Sealing-flow field coupling simulation method of centrifugal pump

Abstract

The invention discloses a sealing-flow field coupling simulation method of a centrifugal pump, and belongs to the field of fluid mechanics, sealing technologies and simulation calculation. The problems of long calculation time and low efficiency in the existing calculation of full flow field simulation of the centrifugal pump considering sealing are solved. According to the method, a non-full flow field calculation model and a sealing leakage model are constructed; a non-full flow field computational grid model is obtained, and the joint position of the water inlet section, the volute and the sealing gap of the centrifugal pump is set as an inlet and outlet coupling interface of the non-full flow field computational grid model; obtaining sealing pressure from the inlet and outlet coupling interface, and taking the sealing pressure as an input boundary condition of a sealing leakage model; obtaining a sealing simulation model of the to-be-detected position; solving to obtain the leakage rate of the simulation model; judging whether the leakage rate data converges or not, taking the leakage rate as a boundary condition of an inlet and outlet coupling interface of the non-full flow field calculation model, and obtaining the pressure of the inlet and outlet coupling interface; and the leakage rate is obtained again until the obtained leakage rate data converges, and a simulation result is obtained.

Description

Technical Field

[0001] The invention belongs to the fields of fluid mechanics, sealing technology and simulation calculation. Background Art

[0002] Centrifugal pumps are widely used in various industrial equipment. The main function of the centrifugal pump mouth ring seal is to prevent fluid leakage. However, because the sealing gap is usually small and requires a large number of grids, the overall simulation of the pump is very computationally intensive. Therefore, in order to improve computational efficiency, most existing projects ignore the impact of seal leakage when simulating centrifugal pumps. Although this simplification can reduce computational complexity, it often introduces certain errors, especially in situations requiring high-precision calculations. When using full-flow field simulation to calculate sealing problems, the large number of grids and the long computational time make it inefficient in practical engineering applications. Summary of the Invention

[0003] The present invention aims to solve the problems of long calculation time and low efficiency in the existing full flow field simulation of a centrifugal pump taking seal into consideration, and provides a seal-flow field coupling simulation method for a centrifugal pump.

[0004] The seal-flow field coupling simulation method of a centrifugal pump described in the present invention includes:

[0005] Step 1: According to the geometric characteristics and fluid dynamics characteristics of the centrifugal pump seal gap, a non-full flow field calculation model and a seal leakage model are constructed based on the overall flow theory; the non-full flow field calculation model is meshed; and the non-full flow field calculation grid model is obtained;

[0006] Step 2: Set the water inlet section, the intersection of the volute and the sealing gap of the centrifugal pump as the inlet coupling interface and the outlet coupling interface of the non-full flow field calculation grid model; use fluid simulation software to simulate the flow field of the set non-full flow field calculation grid model to obtain the sealing pressure of the inlet coupling interface and the outlet coupling interface;

[0007] Step 3: Input the geometric structure, fluid properties, and rotation speed parameters of the position to be detected as inputs to the sealing leakage model, and use the sealing pressure as the input boundary condition of the sealing leakage model; and obtain a sealing simulation model of the position to be detected;

[0008] Using Python to solve the sealing simulation model of the position to be detected, and obtain the leakage amount of the simulation model;

[0009] Step 4: Using the leakage as the boundary condition of the inlet coupling interface and the outlet coupling interface of the non-full flow field calculation model, and combining the general setting parameters of the boundary conditions at the inlet and outlet positions of the centrifugal pump, the non-full flow field calculation model is solved using fluid simulation software to obtain the pressure at the inlet coupling interface and the outlet coupling interface;

[0010] Step 5. Use the pressure obtained in step 4 as the boundary condition of the sealing simulation model again, and use Python to calculate the leakage of the sealing gap of the sealing simulation model; determine whether the leakage data converges. If so, use the current leakage data as the final simulation result; otherwise, use the current leakage as the boundary condition of the inlet coupling interface and the outlet coupling interface of the non-full flow field calculation model, return to step 4, and obtain the final simulation result until the leakage data converges.

