Cavitation erosion strength prediction method and system coupled with multi-scale material model

Abstract

The invention discloses a cavitation erosion strength prediction method and system coupled with a multi-scale material model, relates to the technical field of engineering computational fluid mechanics, and aims to solve the problem that the influence of material response cannot be considered in cavitation erosion assessment of a hydraulic machinery overflow pipeline in the prior art. Calculating the macroscopic evolution process of the cavitation bubbles in the cavitation flow field by using the cavitation model to obtain macroscopic evolution information of the cavitation bubbles, and converting all small cavitation bubbles into single bubbles according to the macroscopic evolution information; and calculating the microcosmic dynamic process of the single bubble to obtain microcosmic dynamic information, calculating the impact load of the single bubble according to the microcosmic dynamic information, and synthesizing the impact load of the single bubble in all time steps to calculate the material cavitation erosion incubation period of the overflowing pipeline, namely the cavitation erosion strength. According to the method, the dynamic evolution process of large-scale cavitation bubbles and small-scale cavitation bubbles can be described at the same time, and the cavitation erosion strength forecasting is spanned from qualitative to quantitative.

Description

Technical Field

[0001] The invention relates to a cavitation intensity prediction method and system for coupling a multi-scale material model, and belongs to the technical field of engineering computational fluid dynamics. Background Art

[0002] In the process of water energy conversion and utilization, cloud cavitation often occurs in the low-pressure area of ​​the flow pipe of hydraulic machinery. Cloud cavitation is essentially a multi-scale complex turbulence in time and space, in which the evolution of macroscopic cavitation and the behavior of mesoscopic bubbles are coupled. It often causes wear and damage to the flow pipe of hydraulic machinery, and thus has become a hot issue in the field of hydraulic machinery with water as the medium.

[0003] At present, most of the cavitation assessments are based on various assumptions to obtain the cavitation risk area on the material surface, and the influence of material response cannot be considered, which brings great challenges and difficulties to the in-depth study of the microscopic mechanism of cavitation damage and the proposal of effective anti-cavitation measures. Therefore, it is necessary to develop a cavitation intensity prediction method that considers material response to deeply study the influence of cavitation distribution and damage characteristics on the surfaces of different materials, and further reveal the microscopic mechanism of cavitation damage. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide a cavitation intensity prediction method and system that couples a multi-scale material model, which can simultaneously describe the dynamic evolution process of large-scale cavitation and small-scale cavitation, thereby achieving a leap from qualitative to quantitative prediction of cavitation intensity.

[0005] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0006] In one aspect, the present invention provides a method for predicting cavitation intensity by coupling a multi-scale material model, comprising: S1. Grid the flow pipe to be tested to obtain the cavitation occurrence area; S2, calculating the transient non-cavitation flow field according to the cavitation occurrence area, and dividing the time when the flow pipe to be tested is exposed to the cavitation flow into multiple time steps; S3. In the current time step, the cavitation flow is simulated based on the flow field of the previous time step to obtain the cavitation flow field, wherein the cavitation flow field of the first time step is obtained based on the transient non-cavitation flow field; S4. Use the cavitation model to calculate the macroscopic evolution process of cavitation bubbles in the cavitation flow field; S5. According to the cavitation macro-evolution process, all cavitations in the cavitation flow field are identified and their macro-evolution information is calculated; S6. Convert all small cavitation bubbles in the cavitation flow field into single bubbles according to the macroscopic evolution information of all cavitation bubbles; S7, calculating the microscopic dynamic process of each single bubble to obtain the microscopic dynamic information of each single bubble; S8, calculating the impact load generated by each single bubble on the wall of the flow pipe to be measured according to the microscopic dynamic information of each single bubble, and adding the impact loads generated by all single bubbles on the wall of the flow pipe to be measured to obtain the impact load of the current time step; S9, repeat S3 to S9 to obtain the impact load of all time steps, and calculate the material cavitation incubation period of the flow pipe to be tested by comprehensively calculating the impact load of all time steps. The material cavitation incubation period is the cavitation intensity.

[0007] Furthermore, the meshing is achieved by using the blockMesh tool in the open source software OpenFOAM.

