Chute for improving performance of saddle area of axial flow pump and design method

Abstract

The invention discloses a chute for improving the performance of a saddle area of an axial flow pump and a design method and belongs to the field of fluid machinery. The inclined groove is formed in the inner wall of the axial-flow pump water inlet pipe which is installed at the front edge of the axial-flow pump body. The inclined groove and the axis of the axial flow pump water inlet pipe form a preset angle. The skewed slot is obliquely formed in the blade profile direction of the impeller, the two ends of the skewed slot are communicated with the two sides of a water inlet pipe of the axial flow pump respectively, and fluid at the inlet rim is rectified. The skewed slots are quadrilateral grooves, the depths of the grooves are the same, and the bottom surfaces of the grooves are on the same conical surface; a protrusion is formed between every two grooves, and the surfaces of the protrusions are located on the same conical surface. According to the design method for the inhibition chute in the saddle area of the axial flow pump, the size of the chute and the size of the axial flow pump are subjected to multi-scale coupling by establishing a new dimensionless number NOG, the size parameters of the chute can be efficiently, rapidly, accurately and reliably determined, and the design method is suitable for the design of the inhibition chute in the saddle area of the axial flow pump. The small-flow performance of the axial flow pump is improved to the maximum extent, and the design efficiency is affected to the minimum extent.

Description

Technical Field

[0001] The invention relates to an inclined groove and a design method for improving the performance of a saddle area of ​​an axial flow pump, and belongs to the field of fluid machinery. Background Art

[0002] As a pump with high specific speed, large flow and low head, axial flow pump has mature technology and is easy to operate and maintain. Therefore, it is widely used in various fields such as farmland irrigation projects, water diversion projects, flood control and drainage projects, municipal water supply projects, chemical industry, shipbuilding industry, etc.

[0003] When the axial flow pump operates under the design conditions, it has high efficiency, good internal flow conditions, stable flow state, and safe and efficient operation. However, under high load conditions, the operation of the axial flow pump deviates from the design conditions, especially when its working flow rate is reduced to 0.6 times or less of the design conditions. Due to the change of the inlet inflow conditions, serious flow separation occurs at the inlet rim of the impeller blade suction surface. At the same time, due to the pressure difference between the pressure surface and the suction surface of the impeller blade, a tip gap leakage flow is generated at the tip gap. The separation flow on the blade suction surface and the tip gap leakage flow are the conditions for the axial flow pump to enter the small flow condition. The fully developed vortex structure will block the entire impeller channel, which will not only cause the performance and efficiency of the axial flow pump to drop sharply under small flow, but also cause strong vibration and noise during operation, which will affect the safety of the pump body. The above shortcomings will have a strong negative impact on the performance and safety of the axial flow pump during the rapid startup process and operation under harsh conditions, and reduce the operating efficiency and service life of the axial flow pump. Therefore, whether from the perspective of performance or safety, suppressing the instability of flow in the saddle area of ​​the axial flow pump is an important direction of current axial flow pump research. Based on the passive flow control technology of fluid machinery, a diversion chute on the wall of the water inlet pipe of an axial flow pump is proposed to control the flow in the saddle area and improve the performance of the stall condition. At the same time, a rapid design method for the optimal size of the chute is given, which can accurately, efficiently and quickly complete the chute design matching the target model axial flow pump. Summary of the invention

[0004] The purpose of the present invention is to solve the problem of performance, efficiency degradation and safety impact caused by deterioration of inflow conditions when an axial flow pump is running at a low flow rate, and to provide a chute and design method for improving the performance of the saddle area of ​​an axial flow pump.

[0005] The objectives of the present invention are achieved through the following technical solutions.

[0006] The invention discloses an inclined groove for improving the saddle area performance of an axial flow pump. The inclined groove is arranged on the inner wall of an axial flow pump water inlet pipe, and the axial flow pump water inlet pipe is installed at the front edge of the axial flow pump body. The inclined groove forms a predetermined angle with the axis of the axial flow pump water inlet pipe.

[0007] Preferably, the inclined groove is opened obliquely along the impeller blade direction, and both ends of the inclined groove are respectively connected to the two sides of the axial flow pump water inlet pipe, which has a rectifying effect on the fluid at the inlet wheel rim.

[0008] Preferably, the inclined groove is a quadrilateral groove, each groove has the same depth, and the bottom surface of the groove is on the same conical surface; a protrusion is formed between every two grooves, and the surface of the protrusion is located on the same conical surface.

[0009] Preferably, the chute and the axis of the axial flow pump water inlet pipe form a predetermined angle, which is determined according to the diameter and rotation speed of the axial flow pump, and the predetermined angle ranges from 6° to 18°. The larger the diameter and the higher the rotation speed, the larger the value of the predetermined angle.

