Design method of mixed-flow pump guide vane and mixed-flow pump guide vane

Abstract

The invention relates to a mixed-flow pump guide vane design method and a mixed-flow pump guide vane The mixed-flow pump guide vane design method comprises the following steps: a hydraulic calculation step: performing hydraulic calculation on a mixed-flow pump guide vane axial surface projection drawing according to a mixed-flow pump guide vane design specification; a boundary condition processing step: extracting the circumferential speed, the axial speed and the circular rector distribution in the wingspan direction at the outlet of the impeller, and fitting by adopting an approximate equation as the boundary condition at the inlet of the guide vane; a hub and rim load distribution processing step: adopting a three-section curve formed by parabola-straight line-parabola to control the load distribution at the hub and the rim; processing load distribution at other positions, namely controlling the load distribution at other positions of the blade by adopting a linear interpolation method according to the load distribution at the hub and the rim; and a shaping step: determining the initial shape of the blade, then carrying out iterative calculation, and determining the final shape of the blade. The problem that the performance of the mixed-flow pump is reduced due to the fact that the guide vane is not matched with the impeller is effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pumps, in particular to a mixed-flow pump guide vane design method and mixed-flow pump guide vane. BACKGROUND

[0002] The specific speed and structural form of the mixed-flow pump are between those of the centrifugal pump and the axial-flow pump, and the mixed-flow pump has a large flow rate and a proper lift, and is widely used in urban sewage treatment, industrial water circulation systems, agricultural irrigation and drainage, and regional water transfer projects. Since the fluid motion in the mixed-flow pump has strong three-dimensionality and instantaneity, the flow state in the mixed-flow pump is very complex, thereby reducing the operation efficiency and operation stability of the mixed-flow pump. As one of the core components of the mixed-flow pump, the guide vane mainly collects fluid at the outlet of the impeller and converts part of the rotational kinetic energy of the fluid into pressure energy, and the conversion capacity of the guide vane has an important influence on the performance of the mixed-flow pump. However, the current research on the performance improvement of the mixed-flow pump mainly focuses on the design optimization of the impeller, and the design optimization of the guide vane is relatively less, and in the few researches, the problem of the influence of the flow state at the outlet of the impeller on the rotational kinetic energy recovery capacity of the guide vane has not been solved from the root, thereby causing the incomplete matching of the performance of the impeller and the guide vane, and causing the performance of the mixed-flow pump to be reduced. SUMMARY

[0003] In view of the deficiencies in the prior art, one of the purposes of the present application is to provide a mixed-flow pump guide vane design method and mixed-flow pump guide vane, which effectively solve the problem of performance reduction of the mixed-flow pump caused by the mismatching of the guide vane and the impeller.

[0004] The above purpose of the present application is realized by the following technical solutions:

[0005] A mixed-flow pump guide vane design method, comprising the following steps: a hydraulic calculation step, performing preliminary hydraulic calculation on a mixed-flow pump guide vane axial plane projection drawing according to a mixed-flow pump guide vane design specification; a boundary condition processing step, performing performance evaluation on an impeller corresponding to the guide vane, extracting the spanwise circumferential velocity, the axial velocity and the circulation distribution at the outlet of the impeller, and fitting the above physical quantities by using an approximate equation to serve as the boundary conditions at the inlet of the guide vane blades; a hub and rim load distribution processing step, controlling the load distribution at the hub and the rim by using a three-section curve composed of a parabola-straight line-parabola; a load distribution processing step at other positions, controlling the load distribution at the remaining positions of the blades by using a linear interpolation method according to the load distribution at the hub and the rim; and a shaping step, determining the initial shape of the blades, and then determining the final blade shape according to the iterative calculation of the flow field and the blade shape.

[0006] The application can be further configured in a preferred example that, in the boundary condition processing step, the extraction of the spanwise circumferential velocity, axial velocity and circulation distribution at the impeller outlet needs to go through impeller three-dimensional modeling, mesh division and numerical calculation, and in order to facilitate the input of the circumferential velocity, axial velocity and circulation at the inlet of the guide vane in the subsequent guide vane design, the approximate equations of the three are all first-order equations as follows:

[0007]

[0008] In the formula:

[0009] V z represents the axial velocity, meter / second;

[0010] V θ represents the circumferential velocity, meter / second;

[0011] Γ represents the circulation, meter 2 / second;

[0012] r represents the radius, meter;

[0013] a1 and b1 represent the undetermined coefficients of the axial velocity distribution;

[0014] a2 and b2 represent the undetermined coefficients of the circumferential velocity distribution;

[0015] a3 and b3 represent the undetermined coefficients of the circulation distribution.