[0008] Furthermore, the calculation of the transient non-cavitation flow field according to the cavitation occurrence area and the simulation of the cavitation flow based on the flow field of the previous time step to obtain the cavitation flow field are both implemented by the open source software OpenFOAM, wherein the calculation of the transient non-cavitation flow field according to the cavitation occurrence area includes:

[0009] PimpleFoam was used to calculate the transient non-cavitation flow field. The calculation parameters were set to 3 to 5 outer loops and 3 to 5 inner loops in each time step, and the variable residual was set to 10 -5 ~10 -4 ;

[0010] The cavitation flow is simulated based on the flow field of the previous time step to obtain the cavitation flow field, including:

[0011] Based on the flow field of the previous time step, interPhaseChangeFoam was used to simulate the cavitation flow. The simulation parameters were set to 2 to 3 external cycles and 3 to 5 internal cycles in each time step, and the pressure residual was set to 10 -8 ~10 -6 , the residuals of the other variables are set to 10 -7 ~10 -5 , and the cavitation flow field is obtained.

[0012] Furthermore, the calculation expression of the macroscopic evolution process of cavitation bubbles in the cavitation flow field is as follows: ; ; ; in, represents the density of the gas-liquid mixture, represents the flow velocity of the gas-liquid mixed fluid in the i direction, represents the flow velocity of the gas-liquid mixed fluid in the j direction, represents the component in the i direction, represents the component in the j direction, represents the pressure of gas-liquid mixed fluid, represents the viscosity of the gas-liquid mixed fluid, represents the source term of the effect of bubbles on macroscopic cavitation, represents the water vapor volume fraction in cavitation flow, represents the cavitation flow calculation time, represents the component of the artificial compression velocity in the j direction, represents the condensation and evaporation rates in cavitation flow, which are calculated by the cavitation model; The cavitation models include the Schnerr-Sauer cavitation model, the Zwart-Gerbera-Belamni cavitation model and the Saito cavitation model.

[0013] Furthermore, according to the cavitation macro-evolution process, identifying all cavitations in the cavitation flow field and calculating their macro-evolution information includes: According to the macroscopic evolution of cavitation, all cavitations in the cavitation flow field are identified using the three-dimensional space connected component labeling algorithm. The macroscopic evolution information contained in each cavitation is calculated, wherein the macroscopic evolution information includes the number of grid cells, the position of the cavitation center of mass, the cavitation volume, and the relative sphericity of the cavitation.

[0014] Furthermore, the method of converting all small cavitation bubbles in the cavitation flow field into single bubbles according to the macroscopic evolution information of all cavitation bubbles includes: According to the macroscopic evolution information of all cavities, it is judged whether each cavitation is a small cavitation. If the number of grid cells is greater than the preset threshold and the relative sphericity of the cavitation is less than 2, the cavitation is a small cavitation.

[0015] Convert all small cavitation bubbles into single bubbles.

[0016] Furthermore, the microscopic dynamic process of each single bubble is calculated to obtain the microscopic dynamic information of each single bubble, including: Based on Newton's second law, the single bubble motion speed is obtained by calculating the single bubble motion process, and its expression is as follows: ; in, represents the mass of a single bubble, represents the velocity of a single bubble, represents the cavitation flow calculation time, represents the virtual mass force, represents the pressure gradient force, represents buoyancy, Indicates resistance, represents lift, Represents the volume change force;

[0017] The modified Rayleigh-Plesset equation is used to calculate the single bubble growth process and the single bubble collapse process to obtain the single bubble radius, wherein the expression of the bubble growth process is: ; in, represents the radius of a single bubble, Represents the first derivative of the change in the radius of a single bubble, represents the second-order derivative of the change in the radius of a single bubble, represents the density of the gas-liquid mixture, represents the pressure inside a single bubble in the cavitation flow field, represents the Euler cavitation flow pressure at the center of a single bubble in the cavitation flow field, represents the surface tension of a single bubble in the cavitation flow field, Indicates the viscosity of gas-liquid mixed fluid;

[0018] The expression of the single bubble collapse process is: ; in, It represents the relative ratio of gas density to liquid density. represents the speed of sound in pure water. represents the saturated vapor pressure of the liquid phase, represents the partial pressure of non-condensable gas in the cavitation flow field, It represents the radius when a single bubble in the cavitation flow field begins to shrink, and k represents the compression constant;

[0019] The single bubble movement speed and the single bubble radius constitute the microscopic dynamic information of the single bubble.