[0010] The present invention also discloses a method for designing a chute for improving the performance of the saddle area of ​​an axial flow pump, which is used to design the chute and is characterized in that it comprises the following steps:

[0011] Step 1, determine the relevant geometric dimensions of the axial flow pump, including the impeller diameter D, the impeller axial length L and the impeller inlet placement angle weighted value θ of the axial flow pump;

[0012] Step 2, determining the chute parameters, which include the number of chute n, the axial length l, the width w, the depth d, and the angle α between the edge of the chute and the central axis of the pipeline;

[0013] Step 3: Non-dimensionalize the parameters in steps 1 and 2 to establish the dimensionless parameter NOG:

[0014] NOG=DWR×VR×DLR×AR

[0015] Among them, the depth-to-width ratio DWR = d / w, which is the ratio of the depth d to the width w of the chute; the volume ratio It is the ratio of the total volume of the chute to the volume of the impeller inlet. The total volume of the chute is the number of chute multiplied by the volume of a single chute. The impeller inlet volume is the impeller inlet area. The product of the impeller axial length L; the diameter-to-length ratio DLR = D / l, which is the ratio of the impeller diameter D to the axial length l of the skew groove; the angle ratio AR = α / θ, which is the ratio of the angle α between the edge of the groove and the central axis of the pipeline to the weighted value θ of the inlet placement angle; where Take m impeller inlet placement angles at equal intervals from the hub to the rim along the blade span direction and record them as θ i , the angle closest to the hub is θ1, followed by θ2, and so on, the angle closest to the rim is θ m ; In the axial flow pump system with the addition of the chute, the closer to the wheel rim, the stronger the influence of the chute;

[0016] Step 4: If the dimensionless parameter NOG obtained by calculating the chute parameters in step 2 satisfies 0.014<NOG<0.022, the chute of the axial flow pump water inlet pipe is processed according to the chute parameters; if not, the chute parameters are redesigned and steps 2 to 4 are repeated until the chute parameters that meet the requirements are obtained.

[0017] The present invention also discloses a method for connecting an axial flow pump water inlet pipe provided with the inclined groove to an axial flow pump, comprising the following steps:

[0018] The connection method comprises the following steps: step 1, assembling an axial flow pump water inlet pipe with an inclined groove, wherein the axial flow pump water inlet pipe comprises a conical axial flow pump water inlet pipe, front and rear end connecting flanges of the pipe, a front support of a water guide cone, a front support bracket of a water guide cone, and an inclined groove on the inner wall of the pipe;

[0019] Connection method step 2: The tapered water inlet pipe refers to a gradually narrowing pipe with a draft angle of 3° to 6°. The wide side and narrow side of the pipe are respectively equipped with connecting flanges. The water flows from the wide side to the narrow side. The wide side pipeline is connected to the front side pipeline of the water inlet pipe with a flange, and the narrow side pipeline is connected to the outer pipeline of the impeller section with a flange.

[0020] Connection method step three, the water guide cone front support refers to a support device for installing the axial flow pump water guide cone, the water guide cone front support is connected and fixed to the conical water inlet pipe through the water guide cone front support bracket, there are six brackets, each bracket is spaced at an angle of 60°, and the bracket is in the shape of a straight plate; the front and rear sides, the connecting pipe wall side and the connecting water guide cone front support side are chamfered, the water guide cone front support has threads inside, and the water guide cone is connected to the front support and installed through the threads.

[0021] Beneficial effects:

[0022] 1. The present invention discloses a flow guide device with an inclined groove installed on the inner wall of a front water inlet pipe of an axial flow pump. Different from the general water inlet pipe form, the inclined groove added to the water inlet pipe wall can not only suppress the inlet circumferential swirl of the axial flow pump under the low flow condition from different dimensions, but also has the ability to suppress the tip leakage vortex of the blade and the blocking vortex of the impeller channel of the axial flow pump, effectively improving the flow separation on the suction surface of the blade and improving the performance of the axial flow pump in the low flow area.

[0023] 2. The present invention discloses a guide device with an inclined groove installed on the inner wall of the water inlet pipe of an axial flow pump. The inclined groove is opened on the inner wall of the water inlet pipe of the axial flow pump. It is a passive flow control method. The inclined groove guide structure is used to control the abnormal flow at the inlet of the axial flow pump. There is no need for the system to provide additional energy to the inclined groove guide device. It has the advantages of simple structure, low cost and easy processing. It can improve the performance of the axial flow pump in small flow operation and the stability and safety during operation at a relatively low cost.