[0011] Furthermore, in the present invention, in step one, the non-full flow field calculation model includes models of the volute, the impeller, the water inlet section, and the water outlet section.

[0012] Furthermore, in the present invention, in step 1, the method for constructing the sealing leakage model is:

[0013] According to the geometric characteristics and fluid mechanics properties of the centrifugal pump sealing gap, a mathematical model of leakage is constructed based on the overall flow theory. The flow behavior, pressure difference and temperature of the fluid at the position to be detected are added to the mathematical model of leakage to establish a sealing leakage model.

[0014] Furthermore, in the present invention, in step 1, the sealing leakage model is:

[0015]

[0016] Where R is the sealing gap diameter, h is the thickness of the liquid film in the sealing gap, U and W are the circumferential and axial velocities of the fluid element respectively, C is the sealing gap, where the upper wall of the element contacts the stator and the circumferential velocity is 0, and the lower wall contacts the rotor and the circumferential velocity is RΩ, Ω is the rotor speed, ρ is the medium density, P is the fluid element pressure, τ θ ,τ z are the circumferential and axial fluid shear stresses, respectively; dz and Rdθ are the dimensions of the element in the axial and circumferential directions, respectively; the subscript i represents the i-th fluid element;

[0017]

[0018] f θ , f r 、f z are the friction coefficients in the circumferential, radial and axial directions respectively; the fluid leakage in the sealing gap Q:

[0019]

[0020] in, is the integrated average axial velocity of the fluid at the sealing port.

[0021] Furthermore, in the present invention, the conditions for leakage data convergence are:

[0022]

[0023] Where: Q j is the leakage amount calculated in the current step, Q j-1 is the leakage amount calculated in the previous step, and ε is the difference percentage between the leakage amounts obtained in two adjacent calculations.

[0024] The present invention, by introducing a leakage model based on overall flow theory, can more accurately reflect the effect of the sealing gap on the flow of the centrifugal pump, thereby improving the accuracy of the simulation results. Compared with the traditional centrifugal pump full flow field simulation calculation method, the present invention avoids detailed calculations of the entire flow field by directly calculating the leakage and inputting it as a boundary condition, greatly reducing the amount of calculation and thus improving the simulation efficiency. The existing technology usually ignores the effect of seal leakage in centrifugal pump simulation, which will lead to certain errors. The leakage model of the present invention can more accurately reflect the effect of seal leakage on the centrifugal pump, thereby reducing errors and improving the reliability of the simulation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of the method of the present invention;

[0026] Figure 2 This is a schematic diagram of the disassembly of the non-full flow field calculation model. In the figure, 1 represents the water inlet section, 2 represents the impeller, 3 represents the volute, and 4 represents the water outlet section.

[0027] Figure 3 The mesh diagram of the volute and the outlet end model and the mesh enlarged diagram of the tongue part; the enlarged part a in the figure is the tongue part;

[0028] Figure 4 This is the mesh diagram of the tongue section;

[0029] Figure 5(a) is a diagram of the axial flow velocity in the sealing gap;

[0030] Figure 5(b) is a diagram of the circumferential flow velocity in the sealing gap;

[0031] FIG6( a ) is a pressure distribution diagram of a centrifugal pump obtained by the simulation method of the present invention;

[0032] Figure 6(b) is the centrifugal pump pressure distribution diagram obtained by simulation of the full flow field calculation model;

[0033] FIG7( a ) is a flow velocity distribution of a centrifugal pump obtained by the simulation method of the present invention;

[0034] Figure 7(b) shows the flow velocity distribution of the centrifugal pump in the full flow field calculation model. DETAILED DESCRIPTION

[0035] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other in the absence of conflict.