[0020] Furthermore, the impact load generated by each single bubble on the wall of the flow pipe to be measured is calculated according to the microscopic dynamic information of each single bubble, and the impact load generated by all single bubbles on the wall of the flow pipe to be measured is added to obtain the impact load of the current time step, including:

[0021] According to the microscopic dynamic information of a single bubble, the ideal bubble symmetric collapse model is used to calculate the impact load on the wall of the flow pipe to be tested caused by the symmetric collapse of a single bubble. The expression is as follows: ; in, represents the impact load caused by the symmetrical collapse of a single bubble in the cavitation flow field, represents the far-field pressure of cavitation flow, r represents the distance from the center of a single bubble in the cavitation flow field to the wall of the flow pipe, , for The first derivative of represents the speed of sound in pure water. It represents the density of gas-liquid mixed fluid;

[0022] The correction coefficient is introduced to consider the primary and secondary impact loads caused by the asymmetric collapse of a single bubble, and the impact load caused by the asymmetric collapse of a single bubble on the wall of the flow pipe to be measured is obtained, that is, the impact load caused by a single bubble on the wall of the flow pipe to be measured, and its expression is as follows: ; in, represents the impact load caused by the asymmetric collapse of a single bubble in the cavitation flow field, Indicates the correction factor for the primary impact load, represents the secondary impact load correction factor, It represents the ratio of the distance from the center of a single bubble to the wall of the flow pipe in cavitation flow to the maximum radius of the single bubble; ; ;

[0023] The impact loads generated by all single bubbles on the wall of the flow pipe to be tested are added together to obtain the impact load in the current time step.

[0024] Furthermore, the calculation of the material cavitation incubation period of the flow-through pipeline to be tested according to the impact load in all time steps includes:

[0025] a. In one time step, the impact load generated by a single bubble on the wall of the flow pipe to be tested is compared with the yield stress of the material of the flow pipe to be tested, and the single bubble whose impact load reaches the yield stress of the material is retained and recorded as single bubble A;

[0026] b. Calculate the material strain caused by the impact load of each single bubble A. The expression is as follows: ; in, It represents the impact load on the wall of the flow pipe to be tested. , represents the yield strength of the material, Represents the strength index of the material, represents material strain, n represents the hardening exponent of material strain;

[0027] c. The material strain generated by the impact load of each single bubble A is calculated to obtain the energy absorbed by the material of the flow-through pipe to be tested during the strain process in the current time step. The expression is as follows: ; in, It represents the energy absorbed by the material during the material strain process. represents the strain caused by the ith impact load, represents the average impact load area, represents the maximum hardening thickness, Indicates that the material reaches the failure stress σ u The strain, l represents the length of the flow pipe to be measured, It represents the strain occurring at the position x where the length of the flow pipe to be measured is x. represents the shape factor of the material, ;

[0028] d. Repeat a~d to obtain the energy absorbed by the flow pipe material to be tested during the strain process in all time steps. Add the energy absorbed by the flow pipe material to be tested during the strain process of single bubble A in all time steps to obtain the cumulative energy absorbed by the flow pipe material to be tested during the strain process. The expression is as follows: ; in, It represents the cumulative energy absorbed by the material of the flow pipe to be tested during the strain process, T represents the time the material is exposed to the cavitation flow, and m represents the number of impact loads that reach the yield stress of the material;

[0029] e. The cavitation incubation period of the material of the flow pipe to be tested is calculated based on the cumulative energy absorbed by the material of the flow pipe to be tested during the strain process. The expression is as follows: ; in, Indicates the material cavitation incubation period of the flow pipe to be tested. It represents the total energy absorbed by the material during the cavitation incubation period. Indicates the material's failure stress σ u The absorbed energy.

