CN115809617A - Inlet water flow channel optimization method based on outlet non-uniform flow and highest efficiency of pump device - Google Patents
Inlet water flow channel optimization method based on outlet non-uniform flow and highest efficiency of pump device Download PDFInfo
- Publication number
- CN115809617A CN115809617A CN202211665137.XA CN202211665137A CN115809617A CN 115809617 A CN115809617 A CN 115809617A CN 202211665137 A CN202211665137 A CN 202211665137A CN 115809617 A CN115809617 A CN 115809617A
- Authority
- CN
- China
- Prior art keywords
- efficiency
- pump
- water
- outlet
- flow
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Images
Landscapes
- Structures Of Non-Positive Displacement Pumps (AREA)
Abstract
The invention provides a pump station elbow-shaped water inlet runner optimization design method based on outlet non-uniform flow and highest pump device efficiency, which belongs to the technical field of pump station engineering and comprises the steps of setting three factors of outlet straight section contraction angle, height and center line deflection angle to a conventional elbow-shaped water inlet runner; taking the efficiency of the pump device as a judgment standard, carrying out three-factor orthogonal test on the outlet straight section of the water inlet flow channel, carrying out CFD (computational fluid dynamics) calculation on the flow field and the efficiency of the pump device in each test scheme, determining the optimal level combination of the three factors of the outlet straight section of the water inlet flow channel, which enables the efficiency of the pump device to be highest, and obtaining the optimal water inlet flow channel, wherein the efficiency of the pump device is obviously improved compared with the conventional optimal design; the CFD calculation result of the flow field in the pump device adopting the optimal water inlet channel is subjected to post-processing, the flow velocity distribution of the outlet of the water inlet channel, namely the cross section of the inlet of the impeller, is not uniform, the conventional evaluation standard of uniform flow of the outlet of the water inlet channel is not scientific, the mechanism is analyzed, and a scientific method is provided for the optimal design and evaluation of the pump device.
Description
Technical Field
The invention belongs to the technical field of pump station engineering, and relates to a pump station elbow-shaped water inlet runner optimization design method based on outlet non-uniform flow and highest pump device efficiency.
Background
Large-scale low-lift pump stations are commonly used for drought resistance and drainage of waterlogging, agricultural irrigation and long-distance water transfer in plain areas and lakeside polder areas in China, such as east line engineering of south-to-north water transfer and industrial circulating cooling water systems. The large low-lift pump device consists of a water inlet flow channel, a pump section and a water outlet flow channel, and is diversified in form. The shape and size of the water inlet channel directly influence the flow speed and pressure distribution at the impeller inlet, and improper design can influence the water pump efficiency and hydraulic loss of the water inlet channel and the water outlet channel, so that the efficiency of the pump device is reduced. Therefore, there is a need for an optimized design of the water inlet channel to improve the performance of the pump device.
Because the water pump impeller is designed according to uniform inflow, the conventional design method and the evaluation method of the water inlet runner both require the outlet of the water inlet runner to provide uniform and axial inflow for the inlet of the water pump impeller, it is generally accepted that the higher the cross-sectional flow uniformity, i.e., closer to 1.0, the better, expressed in terms of flow uniformity and mean azimuth angle. This is not the case in practice. In fact, the incoming flow velocities when the cascade efficiencies at different radiuses of the water pump impeller reach the highest are not equal, and when the flow velocity of the inlet section of the impeller is uniform, the cascade efficiencies at different radiuses do not reach the maximum value at the same time, that is, the impeller efficiency does not reach the highest, and meanwhile, the inlet flow velocity of the impeller affects the hydraulic loss of the water inlet runner and the flow velocity distribution of the outlet of the guide vane behind the water pump, thereby affecting the hydraulic loss of the water outlet runner and finally affecting the efficiency of the pump device. Therefore, the conventional method for designing the water inlet runner according to the uniform flow velocity distribution of the outlet is not scientific, the efficiency of the water pump and the efficiency of the pump device are far from the highest, and a scientific and reasonable design method for the water inlet runner capable of improving the efficiency of the pump device is urgently needed.
Compared with other axial forms, the large vertical direct-coupled pump unit is the most reliable, mature in technology and most applicable, and an elbow-shaped water inlet channel is usually adopted. The elbow-shaped water inlet channel consists of an inlet section, an elbow section and an outlet straight section, a shape line consists of a straight line and an arc line, and the value range of each size in design is given by relevant specifications. In fact, the straight section of the inlet channel outlet most affects the flow velocity distribution at the inlet of the inlet channel, i.e. the impeller.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to overcome the defects that the pump efficiency and the pump device efficiency are not high due to the fact that the elbow-shaped water inlet flow channel is designed according to the outlet uniform flow distribution in the conventional method, and provides an optimal design method of the elbow-shaped water inlet flow channel outlet straight section based on the outlet non-uniform flow and directly taking the highest pump device efficiency as the target aiming at the characteristic that the straight section of the elbow-shaped water inlet flow channel outlet has great influence on the outlet flow speed and the pressure distribution of the water inlet flow channel, so that the pump device efficiency is obviously improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
a water inlet flow channel optimization method based on outlet non-uniform flow and highest efficiency of a pump device comprises the following steps:
A. the conventional method designs an elbow-shaped water inlet channel:
the elbow-shaped water inlet channel is required to provide uniform inflow for a water pump impeller, the distribution uniformity of the axial flow velocity of the cross section of the inlet of the impeller is used as an evaluation standard of the water inlet channel, the higher the distribution uniformity of the axial flow velocity is, the better the distribution uniformity of the axial flow velocity is, and the calculation formula is as follows:
in the formula: v u The flow velocity distribution uniformity of the inlet section of the impeller, namely the outlet section of the water inlet runner;
the average axial speed of the inlet section of the impeller is m/s; u. u ai Calculating the axial speed of each unit, m/s, of the inlet section of the impeller; n is the number of the impeller inlet section calculation units;
the water inlet flow channel shaped line consists of a straight line and an arc;
B. the straight section contraction angle, the height and the center line deflection angle of the elbow-shaped water inlet runner outlet are selected as follows:
on the basis of the original design parameters of the straight section of the outlet of the water inlet flow passage, a plurality of values of three factors of contraction angle, height and center line deflection angle are set at certain intervals in the range of up and down feasible parameters, and the contraction angle is taken from small to large
A total of m levels, wherein
