Vertical centrifugal pump for enhancing hydraulic stability in hump region

Abstract

A vertical centrifugal pump having improved hydraulic stability in a hump region, comprising a volute casing (4) and a centrifugal impeller (2), wherein the centrifugal impeller (2) is located in the volute casing (4); hydrofoil-profile radial guide vanes (3) are provided between an outlet of the centrifugal impeller (2) and an inlet of the volute casing (4), the number of the vanes being coprime to the number of blades of the centrifugal impeller (2); the chord lengths, the cross-sectional areas and the maximum thicknesses of the plurality of radial guide vanes (3) each gradually increase along the increase of the cross-sectional area of the volute casing (4); the radial guide vane (3) having the minimum chord length, the minimum cross-sectional area, and the minimum maximum thickness is located at a position corresponding to the minimum cross-sectional area of the volute casing (4); the plurality of radial guide vanes (3) have the same inlet diameter and the same inlet installation angle. In this way, the hump characteristics of the pump at low flow rates can be suppressed, and the magnitudes and fluctuations of the axial and radial forces on the impeller and the guide vanes in the hump region can be reduced, thereby comprehensively improving the hydraulic stability of the vertical centrifugal pump having the guide vanes in the hump region in many aspects.

Description

TECHNICAL FIELD The present disclosure relates to the technical field of pump designing, and especially a vertical centrifugal pump for enhancing hydraulic stability in a hump region. BACKGROUND Centrifugal pumps are widely applied in various fields such as industry, energy, and agriculture. The vertical centrifugal pumps have advantages such as simple structures, wide use of guide bearing and thrust bearing structures in hydraulic turbines and pumped-storage pump-turbines, and mature design and manufacturing processes. Vertical centrifugal pump apparatuses have become core power equipment in major hydraulic engineering projects such as water resource allocation due to their prominent advantages. Vertical centrifugal pumps deployed in large-scale hydraulic engineering projects are characterized by large sizes, high flow rates, high heads, and high power ratings. The vertical centrifugal pump primarily consists of key hydraulic components such as an elbow-shaped inlet pipe, a centrifugal impeller, a radial guide vane, and a spiral volute casing. The radial guide vane structure is disposed between an outlet of the centrifugal impeller and an inlet of the spiral volute casing, to play a critical role in connecting the upper and lower parts. The radial guide vane has various functions, including flow rectification, pressure diffusion, and mechanical load balancing of the unit, etc. At present, in addition to performance requirements, operational stability has become a primary concern for a guide vane-equipped vertical centrifugal pump unit. To meet operational requirements, especially during the start-up and shutdown transition processes, the vertical centrifugal pump unit often operates under an off-design condition and inevitably needs to pass through a hump region. During operation in the hump region, flow instability phenomena such as stalling and secondary flow in the guide vane may lead to hydraulic instabilities such as enhanced pressure pulsation and increased axial force and radial force, resulting in oscillations in the entire pump system, and seriously affecting the safe and stable operation of the vertical centrifugal pump unit. Currently, a fixed guide vane structure used in a traditional vertical centrifugal pump generally includes a plurality of hydrofoil structures symmetrically distributed along the circumferential direction between an impeller and a volute casing, without considering the hydraulic stability in the hump region. To improve the hydraulic stability in the hump region of the vertical centrifugal pump, the present disclosure provides an incremental guide vane structure, which not only improves the hump characteristics of the vertical centrifugal pump but also improves the unsteady force characteristics of hydraulic components. The present disclosure is of great significance for enhancing the hydraulic stability of the guide vane-equipped vertical centrifugal pump in the hump region and ensuring the safe and stable operation of the apparatus. A patent literature discloses a guide vane combination structure for enhancing the hump instability phenomenon of the volute centrifugal pump, and proposes a structure with large and small guide vanes arranged in combination to alleviate the hump phenomenon of a centrifugal pump under low flow conditions. However, that invention only considers how to alleviate the hump phenomenon but does not consider that the different-sized guide vane structures will lead to an increase and unevenness in the radial force and the axial force on the hydraulic components, thereby posing a greater threat to the operational stability of the rotor system of the unit. SUMMARY In view of the deficiencies existing in the prior art, the present disclosure provides a vertical centrifugal pump for enhancing hydraulic stability in the hump region. By enhancing the compatibility among the impeller, the guide vane, and the spiral volute casing, not only the hump characteristics of the vertical centrifugal pump under low-flow conditions are suppressed, but also the magnitude and fluctuations of an axial force and a radial force exerted on the impeller and the guide vane within the hump region are reduced. Therefore, the hydraulic stability of the guide vane-equipped vertical centrifugal pump in the hump region is comprehensively improved in various aspects. The aforementioned technical objective is achieved through the following technical means: A vertical centrifugal pump for enhancing hydraulic stability in a hump region includes a spiral volute