[0016] The application can be further configured in a preferred example that, in the hub and rim load distribution processing step, the parabola-straight line-parabola segmented equation adopts the following equation group:

[0017]

[0018] In the formula:

[0019] Γ p1 is the first segment parabola circulation, meter 2 / second;

[0020] Γ z1 is the middle straight line circulation, meter 2 / second;

[0021] Γ p2 is the second segment parabola circulation, meter 2 / second;

[0022] m is the axial surface streamline normalized position;

[0023] c1, d1, e1 and f1 represent the undetermined coefficients of the first segment parabola;

[0024] c2 and d2 represent the undetermined coefficients of the middle straight line;

[0025] c3, d3, e3 and f3 represent undetermined coefficients of the second segment parabola.

[0026] In a preferred example, the application can be further configured to, in the other position load distribution processing step, the load at the remaining positions of the blade is obtained by interpolation of the load at the hub and rim, and the interpolation formula is as follows:

[0027]

[0028] In the formula:

[0029] Γ r represents the value of the circulation at the radius to be solved, meter 2 / second;

[0030] r represents the radius to be solved, meter;

[0031] r h represents the hub radius, meter;

[0032] r s represents the rim radius, meter;

[0033] Γ s represents the value of the circulation at the rim, meter 2 / second;

[0034] Γ h represents the value of the circulation at the hub, meter 2 / second.

[0035] The application also discloses a mixed-flow pump guide vane obtained by using the design method.

[0036] The application has the following advantages:

[0037] In the design process, the influence of the flow state at the outlet of the impeller on the rotational kinetic energy recovery capacity of the guide vane is considered, so that the problem of performance reduction of the mixed-flow pump caused by the mismatch between the inlet setting angle of the guide vane blade and the outlet flow angle of the impeller can be effectively avoided;

[0038] The approximate fitting of the axial velocity, the circumferential velocity and the circulation at the outlet of the impeller adopts a first-order equation, and has the advantages of simplicity, easy implementation and good effect.

[0039] The load distribution at the hub and the rim is controlled by a segmented curve composed of a third-order parabola, a first-order straight line and a third-order parabola, and has the advantages of few control parameters, various distribution forms and easy understanding; the load distribution at the remaining positions of the blade between the hub and the rim is obtained by linear interpolation, and the load distribution on the surface of the blade has the advantages of uniformity, continuity and no abrupt change. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1Flow chart for mixed flow pump guide vane design method considering flow pattern at impeller outlet;

[0041] Figure 2 Axial plane projection of mixed flow pump guide vane;

[0042] Figure 3 Axial velocity distribution at impeller outlet and its first order approximation fitting;

[0043] Figure 4 Circumferential velocity distribution at impeller outlet and its first order approximation fitting;

[0044] Figure 5 Circumferential velocity distribution at impeller outlet and its first order approximation fitting;

[0045] Figure 6 Load distribution at hub and shroud;

[0046] Figure 7 Comparison of external characteristics of original model and newly designed model;

[0047] Figure 8 Comparison of internal flow field of original model and newly designed model;

[0048] Reference signs, 1. Guide vane inlet; 2. Guide vane outlet; 3. Guide vane blade inlet; 4. Guide vane blade outlet; 5. Hub; 6. Shroud. DETAILED DESCRIPTION

[0049] The following will be described in detail in combination with the accompanying Figures 1-8 The present application is further described in detail.

[0050] The present application discloses a mixed flow pump guide vane design method, comprising the following steps,

[0051] Hydraulic calculation step (step 1), preliminary hydraulic calculation is performed on the axial plane projection of the mixed flow pump guide vane according to the mixed flow pump guide vane design specification; boundary condition processing step (step 2), performance evaluation is performed on the guide vane corresponding impeller, the spanwise circumferential velocity, axial velocity and circulation distribution at the impeller outlet are extracted, and the above physical quantities are fitted by using an approximate equation, which is used as the boundary condition at the guide vane blade inlet; hub and shroud load distribution processing step (step 3), a three-section curve composed of a parabola-straight line-parabola is used to control the load distribution at the hub and shroud; other position load distribution processing step (step 4), according to the load distribution at the hub and shroud, a linear interpolation method is used to control the load distribution at the remaining positions of the blade; shaping step (step 5), the initial shape of the blade is determined, and then the final blade shape is determined according to the iterative calculation of the flow field and the blade shape.

