A slant groove for improving performance of a saddle area of an axial flow pump and a design method thereof

Abstract

The application discloses a slant groove for improving the performance of a saddle area of an axial flow pump and a design method thereof, and belongs to the field of fluid machinery. The slant groove is arranged on the inner wall of an inlet pipe of the axial flow pump, and the inlet pipe is arranged at the front edge of a pump body of the axial flow pump; the slant groove is at a predetermined angle with the axis of the inlet pipe of the axial flow pump. The slant groove is obliquely arranged along the direction of a blade profile of an impeller, and the two ends of the slant groove are respectively communicated with the two sides of the inlet pipe of the axial flow pump, so that the fluid at the inlet rim is rectified. The slant groove is a quadrilateral groove, the depths of each groove 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 surface of the protrusion is on the same conical surface. The design method of the slant groove for the saddle area of the axial flow pump is disclosed, a new dimensionless number NOG is established, the size of the slant groove is coupled with the size of the axial flow pump in multiple scales, the size parameters of the slant groove can be determined efficiently, quickly, accurately and reliably, the performance of the axial flow pump at a small flow rate is improved to the maximum extent, and the design efficiency is affected to the minimum extent.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of inclined groove and design method for improving the performance of saddle area of axial flow pump, belong to fluid machinery field. BACKGROUND

[0002] As a kind of high specific speed, large flow, low lift pump, axial flow pump is mature in technology, easy to operate and maintain, and is widely used in farmland irrigation engineering, water diversion engineering, flood control and drainage engineering, municipal water supply engineering, chemical industry, shipbuilding industry and other fields.

[0003] When axial flow pump operates at design condition, it has high efficiency, good internal flow condition and stable flow state, and is safe and efficient in operation. However, under high load condition, the operation of axial flow pump deviates from the design condition, especially when the working flow rate is reduced to 0.6 times or less of the design condition. Due to the change of inlet flow condition, severe flow separation occurs at the inlet rim of the suction surface of the impeller blade. At the same time, due to the pressure difference between the pressure surface and the suction surface of the impeller blade, tip clearance leakage flow occurs at the tip clearance. The separation flow on the suction surface of the blade and the tip clearance leakage flow destroy the inlet flow condition of the axial flow pump at low flow rate. The fully developed vortex structure blocks the entire impeller passage, which not only leads to a sharp decrease in performance and efficiency of the axial flow pump at low flow rate, but also causes strong vibration and noise during operation, which affects the safety of the pump body. The above shortcomings have a strong negative impact on the performance and safety of the axial flow pump during rapid start-up and operation under adverse conditions, and reduce the operating efficiency and service life of the axial flow pump. Therefore, from the perspective of performance and safety, it is an important direction for the research of axial flow pump to suppress the flow instability in the saddle area. Based on the passive flow control technology of fluid machinery, an inclined groove is provided on the wall of the inlet pipe of the axial flow pump to control the flow in the saddle area and improve the performance at stall condition. A quick design method for optimizing the size of the inclined groove is also provided, which can accurately and efficiently complete the design of the inclined groove matched with the target axial flow pump. SUMMARY

[0004] The purpose of the present application is to solve the problems of performance and efficiency reduction and safety impact caused by deterioration of inlet flow condition during low flow operation of axial flow pump, and to provide an inclined groove and design method for improving the performance of saddle area of axial flow pump.

[0005] The purpose of the present application is achieved by the following technical solutions.

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

[0007] Preferably, the inclined grooves are inclinedly formed along the direction of the impeller blade profile, and the two ends of the inclined grooves are respectively connected with the two sides of the inlet pipe of the axial flow pump, so as to play a flow regulating role on the fluid at the inlet rim.

[0008] Preferably, the inclined grooves are quadrilateral grooves, the depths of each groove are the same, and the bottom surfaces of the grooves are located 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 inclined grooves are at a predetermined angle with the axis of the inlet pipe of the axial flow pump, the predetermined angle is determined according to the diameter and the rotating speed of the axial flow pump, the predetermined angle ranges from 6° to 18°, the larger the diameter and the higher the rotating speed, the larger the predetermined angle.

[0010] The application further discloses a design method of the inclined grooves for improving the performance of the saddle area of the axial flow pump.