[0024] 3. The present invention discloses a design method for suppressing the saddle area of ​​an axial flow pump. Different from the traditional simple passive control technology, the design method non-dimensionalizes the number of chute, axial length, depth, width, and the angle between the edge of the chute and the central axis of the pipeline with the diameter, axial length, and inlet placement angle weighted values ​​of the axial flow pump impeller to obtain the chute size design parameter NOG, and couples the size of the chute with the size of the axial flow pump in multiple scales. The size parameters of the chute can be determined efficiently, quickly, accurately, and reliably, thereby maximizing the performance of the axial flow pump at small flows and minimizing the impact on the efficiency of the design conditions.

[0025] 4. The method for connecting the water inlet pipe of an axial flow pump with the inclined groove disclosed in the present invention uses a flange to connect the narrow side of the water inlet pipe to the rim of the axial flow pump, and the front support of the water guide cone is connected to the water guide cone of the axial flow pump by a thread, and is connected to the wall of the water inlet pipe of the axial flow pump through the front support bracket of the water guide cone. Compared with the traditional simple flange connection method, the radial runout of the axial flow pump during operation is reduced on the basis of ensuring the water seal, and the spaced front support bracket of the water guide cone has a certain inhibitory effect on the axial flow in the inlet pipe, which ensures the stability and safety of the operation of the axial flow pump, improves the uniformity of the inlet flow, and improves the inflow conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of a tapered water inlet pipe with a chute added;

[0027] Figure 2 for Figure 1 Cross-sectional view along AA direction;

[0028] Among them, 1 is a connecting flange, 2 is a front support bracket of the water guide cone, 3 is a front support of the water guide cone, 4 is an inclined groove protrusion, 5 is an inclined groove channel, and 6 is a conical water inlet pipe;

[0029] Figure 3 It is a schematic diagram of the position of the water inlet pipe with inclined slots in the axial flow pump system;

[0030] Figure 4 To compare the external characteristic curves of the axial flow pump after adding different groove types;

[0031] Figure 5 The figure shows the design value and preferred area curve of NOG. DETAILED DESCRIPTION

[0032] The following is a specific embodiment of the present invention, and the technical solution of the present invention is further fully and detailedly described in conjunction with the accompanying drawings. This embodiment is the best embodiment based on the technical solution of the present invention, but the protection scope of the present invention is not limited to the following embodiment.

[0033] When the operating flow rate of the axial flow pump deviates from the design conditions, especially when it is reduced to 0.6 times or lower than the design conditions, severe flow separation occurs at the inlet rim of the impeller blade suction surface, and the performance of the axial flow pump drops sharply, which is reflected in the formation of a positive slope area on the external characteristic curve, called the saddle area.

[0034] This embodiment discloses a method for designing a saddle area suppression chute for an axial flow pump, and the specific implementation steps are as follows:

[0035] Step 1: Determine the relevant geometric dimensions of the axial flow pump, including the impeller diameter D, impeller axial length L, impeller inlet placement angle θ weighted value and other parameter values. The existing dimensions of the axial flow pump model are shown in the following table:

[0036] parameter Impeller diameter D / mm Impeller axial length L / mm Weighted value of inlet placement angle θ / ° Numeric 536 224 31.422

[0037] The original performance curve of the axial flow pump is as follows Figure 4 The black dotted line in the middle represents the original working condition; in the original working condition where no inclined groove is provided on the inner wall of the axial flow pump inlet pipe, when working in a smaller flow area, the head of the axial flow pump drops abnormally, which has a negative impact on the operation of the axial flow pump.

[0038] Step 2: Assume the parameters of the inclined grooves on the inlet wall of the axial flow pump. Initially assume that the total number of inclined grooves n is 60, the axial length of the inclined grooves l = (2 / 3) D = 357 mm, the width of a single groove w = 21 mm, the depth d = 7.5 mm, and the angle α between the edge of the groove and the central axis of the pipeline is 14.6°.

[0039] Step 3: Based on the parameters of step 1 and step 2, dimensionless processing is performed to establish the dimensionless parameter NOG related to the axial flow pump size and the chute size, and its expression is:

[0040] NOG=DWR×VR×DLR×AR

[0041] Among them, the depth-to-width ratio DWR = d / w, which is the ratio of the depth d to the width w of the chute; the volume ratio It is the ratio of the total volume of the chute to the volume of the impeller inlet. The total volume of the chute is the number of chute multiplied by the volume of a single chute. The impeller inlet volume is the impeller inlet area. The product of the impeller axial length L; the diameter-to-length ratio DLR = D / l, which is the ratio of the impeller diameter D to the axial length l of the skew groove; the angle ratio AR = α / θ, which is the ratio of the angle α between the edge of the groove and the central axis of the pipeline to the weighted value θ of the inlet placement angle; where Take m impeller inlet placement angles at equal intervals from the hub to the rim along the blade span direction and record them as θ i , the angle closest to the hub is θ1, followed by θ2, and so on, the angle closest to the rim is θ m; In this embodiment, m is taken as 11, and the weighted value θ of the inlet placement angle in step one is calculated; the relevant parameters of step one and step two are substituted into the calculation to obtain the dimensionless parameter NOG=0.01669.