casing and a centrifugal impeller, where the centrifugal impeller is located within the spiral volute casing. A plurality of radial guide vanes of a hydrofoil shape are arranged between an outlet of the centrifugal impeller and an inlet of the spiral volute casing, where a vane number of the plurality of the radial guide vanes and a vane number of the centrifugal impeller are prime numbers of each other. A chord length, a cross-sectional area, and a maximum thickness of the plurality of the radial guide vanes progressively increase with an increase of a sectional area of the spiral volute casing, and one of the plurality of the radial guide vanes with minimum values of the chord length, the cross-sectional area, and the maximum thickness is positioned at a minimum sectional area of the spiral volute casing. The plurality of the radial guide vanes are configured with identical inlet diameters and identical inlet arrangement angles, where the plurality of the radial guide vanes are divided into a standard guide vane and an incremental guide vane assembly, where the standard guide vane is located at a volute tongue of the spiral volute casing, and the chord length and the maximum thickness of the radial guide vanes in the incremental guide vane assembly increase linearly along a circumferential direction of the spiral volute casing, while the cross-sectional area of the radial guide vanes in the incremental guide vane assembly increases non-linearly along the circumferential direction of the spiral volute casing. Increasing trends of the chord length, the maximum thickness, and the cross-sectional area of the radial guide vanes in the incremental guide vane assembly corresponds to an increasing trend of the sectional area of the spiral volute casing. One of the radial guide vanes in the incremental guide vane assembly with the minimum values of the chord length, the cross-sectional area, and the maximum thickness is disposed at the minimum sectional area of the spiral volute casing adjacent to the standard guide vane. Further, the one of the radial guide vanes with the minimum values has the chord length of 0.5 times the standard guide vane, the cross-sectional area of 0.25 times the standard guide vane, and the maximum thickness of 0.5 times the standard guide vane. Further, the radial guide vanes in the incremental guide vane assembly are uniformly arranged at intervals of 360 / N° along the circumferential direction with an increasing sectional area of the spiral volute casing, starting from the one of the radial guide vanes with the minimum values, and the chord length Lx of an x-th radial guide vane in the incremental guide vane assembly increases linearly according to a formula as follows: 0.5Zw 0.5Ln-N-1.5L„ L =---— x +-----------— N-2 N-2 where, the Lx is the chord length of the x-th radial guide vane, x e [2,......, N -1], the N is a total guide vane number, and the Z#is the chord length of the standard guide vane. Further, the radial guide vanes in the incremental guide vane assembly are uniformly arranged at intervals of 360IN° along the circumferential direction with an increasing sectional area of the spiral volute casing, starting from the one of the radial guide vanes with the minimum values, and the maximum thickness 8X of an x-th radial guide vane in the incremental guide vane assembly increases linearly according to a formula as follows: ,, 0.54 0.54 -N-1.54 N— 2 N-2 where, the 8X is the maximum thickness of the x-th radial guide vane, x e [2,......, N -1], the N is a total guide vane number, and the 4 is the maximum thickness of the standard guide vane. Further, the radial guide vanes in the incremental guide vane assembly are uniformly arranged at intervals of 3604° along the circumferential direction with an increasing sectional area of the spiral volute casing, starting from the one of the radial guide vanes with the minimum values, and the cross-sectional area of an x-th radial guide vane in the incremental guide vane assembly increases non-linearly according to a formula as follows: A^ = ax1 +bx + c where, the A,. is the cross-sectional area of the x-th radial guide vane, x e [2,.......N -1], the N is a total guide vane number, and the a, the b, and the c are coefficients determined by an equation set as follows: 0.25.4, = ci + b + c < An = (N-1)2 a + (N-\}b + c 0.3.4, — 4a + 2b + c .. where, the An is the cross-sectional area of the standard guide vane. Further, the chord length, the cross-sectional area, and the maximum thickness of the standard guide vane are all determined by an outlet diameter and an outlet arrangement angle of the centrifugal impeller and an inlet diameter and the sectional area of the spiral volute casing. The present disclosure has the following advantages: 1. In the vertical centrifugal pump for enhancing the hydraulic stability in the hump region described in the present disclosure, the chord length, the cross-sectional area, and the maximum thickness of the plurality of the radial guide vanes progressively increase with the increase of the sectional area of the spiral volute casing, for improving the comprehensive hydraulic stability in the hump region of the guide vane-equipped vertical centrifugal pump. The incremental guide vane assembly of the present disclosure can further improve the compatibility between the guide vanes and the impeller, and between the guide vanes and the spiral volute casing, reduce the internal flow loss within the centrifugal pump, improve the flow pattern and the diffuser effect of the guide vanes in the hydraulic components in the hump region, and better balance the axial force and the radial force on the guide vanes and the impeller while suppressing the hump characteristics of the performance curve at low flow rates. The present disclosure is of great significance for enhancing the unit safety and stability of the guide vane-equipped vertical centrifugal pump under off-design operating conditions. 