Designing a contraction angle for the original; the height is h from small to large 1 ，…，h j ＝h d ，…，h n N total levels, wherein h d Designing the height for the original; the deviation angle of the central line is taken as theta 1 ，θ 2 ，…，θ l L levels in total, where θ 1 Designing the central line deflection angle theta 1 ＝0°；
C. Orthogonal test of three factors of straight section shrinkage angle, height and center line deflection angle of an elbow-shaped water inlet runner outlet:
according to three factor levels of straight section contraction angle, height and center line deflection angle of elbow-shaped water inlet runner outlet, making orthogonal meter L T (m × n × l), determining T combination test protocols as in table 1; in table 1, a, B, and C represent different combinations of three elements of the inlet flow channel outlet straight section, respectively;
TABLE 1 orthogonal test sample table for three factors of straight section of inlet channel outlet
D. Designing and modeling a pump device of each orthogonal test geometric parameter combination scheme of a straight section of an outlet of a water inlet runner, determining a flow field calculation area of the pump device, meshing, setting inlet and outlet boundary conditions, performing CFD calculation of an internal flow field, performing post-processing to calculate the efficiency of the pump device, and selecting the highest efficiency of the pump device as an optimal scheme:
(D1) Determining a calculation model according to upstream and downstream water levels of a design working condition of a pump device, wherein the calculation model comprises a forebay, a water inlet flow channel, an impeller, a guide vane, a water outlet flow channel and a water outlet pool, fluid below the water surface is water, and air areas are arranged above the water surfaces of the forebay and the water outlet pool;
setting a boundary condition: the overflow section of the forebay far enough away from the inlet section of the water inlet channel is considered as uniform flow distribution, the overflow section is set as the inlet of a calculation domain, and the boundary condition is gradient static pressure distribution;
the overflow section of the water outlet pool far enough away from the outlet section of the water outlet flow channel is considered as uniform flow distribution, the uniform flow distribution is set as a calculation domain outlet, and the boundary condition is gradient static pressure distribution;
each overflowing side wall is set as a fixed wall boundary;
(D2) A Computational Fluid Dynamics (CFD) method based on a Reynolds time-average method of fluid volume is applied to carry out numerical simulation calculation on a flow field in a pump device:
the Reynolds time-average method introduces a time-average method into a continuity equation and a Navier Stokes equation, and deduces the Reynolds time-average equation as follows:
in the formula: u is the water body velocity; p is the water body pressure; f is an external force acting on the water body; v is the dynamic viscosity of the water body;
the VOF assumes that water and air are immiscible, two phases are defined by a set of standard momentum equations, and the sum of the volume fractions of the two phases in each volume unit is 1; in the case of the q-th phase,
in the formula, alpha q Is the volume fraction of the q-th phase; v is the speed of the q-th phase;
performing three-dimensional flow numerical simulation calculation on the flow field in the pump device with each parameter combination of the water inlet flow channel orthogonal test based on the method;
(D3) Calculating the performance parameters of the external characteristics of the pump device, wherein the flow expression is as follows:
in the formula:
the average flow velocity of the cross section is m/s; a is the area of the cross section, m;
the pump head expression is:
in the formula: z is the elevation of the section water surface, m; p is a radical of total The total pressure of the section is Pa; ρ is the density of water; g is the local gravitational acceleration in m/s 2 (ii) a Subscripts 1 and 2 are respectively an inlet section of the water inlet channel and an outlet section of the water outlet channel;
the shaft power expression is:
in the formula: n is the rotation speed, rad/s; t is i Is the impeller torque, N · m;
the pump unit efficiency expression is:
in the formula: q is the pump flow rate, m 3 /s；H s For pump head, H s ＝z 2 －z 1 ；
(D4) Targeting the highest efficiency of the pump arrangement, i.e. max (η [) s ) Selecting and determining an optimal scheme of a water inlet runner;
E. analyzing and explaining the high-efficiency principle of the non-uniform flow pump device at the outlet of the optimal water inlet flow channel:
the relation between the efficiency of the water pump blade cascade and the radius and the axial flow velocity of the circumference is determined as follows:
the incoming flow velocity is not equal when the cascade efficiency of the impeller of the axial flow pump at different radiuses reaches the maximum, and when the flow velocity of the inlet section of the impeller is uniform, the cascade efficiency at different radiuses does not reach the maximum at the same time, namely the impeller efficiency does not reach the maximum;
on the circumference of any radius of the impeller, all the blades form an infinite plane in-line blade cascade, the efficiency of which is related to the size of the axial velocity of the incoming flow, namely the efficiency of the blade cascade of any circumference is expressed by the function of the radius and the axial velocity of the blade cascade, and for a certain point of the inlet section of the impeller, if the radius and the axial velocity are known, the efficiency of the blade cascade of the point is determined;
the pump efficiency is expressed as:
in the formula, P e Is the effective power; p is shaft power;
effective power P of water pump e Expressed as:
the shaft power P is expressed as:
in the formula: v. of a The axial flow rate of the water pump on a certain circumference; h c The theoretical lift of an impeller and a guide vane cascade on a certain circumference of the water pump; eta c The efficiency of an impeller and a guide vane cascade on a certain circumference of the water pump is shown; r is 1 Is the impeller hub radius; r is a radical of hydrogen 2 Is the radius of the rim of the impeller; the water pump efficiency is then expressed as:
carrying out artificial neural network training according to the blade cascade efficiency characteristic of a specific pump, visually predicting the efficiency distribution of the pump blade cascade according to the axial speed distribution at the inlet of an impeller, providing an artificial neural network with two hidden layers for fitting the relationship between the blade cascade efficiency and the radius and axial speed, and selecting a sigmoid function as an activation function of the hidden layers, wherein the activation function is a linear function of an output layer; for the training process, learning from a portion of the samples using a modified gradient descent algorithm, the samples were divided into two groups, 70% of which were used for training the network and the remaining 30% for testing; determining an original conventional optimization scheme water pump inlet flow velocity distribution contour map and a blade grid efficiency distribution contour map, and an existing optimization scheme water pump inlet flow velocity distribution contour map and a blade grid efficiency distribution contour map, and performing comparative analysis;
under the specific flow of the normal working condition of the water pump, when the axial speed distribution at the impeller inlet is consistent with or close to the efficient characteristic distribution of the efficiency of the pump blade grid, the pump efficiency reaches the highest or is close to the highest;
and calculating the pump efficiency by adopting the efficiency distribution of the pump blade grids, and comparing the calculated pump efficiency with the pump efficiency calculated by CFD (computational fluid dynamics) of the whole internal flow of the water pump device to verify the accuracy of the efficiency distribution of the pump blade grids.