[0052] In the above scheme, the axial velocity in step 2 is the z-direction velocity, and the circumferential velocity is calculated from the x-direction and y-direction velocities by the following formula:

[0053]

[0054] In the formula:

[0055] V θ represents the circumferential velocity, m / s;

[0056] V x represents the x-axis direction velocity, m / s;

[0057] V y represents the y-axis direction velocity, m / s.

[0058] Further, the circulation is calculated by the following formula:

[0059]

[0060] In the formula:

[0061] Γ represents the circulation, m 2 / second;

[0062] r represents the radius, m.

[0063] Further, preferably, due to the strong instantaneous and three-dimensional nature of the flow state in the mixed-flow pump, the axial velocity, circumferential velocity and circulation distribution at the impeller outlet are relatively chaotic, in order to meet the input of the inlet boundary in the guide vane design, the following first-order equation is used to approximate the axial velocity, circumferential velocity and circulation distribution:

[0064]

[0065] In the formula:

[0066] V z represents the axial velocity, m / s;

[0067] a1 and b1 represent the undetermined coefficients of the axial velocity distribution;

[0068] a2 and b2 represent the undetermined coefficients of the circumferential velocity distribution;

[0069] a3 and b3 represent the undetermined coefficients of the circulation distribution.

[0070] In the above scheme, preferably, the piecewise equation of the hub and rim composed of a third-order parabola, a first-order straight line and a third-order parabola can be represented by the following equation group:

[0071]

[0072] In the formula:

[0073] Γ p1 Γ is the first parabolic circulation, meter 2 / second;

[0074] Γ z1 Γ is the intermediate straight line circulation, meter 2 / second;

[0075] Γ p2 Γ is the second parabolic circulation, meter 2 / second;

[0076] m is the normalized position of the axial surface streamline;

[0077] c1, d1, e1 and f1 represent the undetermined coefficients of the first parabolic line;

[0078] c2 and d2 represent the undetermined coefficients of the intermediate straight line;

[0079] c3, d3, e3 and f3 represent the undetermined coefficients of the second parabolic line;

[0080] NC represents the position of the intersection point of the first parabolic line and the intermediate straight line on the axial surface streamline;

[0081] ND represents the position of the intersection point of the intermediate straight line and the second parabolic line on the axial surface streamline;

[0082] In the above scheme, preferably, the load distribution at the remaining positions of the blade is obtained by interpolation according to the width of the axial surface passage and the load distribution at the hub and rim through the following formula:

[0083]

[0084] In the above formula:

[0085] Γ r Γ represents the circulation value at the radius to be solved, meter 2 / second;

[0086] r represents the radius to be solved, meter;

[0087] r h r represents the hub radius, meter;

[0088] r s r represents the rim radius, meter;

[0089] Γ s Γ represents the circulation value at the rim, meter 2 / second;

[0090] Γ h Γ represents the circulation value at the hub, meter 2 / second;

[0091] In the above scheme, the convergence accuracy of the iterative calculation process of the flow field and blade shape is determined by the difference between the blade wrap angles calculated twice, and when the difference is less than 10 -6 The calculation is considered to have converged when , otherwise it is considered to have diverged.

[0092] The present application also provides a mixed flow pump guide vane, which is obtained by adopting the above-mentioned mixed flow pump guide vane design method.

[0093] With a design head H des =12.66m, design flow rate Q des =12.66m, number of impeller blades N y =4, number of guide vanes N D =4, and a rotating speed n=1450 r / min as an example, under the premise of keeping its impeller unchanged, the guide vanes are redesigned by the method of the present invention.

[0094] Step 1: According to the design requirements of the mixed flow pump, the guide vane axial projection diagram is calculated using the fluid machinery design specifications.

[0095] Step 2: Using computational fluid dynamics knowledge, perform 3D modeling, mesh generation, and numerical calculations on the impeller corresponding to the guide vane. Extract the axial velocity, circumferential velocity, and circulation distribution from the flow field information at the impeller outlet, and fit them using a first-order equation as the initial conditions for the guide vane design inlet. The circumferential velocity and circulation are calculated using the following formula:

[0096]

[0097] Where: V θ Indicates circumferential speed, m / s; V x Indicates the speed in the x-axis direction, m / s; V y represents the speed in the y-axis direction, m / s; Γ represents the circulation, m 2 / second; r represents the radius, in meters.

[0098] It is worth noting that, see Figure 3 、 Figure 4 and Figure 5 Due to the strong three-dimensionality of the fluid motion in the mixed flow pump, the axial velocity, circumferential velocity and circulation distribution at the impeller outlet are all non-uniform, especially near the hub and rim. However, in the range of 0.1 times the wingspan to 0.9 times the wingspan, the distributions of the three can be approximately considered as first-order linear distributions.

[0099] Furthermore, the axial velocity, circumferential velocity and circulation distribution at 0.1 times the wingspan to 0.9 times the wingspan are fitted using the following first-order linear equations:

[0100]

[0101] wherein V z represents axial velocity, m / s; a1 and b1 represent axial velocity distribution undetermined coefficients; a2 and b2 represent circumferential velocity distribution undetermined coefficients; a3 and b3 represent circulation distribution undetermined coefficients. In the embodiment, a1 =-0.8042; b1 =4.3985; a2 =-1.2937; b2 =8.8247; a3 =-26.949; b3 =8.8247.

[0102] It should be noted that the axial velocity and circumferential velocity after the first-order linear equation fitting are applied at the inlet of the guide vane, and the circulation after the fitting is applied at the inlet of the guide vane blade.

[0103] Step 3, the load distribution at the hub and rim is controlled by using a classical three-section piecewise curve. It should be noted that the piecewise curve in the embodiment of the application is composed of a third-order parabola, a first-order straight line and a third-order parabola, and the specific equation is as follows:

[0104]

[0105] wherein Γ p1 is the circulation of the first section parabola, m 2 / s; Γ z1 is the circulation of the middle straight line, m 2 / s; Γ p1 is the circulation of the second section parabola, m 2 / s; m is the normalized position of the axial surface streamline; c1, d1, e1 and f1 represent the undetermined coefficients of the first section parabola; c2 and d2 represent the undetermined coefficients of the middle straight line; c3, d3, e3 and f3 represent the undetermined coefficients of the second section parabola; NC represents the position of the intersection point of the first section parabola and the middle straight line on the axial surface streamline; ND represents the position of the intersection point of the middle straight line and the second section parabola on the axial surface streamline.

[0106] Further, referring to Figure 6 , in the embodiment of the application, the hub is post-loaded and the rim is pre-loaded. Specifically, the load control parameters LEh, NCh, NDh and Kh at the hub are-0.08, 0.19, 0.75 and-0.15 respectively; and the load control parameters LEs, NCs, NDs and Ks at the rim are 0.018, 0.375, 0.875 and 0.56 respectively.

[0107] Step 4, according to the shape of the axial surface projection determined in step 1 and the load distribution at the hub and rim determined in step 3, the load distribution at the remaining positions on the axial surface projection is calculated by using the linear interpolation equation shown as follows:

[0108]

[0109] wherein: Γ r represents the value of the circulation at the radius sought, meter 2 / second; r represents the radius sought, meter; r h represents the hub radius, meter; r s represents the rim radius, meter; Γ s represents the value of the circulation at the rim, meter 2 / second; Γ h represents the value of the circulation at the hub, meter 2 / second.

[0110] Step 5, according to the axial projection map and the circulation distribution determined jointly by steps 1, 2, 3 and 4, the initial shape of the blade is determined, and the final blade shape is determined according to the iterative calculation of the blade shape and the flow field.

[0111] Based on the above embodiment, the final shape of the blade is obtained. As an optional embodiment, the inviscid computational fluid dynamics can be used to quickly evaluate the static pressure and flow velocity distribution of the blade surface through the blade surface load distribution, so as to preliminarily judge the performance of the blade. Further, the viscous computational fluid dynamics can be used to calculate the precise performance of the blade designed in the embodiment, and the blade shape is further fine-tuned according to the details of the flow field.

[0112] To illustrate the advancement of the method provided by the embodiment of the application in the design of the mixed-flow pump guide vane in detail, the performance of the guide vane designed by the method for designing the guide vane of the mixed-flow pump considering the influence of the flow state at the outlet of the impeller is compared with the performance of the guide vane designed by the traditional design method. The comparison contents include but are not limited to the blade shape, energy characteristics and internal flow field.

[0113] Figure 7 The external characteristics of the guide vane designed by the method for designing the guide vane of the mixed-flow pump considering the influence of the flow state at the outlet of the impeller are compared with the external characteristics of the guide vane designed by the traditional design method. It can be seen that, under the design condition, the efficiency of the mixed-flow pump corresponding to the traditional guide vane is 85.21%, and the head is 12.66 m; the efficiency of the mixed-flow pump corresponding to the guide vane of the embodiment of the application is 88.89%, and the head is 12.7 m. In the case of maintaining the head basically unchanged, the efficiency is increased by about 3.68 percentage points. In addition, when the flow rate is greater than 0.8Qdes, the mixed-flow pump model corresponding to the embodiment of the application has a higher efficiency, and the greater the flow rate, the more the efficiency is increased.

[0114] Figure 8 The internal flow field of the guide vane designed by the method for designing the guide vane of the mixed-flow pump considering the influence of the flow state at the outlet of the impeller is compared with the internal flow field of the guide vane designed by the traditional design method. It can be seen that there are obvious backflow and flow separation phenomena in the guide vanes of both. However, compared with the mixed-flow pump guide vane designed by the traditional design method, the backflow intensity and range in the guide vane designed by the application are significantly reduced.

[0115] The implementation principle of the embodiment is that: through accurate calculation of the flow state at the outlet of the impeller, then through appropriate equation to approximately fit, and taking the fitted peripheral velocity, axial velocity and circulation distribution as the initial conditions of the guide vane design inlet, a guide vane design method of the mixed-flow pump considering the influence of the flow state at the outlet of the impeller is proposed. The method considers the influence of the flow state at the outlet of the impeller on the performance of the guide vane at the beginning of the guide vane design, which can effectively improve the matching degree of the guide vane and the impeller, thereby maximizing the ability of the guide vane to recover the rotational kinetic energy of the fluid at the outlet of the impeller and convert it into pressure energy, and is beneficial to the designer to obtain a more ideal result.

[0116] The embodiments of the specific implementation are the preferred embodiments of the application, but do not limit the protection scope of the application, so: any equivalent changes made according to the structure, shape, principle of the application should be covered within the protection scope of the application.

Claims

1. A mixed flow pump guide vane design method, characterized by: The method includes the following steps: a hydraulic calculation step, in which a preliminary hydraulic calculation is performed on the axial projection of the guide vane of the mixed flow pump according to the design specification of the guide vane of the mixed flow pump; a boundary condition processing step, in which a performance evaluation is performed on the impeller corresponding to the guide vane, the circumferential velocity, axial velocity and annular distribution in the span direction at the impeller outlet are extracted, and the above physical quantities are fitted using approximate equations, which are used as boundary conditions at the inlet of the guide vane; a hub and rim load distribution processing step, in which a three-segment curve consisting of a parabola-straight line-parabola is used to control the load distribution at the hub and rim; a load distribution processing step at other positions, in which a linear interpolation method is used to control the load distribution at other positions of the blade according to the load distribution at the hub and rim; a shaping step, in which the initial shape of the blade is determined, and then the final blade shape is determined based on iterative calculation of the flow field and the blade shape.

2. A mixed flow pump guide vane design method according to claim 1, characterized in that: In the boundary condition processing step, the extraction of the spanwise circumferential velocity, axial velocity, and circulation distribution at the impeller outlet requires three-dimensional impeller modeling, meshing, and numerical calculation. To facilitate the input of the circumferential velocity, axial velocity, and circulation at the inlet in the subsequent guide vane design, the following first-order equations are used for the approximate equations of the three: Where: V z represents the axial velocity, m / s; V θ represents the circumferential speed, m / s; Γ represents the circulation, m 2 / Second; r represents the radius, in meters; a1 and b1 represent the unknown coefficients of axial velocity distribution; a2 and b2 represent the unknown coefficients of circumferential velocity distribution; a3 and b3 represent the unknown coefficients of circulation distribution.

3. The method for designing guide vanes of a mixed flow pump according to claim 1, characterized in that: In the hub and rim load distribution processing step, the parabola-straight-parabola segmented equation uses the following equation system: Where: Γ p1 is the length of the first parabola, m 2 / Second; Γ z1 is the middle straight line circulation, m 2 / Second; Γ p2 is the length of the second parabola, m 2 / Second; m is the normalized position of the axial streamline; c1, d1, e1 and f1 represent the unknown coefficients of the first parabola; c2 and d2 represent the undetermined coefficients of the middle straight line; c3, d3, e3 and f3 represent the unknown coefficients of the second parabola; NC represents the axial streamline position of the intersection of the first parabola and the middle straight line; ND represents the axial streamline position of the intersection of the middle straight line and the second parabola.

4. The method for designing guide vanes of a mixed flow pump according to claim 1, characterized in that: In the load distribution processing step at other locations, the loads at other locations of the blade are obtained by interpolating the loads at the hub and rim. The interpolation formula is as follows: Where: Γ r Indicates the circular value at the required radius, meters 2 / Second; r represents the required radius, in meters; r h Indicates the hub radius, meters; r s represents the rim radius, in meters; Γ s Indicates the circumference value at the wheel rim, m 2 / Second; Γ h Indicates the ring value at the hub, meter 2 / Second.

5. A mixed flow pump guide vane, characterized in that: The method is obtained by a mixed flow pump guide vane design method as claimed in any one of claims 1 to 4.

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