[0011] Step one: determining the related geometric dimensions of the axial flow pump, including the diameter D of the impeller, the axial length L of the impeller and the weighted value θ of the inlet installation angle of the impeller;

[0012] Step two: determining the parameters of the inclined grooves, the parameters of the inclined grooves including the number n of the inclined grooves, the axial length l of the inclined grooves, the width w, the depth d, and the included angle α between the side line of the inclined grooves and the central axis of the pipe;

[0013] Step three: performing dimensionless processing on the parameters in steps one and two, and establishing the dimensionless parameter NOG:

[0014] NOG=DWR*VR*DLR*AR

[0015] wherein the depth-width ratio DWR=d / w is the ratio of the depth d to the width w of the inclined grooves; the volume ratio VR=Vtotal / Vinlet is the ratio of the total volume of the inclined grooves to the inlet volume of the impeller, the total volume of the inclined grooves is the product of the number of the inclined grooves and the volume of a single inclined groove, and the inlet volume of the impeller is the product of the inlet area of the impeller and the axial length L of the impeller; the diameter-length ratio DLR=D / l is the ratio of the diameter D of the impeller to the axial length l of the inclined grooves; and the angle ratio AR=α / θ is the ratio of the included angle α between the side line of the inclined grooves and the central axis of the pipe to the weighted value θ of the inlet installation angle. The diameter-length ratio DLR=D / l is the ratio of the diameter D of the impeller to the axial length l of the inclined grooves; and the angle ratio AR=α / θ is the ratio of the included angle α between the side line of the inclined grooves and the central axis of the pipe to the weighted value θ of the inlet installation angle. Along the blade span direction, m impeller inlet installation angle values are taken at equal intervals from the hub to the rim, and the values are denoted as θ1, θ2, …, and θm. i The value closest to the hub is θ1, the value second closest to the hub is θ2, and so on, and the value closest to the rim is θm. m In the axial flow pump system with the inclined grooves, the closer to the rim, the stronger the influence of the inclined grooves.

[0016] ​Step four, if the non-dimensional parameter NOG calculated from the chute parameter of step two satisfies 0.014 < NOG < 0.022, then the chute parameter is used to process the chute of the axial flow pump inlet pipe; if not, the chute parameter is redesigned, and steps two to four are repeated until the chute parameter that meets the requirements is obtained.

[0017] The application also discloses a method for connecting the axial flow pump with the axial flow pump inlet pipe with the chute.

[0018] The connecting method step one assembles the axial flow pump inlet pipe with the chute, and the axial flow pump inlet pipe comprises a tapered axial flow pump inlet pipe, pipe front and rear end connecting flanges, a guide vane front support, a guide vane front support bracket and a pipe inner wall inclined channel.

[0019] The connecting method step two discloses that the tapered inlet pipe is a pipe with a draft angle of 3-6 degrees, the wide side and the narrow side of the pipe are respectively provided with connecting flanges, the water flow direction is from the wide side to the narrow side, the wide side pipe is connected with the front side pipe of the inlet pipe by the flanges, and the narrow side pipe is connected with the outer pipe of the impeller section by the flanges.

[0020] The connecting method step three discloses that the guide vane front support is a support device for installing the guide vane of the axial flow pump, the guide vane front support is connected and fixed with the tapered inlet pipe through the guide vane front support bracket, there are six brackets, the interval angle between each bracket is 60 degrees, and the bracket is in a straight plate shape; the front and rear sides, the connecting pipe wall side and the connecting guide vane front support side are all chamfered, the guide vane front support is internally threaded, and the guide vane is connected and installed with the front support through the threads.

[0021] Advantages:

[0022] 1. The guide device for installing the chute in the inner wall of the front inlet pipe of the axial flow pump is different from the general inlet pipe form, the chute added in the inlet pipe wall can suppress the inlet circumferential flow under the small flow condition of the axial flow pump from different dimensions, has the ability to suppress the blade tip leakage vortex and the axial flow pump impeller passage blocking vortex, effectively improves the flow separation of the blade suction surface, and improves the performance of the axial flow pump in the small flow area.