The beneficial effects of the invention are: aiming at the characteristic that the straight section of the elbow-shaped water inlet runner outlet of the pump station has great influence on the outlet flow speed and the pressure distribution of the water inlet runner, the optimal design method of the straight section of the elbow-shaped water inlet runner outlet based on the outlet non-uniform flow and with the highest efficiency of the pump device as the target is provided, the defects of low pump efficiency and great hydraulic loss of the runner due to the fact that the elbow-shaped water inlet runner is optimally designed according to the outlet uniform flow distribution in the conventional method are overcome, the efficiency of the pump device is obviously improved, and the scientific and reasonable design and evaluation method is provided for the water inlet runner of the pump station. The mechanism of influence of the inlet flow state of the impeller on the characteristics of water pumps, inflow channels and outflow channels on the hydraulic flow is given, and the results and the principle can be popularized and applied to other impeller mechanical systems, so that the method has important theoretical significance and practical application value.
Drawings
FIG. 1 is a schematic diagram of a large pumping station pumping arrangement;
FIG. 2 is a schematic illustration of the main design parameters of the elbow-shaped inlet channel;
FIG. 3 is a schematic diagram of three factors of the straight section contraction angle, height and centerline deflection angle of the elbow-shaped inlet channel outlet;
FIG. 4 is a schematic diagram of a pump device computational domain;
FIG. 5 is a schematic view of a fluid field grid of the primary flow components of the pump apparatus;
FIG. 6 is a graph of axial flow pump impeller cascade efficiency versus radius and axial flow rate;
FIG. 7 is a graph comparing the inlet axial flow velocity distribution and cascade efficiency distribution of the prior and optimized impeller.
Detailed Description
A method for optimally designing the straight section of an outlet of an elbow-shaped water inlet runner of a large-sized pump station based on outlet non-uniform flow and with the aim of highest pump device efficiency is characterized by comprising the following steps of:
A. the conventional method designs an elbow-shaped water inlet channel:
as shown in figure 1, the elbow-shaped water inlet channel of the pump station is positioned between the water pump and the front pool of the pump station, and is mainly used for receiving water flow of the front pool, providing ideal incoming flow for a water pump impeller and ensuring stable and efficient operation of the water pump. The elbow-shaped water inlet channel is required to provide uniform inflow for a water pump impeller, the uniformity of the axial flow velocity distribution of the inlet section of the impeller is used as an evaluation standard of the water inlet channel, the higher the uniformity of the axial flow velocity distribution is, namely, the closer to 1.0, the better the distribution is, and the calculation formula is as follows
In the formula: v u The flow velocity distribution uniformity of the inlet section of the impeller, namely the outlet section of the water inlet flow channel; u. u a The average axial speed of the inlet section of the impeller is m/s; u. of ai Calculating the axial speed of each unit, m/s, of the inlet section of the impeller; and n is the number of the calculation units of the inlet section of the impeller.
The pump station design requires a water inlet channel: (1) the shape line is smooth, and the area of each section changes uniformly along the way; (2) the water inlet flow velocity and the pressure are uniformly distributed; (3) the flow velocity of the inlet cross section is preferably 0.8 to 1.0m/s; (4) vortex strips are not generated in the flow channel under various working conditions; (5) the construction is convenient. The elbow-shaped water inlet channel consists of an inlet section, an elbow section and an outlet straight section, is generally a gradually-reduced channel, changes the direction of the channel from horizontal to vertical upwards, gradually reduces the section of the channel from rectangular to circular, and is butted with the inlet of the vertical water pump. As shown in fig. 2, the elbow-shaped inlet channel line is composed of a straight line and an arc for the convenience of design and construction. The diameter of the water pump impeller is D, and the main size of the flow channel is drawn by referring to empirical data:
(A1) An inlet section: length L i D is 3.5 to 4.0, width B i D is 2.0 to 2.5, the height of the inlet cross section H t The angle alpha between the top surface and the horizontal plane is 12 degrees to 30 degrees, and the angle beta between the bottom surface and the horizontal plane is 5 degrees to 12 degrees;
(A2) Bending an elbow section: the radius R/D of the inner circular arc is 0.35 to 0.45, and the radius R/D of the outer circular arc is 0.8 to 1.0;
(A3) An outlet straight section: height h o a/D of 0.1 to 0.5, a contraction angle
The angle is 0-12 degrees, and the central line of the outlet section flow channel is a lead straight line;
drawing a plane outline graph, drawing a section graph to obtain each size of the flow channel, calculating the area of each flow cross section along the flow channel, solving the flow velocity of each cross section according to the designed flow to obtain a relation curve of the flow velocity and the length of the flow channel, and the relation curve of the cross section area and the length of the flow channel, if the two curves are smooth, the relation curve meets the requirement, otherwise, the relation curve needs to be readjusted until the requirement is met.