[0030] On the other hand, the present invention also provides a cavitation intensity prediction system coupled with a multi-scale material model, comprising:

[0031] A memory for storing instructions;

[0032] A processor is used to execute the instructions so that the system performs operations to implement the cavitation intensity prediction method of the coupled multi-scale material model as described in any one of the above items.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention adopts a bidirectionally coupled Euler-Lagrangian method to calculate the unsteady multi-scale cavitation flow, which can simultaneously describe the dynamic evolution process of large-scale cavitation bubbles and small-scale bubbles, and considers the dynamic response process of the impact load on the material surface by using the ductile material model, thus realizing the transition from qualitative to quantitative prediction of cavitation intensity.

[0035] The present invention provides an automatic calculation method for impact load, which can accurately calculate the impact load released by each bubble after each time step, screen and save the impact load higher than the yield strength of the material, which is convenient, fast and easy to apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram of a flow chart of a method for predicting cavitation intensity by coupling a multi-scale material model in an embodiment of the present invention;

[0037] Figure 2 A schematic diagram of a calculation domain for predicting cavitation intensity in a flow-through pipe in a cavitation intensity prediction method coupled with a multi-scale material model in an embodiment of the present invention;

[0038] Figure 3 It is a schematic diagram of the cumulative strain distribution of the bottom plate of the flow pipe in the cavitation intensity prediction method coupled with the multi-scale material model in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention. Example 1

[0040] like Figure 2 As shown, Figure 2 Schematic diagram of the calculation domain for predicting the cavitation intensity of 1 / 8 of a flow pipe of a hydraulic machinery according to an embodiment of the present invention. In this embodiment, the vertical inlet diameter of the flow pipe to be tested is 16 mm, the height of the horizontal section flow channel is 2.5 mm, the cavitation number σ = 0.9, and the upstream flow velocity V0 = 6.25 L / s.

[0041] like Figure 1 As shown in FIG. 1 , the cavitation intensity prediction method of the coupled multi-scale material model includes the following steps:

[0042] S1. Grid the flow pipe to be tested and obtain the cavitation occurrence area:

[0043] The computational domain meshing is implemented using the blockMesh tool in the open source software OpenFOAM. The cavitation area is encrypted while ensuring uniform mesh transition in the wall area.

[0044] S2~S3, the time when the flow pipe to be tested is exposed to the cavitation flow is divided into multiple time steps, and the transient cavitation-free flow field is calculated according to the cavitation occurrence area. In the first time step, the cavitation flow is simulated based on the transient cavitation-free flow field to calculate the cavitation flow field of the current time step, and in the subsequent time steps, the cavitation flow is simulated based on the flow field of the previous time step to calculate the cavitation flow field of the current time step.

[0045] The cavitation calculations were all performed in the open source software OpenFOAM. First, pimpleFoam was used to calculate the transient non-cavitation flow field. To ensure the convergence of the calculation, the inner and outer loops were repeated twice and the inner loop was repeated three times in each time step. The pressure residual was set to 10 -8 Then, based on the flow field of the previous time step, interPhaseChangeFoam considering the influence of bubbles is used to simulate the cavitation flow. In each time step, the outer loop is repeated twice and the inner loop is repeated three times. The pressure residual is set to 10 -8 , the residuals of the other variables are set to 10 -7 , and finally the cavitation flow field of the current time step is obtained.

[0046] In the current time step:

[0047] S4. The homogeneous equilibrium flow model is used under the Euler framework to calculate the macroscopic evolution process of cavitation bubbles in the cavitation flow field. The calculation expression is as follows: ; ; ; in, represents the density of the gas-liquid mixture, represents the flow velocity of the gas-liquid mixed fluid in the i direction, represents the flow velocity of the gas-liquid mixed fluid in the j direction, represents the component in the i direction, represents the component in the j direction, represents the pressure of gas-liquid mixed fluid, represents the viscosity of the gas-liquid mixed fluid, represents the source term of the effect of bubbles on macroscopic cavitation, represents the water vapor volume fraction in cavitation flow, represents the cavitation flow calculation time, represents the component of the artificial compression velocity in the j direction, Represents the condensation and evaporation rates in cavitating flows, which are calculated using the cavitation model.

[0048] The cavitation models that can be used include the Schnerr-Sauer cavitation model, the Zwart-Gerbera-Belamni cavitation model, the Saito cavitation model, etc., but are not limited thereto. An appropriate cavitation model can be selected for solution according to actual needs.