[0023] 2. The guide device for installing the chute in the inner wall of the front inlet pipe of the axial flow pump is a passive flow control method, the chute guide structure is used to control the abnormal flow of the axial flow pump inlet, no additional energy needs to be provided for the chute guide device by the system, and the chute guide structure has the advantages of simple structure, low cost and easy processing, so that the performance of the axial flow pump in the small flow operation and the stability and safety in the operation process are improved at a low cost.

[0024] 3. The design method for suppressing the inclined groove in the saddle area of an axial flow pump, which is different from the traditional simple passive control technology, the design method is characterized in that the number, axial length, depth, width of the inclined groove, and the angle between the edge line of the groove and the center axis of the pipeline are weighted with the diameter, axial length, and inlet installation angle of the axial flow pump impeller, and then the dimension design parameter NOG of the inclined groove is obtained, the size of the inclined groove is coupled with the size of the axial flow pump in multiple scales, the size parameter of the inclined groove can be determined efficiently, quickly, accurately and reliably, and the performance of the axial flow pump at a small flow rate is improved to the maximum extent and the efficiency of the design working condition is affected to the minimum extent.

[0025] 4. The method for connecting the axial flow pump with the water inlet pipe provided with the inclined groove, the narrow side of the water inlet pipe is connected with the rim of the axial flow pump by a flange, the front support of the water guide cone is connected with the water guide cone of the axial flow pump by threads, and the front support bracket of the water guide cone is connected with the wall of the water inlet pipe of the axial flow pump, compared with the traditional simple flange connection mode, the radial runout during the operation of the axial flow pump is reduced on the basis of ensuring the water seal, the front support bracket of the water guide cone installed at intervals has a certain inhibitory effect on the axial flow in the inlet pipe, that is, the stability and safety of the operation of the axial flow pump are ensured, the uniformity of the inlet flow is improved, and the inlet flow condition is improved. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Schematic diagram of the conical water inlet pipe with added inclined grooves;

[0027] Figure 2 Schematic diagram of the conical water inlet pipe with added inclined grooves; Figure 1 Schematic diagram of the conical water inlet pipe with added inclined grooves;

[0028] In the drawings, 1 is a connection flange, 2 is a front support bracket of a water guide cone, 3 is a front support of a water guide cone, 4 is an inclined groove protrusion, 5 is an inclined groove channel, and 6 is a conical water inlet pipe pipeline.

[0029] Figure 3 Schematic diagram of the position of the water inlet pipe provided with inclined grooves in the axial flow pump system;

[0030] Figure 4 Comparison of the external characteristic curves of the axial flow pumps with different groove types;

[0031] Figure 5 Curve diagram of the design value and preferred area of NOG. DETAILED DESCRIPTION

[0032] The technical solutions of the present application are further completely and specifically described below with reference to the drawings. The present application is based on the best embodiment of the technical solutions, but the protection scope of the present application is not limited to the following embodiments.

[0033] When the flow rate of the axial flow pump deviates from the design condition, especially when it is reduced to 0.6 times or less of the design condition, serious flow separation occurs at the suction surface inlet of the impeller blade, and the performance of the axial flow pump decreases sharply, which is manifested as the formation of a positive slope region on the external characteristic curve, referred to as a horse saddle region.

[0034] The design method for the inclined groove of the horse saddle region of the axial flow pump is disclosed, and the specific implementation steps are as follows:

[0035] Step one, determine the relevant geometric dimensions of the axial flow pump, including the impeller diameter D, the axial length L of the impeller, the weighted value of the inlet installation angle θ of the impeller, and other parameter values. The existing size is shown in the following table:

[0036] Parameter Impeller diameter D / mm Impeller axial length L / mm Inlet setting angle weighting value θ / ° Numerical value 536 224 31.422

[0037] The original performance curve of the axial flow pump is shown in Figure 4 The black dotted line in the figure represents the original working condition; in the original working condition without the inclined groove on the inner wall of the inlet pipe of the axial flow pump, when working in the small flow rate region, the head of the axial flow pump abnormally decreases, which has a negative impact on the operation of the axial flow pump.

[0038] Step two, assume the parameters of the inclined groove on the inlet pipe wall of the axial flow pump. The total number of the inclined grooves is initially set to 60, the axial length of the inclined groove is l=(2 / 3)D=357 mm, the width of a single groove is w=21 mm, the depth of a single groove is d=7.5 mm, and the included angle between the edge line of the groove and the center axis of the pipe is α=14.6°.