B. Three factors of contraction angle, height and center line deflection angle of an elbow-shaped water inlet runner outlet are drawn:
FIG. 3 is a schematic view of the contraction angle, height and center line deflection angle of the straight section of the inlet channel outlet.
The straight section of the elbow-shaped water inlet runner outlet of the pump station is connected with the elbow-shaped section of the water inlet runner and the inlet of the water pump impeller, and the shape of the elbow-shaped water inlet runner outlet has great influence on the flow state of the inlet of the impeller. The outlet straight section is in a tapered straight circular truncated cone shape, and the shape of the outlet straight section is determined by the contraction angle and the height. The water flow turns from horizontal flow direction to vertical flow direction in the elbow section of the water inlet channel, but secondary flow is formed at the same time, and the water flow at the tail end of the elbow section has larger horizontal flow velocity and needs to be rectified in the straight outlet section.
The contraction angle of the straight pipe at the outlet is beneficial to ensuring that the flow velocity of water flow tends to be uniform, but the contraction angle is too large, so that the flow velocity of the peripheral area of the outlet is too large.
The higher the straight section of the outlet, the better the rectification effect, but too high results in increased hydraulic loss, and the result is irretrievable, and too short cannot achieve the rectification effect.
The central line of the straight outlet section flow channel is a straight line, and the water flow from the elbow section is rectified by the straight outlet section, so that the total horizontal flow velocity of the water flow is not completely eliminated due to inertia and has a horizontal flow velocity component pointing to the water outlet direction. Considering that the central line of the outlet straight section has a deflection angle in the water inlet and outlet direction, namely in a longitudinal section of the water inlet flow channel, the deflection angle of the central line of the outlet straight section is an included angle between the central line of the outlet straight section and a vertical line. In order to ensure that the total outlet flow direction of the outlet straight section is consistent with the axial direction of the pump unit and the average inflow angle of the impeller is axial, the central line of the outlet straight section needs a deflection angle towards the water inlet side, but the bending angle and the height of the elbow section are increased, and the hydraulic loss is increased; on the contrary, the central line of the straight outlet section has an inclination angle towards the water outlet side, so that the bending angle and the height of the elbow section are reduced, the hydraulic loss is reduced, but the inflow non-axial component of the impeller is increased, and therefore, the straight outlet section has an optimal central line inclination angle. It is specified that the centerline declination is marked positive inward and negative outward. After the three geometric factors of the straight section of the outlet of the water inlet runner are changed, the elbow section is changed, the efficiency of the pump device is influenced by the flow field in the pump device, and the three factors are influenced mutually, so that the relation is complex. Therefore, it is necessary to determine the proper height, contraction angle and center line deflection angle of the straight section of the elbow-shaped water inlet channel outlet.
On the basis of the original design parameters of the straight section of the outlet of the water inlet flow passage, a plurality of values of three factors of contraction angle, height and center line deflection angle are set at certain intervals in the range of up and down feasible parameters, and the contraction angle is taken from small to large
In total m levels, wherein
Designing a contraction angle for the original; the height is h from small to large 1 ，…，h j ＝h d ，…，h n N levels in total, wherein h d Designing the height for the original; the deviation angle of the central line is taken as theta 1 ，θ 2 ，…，θ l L levels in total, where θ 1 Designing the central line deflection angle theta 1 ＝0°。
C. Orthogonal test of three factors of straight section shrinkage angle, height and center line deflection angle of an elbow-shaped water inlet runner outlet:
according to three factor levels of straight section contraction angle, height and center line deflection angle of elbow-shaped water inlet runner outlet, making orthogonal meter L T (m × n × l), determining T combination test protocols as in table 1; in table 1, a, B, and C represent different combinations of three elements of the straight section of the inlet flow channel, and the distribution characteristics satisfy orthogonality, that is:
(1) In any column, the number of different numbers is the same;
(2) Any two columns, all combinations of various levels appear with equal numbers of occurrences.
Table 1 water inlet channel outlet straight section three-factor orthogonal test sample table
D. Designing and modeling a pump device of each orthogonal test geometric parameter combination scheme of a straight section of an outlet of a water inlet runner, determining a flow field calculation area of the pump device, meshing, setting inlet and outlet boundary conditions, performing CFD calculation of an internal flow field, performing post-processing to calculate the efficiency of the pump device, and selecting the highest efficiency of the pump device as an optimal scheme:
(D1) The calculation model is determined according to upstream and downstream water levels of the design working condition of the pump device and comprises a forebay, a water inlet flow channel, an impeller, a guide vane, a water outlet flow channel and a water outlet pool, fluid below the water surface is used as water, and an air area with the height of 2m is arranged above the water surfaces of the forebay and the water outlet pool. The computational domain is shown in figure 4, and the main flow passage component grid is divided in figure 5.
Setting a boundary condition: the overflow section of the forebay far enough away from the inlet section of the water inlet runner can be regarded as uniform flow distribution, the position is set as an inlet of a calculation domain, and the boundary condition is gradient static pressure distribution;
the overflow section of the water outlet pool far enough away from the outlet section of the water outlet flow channel can be regarded as uniform flow distribution, the position is set as a calculation domain outlet, and the boundary condition is gradient static pressure distribution;
each overflowing side wall is set as a fixed wall boundary;
(D2) A CFD method based on a Reynolds-time average method (RANS-VOF) of the fluid volume is applied to carry out numerical simulation calculation on a flow field in a pump device:
the Reynolds time average method is introduced into a continuity equation and a Navier Stokes equation, and the Reynolds time average equation is deduced as follows:
in the formula: u is the water velocity; p is the water pressure; f is an external force acting on the water body; v is the dynamic viscosity of the water body.