[0036] Specific implementation method 1: refer to Figure 1 Specifically describing this embodiment, a sealed integral flow theory and a CFD centrifugal pump coupled simulation method described in this embodiment include:

[0037] Step 1: According to the geometric characteristics and fluid dynamics characteristics of the centrifugal pump seal gap, a non-full flow field calculation model and a seal leakage model are constructed based on the overall flow theory; the non-full flow field calculation model is meshed; and the non-full flow field calculation grid model is obtained;

[0038] Step 2: Set the water inlet section, the intersection of the volute and the sealing gap of the centrifugal pump as the inlet coupling interface and the outlet coupling interface of the non-full flow field calculation grid model; use fluid simulation software to simulate the flow field of the set non-full flow field calculation grid model to obtain the sealing pressure of the inlet coupling interface and the outlet coupling interface;

[0039] Step 3: Input the geometric structure, fluid properties, and rotation speed parameters of the position to be detected as inputs to the sealing leakage model, and use the sealing pressure as the input boundary condition of the sealing leakage model; and obtain a sealing simulation model of the position to be detected;

[0040] Using Python to solve the sealing simulation model of the position to be detected, and obtain the leakage amount of the simulation model;

[0041] Step 4: Using the leakage as the boundary condition of the inlet coupling interface and the outlet coupling interface of the non-full flow field calculation model, and combining the general setting parameters of the boundary conditions at the inlet and outlet positions of the centrifugal pump, the non-full flow field calculation model is solved using fluid simulation software to obtain the pressure at the inlet coupling interface and the outlet coupling interface;

[0042] Step 5. Use the pressure obtained in step 4 as the boundary condition of the sealing simulation model again, and use Python to calculate the leakage of the sealing gap of the sealing simulation model; determine whether the leakage data converges. If so, use the current leakage data as the final simulation result; otherwise, use the current leakage as the boundary condition of the inlet coupling interface and the outlet coupling interface of the non-full flow field calculation model, return to step 4, and obtain the final simulation result until the leakage data converges.

[0043] Furthermore, in the present invention, in step one, the non-full flow field calculation model includes models of the volute, the impeller, the water inlet section, and the water outlet section.

[0044] Furthermore, in the present invention, in step 1, the method for constructing the sealing leakage model is:

[0045] According to the geometric characteristics and fluid mechanics properties of the centrifugal pump sealing gap, a mathematical model of leakage is constructed based on the overall flow theory. The flow behavior, pressure difference and temperature of the fluid at the position to be detected are added to the mathematical model of leakage to establish a sealing leakage model.

[0046] Furthermore, in the present invention, in step 1, the sealing leakage model is:

[0047]

[0048]

[0049] Where R is the sealing gap diameter (mm), h is the thickness of the liquid film in the sealing gap (mm), U and W are the circumferential and axial velocities of the fluid element (m / s), respectively, and C is the sealing gap (mm). The upper wall of the element contacts the stator with a circumferential velocity of 0, and the lower wall contacts the rotor with a circumferential velocity of RΩ (r / min), Ω is the rotor speed, and ρ is the medium density (kg / m 3 , P is the fluid microelement pressure, unit is Pa, τ θ ,τ z are the circumferential and axial fluid shear stresses, respectively; dz and Rdθ are the axial and circumferential dimensions of the microelement, respectively, in mm; the subscript i represents the i-th fluid microelement;

[0050]

[0051] f θ , f r 、f z are the friction coefficients in the circumferential, radial and axial directions respectively; the fluid leakage in the sealing gap Q:

[0052] in, is the integrated average axial velocity of the fluid at the sealing port.

[0053] Furthermore, in the present invention, the conditions for leakage data convergence are:

[0054]

[0055] Where: Q j is the leakage amount calculated in the current step, Q j-1 is the leakage amount calculated in the previous step, and ε is the difference percentage between the leakage amounts obtained in two adjacent calculations.

[0056] Furthermore, in the present invention, the fluid simulation software in step 4 adopts fluent software.

