Hydraulic pump cavitation flow field simulation analysis method based on CFD

Abstract

A hydraulic pump cavitation flow field simulation analysis method based on CFD comprises the steps of pump body structure modeling, fluid domain modeling, meshing of a fluid domain model and establishment of an applicable cavitation model, and the cavitation process of a single-plunger electro-hydraulic pump comprises gas cavitation and steam cavitation; performing simulation setting on a cavitation model used by the fluid domain model to obtain numerical simulation data; and performing image post-processing on the simulation data to obtain a cloud picture and a curve graph of the cavitation flow field, and judging whether cavitation occurs or not and the cavitation position. According to the method, the cavitation flow field of the single-plunger electro-hydraulic pump can be accurately analyzed, and a theoretical basis can be provided for structural optimization of the single-plunger electro-hydraulic pump.

Description

Technical Field

[0001] The invention belongs to the field of fluid transmission, and in particular relates to a simulation analysis method for predicting the cavitation flow field of a single-plunger electro-hydraulic pump. Background Art

[0002] The single plunger electro-hydraulic pump is a single plunger pump radially integrated with a motor. The motor rotor drives the plunger shaft to rotate through the coupling, and the spatial cam mechanism converts the rotary motion of the plunger shaft into a regular rotation plus translation compound motion, and the compound motion is used to complete the change of the chamber volume and the distribution area, thereby realizing the oil suction and discharge of the electro-hydraulic pump.

[0003] The most direct research method to analyze the cavitation characteristics and structural optimization of single-plunger electro-hydraulic pumps is experimental research. However, the experimental research method has very high requirements on experimental equipment and requires a high-speed camera to observe its internal flow state. However, the working medium of the single-plunger electro-hydraulic pump is mainly hydraulic oil, which is not as easy to observe as the medium water. Therefore, it is of great significance to use simulation analysis methods to study the cavitation flow field.

[0004] The essence of the cavitation process is the phase change process of the fluid medium. The phase change process involved in the traditional cavitation numerical simulation is mainly steam cavitation. However, the actual situation is that at normal temperature and pressure, if the hydraulic oil is not specially treated, a certain amount of air will inevitably dissolve in the hydraulic oil. Under normal circumstances, the volume fraction of gas dissolved in the hydraulic oil is 5%-10%. Therefore, the cavitation phenomenon in the single-plunger electro-hydraulic pump is divided into two types: the first is gas cavitation, and the second is steam cavitation. When the single-plunger electro-hydraulic pump is working, the working medium exists in four states, namely hydraulic oil, hydraulic oil vapor, air dissolved in the hydraulic oil, and precipitated air. Therefore, it is of great significance to establish a cavitation model suitable for the single-plunger electro-hydraulic pump, further study the cavitation flow field of the single-plunger electro-hydraulic pump through numerical simulation results, and optimize the pump body structure to avoid and suppress the occurrence of cavitation. Summary of the invention

[0005] In order to overcome the shortcomings of the existing technology, the present invention provides a CFD-based hydraulic pump cavitation flow field simulation analysis method, which can accurately analyze the cavitation flow field of a single-plunger electro-hydraulic pump and provide a theoretical basis for the structural optimization of the single-plunger electro-hydraulic pump.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A CFD-based hydraulic pump cavitation flow field simulation analysis method includes the following steps:

[0008] Step 1, using 3D modeling software (such as SolidWorks) to model and assemble the pump body parts of the single-plunger electro-hydraulic pump;

[0009] Step 2, import the model file of the part into the DesignModeler module in AnsysWorkbenc software, use the Fill By Caps method for the pump body model, and extract the fluid domain model;

[0010] Step 3, setting up fluid domain simulation in Ansys Workbench software;

[0011] Step 4, performing cavitation simulation calculation;

[0012] Step 5: Analyze the cavitation simulation calculation results using post-processing software to obtain the cavitation distribution cloud map and bubble change map of the flow field structure of the single-plunger electro-hydraulic pump.

[0013] Furthermore, in step 1, the assembly model is saved as a general type file in the three-dimensional modeling software.

[0014] Furthermore, the process of step 3 is as follows:

[0015] Step 3.1, import the fluid domain model into the Fluent module, and use the Mesh module provided by the Fluent module to mesh the fluid domain model;

[0016] Step 3.2, define boundary conditions: set them to four forms: pressure inlet, pressure outlet, interface and wall;

[0017] Step 3.3, define the time step, total time, and solver type for the fluid domain.

[0018] Furthermore, in step 4, in order to calculate the cavitation flow field of the single-plunger electro-hydraulic pump fluid domain, a flow field multiphase flow model and a cavitation model are established, and the establishment process is as follows:

[0019] The essence of the cavitation process is the phase change process of the fluid medium. Here, the Mixture multiphase flow model in the Euler-Euler method is used, and its continuity equation is described as follows:

[0020]

[0021] ρ m =ρ v α+ρ l (1-α);

[0022]

[0023] Where: m is the density of the gas-liquid mixture; ρ v is the density of the gas phase; ρ lis the density of the liquid phase; v m is the average velocity of the mixed phase; v v is the velocity of the gas phase; v l is the velocity of the liquid phase; α is the volume fraction of the gas phase;

[0024] The cavitation model is the Schnerr-Sauner model, and the evaporation source term R in the model e and the condensation source term R c as follows:

[0025]

[0026] In step 5, the post-processing software is Tecplot software.

[0027] The beneficial effects of the present invention are mainly manifested in:

[0028] 1. For components such as electro-hydraulic pumps whose internal flow conditions are difficult to directly observe, expensive and high-precision experimental instruments are required to analyze their working characteristics through experimental research. The cavitation flow field simulation analysis method of the present invention can approximately reflect its internal working conditions through simulation, which is simpler and has lower costs. For new components, their cavitation characteristics can be analyzed through the cavitation flow field simulation analysis method of the present invention. According to the simulation results, the structural optimization design of the parts or deficiencies of the components where cavitation occurs can be carried out to reduce costs and improve efficiency.

[0029] 2. Before calculating the multiphase flow, the present invention takes into account that the air dissolved in the hydraulic oil will precipitate during the operation of the electro-hydraulic pump, thereby generating cavitation. Therefore, two mass transfer equations are created in the phase change process setting in the Fluent software, which are used for steam cavitation and gas cavitation respectively. The results obtained by the numerical calculation method provided by the present invention are more reliable and more in line with actual working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flow chart of the CFD-based hydraulic pump cavitation flow field simulation analysis method of the present invention;

[0031] Figure 2 It is a schematic diagram of the pump body structure model of the single plunger electro-hydraulic pump of the present invention;

[0032] Figure 3 It is a schematic diagram of the fluid domain model of the present invention;

[0033] Figure 4 , Figure 5 and Figure 6 A schematic diagram of setting the fluid domain boundary conditions of the present invention;

[0034] Figure 7A diagram showing changes in chamber pressure according to the present invention;

[0035] Figure 8 is a volume fraction diagram of oil vapor in the chamber according to the present invention;

[0036] Fig. 9 This is a volume fraction diagram of the air released in the chamber according to the present invention.

[0037] In the figure, 1 is the cylinder body; 2 is the plunger; 3 is the oil inlet; 4 is the oil outlet; 5 is the oil inlet flow channel; 6 is the oil outlet flow channel; 7 is the oil suction chamber; 8 is the oil discharge chamber; and 9 is the distribution groove. DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the accompanying drawings.

[0039] Reference Figure 1 A CFD-based hydraulic pump cavitation flow field simulation analysis method includes the following steps:

[0040] Step 1: Pump structure modeling

[0041] In Solidworks software, the pump body parts are modeled according to the basic dimensions, and assembled according to their working principles. The assembled model is saved as a more common model file type such as .igs. Figure 2 shown.

[0042] Step 2: Fluid Domain Modeling

[0043] Import the model into the Design Modeler module in Ansys Workbench software, click Concept and select Surface From Edges, create surfaces on the left and right surfaces of the cylinder, then click Tools and select Fill, and use the Fill by Caps method to extract the fluid domain of the pump model. The model is shown in the figure below. Figure 3 shown.

[0044] Step 3, Fluid Domain Simulation Settings

[0045] Import the fluid domain model into the Fluent module, and use the Mesh module that comes with the Fluent module to mesh the pump body model. The mesh type is tetrahedral mesh, and the size is 1mm. Boundary condition definition: set to four forms: pressure inlet, pressure outlet, interface, and wall. The boundary conditions are as follows: Figure 4 and Figure 5 As shown, the other unmarked surfaces are walls. Figure 4 The figure shows the oil inlet and outlet flow channels in the fluid domain, 3 is the oil inlet, 4 is the oil outlet, and interface 1 is the flow distribution window; Figure 5 The figure shows the oil suction and discharge chamber and the distribution groove in the fluid domain, and interface 2 is the outer surface of the distribution groove; when the distribution window (interface 1) is connected to the outer surface of the distribution groove (interface 2), oil interaction occurs. In the Fluent software, use the scale option in the General tab to unify the unit to millimeters, select the pressure-based solver, apply gravity acceleration, and finally check transient for Time; set the working medium parameters of the fluid domain in the Material tab in Fluent; the working medium includes hydraulic oil (oil), air dissolved in hydraulic oil (oil-air), oil vapor (oil-vapor), and precipitated air (air); the fluid domain medium parameters are shown in Table 1;

[0046]

[0047] Table 1

[0048] Step 4: Cavitation simulation calculation settings

[0049] In the Models tab of Fluent, set the turbulence model, cavitation model and phase change process; select SST-Kω as the turbulence model, select Schnerr-Sauer model as the cavitation model, and select Mixture multiphase flow model as the multiphase flow model. The phase change process here is divided into steam cavitation and gas cavitation, so two mass transfer equations are created, and the mass transfer mechanism is selected as cavitation; the steam cavitation is set to From oil to oil-vapor, the saturated vapor pressure is set to 1325Pa, and the bubble density is set to 1*10 5, gas cavitation is set to From oil-air to air, air separation pressure is 3540Pa; in Fluent, the boundary conditions of the fluid domain are set in the Boundary Condition tab, including the pressure settings of the oil inlet and outlet and the volume fraction of air dissolved in the hydraulic oil at the oil inlet; the oil inlet pressure is the atmospheric pressure 101000Pa, the oil outlet pressure is 12000000Pa, and the oil-air gas volume fraction at the oil inlet is set to 0.06526; the fluid domain grid is in motion, and UDF is used to simulate the dynamic grid motion. The dynamic grid uses the Smoothing and Remeshing update methods, and the pressure-velocity coupling algorithm uses COUPLED. The rest are default settings. Double-click Initialization to initialize and select standard initialization; after initialization, create a cloud map in Graphic, select Phase as the cloud map type, select oil-vapor and oil respectively, and then save; output the gas volume fractions of oil-vapor and air in the chamber in Solution Report Definitions; in Calculation Activities In the solutionAnimations tab, set the animation for the previously created cloud map, save the time step interval to 1, set the save file in the Autosave tab, save the data file every 2 steps, and save the related Case file each time. Finally, set the number of steps to 400, the number of iterations to 100, and the step length to 0.000025s in the RunCalculation tab, click Calculation to calculate, and get the simulation data of the Case file and the Data file after the calculation is completed.

[0050] The turbulence model uses SST-kω, where k, ω and μ t The expression can be expressed as:

[0051]

[0052] Where: P k is the turbulence production rate; α, β, β' are empirical coefficients, which are 5 / 9, 0.075, and 0.09 respectively; σ k ,σ ω Take 1.0 and 2.0.

[0053] Mixture multiphase flow model continuity equation:

[0054]

[0055] ρ m =ρ v α+ρl (1-α)

[0056]

[0057] Where: m is the density of the gas-liquid mixture; ρ v is the density of the gas phase; ρ l is the density of the liquid phase; v m is the average velocity of the mixed phase; v v is the velocity of the gas phase; v l is the velocity of the liquid phase; α is the volume fraction of the gas phase;

[0058] Schnerr-Sauner cavitation model, the evaporation source term R in the model e and the condensation source term R c as follows:

[0059]

[0060]

[0061] Step 5: Post-processing analysis

[0062] Import the calculated Case file and Data file into Tecplot software, select the Coutour option, click the Details button, select Phase4 or Phase5 in the drop-down menu on the upper left, double-click the ruler on the right to set the ruler's Aligment, Legend Box, ruler length and font in turn, and export the set gas phase cloud map to TIFF file format to obtain the cavitation flow field cloud map of the single-plunger electro-hydraulic pump; in order to better observe the evolution of bubbles in the electro-hydraulic pump, select Iso-surface to create 11 gas volume fraction isosurfaces; click slice to create two slices in the upper and lower chambers, click Perform Integration in the Analyze option to calculate the chamber pressure and then export the data, and then import the data into origin for processing, such as Figure 7 As shown in the figure, the gas volume fraction in the chamber can also be calculated by the same method, as shown in the figure. Figure 8 and Fig. 9 shown.

[0063] The scheme of this embodiment is applied to a method for predicting the cavitation flow field of a single-plunger electro-hydraulic pump, which is used to predict where cavitation mainly occurs, analyze the cavitation flow field in the pump, and optimize the structural parameters of the single-plunger electro-hydraulic pump according to the cavitation phenomenon. Simulation calculations are performed on electro-hydraulic pumps with different structural parameters, and the optimal structural parameter scheme is obtained according to the simulation results.

[0064] The cavitation simulation analysis method of this embodiment is used to perform multiple simulation analyses. Different structural parameters are set for the single-plunger electro-hydraulic pump model in each simulation analysis. The optimal parameter solution is obtained according to the simulation results, thereby optimizing the structure of the single-plunger electro-hydraulic pump.

[0065] The contents described in the embodiments of this specification are merely enumerations of implementation forms of the inventive concept and are for illustrative purposes only. The protection scope of the present invention should not be considered to be limited to the specific forms described in this embodiment, and the protection scope of the present invention also extends to equivalent technical means that can be thought of by ordinary technicians in this field based on the inventive concept.

Claims

1. A CFD-based hydraulic pump cavitation flow field simulation analysis method, characterized in that: The method comprises the following steps: Step 1, using 3D modeling software to model and assemble the pump body parts of the single plunger electro-hydraulic pump; Step 2, import the model file of the part into the DesignModeler module in AnsysWorkbenc software, use the Fill By Caps method for the pump body model, and extract the fluid domain model; Step 3, setting up fluid domain simulation in Ansys Workbench software; Step 4, performing cavitation simulation calculation; Step 5: Analyze the cavitation simulation calculation results using post-processing software to obtain the cavitation distribution cloud map and bubble change map of the flow field structure of the single-plunger electro-hydraulic pump.

2. The CFD-based hydraulic pump cavitation flow field simulation analysis method according to claim 1, characterized in that: In the step 1, the assembly model is saved as a general type file in the three-dimensional modeling software.

3. The CFD-based hydraulic pump cavitation flow field simulation analysis method according to claim 1 or 2, characterized in that: The process of step 3 is as follows: Step 3.1, import the fluid domain model into the Fluent module, and use the Mesh module provided by the Fluent module to mesh the fluid domain model; Step 3.2, define boundary conditions: set them to four forms: pressure inlet, pressure outlet, interface and wall; Step 3.3, define the time step, total time, and solver type for the fluid domain.

4. The CFD-based hydraulic pump cavitation flow field simulation analysis method according to claim 1 or 2, characterized in that: In step 4, in order to calculate the cavitation flow field of the single-plunger electro-hydraulic pump fluid domain, a flow field multiphase flow model and a cavitation model are established, and the establishment process is as follows: The essence of the cavitation process is the phase change process of the fluid medium. Here, the Mixture multiphase flow model in the Euler-Euler method is used, and its continuity equation is described as follows: r m =ρ v a+r l (1-a); Where: m is the density of the gas-liquid mixture; ρ v is the density of the gas phase; ρ l is the density of the liquid phase; v m is the average velocity of the mixed phase; v v is the velocity of the gas phase; v l is the velocity of the liquid phase; α is the volume fraction of the gas phase; the cavitation model is the Schnerr-Sauner model, and the evaporation source term R in the model e and the condensation source term R c as follows:

5. The CFD-based hydraulic pump cavitation flow field simulation analysis method according to claim 1 or 2, characterized in that: In step 5, the post-processing software is Tecplot software.

Images