The VOF assumes that water and air are immiscible, two phases are defined by a set of standard momentum equations, and the sum of the volume fractions of the two phases in each volume unit is 1. For the q-th phase, the phase is,
in the formula, alpha q Is the volume fraction of the q phase; v is the speed of the q-th phase;
performing three-dimensional flow numerical simulation calculation on the flow field in the pump device with each parameter combination in the water inlet flow channel orthogonal test based on the method;
(D3) Calculating the performance parameters of the external characteristics of the pump device, wherein the flow expression is as follows:
in the formula:
the average flow velocity of the cross section is m/s; a is the cross-sectional area, m;
the pump head expression is:
in the formula: z is the elevation of the water surface of the section, m; p is a radical of formula total Total pressure of the section Pa; ρ is the density of water; g is the local gravitational acceleration, m/s 2 (ii) a Subscripts 1 and 2 are respectively an inlet section of the water inlet channel and an outlet section of the water outlet channel;
the shaft power expression is:
in the formula: n is the rotation speed, rad/s; t is a unit of i Is the impeller torque, N · m;
the pump unit efficiency expression is:
in the formula: q is the pump flow rate, m 3 /s；H s For pumping unit head, H s ＝z 2 －z 1 。
(D4) Targeting the highest efficiency of the pump arrangement, i.e. max (η [) s ) And selecting and determining the optimal scheme of the water inlet flow channel, wherein the efficiency of the pump device is obviously higher than that of the pump device with the water inlet flow channel which is designed in a conventional optimization mode.
E. Efficient principle analysis and explanation of non-uniform flow pump device at outlet of optimal water inlet runner
(E1) Influence of water pump cascade efficiency distribution characteristic and inlet flow velocity on cascade efficiency, pump efficiency and pump unit efficiency:
the incoming flow velocity is not equal when the cascade efficiency of the impeller of the axial flow pump at different radiuses reaches the maximum, and when the flow velocity of the inlet section of the impeller is uniform, the cascade efficiency at different radiuses does not reach the maximum at the same time, namely the impeller efficiency does not reach the maximum;
on the circumference of any radius of the impeller, all the blade hydrofoils form an infinite plane in-line blade cascade, the efficiency of which is related to the magnitude of the axial velocity of the incoming flow, namely, the efficiency of the blade cascade of any circumference can be expressed by the function of the radius and the axial velocity, as shown in fig. 6. For a certain point of the impeller inlet section, if the radius and axial velocity are known here, the cascade efficiency at that point can be determined. The pump efficiency can be expressed as:
in the formula, P e Is the active power; p is shaft power;
effective power P of water pump e Can be expressed as:
the shaft power P can be expressed as:
in the formula: v. of a The axial flow rate of the water pump on a certain circumference; h c The theoretical lift of an impeller and a guide vane cascade on a certain circumference of the water pump; eta c The efficiency of an impeller and a guide vane cascade on a certain circumference of the water pump is shown; r is 1 Is the impeller hub radius; r is a radical of hydrogen 2 Is the radius of the rim of the impeller; the water pump efficiency can be expressed as:
carrying out artificial neural network training according to the blade cascade efficiency characteristic of a specific pump, visually predicting the efficiency distribution of the pump blade cascade according to the axial speed distribution at the inlet of an impeller, providing an artificial neural network with two hidden layers for fitting the relationship between the blade cascade efficiency and the radius and axial speed, and selecting a sigmoid function as an activation function of the hidden layers, wherein the activation function is a linear function of an output layer;
for the training process, learning from a portion of the samples using a modified gradient descent algorithm, the samples were divided into two groups, 70% of which were used for training the network and the remaining 30% for testing; the water pump inlet flow velocity distribution and the cascade efficiency distribution of the original conventional optimization scheme, and the water pump inlet flow velocity distribution and the cascade efficiency distribution of the optimization scheme of the invention are shown in FIG. 7.
The effective power and the axial power of the pump are respectively calculated by adopting the cascade head, the cascade efficiency and the axial speed of each grid unit, the effective power and the axial power are divided to obtain the pump efficiency, the pump efficiency is used for verifying the accuracy of the distribution prediction result of the cascade efficiency, and the expression is
In the formula: delta A i Is the area of the cell in a cross section perpendicular to the axis; v. of ai Calculating the axial speed of the unit; h ci Calculating the lift of the blade cascade where the unit is located; eta ci To calculate the cascade efficiency of the cell.
Under the specific flow of the normal working condition of the water pump, when the axial speed distribution at the impeller inlet is consistent with the high-efficiency characteristic of the impeller cascade efficiency distribution characteristic of the pump, the pump efficiency reaches the highest.
(E2) The distribution of the flow velocity at the inlet of the water pump impeller not only influences the distribution of the efficiency of a water pump cascade, but also influences the hydraulic loss of a water inlet flow channel due to the influence of the shape of the water inlet flow channel, influences the distribution of the flow velocity and the circulation quantity at the outlet of a rear guide vane of the water pump, further influences the hydraulic loss of a water outlet flow channel, and finally influences the efficiency of a pump device. When the same flow passes through the water outlet flow channel, the optimal inlet flow velocity and circulation distribution can reduce the flow separation and flow velocity gradient in the flow channel and reduce the hydraulic loss. The invention aims to improve the pump efficiency, reduce the hydraulic loss of the water inlet flow channel and the water outlet flow channel and finally improve the efficiency of the pump device by optimizing the shape and the size of the water inlet flow channel and optimizing the flow velocity distribution of the water pump inlet.
The technical solution provided by the above embodiment is verified by a specific application case as follows:
a water level difference of 3.8m is designed at the upstream and downstream of a certain large-sized low-lift pump station, a vertical axial flow pump with an impeller diameter D =1740mm and a rotating speed of 250r/min is installed, and an elbow-shaped water inlet flow channel and a siphon-type water outlet flow channel are adopted to optimally design the water inlet flow channel.