[0042] Step 4: Figure 5 As shown, the black scattered points represent the change of dimensionless parameter NOG at 0.5Q des Under the flow condition, the lift of the axial flow pump is increased compared with the original condition. The red scattered points represent the 1.0Q des The decrease in the efficiency of the axial flow pump compared to the original working condition under the flow condition, where Q des represents the design flow rate of the axial flow pump; the black solid line and the red solid line are the fitting curves of the two scattered points, respectively. Figure 5 It can be seen that when the value of NOG is between 0.014 and 0.022, 0.5Q des The performance improvement of traffic reaches the highest value, while 1.0Q des The efficiency drop of the flow rate is located in the valley area; therefore, the optimal value area of ​​NOG is 0.014<NOG<0.022;

[0043] The NOG value calculated in step 3 is compared with Figure 5 If the dimensionless parameter NOG calculated by the design size in step 2 satisfies Figure 5 If the dimensionless parameter NOG calculated by the design in step 2 does not meet the requirements of the dimensionless optimal value range, the chute of the axial flow pump water inlet pipe is processed according to the chute parameters; Figure 5 If the dimensionless optimal value range is not met, the chute parameters are redesigned and steps 2 to 4 are repeated until the design parameters that meet the optimal value range are obtained;

[0044] In this embodiment, NOG=0.01669 is calculated in step 3, satisfying Figure 5 The dimensionless optimal value range is required; according to the parameters at this time, the processing is designed as follows Figure 1 , Figure 2 The axial flow pump water inlet pipe with an inclined groove shown in the figure; comprising a connecting flange 1, a water guide cone front support bracket 2, a water guide cone front support 3, an inclined groove protrusion 4, an inclined groove channel 5 and a tapered water inlet pipe 6; in this embodiment, the draft angle of the tapered water inlet pipe is 3°, and the water flow direction is Figure 2The water flows from right to left in the cone inlet pipe 6. The cone inlet pipe 6 is divided into a wide side and a narrow side, that is, the left end is the narrow side and the right end is the wide side. The narrow side flange is connected to the impeller section flange, and the wide side flange is connected to the front end of the water inlet pipe. A circumferentially inclined groove is opened on the inner wall of the cone inlet pipe 6 to form an inclined groove channel 5. Adjacent inclined groove channels 5 form channel protrusions 4. Front support brackets 2 are installed on the inner wall of the cone inlet pipe 6. There are 6 front support brackets 2 with an interval angle of 60°. A water guide cone front support 3 is installed at the end of the front support bracket 2. The inner side of the water guide cone front support 3 is provided with a thread for installing the water guide cone. The installation position relationship between the axial flow pump water inlet pipe and the axial flow pump section with the inclined groove finally provided in this embodiment is as shown in FIG. Figure 3 As shown, the pipeline of the axial flow pump is connected to the narrow side of the tapered water inlet pipe through a flange;

[0045] The axial flow pump system with the inlet pipe of the inclined slot designed in step 2 was simulated and tested. The results are as follows: Figure 5 As shown by the red dotted line, 0.4Q des The lift coefficient is increased by 56.5% compared with the original working condition, 0.5Q des The lift coefficient increased by 40.17%, 0.6Q des The lift coefficient of Figure 5 As shown by the blue dotted line in the figure, when the inclination angle of the inclined groove is changed to a straight groove of 0° without changing the axial length, depth, width and number of the grooves, 0.4Q des The lift coefficient is increased by 55.27% compared with the original working condition, 0.5Q des The lift coefficient increased by 14.2%, 0.6Q des The lift coefficient is the same as the original working condition; the improvement performance of the axial flow pump inlet pipe with straight grooves on small flow is not as good as that of the axial flow pump inlet pipe with inclined grooves.

[0046] The saddle area suppression chute of the axial flow pump designed by the above design method can achieve the goal of effectively improving the performance of the axial flow pump at small flow rates and minimizing the impact on the efficiency of the design working conditions.