[0039] Step three, based on the parameters in steps one and two, perform dimensionless processing to establish a dimensionless parameter NOG related to the size of the axial flow pump and the size of the inclined groove, and the expression is:

[0040] NOG=DWR×VR×DLR×AR

[0041] Wherein, the depth-width ratio DWR=d / w is the ratio of the depth d of the inclined groove to the width w; the volume ratio VR=Vg / Vi is the ratio of the total volume of the inclined groove to the volume of the impeller inlet; the diameter-length ratio DLR=D / l is the ratio of the diameter D of the impeller to the axial length l of the inclined groove; and the angle ratio AR=α / θ is the ratio of the included angle α of the edge line of the groove to the center axis of the pipe to the weighted value θ of the inlet installation angle. The volume of a single inclined groove is the product of the area of the inclined groove and the axial length l of the inclined groove; the volume of the impeller inlet is the product of the area of the impeller inlet and the axial length L of the impeller; and the volume of the inclined groove is the product of the number of the inclined grooves and the volume of a single inclined groove. The m impeller inlet installation angle values are taken at equal intervals from the hub to the rim along the blade span, denoted as θ i The angle value closest to the hub is θ1, followed by θ2, and so on, and the angle value closest to the rim is θ m ​In this embodiment, m is set to 11, and the weighted value θ of the inlet placement angle in step one is calculated. Substituting the relevant parameters from step one and step two into the calculation, the dimensionless parameter NOG = 0.01669 is obtained.

[0042] Step 4, as follows Figure 5 As shown, the black scatter dots represent the changes in the dimensionless parameter NOG at 0.5Q. des The increase in head of the axial flow pump compared to the original operating condition under flow rate conditions is represented by the red scattering at 1.0Q. des Under flow conditions, the decrease in axial flow pump efficiency compared to the original operating conditions, where Q des This represents the design flow rate of the axial flow pump; the black solid line and the red solid line represent the fitted curves of the two scatter points, respectively. Figure 5 As can be seen, when the value of NOG is between 0.014 and 0.022, 0.5Q des The performance improvement in traffic reached its maximum value, while 1.0Q des The efficiency reduction of the flow rate is located in the trough region; therefore, the preferred value range for NOG is 0.014 < NOG < 0.022.

[0043] Compare the NOG value calculated in step three with... Figure 5 Comparing the dimensionless preferred value region shown, if the dimensionless parameter NOG obtained by calculating the size designed in step two satisfies... Figure 5 If the dimensionless optimal value range requirement is met, then the inclined groove of the axial flow pump inlet pipe is machined according to the inclined groove parameters; if the dimensionless parameter NOG obtained by calculation of the dimensions designed in step two does not meet the requirements... Figure 5 If the dimensionless preferred value range is required, the sloping groove parameters are redesigned, and steps two to four are repeated until design parameters that meet the preferred value range are obtained.

[0044] In this embodiment, NOG = 0.01669 is calculated in step three, which satisfies... Figure 5 Requirements for the optimal value range of dimensionless quantities; design and process according to the parameters at this time, such as... Figure 1 , Figure 2 The axial flow pump inlet pipe with an inclined groove shown includes a connecting flange 1, a guide cone front support bracket 2, a guide cone front support 3, an inclined groove protrusion 4, an inclined groove channel 5, and a conical inlet pipe 6. In this embodiment, the draft angle of the conical inlet pipe is 3°, and the water flow direction is... Figure 2The cone-shaped inlet pipe 6 is divided into a wide side and a narrow side, i.e. the left end is the narrow side and the right end is the wide side, the narrow side flange plate is connected with the impeller section flange plate, the wide side flange plate is connected with the front end pipe of the inlet pipe, a circumferential inclined groove is formed on the inner wall of the cone-shaped inlet pipe 6 to form the inclined groove channel 5, adjacent inclined groove channels 5 form the channel protrusion 4, the front support bracket 2 is arranged on the inner wall of the cone-shaped inlet pipe 6, and there are six front support brackets 2 with an interval angle of 60°, the front support bracket 2 is provided with the water guide cone front support 3 at the end, the inner side of the water guide cone front support 3 is provided with threads for mounting the water guide cone, and the installation position relationship between the final inclined groove provided on the inlet pipe of the axial flow pump and the axial flow pump section of the embodiment is as shown in Figure 3 The pipe of the axial flow pump is connected with the narrow side of the cone-shaped inlet pipe through a flange;