A. Elbow-shaped water inlet channel designed by conventional method
The main structural parameters are as follows:
as shown in fig. 2, the inlet height H of the inlet channel i Width B of =1.71D i =2.4D; transverse length L from inlet of water inlet runner to pump shaft i =4.67D, inlet straight segment top corner α =14 °, bottom corner β =2 °, throat height H t =0.9D, height H of cross section of bend e =1.25D, outerArc radius R =0.92D, inner arc radius R =0.33D, inlet channel outlet diameter D 1 =1.0D, (D is the impeller diameter). According to the original conventional design scheme, the contraction angle is 0 degrees, the height is (1/2) D, the deflection angle of a center line is 0 degree, and the efficiency of the pump device in the original scheme is 79.41 percent through calculation.
B. Three factors of contraction angle, height and center line deflection angle of an elbow-shaped water inlet runner outlet are drawn:
angle of contraction
Height h o And the center line declination angle theta are respectively expressed as A, B and C. Angle of contraction
The settings are in four levels: 0 ° (A1), 4 ° (A2), 8 ° (A3) and 12 ° (A4); height h o The settings are in three levels: (1/6) D (B1), (1/3) D (B2) and (1/2) D (B3); the centerline bias angle θ is set to seven levels: 0 ° (C1), -3.0 ° (C2), +3.0 ° (C3), -5.5 ° (C4), +5.5 ° (C5), -8.0 ° (C6), and +8.0 ° (C7).
C. Orthogonal test of three factors of straight section shrinkage angle, height and center line deflection angle of an elbow-shaped water inlet runner outlet:
making an orthogonal Table L 32 As shown in table 2.
Table 2 intake runner geometric three-factor orthogonal test table L 32
D. Designing and modeling the pump device of each orthogonal test geometric parameter combination scheme of the straight section of the outlet of the water inlet flow channel, determining a flow field calculation area of the pump device, meshing, setting inlet and outlet boundary conditions, performing CFD (computational fluid dynamics) calculation of an internal flow field, performing post-processing to calculate the efficiency of the pump device, and selecting the highest efficiency of the pump device as an optimal scheme:
the design modeling is carried out on the water inlet channel pump device with the parameter combination determined by the orthogonal test, the flow calculation area of the pump device is determined as shown in figure 4, and the mesh division of the main flow passage component is shown in figure 5.
The front pool is arranged at the position 10 times of the diameter of the impeller from the inlet section of the water inlet channel as an inlet of a calculation domain, the boundary condition is gradient static pressure distribution related to depth, the position 10 times of the diameter of the impeller from the outlet section of the water outlet channel as an outlet of the calculation domain, the boundary condition is gradient static pressure distribution related to depth, and free outflow is arranged above an air domain; each side wall is set as a fixed wall boundary; an interface is provided between the grid members.
And performing numerical simulation calculation on the flow field in the pump device by adopting an RANS-VOF method. The external characteristic parameters such as the pump unit efficiency are calculated by the equations (6) to (9) with the aim of maximizing the pump unit efficiency, i.e., max (η) s ) Determining the scheme with the highest efficiency of the pump device as the optimal scheme, wherein the parameters of the water inlet flow channel of the scheme are combined into the contraction angle
Is 12 DEG, height h o The central line deflection angle theta is +5.5 degrees and is (1/3) D, and the highest pump device efficiency reaches 82.12 percent at the moment and is 2.71 percent higher than that of the original design scheme.
E. And (4) analyzing and explaining the high-efficiency principle of the non-uniform flow pump device at the outlet of the optimal water inlet flow channel.
Table 3 shows the external property performance of the optimized scheme, the pump section efficiency of the optimized scheme is the highest, and is 90.32%, and the hydraulic loss of the water outlet channel is the lowest, and is 0.3962m; the water inlet flow channel has larger hydraulic loss but smaller occupation ratio and is basically not influenced.
TABLE 3 optimal scheme external characteristic parameters of pump device
The characteristic diagram of the cascade efficiency of the impeller of the model shown in figure 6 is obtained by simulating the boundary conditions of uniform incoming flows with different speeds at the inlet of the impeller, the diagram shows the relationship between the cascade efficiency with different radiuses and the axial flow speed, the maximum peak value of the cascade efficiency is found at the normalized radius of 0.67, and the peak value reaches 95.26% when the axial speed is 5.2 m/s; the high efficiency zone is between the normalized radius of 0.6 and 0.8, and the axial velocity range is between 4.9m/s and 5.3 m/s.
As shown in fig. 7, the flow velocity distribution of the inlet section of the impeller is predicted by applying machine learning through the original scheme and the optimized scheme, the axial flow velocity distribution of the inlet section of the impeller in the original scheme is more uniform than that in the optimized scheme, but the optimized scheme has a larger area in a cascade high-efficiency area, so that the efficiency of the pump section is higher, the hydraulic loss of the water outlet channel is smaller, and the efficiency of the pump device is improved by 2.71 percentage points compared with the original scheme.