[0057] The method of the present invention constructs a leakage model based on the overall flow theory and applies the model to the sealing simulation calculation, thereby reducing the complexity of the full flow field calculation while ensuring the simulation accuracy.

[0058] To achieve the above objectives, the present invention provides a seal-flow field coupling model that improves the accuracy and efficiency of CFD simulations of centrifugal pumps. The model uses the difference between the impeller outlet pressure and the ring inlet pressure as the seal pressure differential condition. Ring leakage boundary conditions are set in the mesh model at ring locations such as the water inlet and impeller outlet. The leakage rate is then input into the centrifugal pump simulation model as the computational boundary condition for the fluid domain, replacing the traditional gap mesh model. Specifically, the model includes the following steps:

[0059] The establishment of a non-full flow field calculation model for a centrifugal pump is completely consistent with the conventional CFD simulation method for centrifugal pumps. It is divided into the establishment of a three-dimensional model of the calculation domain, the division of the calculation domain mesh, and then the calculation domain mesh is imported into the flow field simulation software (such as Fluent, CFX, etc.) for boundary condition setting and calculation. The specific process is as follows:

[0060] 1. Establishment of 3D model of centrifugal pump calculation domain

[0061] The flow-through components inside a centrifugal pump mainly include the impeller, volute, front and rear pump chambers, and front and rear sealing ring gaps. Since the geometric dimensions of the sealing gap are too small, modeling and numerical discretization are relatively cumbersome and difficult. Usually, the sealing ring gap, front and rear pump chambers, and balance holes are ignored in the modeling process of the computational domain. In order to ensure the stability and convergence of the numerical calculation, inlet and outlet sections are usually added at the impeller inlet and volute outlet respectively. Figure 2 The simplified components of the non-full flow field calculation domain are currently the more commonly used calculation domain composition form. The non-full flow field calculation domain usually includes the water inlet section, impeller, volute and water outlet section.

[0062] 2. Computational domain mesh division

[0063] The volute, impeller, water inlet section, water outlet section and other components created in step 1 are meshed and assembled. The mesh and details are shown in the figure below. Figure 3 and Figure 4 shown.

[0064] 3. Import mesh and model settings

[0065] Import the mesh generated in step 2 into the flow field analysis software and set the calculation conditions, interfaces, etc. according to the general centrifugal pump simulation method. The inlet and outlet of the water inlet section are set as boundary conditions. The difference is that the general method sets the intersection of the seal with the water inlet and outlet sections of the model established above as the wall surface, while the present invention sets this location as the inlet coupling interface and the outlet coupling interface.

[0066] 4. Sealing model establishment

[0067] Seal leakage model based on integral flow theory: First, based on the geometric characteristics of the sealing gap and the fluid dynamics characteristics, a mathematical model of leakage is constructed based on the integral flow theory. This model takes into account factors such as the sealing gap, fluid flow behavior, pressure difference, and temperature. The seal leakage model can be established by constructing the differential format of the following equation.

[0068]

[0069] Where R is the sealing gap diameter, h is the thickness of the liquid film in the sealing gap, U and W are the circumferential and axial velocities of the fluid element respectively, C is the sealing gap, where the upper wall of the element contacts the stator and the circumferential velocity is 0, and the lower wall contacts the rotor and the circumferential velocity is RΩ, Ω is the rotor speed, ρ is the medium density, P is the fluid element pressure, τ θ ,τ z are the circumferential and axial fluid shear stresses, respectively; dz and Rdθ are the dimensions of the element in the axial and circumferential directions, respectively; the subscript i represents the i-th fluid element;

[0070]

[0071] f θ , f r 、f z are the friction coefficients in the circumferential, radial and axial directions respectively; the fluid leakage in the sealing gap Q:

[0072]

[0073] in, is the integrated average axial velocity of the fluid at the sealing port.