2. In the vertical centrifugal pump for enhancing the hydraulic stability in the hump region described in the present disclosure, the incremental guide vane assembly improves the hydraulic compatibility between the guide vanes and the impeller, and between the guide vanes and the spiral volute casing, and relieves the problem that the traditional guide vane structure is prone to unstable flow at low flow rates, thereby suppressing the hump characteristics of the vertical centrifugal pump at low flow rates, improving the hydraulic efficiency of the pump at low flow rates, and saving energy. 3. In the vertical centrifugal pump for enhancing the hydraulic stability in the hump region described in the present disclosure, the increasing trends of the chord length, the cross-sectional area, and the maximum thickness of the guide vanes in the incremental guide vane assembly correspond to the increasing trend of the sectional area of the spiral volute casing, greatly improving the compatibility between the guide vanes and the spiral volute casing. Therefore, the unsteady characteristics of the axial force and the radial force on the impeller and the radial guide vanes in the hump region are effectively improved while the hump characteristics are suppressed. This is mainly reflected in the fact that the amplitudes of the axial force and the radial force on the impeller and the guide vanes are significantly reduced over time, and the distribution of the force magnitude is more uniform over time, that is, the axial force and the radial force are better balanced, thereby ensuring the safe and stable operation of the rotor system and improving the comprehensive hydraulic stability of the vertical centrifugal pump in the hump region. 4. In the vertical centrifugal pump for enhancing hydraulic stability in the hump region described in the present disclosure, the incremental guide vane assembly enhances hydraulic compatibility between the guide vanes and the impeller, and between the guide vanes and the spiral volute casing. This significantly alleviates the flow separation and the channel blockage within the guide vanes, thereby narrowing the hump region, suppressing the hump characteristic curve, and improving efficiency. As a result, the vertical centrifugal pump unit achieves high-efficiency and stable operation across an extended flow rate range. 5. In the vertical centrifugal pump for enhancing the hydraulic stability in the hump region described in the present disclosure, the incremental guide vane assembly can effectively improve the unsteady characteristics of the axial force and the radial force on the impeller and the guide vanes in the hump region while suppressing the hump characteristics. This is mainly reflected in the fact that the amplitudes of the axial force and the radial force on the impeller and the guide vanes are significantly reduced over time. Specifically, the peak amplitude of the axial force on the incremental guide vane assembly is 24% lower than the large-and-small guide vane structure in the prior art, and 41% lower than the all-standard guide vane structure; the peak amplitude of the radial force on the incremental guide vane assembly is 10% lower than the all-standard guide vane structure and the large-and-small guide vane structure; for the incremental guide vane assembly, the peak amplitude of the radial force on the impeller is 32% lower than the all-standard guide vane structure, and another 19% lower than the large-and-small guide vane structure; and for the incremental guide vane assembly, the peak amplitude of the axial force on the impeller is 25% lower than the all-standard guide vane structure, and 4% lower than the large-and-small guide vane structure. Therefore, when the incremental guide vane assembly is used, the fluctuations of the axial force and the radial force on the impeller and the guide vanes are significantly reduced, thereby significantly enhancing the hydraulic stability of the vertical centrifugal pump unit in the hump region. BRIEF DESCRIPTION OF THE DRAWINGS In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, the drawings required for describing the embodiments or the prior art will be briefly introduced below. The drawings in the following description are some embodiments of the present disclosure. It will be obvious to those of ordinary skill in the art that other drawings can be obtained according to these drawings without creative efforts. FIG. 1 is a schematic structural diagram of a vertical centrifugal pump for enhancing hydraulic stability in a hump region according to the present disclosure. FIG. 2 is a schematic installation diagram of radial guide vanes according to the present disclosure. FIG. 3 is a schematic diagram of locations of a standard guide vane and an incremental guide vane assembly according to the present disclosure. FIG. 4 is a schematic diagram of parameters of radial guide vanes of a hydrofoil shape according to the present disclosure. FIG. 5 shows a curve illustrating an increasing law of chord lengths of guide vanes in the incremental guide vane assembly according to the present disclosure. FIG. 6 shows a curve illustrating an increasing law of cross-sectional areas of guide vanes in the incremental guide vane assembly according to the present disclosure. FIG. 7 shows a curve illustrating an increasing law of maximum thicknesses of guide vanes in the incremental guide vane assembly according to the present disclosure. FIG. 8 shows flow rate-head curves of vertical centrifugal pumps with standard guide vanes, combined guide vanes, and guide vanes of the present disclosure respectively under different operating conditions in the hump region. FIG. 9 shows flow rate-efficiency curves of vertical centrifugal pumps with standard guide vanes, combined guide vanes, and guide vanes of the present disclosure respectively under different operating conditions in the hump region. FIG. 10 is a schematic diagram of streamline distributions within a standard guide vane, a combined guide vane, and a guide vane of the present