[0045] The simulation and experimental research are conducted on the axial flow pump system with the inlet pipe provided with the inclined groove designed in step two, and the results are shown by the red dotted line in Figure five The head coefficient of 0.4Q des is increased by 56.5% compared with the original working condition, the head coefficient of 0.5Q des is increased by 40.17%, and the head coefficient of 0.6Q des is increased by 11.47%; as a comparison, as shown by the blue dotted line in Figure 5 , when the inclined angle of the inclined groove is changed to 0° of the straight groove without changing the axial length, depth, width and number of the channel, the head coefficient of 0.4Q des is increased by 55.27% compared with the original working condition, the head coefficient of 0.5Q des is increased by 14.2%, and the head coefficient of 0.6Q des is the same as the original working condition; the axial flow pump inlet pipe provided with the straight groove has a lower improvement performance than the axial flow pump inlet pipe provided with the inclined groove.

[0046] The inclined groove provided in the saddle area of the axial flow pump designed by the above design method can effectively improve the performance of the small flow of the axial flow pump and minimally affect the efficiency of the design working condition.

[0047] The above specific description further details the purpose, technical scheme and beneficial effects of the application, and it should be understood that the above description is only a specific embodiment of the application and is not used to limit the protection scope of the application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A method for designing a sloping groove to improve the performance of an axial flow pump in the saddle region, characterized in that: Includes the following steps, Step 1: Determine the relevant geometric dimensions of the axial flow pump, including the impeller diameter D, impeller axial length L, and weighted value θ of the impeller inlet installation angle; Step 2: Determine the parameters of the inclined groove, including the number of inclined grooves n, the axial length l, width w, depth d, and the angle α between the edge of the inclined groove and the central axis of the axial flow pump inlet pipe. Step 3: Perform dimensionless processing on the parameters from Steps 1 and 2 to establish the dimensionless parameter NOG: NOG = DWR × VR × DLR × AR Wherein, the depth-to-width ratio DWR = d / w, is the ratio of the depth d to the width w of the inclined groove; the volume ratio This is the ratio of the total volume of the inclined slots to the impeller inlet volume. The total volume of the inclined slots is the number of inclined slots multiplied by the volume of a single inclined slot. The impeller inlet volume is the impeller inlet area. The product of the impeller's axial length L and the diameter-to-length ratio DLR = D / l, which is the ratio of the impeller diameter D to the axial length l of the inclined 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 pipe to the weighted value θ of the inlet installation angle; where Along the blade span, take m impeller inlet installation angle values ​​at equal intervals from the hub to the rim, and denot them as θ. i The angle closest to the wheel hub is θ1, followed by θ2, and so on, with the angle closest to the wheel rim being θ. m In axial flow pump systems with added sloping grooves, the closer to the rim, the stronger the influence of the sloping grooves. Step 4: If the dimensionless parameter NOG obtained by calculating the sloping groove parameters in Step 2 satisfies 0.014 < NOG < 0.022, then process the sloping groove of the axial flow pump inlet pipe according to the sloping groove parameters; if it does not satisfy the condition, then redesign the sloping groove parameters and repeat Steps 2 to 4 until the compliant sloping groove parameters are obtained. The inclined groove is formed on the inner wall of the axial flow pump inlet pipe, which is installed at the front edge of the axial flow pump body; the inclined groove is at a predetermined angle to the axis of the axial flow pump inlet pipe.

2. A sloping groove for improving the saddle region performance of an axial flow pump, designed using the sloping groove design method for improving the saddle region performance of an axial flow pump as described 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 to both sides of the axial flow pump inlet pipe, which plays a rectifying role for the fluid at the inlet rim. The inclined groove is a quadrilateral groove, each groove has the same depth, and the bottom surfaces of the grooves are 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; The inclined trough is at a predetermined angle to the axis of the axial flow pump inlet pipe. The predetermined angle is determined according to the diameter and rotational speed of the axial flow pump. The predetermined angle ranges from 6° to 18°. The larger the diameter and the higher the rotational speed, the larger the predetermined angle value.

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