[0074] Fluid leakage in the sealing gap Q:

[0075]

[0076] in, is the integrated average axial velocity of the fluid at the sealing port.

[0077] 5. Based on the seal leakage model established in step 4, the geometric structure of the seal gap, fluid properties, rotation speed, etc. are used as model calculation parameters, and the seal pressure and velocity are read from the interface position in step 3 as the input boundary conditions of the model. Then, based on Python, the seal leakage model established in step 4 is solved to obtain the leakage of the seal gap, axial and circumferential flow velocities, such as Figure 5(a) and 5(b) shown.

[0078] 6. Based on the coupling interface established in step 3 as the coupling interface between the centrifugal pump non-full flow field calculation model and the sealing model (which is the key to the correct operation of the model), when performing the simulation calculation of the centrifugal pump non-full flow field calculation model, the flow velocity calculated from the sealing model is used as the boundary condition of the centrifugal pump non-full flow field calculation model for calculation; when performing the sealing model calculation, the calculation result (pressure) of the centrifugal pump non-full flow field calculation model at the coupling interface is extracted as the boundary condition of the sealing model for calculation. The specific process is as follows:

[0079] Simulation solution: This is achieved through the function compilation of the flow field simulation software and the joint solution of Python. The specific process is as follows:

[0080] 1. First, the general boundary conditions of the centrifugal pump non-full flow field calculation model, the velocity of the inlet and outlet coupling boundaries are set to 0, and the initial leakage of the sealing model is 0;

[0081] 2. Secondly, the centrifugal pump flow field is calculated based on the general flow field method. After the flow field calculation is completed, the pressure of the inlet and outlet coupling boundaries is extracted; then the extracted pressure data of the inlet and outlet coupling boundaries are sent to Python to calculate the flow rate and leakage of the sealing model, and the calculated leakage is compared with the leakage calculated in the previous step. If the result converges, the calculation is stopped and the centrifugal pump performance is output; otherwise, the calculated flow rate is used as the new inlet and outlet coupling boundary conditions, and the iteration is repeated until the convergence condition is reached. The convergence condition is shown in the following formula:

[0082]

[0083] Where: Q i is the leakage amount calculated in the current step, Q i-1 is the leakage amount calculated in the previous step.

[0084] Applications: This method is suitable for simulating the performance of centrifugal pumps with various seal structures. It can effectively reduce computational complexity and improve efficiency while ensuring accuracy, especially when the computational workload is large. It is also suitable for simulating mechanical equipment such as pumps and turbines with seals.

[0085] Example: In one example, the sealing structure of a centrifugal pump is considered. In traditional full-flow field simulation, since the sealing gap is very small and the number of grids is huge, the simulation calculation is huge. According to the method of the present invention, the leakage of the seal is first calculated through the leakage model, and then the leakage is input into the fluid simulation model as a boundary condition, replacing the full-flow field simulation, as shown in Table 1. After comparison with the experimental data, it was found that the accuracy of the simulation results was improved by about 5%, and the calculation time was reduced by more than 50%. The pressure distribution calculated based on this method and the full-flow field simulation method is as follows: Figure 6(a) and 6(b) As shown, the flow velocity distribution is Figure 7(a) and 7(b) shown.

[0086] Table 1. Number of meshes in computational domain and mesh quality

[0087]

[0088] This paper provides a method for improving the accuracy and efficiency of seal simulations based on a leakage model. By simplifying the calculation process, it reduces the complexity of solving the flow field and significantly improves computational efficiency while maintaining simulation accuracy. This method is widely applicable to fluid dynamics simulations of various sealing systems and effectively addresses the low accuracy and poor computational efficiency of existing seal simulations, demonstrating significant engineering application value.

[0089] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the invention. It should be understood that many modifications may be made to the illustrative embodiments, and that other arrangements may be devised, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in ways other than those described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in conjunction with other described embodiments.