disclosure under operating conditions in the hump region. FIG. 11 is a schematic diagram of radial force distributions of a standard guide vane, a combined guide vane, and a guide vane of the present disclosure under operating conditions in the hump region. FIG. 12 is a schematic diagram of axial force distributions of a standard guide vane, a combined guide vane, and a guide vane of the present disclosure under operating conditions in the hump region. FIG. 13 is a comparative diagram of force amplitudes on an impeller and a guide vane of a standard guide vane, a combined guide vane, and a guide vane of the present disclosure under operating conditions in the hump region. In the drawings: 1: elbow-shaped inlet pipe; 2: centrifugal impeller; 3: radial guide vane; 3-1: standard guide vane; 4: spiral volute casing. DETAILED DESCRIPTION OF THE EMBODIMENTS Embodiments of the present disclosure are described in detail below, and exemplification of the embodiments is shown in the drawings, where the same or similar reference numerals throughout denote the same or similar elements or elements having the same or similar function. The embodiments described below by reference to the drawings are exemplary and are intended for explaining the present disclosure and are not to be construed as limiting the disclosure. In the description of the present disclosure, it is to be understood that terms such as “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “top”, “bottom”, “axial”, “radial”, “vertical”, “horizontal”, “inner”, “outer”, and the like indicate orientational or positional relationships based on those shown in the drawings. These terms are used merely for convenience in describing the disclosure and simplifying the description, and do not indicate or imply that the referred apparatus or element must have a particular orientation or be constructed and operated in a particular orientation. Thus, such descriptions shall not be construed as a limitation of the disclosure. Furthermore, the terms “first” and “second” are used merely for descriptive purposes, and should not be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, a feature defined with the term “first” or “second” may expressly or implicitly include one or more such features. In the description of the present disclosure, unless otherwise explicitly and specifically defined, the term “a plurality of’ means two or more. In the present disclosure, unless expressly specified or defined otherwise, the terms “mount”, “connect”, “couple”, “fix”, and the like shall be understood broadly. For example, connection may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; and it may be a direct connection, an indirect connection through an intermediary medium, or an internal connection between two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present disclosure may be understood according to the specific circumstance. As shown in FIG. 1 and FIG. 2, a vertical centrifugal pump for enhancing hydraulic stability in a hump region according to the present disclosure includes an elbow-shaped inlet pipe 1, a centrifugal impeller 2, a plurality of radial guide vanes 3, and a spiral volute casing 4. The elbow-shaped inlet pipe 1 is in communication with an inlet of the spiral volute 4, and the centrifugal impeller 2 is located within the spiral volute casing 4. The plurality of radial guide vanes 3 of a hydrofoil shape are arranged between the outlet of the centrifugal impeller 2 and the inlet of the spiral volute casing 4, where a vane number of the radial guide vanes 3 and a vane number of the centrifugal impeller 2 are prime numbers of each other. A chord length, a cross-sectional area, and a maximum thickness of the plurality of the radial guide vanes 3 progressively increase with the increase of a sectional area of the spiral volute casing 4, and one of the plurality of radial guide vanes 3 with the minimum values of the chord length, the cross-sectional area, and the maximum thickness is positioned at a minimum sectional area of the spiral volute casing 4. The plurality of the radial guide vanes 3 are configured with identical inlet diameters and identical inlet arrangement angles. As shown in FIG. 3 and FIG. 4, the plurality of the radial guide vanes 3 are divided into a standard guide vane 3-1 and an incremental guide vane assembly, where the standard guide vane 3-1 is located at a volute tongue of the spiral volute casing 4. The chord length and the maximum thickness of the radial guide vanes 3 in the incremental guide vane assembly increase linearly along the circumferential direction of the spiral volute casing 4, while the cross-sectional area of the radial guide vanes 3 in the incremental guide vane assembly increases non-linearly along the circumferential direction of the spiral volute casing 4, with the increasing trends of the chord length, the maximum thickness, and the cross-sectional area of the radial guide vanes 3 in the incremental guide vane assembly corresponding to the increasing trend of the sectional area of the spiral volute casing 4. One of the radial guide vanes 3 in the incremental guide vane assembly with the minimum values of the chord length, the cross-sectional area, and the maximum thickness is disposed at the minimum sectional area of the spiral volute casing 4 adjacent to the standard guide vane 3-1. As shown in the embodiment of FIG. 2, a number of the radial guide vanes 3 is 13. The radial guide vane 3 numbered 1 ’ is the radial guide vane 3 with the minimum values, and the radial guide vane 3 numbered 13’ is the standard guide vane 3-1. The radial guide vanes 3 numbered from 1’ to 12’ constitute the incremental guide vane assembly. The incremental guide vane assembly of the present disclosure improves the hydraulic compatibility between the guide vanes and the centrifugal impeller, and between the guide vanes and the spiral volute casing, and alleviates the problem that the traditional guide vane structure is prone to unstable flow at low flow