Claims (3)
1. A water inlet flow channel optimization method based on outlet non-uniform flow and highest efficiency of a pump device is characterized by comprising the following steps:
A. the conventional method designs an elbow-shaped water inlet flow channel:
the elbow-shaped water inlet flow channel is required to provide uniform incoming flow for the water pump impeller, the distribution uniformity of the axial flow velocity of the inlet section of the impeller is used as an evaluation standard of the water inlet flow channel, the higher the distribution uniformity of the axial flow velocity is, the better the distribution uniformity of the axial flow velocity is, and the calculation formula is as follows:
in the formula: v u The flow velocity distribution uniformity of the inlet section of the impeller, namely the outlet section of the water inlet runner;
the average axial speed of the inlet section of the impeller is m/s; u. u ai Calculating the axial speed of each unit, m/s, of the inlet section of the impeller; n is the number of the impeller inlet section calculating units;
the water inlet runner shaped line consists of a straight line and an arc;
B. the straight section contraction angle, the height and the center line deflection angle of the elbow-shaped water inlet runner outlet are selected as follows:
on the basis of the original design parameters of the straight section of the outlet of the water inlet flow passage, a plurality of values of three factors of contraction angle, height and center line deflection angle are set at certain intervals in the range of up and down feasible parameters, and the contraction angle is taken from small to large
A total of m levels, wherein
Designing a contraction angle for the original; the height is h from small to large 1 ，…，h j ＝h d ，…，h n N levels in total, wherein h d Designing the height for the original; the deviation angle of the central line is taken as theta 1 ，θ 2 ，…，θ l L levels in total, where θ 1 Designing the central line deflection angle theta 1 ＝0°；
C. An elbow-shaped water inlet runner outlet straight section contraction angle, height and center line deflection angle three-factor orthogonal test:
according to three factor levels of straight section contraction angle, height and center line deflection angle of elbow-shaped water inlet runner outlet, making orthogonal meter L T (m × n × l), determining T combination test protocols as in table 1; in the table 1, A, B and C respectively represent different combinations of three elements of the straight section of the outlet of the water inlet channel;
table 1 water inlet channel outlet straight section three-factor orthogonal test sample table
D. Designing and modeling the pump device of each orthogonal test geometric parameter combination scheme of the straight section of the outlet of the water inlet flow channel, determining a flow field calculation area of the pump device, meshing, setting inlet and outlet boundary conditions, performing CFD (computational fluid dynamics) calculation of an internal flow field, performing post-processing to calculate the efficiency of the pump device, and selecting the highest efficiency of the pump device as an optimal scheme:
(D1) Determining a calculation model according to upstream and downstream water levels of a design working condition of a pump device, wherein the calculation model comprises a forebay, a water inlet flow channel, an impeller, a guide vane, a water outlet flow channel and a water outlet pool, fluid below the water surface is water, and air areas are arranged above the water surfaces of the forebay and the water outlet pool;
setting a boundary condition: the overflow section of the forebay far enough away from the inlet section of the water inlet runner is considered as uniform flow distribution, the position is set as an inlet of a calculation domain, and the boundary condition is that gradient static pressure distribution exists;
the overflow section of the water outlet pool far enough away from the outlet section of the water outlet flow channel is considered as uniform flow distribution, the uniform flow distribution is set as a calculation domain outlet, and the boundary condition is gradient static pressure distribution;
each overflowing side wall is set as a fixed wall boundary;
(D2) A Computational Fluid Dynamics (CFD) method based on a Reynolds time-average method of fluid volume is applied to carry out numerical simulation calculation on a flow field in a pump device:
the Reynolds time-average method introduces a time-average method into a continuity equation and a Navier Stokes equation, and deduces the Reynolds time-average equation as follows:
in the formula: u is the water body velocity; p is water body pressure; f is an external force acting on the water body; v is the dynamic viscosity of the water body;
the VOF assumes that water and air are immiscible, two phases are defined by a set of standard momentum equations, and the sum of the volume fractions of the two phases in each volume unit is 1; for the q-th phase, the phase is,
in the formula, alpha q Is the volume fraction of the q-th phase; v is the speed of the q-th phase;
performing three-dimensional flow numerical simulation calculation on the flow field in the pump device with each parameter combination in the water inlet flow channel orthogonal test based on the method;
(D3) Calculating the performance parameters of the external characteristics of the pump device, wherein the flow expression is as follows:
in the formula:
the average flow velocity of the cross section is m/s; a is the area of the cross section, m;
the pump head expression is:
in the formula: z is the elevation of the water surface of the section, m; p is a radical of total Total pressure of the section Pa; ρ is the density of water; g is the local gravitational acceleration in m/s 2 (ii) a Subscripts 1 and 2 are respectively an inlet section of the water inlet channel and an outlet section of the water outlet channel;
the shaft power expression is:
in the formula: n is the rotation speed, rad/s; t is a unit of i Is the impeller torque, N · m;
the pump unit efficiency expression is:
in the formula: q is the pump flow rate, m 3 /s；H s For pump head, H s ＝z 2 －z 1 ；
(D4) Targeting the highest efficiency of the pump arrangement, i.e. max (η [) s ) Selecting and determining an optimal scheme of a water inlet runner;
E. analyzing and explaining the high-efficiency principle of the non-uniform flow pump device at the outlet of the optimal water inlet flow channel:
the relation between the efficiency of the water pump blade cascade and the radius and the axial flow velocity of the circumference is determined as follows:
the flow velocity of the incoming flow is not equal when the cascade efficiency of the impeller of the axial flow pump at different radiuses reaches the highest, and the cascade efficiency at different radiuses does not reach the maximum value at the same time when the flow velocity of the inlet section of the impeller is uniform, namely the impeller efficiency does not reach the highest;
on the circumference of any radius of the impeller, all the blades form an infinite plane in-line blade cascade, the efficiency of which is related to the magnitude of the axial velocity of the incoming flow, namely the efficiency of the blade cascade of any circumference is expressed by the function of the radius and the axial velocity of the blade cascade, and for a certain point of the inlet section of the impeller, if the radius and the axial velocity are known, the efficiency of the blade cascade of the point is determined;
the pump efficiency is expressed as:
in the formula, P e Is the effective power; p is shaft power;
effective power P of water pump e Expressed as:
the shaft power P is expressed as:
in the formula: v. of a The axial flow rate of the water pump on a certain circumference; h c The theoretical lift of an impeller and a guide vane cascade on a certain circumference of the water pump; eta c The efficiency of an impeller and a guide vane cascade on a certain circumference of the water pump is shown; r is a radical of hydrogen 1 Is the impeller hub radius; r is 2 Is the radius of the rim of the impeller; the water pump efficiency is then expressed as:
carrying out artificial neural network training according to the blade cascade efficiency characteristic of a specific pump, visually predicting the blade cascade efficiency distribution of the pump according to the axial speed distribution at the inlet of an impeller, providing an artificial neural network with two hidden layers for fitting the relationship between the blade cascade efficiency and the relationship between the radius and the axial speed, and selecting a sigmoid function as an activation function of the hidden layers, wherein the sigmoid function is a linear function of an output layer; for the training process, learning from a portion of the samples using a modified gradient descent algorithm, the samples were divided into two groups, 70% of which were used for training the network and the remaining 30% for testing; determining an original conventional optimization scheme water pump inlet flow velocity distribution contour map and a blade grid efficiency distribution contour map, and an existing optimization scheme water pump inlet flow velocity distribution contour map and a blade grid efficiency distribution contour map, and performing comparative analysis;
under the specific flow of the normal working condition of the water pump, when the axial speed distribution at the impeller inlet is consistent with or close to the efficient characteristic distribution of the efficiency of the pump blade grid, the pump efficiency reaches the highest or is close to the highest;
and calculating the pump efficiency by adopting the efficiency distribution of the pump blade grids, and comparing the calculated pump efficiency with the pump efficiency calculated by CFD (computational fluid dynamics) of the whole internal flow of the water pump device to verify the accuracy of the efficiency distribution of the pump blade grids.