Claims

1. A centrifugal pump seal-flow field coupling simulation method, characterized in that: include: Step 1: Based on the geometric characteristics and fluid dynamics of the centrifugal pump seal gap, a non-full flow field calculation model and a seal leakage model are constructed based on the overall flow theory; Performing grid division on the non-full flow field calculation model; obtaining the non-full flow field calculation grid model; Step 2: Using flow field analysis software, set the water inlet section, volute and sealing gap intersection of the centrifugal pump as the inlet coupling interface and outlet coupling interface of the non-full flow field calculation grid model; Step 3: Input the geometric structure, fluid properties, and rotational speed parameters of the sealing gap at the position to be tested as inputs to the sealing leakage model, obtain the sealing pressure from the inlet coupling interface and the outlet coupling interface, and use the sealing pressure as the input boundary condition of the sealing leakage model; and obtain a sealing simulation model of the position to be tested; Using Python to solve the sealing simulation model of the position to be detected, and obtain the leakage amount of the simulation model; Step 4: Using the leakage as the boundary condition of the inlet coupling interface and the outlet coupling interface of the non-full flow field calculation model, and combining the general setting parameters of the boundary conditions at the inlet and outlet positions of the centrifugal pump, the non-full flow field calculation model is solved using fluid simulation software to obtain the pressure at the inlet coupling interface and the outlet coupling interface; Step 5. Use the pressure obtained in step 4 as the boundary condition of the sealing simulation model again, and use Python to calculate the leakage of the sealing gap of the sealing simulation model; determine whether the leakage data converges. If so, use the current leakage data as the final simulation result; otherwise, use the current leakage as the boundary condition of the inlet coupling interface and the outlet coupling interface of the non-full flow field calculation model, return to step 4, and obtain the final simulation result until the leakage data converges.

2. The method for coupling simulation of a centrifugal pump using sealed integral flow theory and CFD according to claim 1 is characterized in that: In step 1, the non-full flow field calculation model includes the models of the volute, impeller, water inlet section and water outlet section.

3. The method for coupling simulation of a centrifugal pump using sealed integral flow theory and CFD according to claim 1 is characterized in that: In step 1, the method for constructing the sealing leakage model is: According to the geometric characteristics and fluid mechanics properties of the centrifugal pump sealing gap, a mathematical model of leakage is constructed based on the overall flow theory. The flow behavior, pressure difference and temperature of the fluid at the position to be detected are added to the mathematical model of leakage to establish a sealing leakage model.

4. The method for coupling simulation of a centrifugal pump using sealed integral flow theory and CFD according to claim 2, characterized in that: In step 1, the seal leakage model is: Where R is the sealing gap diameter, h is the thickness of the liquid film in the sealing gap, U and W are the circumferential and axial velocities of the fluid element respectively, C is the sealing gap, where the upper wall of the element contacts the stator and the circumferential velocity is 0, and the lower wall contacts the rotor and the circumferential velocity is RΩ, Ω is the rotor speed, ρ is the medium density, P is the fluid element pressure, τ θ ,τ z are the circumferential and axial fluid shear stresses, respectively; dz and Rdθ are the dimensions of the element in the axial and circumferential directions, respectively; the subscript i represents the i-th fluid element; f θ , f r 、f z are the friction coefficients in the circumferential, radial and axial directions respectively; the fluid leakage in the sealing gap Q: in, is the integrated average axial velocity of the fluid at the sealing port.

5. The method for coupling simulation of a centrifugal pump using sealed integral flow theory and CFD according to claim 4 is characterized in that: The conditions for leakage data convergence are: Where: Q j is the leakage amount calculated in the current step, Q j-1 is the leakage amount calculated in the previous step, and ε is the difference percentage between the leakage amounts obtained in two adjacent calculations.

6. The method for coupling simulation of a centrifugal pump using sealed integral flow theory and CFD according to claim 4 is characterized in that: In step 4, the fluid simulation software used is Fluent software.

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