rates, thereby suppressing the hump characteristics of the vertical centrifugal pump at low flow rates, improving the hydraulic efficiency of the pump at low flow rates, and saving energy. The increasing trends of the chord length, the cross-sectional area and the maximum thickness of the guide vanes in the incremental guide vane assembly correspond to the increasing trend of the sectional area of the spiral volute casing, which greatly improves the compatibility between the guide vanes and the spiral volute casing. The amplitudes of the axial force and the radial force on the impeller and the guide vanes are significantly reduced over time, and the distribution of the force magnitude is more uniform over time, that is, the axial force and the radial force are better balanced, thereby ensuring the safe and stable operation of the rotor system, and improving the comprehensive hydraulic stability of the vertical centrifugal pump unit in the hump region. The one of the radial guide vanes 3 with the minimum values has a chord length of 0.5 times the standard guide vane 3-1, a cross-sectional area of 0.25 times the standard guide vane 3-1, and a maximum thickness of 0.5 times the standard guide vane 3-1. The radial guide vanes 3 in the incremental guide vane assembly are uniformly arranged at intervals of 360 / ' / V° along the circumferential direction with an increasing sectional area of the spiral volute casing 4, starting from the one of the radial guide vanes 3 with the minimum values, and the chord length Lx of an x-th radial guide vane 3 in the incremental guide vane assembly increases linearly according to a formula as follows: T 0.5£v Q.5LN ■ N-\.5LX, L =---^x +-----------— x N-2 N-2 where, the Lx is the chord length of the x-th radial guide vane 3, x e [2,......, N -1], the N is a total guide vane number, and the Zvis the chord length of the standard guide vane 3-1. The maximum thickness bx of the x-th radial guide vane 3 in the incremental guide vane assembly increases linearly according to a formula as follows: 0,54 0.5<5n-N-1.56n N-2 N-2 where, the 8X is the maximum thickness of the x-th radial guide vane 3, x e [2,......, N -1], the N is a total guide vane number, and the rkisthe maximum thickness of the standard guide vane 3-1. The cross-sectional area of the x-th radial guide vane 3 111 the incremental guide vane assembly increases non-linearly according to a formula as follows: A* = ax2 + bx + c where, the Ax is the cross-sectional area of the x-th radial guide vane 3, x e [2,......, N -1], the N is a total guide vane number, and the a, the b, and the c are coefficients determined by an equation set as follows: 0.25.4, =a+b+c < An = (N-tf a + (N-\)b + c 0.3Jv = 4a + 2b + c where, the A.v is the cross-sectional area of the standard guide vane 3-1. Embodiment 1 In this embodiment, the centrifugal impeller 2 has an outer diameter of 360 mm, a rotation speed of 1150 r / min, a design flow rate of 214 kg / s, and a design head of 18.74 m. The centrifugal impeller 2 has 7 vanes, and 13 pieces of hydrofoil-shaped radial guide vanes 3 are arranged between the outlet of the centrifugal impeller 2 and the inlet of the spiral volute casing 4. The vane number 13 of the radial guide vanes 3 and the vane number 7 of the impeller are prime numbers of each other, as shown in FIG. 2. Under the acceleration of the centrifugal force of the centrifugal impeller 2, the fluid entered the radial guide vanes 3. The radial guide vanes 3 play a critical role in connecting the upper and lower parts. The radial guide vanes enable the fluid to have a more smooth flow pattern before entering the spiral volute casing 4, reduce the flow rate, convert kinetic energy into pressure energy, and meanwhile balance the radial force on the unit. As shown in FIG. 2 and FIG. 3, the plurality of the radial guide vanes 3 are divided into a standard guide vane 3-1 and an incremental guide vane assembly, where the standard guide vane 3-1 is located at a volute tongue of the spiral volute casing 4. According to the design parameters of the outlet of the centrifugal impeller 2 and the inlet of the spiral volute casing 4, parameters of the standard guide vane 3-1 (i.e., the radial guide vane 3 numbered 13’ in FIG. 2) are obtained by using the existing design method. For example, the standard guide vane 3-1 has an inlet diameter of 372 mm, an axial width of 75 mm, an inlet arrangement angle of 30°, a hydrofoil chord length Ln of 66.33 mm, a hydrofoil cross-sectional area An of 487.53 mm2, and a hydrofoil maximum thickness Sn of 9.57 mm. Referring to FIG. 3, one of the radial guide vanes 3 with the minimum values of the chord length, the cross-sectional area, and the maximum thickness of the hydrofoil (i.e., the radial guide vane 3 numbered 1’ in FIG. 2) is disposed at a position adjacent to the standard guide vane 3-1 where the sectional area of the spiral volute casing is smaller. The inlet diameter, the inlet arrangement angle, and the axial width of the radial guide vane 3 numbered 1 ’ are the same as the standard guide vane 3-1. The radial guide vane 3 numbered 1’ is arranged at an interval of 27.69° (calculated by 360° / 13) along the circumferential direction from the standard guide vane 3-1. As shown in FIG. 2, the radial guide vane 3 with the minimum values has a chord length of 0.5 times the standard guide vane 3-1, i.e., 33.165 mm, a cross-sectional area of 0.25 times the standard guide vane 3-1, i.e., 121.91 mm2, and a maximum thickness of 0.5 times the standard guide vane 3-1, i.e., 4.785 mm. Finally, the radial guide vane 3 with the minimum values (i.e., the radial guide vane 3 numbered 1’ in FIG. 2) is obtained according to the above specific design parameters. As shown in FIG. 2, starting from the radial guide vane 3 with the minimum values, radial guide vanes 3 are uniformly arranged at intervals of 360 / 13=27.69° along the circumferential direction with an increasing sectional area of the spiral volute casing, until the radial guide vane 3 numbered 12’, where