2. The method of claim 1, wherein the pump device flow field calculation area in step (D1) is determined to be an air area 2m above the water surface of the forebay and the effluent pool; the front pool is arranged at the position 10 times the diameter of the impeller from the inlet section of the water inlet flow channel and is provided with a calculation domain inlet, and the water outlet pool is arranged at the position 10 times the diameter of the impeller from the outlet section of the water outlet flow channel and is provided with a calculation domain outlet; an interface is provided between each of the component meshes.
3. The method as claimed in claim 1, wherein the step (E1) of calculating the pump efficiency using the distribution of the efficiency of the blade cascade of the pump is that the effective power and the axial power of the pump are calculated using the blade cascade lift, the blade cascade efficiency and the axial speed of each computational grid unit of the cross section, and the pump efficiency is obtained by dividing the effective power and the axial power and is used for verifying the accuracy of the prediction result of the distribution of the blade cascade efficiency, and the expression is that
In the formula: delta A i Calculating the area of a grid unit on the inlet section; v. of ai Calculating the axial speed of the grid unit; h ci Calculating the head of the blade grid where the grid unit is located; eta ci To calculate the cascade efficiency of the grid cells.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211665137.XA CN115809617A (en) | 2022-12-23 | 2022-12-23 | Inlet water flow channel optimization method based on outlet non-uniform flow and highest efficiency of pump device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211665137.XA CN115809617A (en) | 2022-12-23 | 2022-12-23 | Inlet water flow channel optimization method based on outlet non-uniform flow and highest efficiency of pump device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN115809617A true CN115809617A (en) | 2023-03-17 |
Family
ID=85486584
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202211665137.XA Pending CN115809617A (en) | 2022-12-23 | 2022-12-23 | Inlet water flow channel optimization method based on outlet non-uniform flow and highest efficiency of pump device |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN115809617A (en) |
-
2022
- 2022-12-23 CN CN202211665137.XA patent/CN115809617A/en active Pending
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Rezaeiha et al. | Towards optimal aerodynamic design of vertical axis wind turbines: Impact of solidity and number of blades | |
| CN102032217B (en) | Method for optimizing dummy plate of double-volute type double-suction pump and product produced with same | |
| Wang et al. | A novel design of composite water turbine using CFD | |
| Guo et al. | Aerodynamic analysis of a step adjustment method for blade pitch of a VAWT | |
| CN105179303A (en) | Axial flow pump impeller all-operating-condition design method | |
| CN105465037B (en) | The hydraulic optimization method and device of a kind of impeller for double suction centrifugal pump | |
| Bing et al. | Effects of meridional flow passage shape on hydraulic performance of mixed-flow pump impellers | |
| CN105201916A (en) | Designing method for hydraulic power of space guide-blade centrifugal pump | |
| CN109344444B (en) | Energy loss evaluation method for blade angle optimization effect of hydraulic torque converter | |
| Bing et al. | Multi-parameter optimization design, numerical simulation and performance test of mixed-flow pump impeller | |
| CN105205259B (en) | A kind of centrifugal multistage pump multiple centrifugal pump flow channel type guide blade vane inlet laying angle design method | |
| CN102720622B (en) | Vortex generator for turbine draft tube | |
| CN113434965B (en) | Ship gas turbine compressor performance optimization method based on three-dimensional flow field analysis | |
| CN103195757A (en) | Pneumatic designing method of counter rotating compressor combining pumping of boundary layer | |
| Li et al. | Optimum design on impeller blade of mixed-flow pump based on CFD | |
| CN105608287B (en) | Design method for water outlet flow passage three-dimensional-form flow surface of high-performance and large-flow pump station | |
| Xu et al. | Flow pattern and anti-silt measures of straight-edge forebay in large pump stations. | |
| CN115809617A (en) | Inlet water flow channel optimization method based on outlet non-uniform flow and highest efficiency of pump device | |
| CN116595682A (en) | Blade pump transient process performance optimization design method | |
| Xue et al. | Research and optimization of performances of a pump turbine in pump mode | |
| Shen et al. | Investigation of the effect of critical structural parameters on the aerodynamic performance of the double darrieus vertical axis wind turbine | |
| CN109344535A (en) | A kind of Diffusion Vanes of Axial Pumps body automatic optimizing design method based on self-adaption flow-field | |
| Höfler et al. | Hydraulic design and analysis of the saxo-type vertical axial turbine | |
| CN111079367B (en) | Axial flow pump spoke optimization design method suitable for different water inlet taper pipes | |
| CN203939528U (en) | A kind of rotor blade with leaf top cascade structure that improves gas turbine aeroperformance |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |