 1, the form of the unsmooth structure of the anti-cavitation vane surface is illustrated, considering that centrifugal pump cavitation occurs first at the impeller inlet, the suction surface of the vane is located close to the front cover plate, and the profile of the vane leading edge and the shape of the suction surface have a great influence on the centrifugal pump cavitation performance. A circular convex structure is added to the position of a suction surface of a centrifugal pump impeller close to a front cover plate through a bionic principle.

The combination of fig. 2a and 2b and fig. 3a, 3b and 3c illustrates how the non-smooth structure of the cavitation erosion resistant blade surface improves the cavitation erosion resistance at the blade position. Fig. 2a and 2b show the distribution cloud of cavitation bubbles on smooth surface and straight round non-smooth surface blades. The region where primary cavitation occurs is at the leading edge of the blade, where there is a higher volume fraction of vapor phase. Because of the asymmetry of the distribution of the cavitation bubbles, the influence degrees of the liquid flow angles of the blades on the cavitation bubble evolution are different, the non-uniformity of the stress of the blades on each flow channel in the centrifugal pump is increased, particularly in the working process of the centrifugal pump, the rotation motion of the impeller enables the attack angles of the blades to be changed alternately in a positive mode and a negative mode, the condition can generate larger stress action on the impeller of the centrifugal pump, the fatigue damage of the blades is caused, and the damage and the damage of the blades are caused by the action of the positive and negative alternate changes together with the cavitation erosion caused by the collapse of. It can be seen from fig. 2a, 2b that when the blade surface is smooth, the cavitation bubbles substantially adhere to the blade surface. When the surface of the blade is of a non-smooth structure, the volume fraction of a vapor phase of the bionic structure in a flow layer close to the wall surface of the blade is low, most of the vapor phase is concentrated at the convex tip part of the bionic structure, so that when the surface of the blade is of the non-smooth convex structure, the cavitation bubble tends to rise upwards, the convex structure mainly interferes with the motion track of the cavitation bubble like an obstacle, and the cavitation bubble is far away from the surface of the blade. The phenomenon exists, so that when the cavitation bubbles collapse, cavitation damage areas of the blades with the non-smooth surfaces are mainly concentrated on the tops of the bionic bulge structures, damage to the surfaces of the blades is small, and the cavitation damage areas and the cavitation damage strength are obviously reduced.

The velocity vector diagram at the suction surface of the bionic non-smooth centrifugal pump blade is shown in figure 3. As can be seen from FIG. 3, the fluid in the pits forms reverse flowing vortices along with the main flow field, the formation of the vortices hinders the sweeping-down motion of the upper high-speed fluid, the reverse vortices in the pits form an independent low-speed layer, and the reverse vortices reduce momentum exchange with the main flow field, thereby reducing the contact area between cavitation bubbles and the wall surface and simultaneously reducing the damage degree to the wall surface of the blade when the cavitation bubbles collapse. The generation of the reverse vortex weakens the strength of the flow direction of the suction surface of the blade close to the wall surface to the vortex, reduces the energy of the high-speed flow direction vortex, weakens the strength of turbulence burst and the momentum exchange between the expansion direction and the normal direction of the reverse vortex and the main flow field from the source, and further weakens the capacity of generating cavitation bubbles on the close wall surface of the blade. If the mechanical principle is used, the method is similar to the air bearing theory.

The cavitation area and the cavitation damage area are not completely consistent, so that the cavitation damage area is generally in the cavitation collapse area and is related to the physical characteristics of the fluid medium, the material property of the wall surface of the flow channel and the collapse speed of the cavitation. The evolution of the cavitation zone at the front cover plate is closely related to the evolution of the gas volume zone. The air bubbles are small in size during primary cavitation, most of the air bubbles are unstable and irregular foam-shaped air bubbles, and the air bubbles are basically concentrated on the front edge of the suction surface of the blade at the inlet of the impeller. The irregular small cavitation bubbles are broken at the front cover plate to greatly damage the wall surface of the impeller, cavitation erosion areas on the front cover plate of the impeller are distributed in a dotted manner, the physical characteristics of the irregular small cavitation bubbles are matched with those of pits with uneven pits formed on the surface of the impeller during actual cavitation erosion damage, and the size of the cavitation erosion areas of the non-smooth blade impeller is basically consistent with the cavitation erosion damage strength of the smooth blade impeller. In the cavitation development stage, the air bubbles in the impeller flow passage gradually expand towards the outlet of the impeller flow passage, and the cavitation erosion area migrates towards the outlet of the impeller flow passage along with the expansion direction of the air bubbles. At the moment, the form of the cavitation bubbles is not completely converted into the layered large cavitation bubbles from the small foam-shaped cavitation bubbles, the cavitation erosion area on the front cover plate is expanded, and the cavitation erosion areas which are distributed uniformly in a scattered point shape in the impeller flow passage gradually develop into the strip-shaped cavitation erosion area. With the decrease of cavitation allowance, cavitation in the smooth blade impeller develops most rapidly, and the cavitation volume occupies half of the impeller flow passage. The cavitation erosion area and the strength are rapidly increased, and the damage to the wall surface of the impeller is intensified. The cavitation bubble increase amplitude of the non-smooth surface blade impeller is smaller than that of the smooth blade impeller, the volume fraction of gas on the front cover plate is lower, the cavitation erosion damage area is smaller than that of the smooth blade impeller, and the cavitation erosion damage strength is weaker than that of the smooth blade impeller. When severe cavitation is generated, the cavitation erosion area of the wall surface of the front cover plate of the impeller is further expanded to the outlet of the impeller, and the cavitation erosion area and the cavitation erosion damage strength are further enhanced. Due to the dynamic and static interference effect of the impeller and the partition tongue, bubbles in the flow channel are asymmetrically distributed, so that cavitation erosion areas are also asymmetrically distributed. Cavitation is not easy to occur in the non-smooth blade impeller, and the cavitation erosion area is relatively small. In the process of developing from primary cavitation to severe cavitation, cavitation areas are basically concentrated in the area from the impeller inlet to the 1/2 flow passage, the cavitation strength is weaker than that of a smooth blade impeller, and cavitation is well inhibited, so that the cavitation performance of the impeller is improved.