the radial guide vanes 3 have a hydrofoil similar to the standard guide vane 3-1, and a chord length, a cross-sectional area, and a maximum thickness of the hydrofoil gradually increasing. The radial guide vane 3 numbered 12’ is adjacent to the standard guide vane 3-1, and has a size similar to or identical with the standard guide vane 3-1 because the sectional area of the spiral volute casing at the radial guide vane 3 numbered 12’ is almost the same as that at the radial guide vane 3 numbered 13’. As shown in FIG. 3 and FIG. 5, the chord length Lx of the x-th radial guide vane 3 in the incremental guide vane assembly increases linearly according to a formula as follows: T 0.5 / ., 0.5Lv ■ N-1.5LK t =------i----------A = 3 015x + 30.15 A^2 where, Lx is the chord length of the x-th radial guide vane 3, x g [2,......, N l], and A is a total guide vane number, i.e., Ais 13. As shown in FIG. 3 and FIG. 6, the cross-sectional area of the x-th radial guide vane 3 in the incremental guide vane assembly increases linearly according to a formula as follows: A^ = ax1 + bx + c where, a, b, and c are determined by an equation set as follows: \2\.^=a + b + c <2 = 0.886 M87.53=144a + 126 + c^Z> = 21.722 146.26 — 4 <2 + 2 / ) + c c = 99.272 According to the above equation set, A* = 0.886x2 +21.722x + 99.272 As shown in FIG. 3 and FIG. 7, the maximum thickness dx of the x-th radial guide vane 3 in the incremental guide vane assembly increases linearly according to a formula as follows: In the embodiment provided by the present disclosure, the design parameters of the radial guide vane 3 numbered 2’ to 12’ are calculated based on the aforementioned formulas for the increasing laws of the chord length, the cross-sectional area, and the maximum thickness. Where, the chord length L and the maximum thickness <5 of the hydrofoil of each of the guide vanes follow a linear growth pattern, while the cross-sectional area A of the hydrofoil of each of the guide vanes follow a non-linear growth pattern. The increasing trends of the chord length L, the cross-sectional area A, and the maximum thickness 6 of the incremental guide vane assembly correspond to the increasing trend of the sectional area of the spiral volute casing. For convenience of description, the uniformly distributed standard guide vane 3-1 in the prior art is referred to as a standard guide vane structure, and the large-and-small combined guide vane structure in another prior art is referred to as a combined guide vane structure. As shown in FIG. 8, within a range of different flow rates 7 0+ from 0.6 to 0.8 in the hump region, flow rate-head curves for the standard guide vane structure, the combined guide vane structure, and the radial guide vane structure of the present disclosure are obtained through simulation based on a computational fluid dynamics (CFD) method. As shown in FIG. 8, for the vertical centrifugal pump with the standard guide vane structure, the head suddenly drops when the flow rate decreases from 0.75 Q / Qa^ to 0.74 (AA, resulting in a positive slope in the flow rate-head curve, i.e., the hump phenomenon. When the flow rate decreases to 0.72 g / gdes and further to 0.71 0 / Qdes, the head exhibits a second slight drop. When the flow rate further decreases to 0.66 Q / Qa^ and then to 0.65 0 / Odes, the head exhibits a third significant drop. Therefore, the vertical centrifugal pump with the standard guide vane structure undergoes a plurality of hump phenomena. The head of the vertical centrifugal pump with the combined guide vane structure in the hump region is significantly higher than the standard guide vane structure, and the first drop condition is postponed to 0.71 0 / Odes. However, a second hump phenomenon is still observed in the flow rate range of 0.68 0 / 0 Aes to 0.65 O / gdes. Overall, compared to the standard guide vane structure, the hump region of the combined guide vane structure is reduced and the head is increased. When the guide vane structure of the present disclosure is used, the head in the hump region is further increased, and only a hump phenomenon with a small positive slope is observed in the flow rate range of 0.74 Q / Qa^s to 0.72 0 / 0des. Therefore, the incremental guide vane structure of the present disclosure can significantly reduce the hump region, suppress the hump characteristic curve, and increase the head, allowing the vertical centrifugal pump unit to operate stably within a larger flow rate range. In the drawings, (Odes represents the flow rate under the design condition. As shown in FIG. 9, within a range of different flow rates (M2des from 0.6 to 0.8 in the hump region, efficiency-flow rate curves for the standard guide vane structure, the combined guide vane structure, and the guide vane structure of the present disclosure are obtained through simulation based on the CFD method. The figure indicates that the efficiency of the vertical centrifugal pump with the standard guide vane structure has a minimal difference from the efficiency of the vertical centrifugal pump with the combined guide vane structure. However, the efficiency of the vertical centrifugal pump with the guide vane structure of the present disclosure is significantly improved, and increased uniformly. Especially in the range of 0.73 Q / QAes to 0.8 the efficiency improvement is obvious. That is, the incremental guide vane structure of the present disclosure improves the efficiency of the vertical centrifugal pump under small flow conditions, and reduces the efficiency fluctuations. As shown in FIG. 10, the streamline distributions on the mid-span cross-section of the guide vane under the hump condition for the standard guide vane structure, the combined guide vane structure, and the guide vane structure of the present disclosure are obtained through simulation based on the CFD method. The figure indicates that the standard guide vane structure exhibits a flow blockage at label A and a significant flow separation with flow blockage at label B. The combined guide