[0047] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A chute for improving the performance of the saddle area of ​​an axial flow pump, characterized in that: The inclined groove is arranged on the inner wall of the water inlet pipe of the axial flow pump, and the water inlet pipe of the axial flow pump is installed at the front edge of the pump body of the axial flow pump; the inclined groove and the axis of the water inlet pipe of the axial flow pump form a predetermined angle.

2. A chute for improving the saddle performance of an axial flow pump as claimed in claim 1, characterized in that: The inclined groove is opened obliquely along the impeller blade direction, and the two ends of the inclined groove are respectively connected with the two sides of the axial flow pump water inlet pipe, which plays a rectifying role on the fluid at the inlet wheel rim.

3. A chute for improving the saddle performance of an axial flow pump as claimed in claim 1, characterized in that: The inclined groove is a quadrilateral groove, each groove has the same depth, and the bottom surface of the groove is on the same conical surface; a protrusion is formed between every two grooves, and the surface of the protrusion is located on the same conical surface.

4. A chute for improving the saddle performance of an axial flow pump as claimed in claim 1, characterized in that: The chute and the axis of the axial flow pump water inlet pipe form a predetermined angle, which is determined according to the diameter and rotation speed of the axial flow pump. The predetermined angle ranges from 6° to 18°. The larger the diameter and the higher the rotation speed, the larger the value of the predetermined angle.

5. A method for designing an inclined slot for improving the performance of the saddle area of ​​an axial flow pump, used for designing the inclined slot as claimed in claim 1, 2 or 3, characterized in that: The following steps are included: Step 1, determine the relevant geometric dimensions of the axial flow pump, including the impeller diameter D, the impeller axial length L and the weighted value θ of the impeller inlet placement angle; Step 2, determining the chute parameters, which include the number of chute n, the axial length l, the width w, the depth d, and the angle α between the edge of the chute and the central axis of the pipeline; Step 3: Non-dimensionalize the parameters in steps 1 and 2 to establish the dimensionless parameter NOG: NOG=DWR×VR×DLR×AR Among them, the depth-to-width ratio DWR = d / w, which is the ratio of the depth d to the width w of the chute; the volume ratio It is the ratio of the total volume of the chute to the volume of the impeller inlet. The total volume of the chute is the number of chute multiplied by the volume of a single chute. The impeller inlet volume is the impeller inlet area. The product of the impeller axial length L; the diameter-to-length ratio DLR = D / l, which is the ratio of the impeller diameter D to the axial length l of the skew groove; the angle ratio AR = α / θ, which is the ratio of the angle α between the edge of the groove and the central axis of the pipeline to the weighted value θ of the inlet placement angle; where Take m impeller inlet placement angles at equal intervals from the hub to the rim along the blade span direction and record them as θ i , the angle closest to the hub is θ1, followed by θ2, and so on, the angle closest to the rim is θ m ; In the axial flow pump system with the addition of the chute, the closer to the wheel rim, the stronger the influence of the chute; Step 4: If the dimensionless parameter NOG obtained by calculating the chute parameters in step 2 satisfies 0.014<NOG<0.022, the chute of the axial flow pump water inlet pipe is processed according to the chute parameters; if not, the chute parameters are redesigned and steps 2 to 4 are repeated until the chute parameters that meet the requirements are obtained.

6. A method for connecting an axial flow pump water inlet pipe provided with an inclined slot as claimed in claim 1, 2, 3 or 4 to an axial flow pump, characterized in that: The steps include: The connection method comprises the following steps: step 1, assembling an axial flow pump water inlet pipe with an inclined groove, wherein the axial flow pump water inlet pipe comprises a conical axial flow pump water inlet pipe, front and rear end connecting flanges of the pipe, a front support of a water guide cone, a front support bracket of a water guide cone, and an inclined groove on the inner wall of the pipe; Connection method step 2: The tapered water inlet pipe refers to a gradually narrowing pipe with a draft angle of 3° to 6°. The wide side and narrow side of the pipe are respectively equipped with connecting flanges. The water flows from the wide side to the narrow side. The wide side pipeline is connected to the front side pipeline of the water inlet pipe with a flange, and the narrow side pipeline is connected to the outer pipeline of the impeller section with a flange. Connection method step three, the water guide cone front support refers to a support device for installing the axial flow pump water guide cone, the water guide cone front support is connected and fixed to the conical water inlet pipe through the water guide cone front support bracket, there are six brackets, each bracket is spaced at an angle of 60°, and the bracket is in the shape of a straight plate; the front and rear sides, the connecting pipe wall side and the connecting water guide cone front support side are chamfered, the water guide cone front support has threads inside, and the water guide cone is connected to the front support and installed through the threads.

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