With reference to fig. 4, the gas volume area on the back cover plate is larger than that of the front cover plate, but the gas content is relatively small, and the evolution of the cavitation erosion process, the cavitation erosion area and the cavitation erosion damage strength of the two types of blade impellers is basically consistent with the evolution of the cavitation erosion on the front cover plate. Meanwhile, in the process from primary cavitation to severe cavitation, the cavitation position and the cavitation strength in the impeller are changed at any time along with the development of cavitation bubbles, the region with the most severe cavitation is the joint of the back surface of the blade and the rear cover plate, and no obvious cavitation phenomenon exists near the outlet of the impeller flow channel. During primary cavitation, the pressure of the corresponding point of the suction surface on the blade is lower than the pressure of the pressure surface, and the low-pressure area appears at the front edge of the blade close to the front cover plate firstly, so that the position is most prone to cavitation erosion in the impeller. Under severe cavitation, where the air bubbles occupy 2/3 area in the impeller flowpath from the leading edge of the blade to the trailing edge of the blade, the pressure side of the blade is more severely cavitated than the suction side.

When the primary cavitation NPSH is 2.0m, cavitation damage to the blade and the back cover plate is easily caused by bubble breakage, so when the primary cavitation NPSH is 2.0m, the damage area is at the inlet of the impeller flow passage. When the primary cavitation NPSH is 2.0m, the cavitation area in the impeller flow passage is small, the cavitation density is also small, the pressure surface of the blade basically has no bubbles, and the pressure surface of the blade is basically not influenced by cavitation damage. As the cavitation margin decreases, the cavitation zone on the blade is gradually displaced from the leading suction side of the blade to the pressure side of the blade. When the primary cavitation NPSH is 2.0m, the cavitation area and the intensity on the back cover plate of the two blade impellers are not greatly distinguished.

In the cavitation development stage, the cavitation damage area of the smooth blade impeller is increased most rapidly and the cavitation damage strength is strongest in the two blade impellers. The non-smooth blade impeller has the bionic protruding structure on the suction surface of the blade, so that cavitation is effectively inhibited, and after cavitation bubbles are generated, the bionic protruding structure on the non-smooth surface effectively lifts the cavitation bubbles, so that the cavitation bubbles are far away from the suction surface of the blade. Compared with the initial cavitation and the cavitation development period, the cavitation damage degree of the serious cavitation is wide in a large range, materials at the blades and the rear cover plate are easily damaged to form cavitation pits, and the impeller can be subjected to cavitation corrosion and rupture in serious conditions. During severe cavitation, bubbles gradually migrate from the suction surface of the blade to the pressure surface of the blade, the flow channel is damaged to different degrees during the cavitation transfer process, and meanwhile, the cavitation erosion area of the blade is converted from the initial suction surface of the blade to the pressure surface of the blade. The smooth vane impeller is substantially filled with 4/5 impeller channels with air bubbles. In the severe cavitation stage, the cavitation volume fraction in the flow channel of the smooth blade impeller is the highest, and the generated cavitation erosion damage is the most severe. The non-smooth blade impeller has the weakest cavitation phenomenon and the least cavitation damage intensity and cavitation erosion area. The non-smooth surface blade impeller can better improve the flow state in the impeller flow channel without influencing the external characteristics of the centrifugal pump, improve the cavitation characteristics of the centrifugal pump and effectively improve the size of a cavitation area and the cavitation damage degree.

The embodiments described in this specification are merely illustrative of implementations of the inventive concepts, and the scope of the invention should not be considered limited to the specific forms set forth in the embodiments, but rather the scope of the invention includes equivalent technical means that can be conceived by those skilled in the art based on the inventive concepts.

Claims

1. A centrifugal pump with cavitation erosion resistant blades comprises a centrifugal pump body, wherein the centrifugal pump body comprises a volute, a connecting shaft, a motor and an impeller, the motor is fixed outside the casing, and the connecting shaft is supported on the volute and extends into the volute; the impeller include blade, front shroud and back shroud, the blade dress on the connecting axle between the front and back shroud and be located the spiral case, the motor pass through connecting axle and impeller coupling, its characterized in that: the suction surface of the blade close to the front cover plate is provided with a non-smooth structure, and the non-smooth structure is a plurality of bulges.

2. A centrifugal pump having cavitation erosion resistant vanes as recited in claim 1, wherein: the bulges are arranged in rows, and each row of bulges extends from the center of the impeller to the edge of the impeller in a spiral shape.

3. A centrifugal pump having cavitation erosion resisting vanes as set forth in claim 2, wherein: the protrusions are spherical protrusions.

4. A centrifugal pump having cavitation erosion resisting vanes as set forth in claim 3, wherein: the spherical bulges are distributed in rows along the length direction of the blade, and the spherical pits in each row are arranged at equal intervals.