vane structure eliminates the flow blockage at label A, and yet retains the flow separation and blockage phenomena at label B. While the guide vane structure of the present disclosure demonstrates smooth streamline distributions at both label A and label B, with complete elimination of the flow blockage and separation phenomena. This is because the compatibility of the hydraulic components has been significantly improved, and the hump characteristic curve is significantly suppressed and the efficiency is increased. As shown in FIG. 11, distributions of radial force vector points under the hump condition for the standard guide vane structure, the combined guide vane structure, and the guide vane structure of the present disclosure are obtained through simulation based on the CFD method. The figure indicates that the radial force vector points for the standard guide vane structure are highly scattering at different times, with a significant portion of the vector points deviating far from the origin, indicating a substantial radial force fluctuation. The radial force vector points for the combined guide vane structure are more clustered compared with the standard guide vane structure, but the vector points are basically clustered in the area where both X and Y directions are negative values. Therefore, although the fluctuation of the radial force on the combined guide vane structure is reduced, the distribution is still uneven in the circumferential direction. The radial force vector points for the guide vane structure of the present disclosure are more clustered and closer to the origin compared with the standard guide vane structure and the combined guide vane structure. Therefore, the guide vane structure of the present disclosure can effectively improve the unsteady characteristics of the radial force on the guide vane structure, that is, the radial force is better balanced. As shown in FIG. 12, fluctuations of the axial force under the hump condition for the standard guide vane structure, the combined guide vane structure, and the guide vane structure of the present disclosure are obtained through simulation based on the CFD method. The figure indicates that the axial forces on the standard guide vane structure and the combined guide vane structure exhibit significant fluctuations over time without obvious periodicity. Whereas the axial force on the guide vane structure of the present disclosure exhibits significantly reduced fluctuation over time and demonstrates periodicity. That is, the unsteady characteristic of axial force on the guide vane structure of the present disclosure has been significantly improved. The axial force on the standard guide vane structure exhibits a peak amplitude of AFn=64.23 N, while the axial force on the combined guide vane structure exhibits a reduced peak amplitude of AFc=49.54 N, representing a 23% decrease compared with the standard guide vane structure. The guide vane structure of the present disclosure further reduces the peak amplitude of the axial force to AFg=37.72 N, achieving a 24% reduction relative to the combined guide vane structure and a 41% reduction relative to the standard guide vane structure. Therefore, the guide vane structure of the present disclosure can substantially reduce the axial force on the guide vane. FIG. 13 shows comparison of amplitudes of the axial force and the radial force under the hump condition on the impeller and the guide vane of the standard guide vane structure, the combined guide vane structure, and the guide vane structure of the present disclosure. The figure indicates that the peak amplitudes of the radial force on the standard guide vane structure and the combined guide vane structure are basically the same. Whereas the peak amplitude of the radial force on the guide vane structure of the present disclosure is significantly reduced, by 10% compared with the combined guide vane structure. Relative to the standard guide vane structure and the combined guide vane structure, the peak amplitude of the axial force on the guide vane structure of the present disclosure is also significantly reduced, by 26% compared with the standard guide vane structure and by 13% compared with the combined guide vane structure. For the guide vane structure of the present disclosure, the peak amplitudes of the radial force and the axial force on the impeller are significantly lower than the standard guide vane structure and the combined guide vane structure. The peak amplitude of the radial force on the impeller decreases by 32% compared with the standard guide vane structure and decreases by another 19% compared with the combined guide vane structure. The peak amplitude of the axial force on the impeller decreases by 25% compared with the standard guide vane structure and decreases by another 4% compared with the combined guide vane structure. Therefore, the guide vane structure of the present disclosure in the embodiment can suppress the hump characteristics of the vertical centrifugal pump, and meanwhile effectively reduce the magnitude and fluctuation of the axial force and the radial force on the impeller and the guide vane. It should be understood that although the specification is described in accordance with various embodiments, not each of the embodiments contains only one independent technical solution. The specification is described in a manner only for clarity. Those of skill in the art should take the specification as a whole, and the technical solutions in the various embodiments can be combined appropriately to form other embodiments that can be understood by those of skill in the art. The series of detailed descriptions listed above are merely specific descriptions for the feasible embodiments of the present disclosure. They are not intended to limit the protection scope of the present disclosure. Any equivalent embodiments or changes without departing from the spirit of the present disclosure should fall within the protection scope of the present disclosure.

Claims

1. A vertical centrifugal pump for enhancing hydraulic stability m a hump region, comprising a spiral volute casing (4) and a centrifugal impeller (2), wherein the centrifugal impeller (2) is located within the spiral volute casing (4), characterized in that a plurality of radial guide vanes (3) of a hydrofoil shape are arranged between an outlet of the centrifugal impeller (2) and an inlet of the spiral volute casing (4), wherein a vane number of the plurality of the radial guide vanes (3) and a vane number of the centrifugal impeller (2) are prime numbers of each other; a chord length, a cross-sectional area, and a maximum thickness of the plurality of the radial guide vanes (3) progressively increase with an increase of a sectional area of the spiral volute casing (4), and one of the plurality of the radial guide vanes (3) with minimum values of the chord length, the cross-sectional area, and the maximum thickness is positioned at a minimum sectional area of the spiral volute casing (4); and the plurality of the radial guide vanes (3) are configured with identical inlet diameters and identical inlet arrangement angles, whereinthe plurality of the radial guide vanes (3) are divided into a standard guide vane (3-1) and an incremental guide vane assembly, wherein the standard guide vane (3-1) is located at a volute tongue of the spiral volute casing (4), and the chord length and the maximum thickness of the radial guide vanes (3) in the incremental guide vane assembly increase linearly along a circumferential direction of the spiral volute casing (4) while the cross-sectional area of the radial guide vanes (3) in the incremental guide vane assembly increases non-linearly along the circumferential direction of the spiral volute casing (4), with increasing trends of the chord length, the maximum thickness, and the cross-sectional area of the radial guide vanes (3) in the incremental guide vane assembly corresponding to an increasing trend of the sectional area of the spiral volute casing (4); and one of the radial guide vanes (3) in the incremental guide vane assembly with the minimum values of the chord length, the cross-sectional area, and the maximum thickness is disposed at the minimum sectional area of the spiral volute casing (4) adjacent to thestandard guide vane (3-1).

2. The vertical centrifugal pump for enhancing the hydraulic stability in the hump region according to claim 1, characterized in that the one of the radial guide vanes (3) with the minimum values has the chord length of 0.5 times the standard guide vane (3-1), the cross-sectional area of 0.25 times the standard guide vane (3-1), and the maximum thickness of 0.5 times the standard guide vane (3-1).

3. The vertical centrifugal pump for enhancing the hydraulic stability in the hump region according to claim 1, characterized in that the radial guide vanes (3) in the incremental guide vane assembly are uniformly arranged at intervals of 360 / N° along the circumferential direction with an increasing sectional area of the spiral volute casing (4), starting from the one of the radial guide vanes (3) with the minimum values, and the chord length Lx of an x-th radial guide vane (3) in the incremental guide vane assembly increases linearly according to a formula as follows:r 0.5£v 0.5Ln-N^1.5LvT _ _____A „ j__A____________AJL? — A- 1“x N-2 N-2wherein, the Lx is the chord length of the x-th radial guide vane (3), x e [2,......, N -1], the N is atotal guide vane number, and the La?is the chord length of the standard guide vane (3-1).

4. The vertical centrifugal pump for enhancing the hydraulic stability in the hump region according to claim 1, characterized in that the radial guide vanes (3) in the incremental guide vane assembly are uniformly arranged at intervals of 360 / N° along the circumferential direction with an increasing sectional area of the spiral volute casing (4), starting from the one of the radial guide vanes (3) with the minimum values, and the maximum thickness 3X of an x-th radial guide vane (3) in the incremental guide vane assembly increases linearly according to a formula as follows:e 0.55v Q.53n-N^1.56v<5 =----2-X +----"---------Ux N-2 N^2wherein, the 3X is the maximum thickness of the x-th radial guide vane (3), x e [2,......, N -1], theN is a total guide vane number, and the <5# is the maximum thickness of the standard guide vane (3-1).

5. The vertical centrifugal pump for enhancing the hydraulic stability in the hump region according to claim 1, characterized in that the radial guide vanes (3) in the incremental guide vane assembly are uniformly arranged at intervals of 360 / N° along the circumferential direction with an increasing sectional area of the spiral volute casing (4), starting from the one of the radial guide vanes (3) with the minimum values, and the cross-sectional area of an x radial guide vane (3) in the incremental guide vane assembly increases non-linearly according to a formula as follows:A^ = ax2 + bx + cwherein, the Ax is the cross-sectional area of the x-th radial guide vane (3), x e [2,......, TV l], theN is a total guide vane number, and the a, the b, and the c are coefficients determined by an equation set as follows:0.25^ =a + b + c< An =(N^1)2 a + (N^l)b + c0.3 A- — 4a + 2b + c Vwherein, theXv is the cross-sectional area of the standard guide vane (3-1).6 The vertical centrifugal pump for enhancing the hydraulic stability in the hump region according to claim 1, characterized in that an inlet diameter, an inlet arrangement angle, a chord length, a cross-sectional area, and a maximum thickness of the standard guide vane (3-1) are all determined by an outlet diameter and an outlet arrangement angle of the centrifugal impeller (2), and an inlet diameter and the sectional area of the spiral volute casing (4).

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