[0049] In the calculation of this step, the flow velocity and pressure of the gas-liquid mixed fluid are unknown quantities, and the rest are known quantities. The flow velocity and pressure of the gas-liquid mixed fluid are used for subsequent cavitation conversion and are also used for the calculation of several typical forces in step S7.

[0050] S5. According to the macroscopic evolution process of cavitation, a three-dimensional space connected component labeling algorithm is used to identify all cavitations in the cavitation flow field, and the macroscopic evolution information contained in each cavitation is calculated. The macroscopic evolution information includes the number of grid cells, the position of the cavitation center of mass, the volume of the cavitation, the relative sphericity of the cavitation, etc. Among them, the number of grid cells and the relative sphericity of the cavitation are used for the subsequent judgment of small cavitations, and the position of the cavitation center of mass and the volume of the cavitation are used for the subsequent conversion of small cavitations into single bubbles, so that the single bubbles meet the same volume as the original small cavitations and are in the same position.

[0051] S6. Determine whether each cavitation is a small cavitation based on the macroscopic evolution information of all cavitations. If the number of grid cells is greater than the preset threshold and the relative sphericity of the cavitation is less than 2, the cavitation is a small cavitation. All small cavitations are converted into single bubbles to facilitate the subsequent solution under the Lagrangian framework.

[0052] S7. Calculate the microscopic dynamic process of a single bubble using the discrete bubble model

[0053] Considering several typical forces acting on a single bubble in a cavitation flow field, the velocity of a single bubble is obtained by calculating the motion process of the single bubble based on Newton's second law. The expression is as follows: ; in, represents the mass of a single bubble, represents the velocity of a single bubble, represents the cavitation flow calculation time, represents the virtual mass force, represents the pressure gradient force, represents buoyancy, Indicates resistance, represents lift, Represents the volume change force.

[0054] The above equations of motion are solved by the “explicit-semi-implicit” method in each time step.

[0055] The modified Rayleigh-Plesset equation considering the compressible effect of the liquid phase is used to calculate the single bubble growth process and the single bubble collapse process to obtain the single bubble radius. The expression of the bubble growth process is: ; in, represents the radius of a single bubble, Represents the first derivative of the change in the radius of a single bubble, represents the second-order derivative of the change in the radius of a single bubble, represents the density of the gas-liquid mixture, represents the pressure inside a single bubble in the cavitation flow field, represents the Euler cavitation flow pressure at the center of a single bubble in the cavitation flow field, represents the surface tension of a single bubble in the cavitation flow field, Indicates the viscosity of gas-liquid mixed fluid;

[0056] The expression of the single bubble collapse process is:

[0057] ;

[0058] in, It represents the relative ratio of gas density to liquid density. represents the speed of sound in pure water. represents the saturated vapor pressure of the liquid phase, represents the partial pressure of non-condensable gas in the cavitation flow field, It represents the radius when a single bubble in the cavitation flow field begins to shrink, and k represents the compression constant;

[0059] The single bubble movement speed and the single bubble radius constitute the microscopic dynamic information of the single bubble.

[0060] S8. According to the microscopic dynamic information of a single bubble, the ideal bubble symmetric collapse model is used to calculate the impact load generated by the symmetric collapse of a single bubble on the wall of the flow pipe to be tested. The expression is as follows: ; in, represents the impact load caused by the symmetrical collapse of a single bubble in the cavitation flow field, represents the far-field pressure of cavitation flow, r represents the distance from the center of a single bubble in the cavitation flow field to the wall of the flow pipe, , for The first derivative of represents the speed of sound in pure water. Represents the density of gas-liquid mixed fluid.

[0061] Further considering the influence of asymmetric collapse of bubbles, according to the experimental and data simulation structure of single bubble collapse near the wall, the correction coefficient is introduced to consider the primary and secondary impact loads caused by the asymmetric collapse of single bubbles, respectively, and the impact load caused by the asymmetric collapse of single bubbles on the wall of the flow pipe to be tested is obtained, that is, the impact load caused by the single bubble on the wall of the flow pipe to be tested, and its expression is as follows: ; in, represents the impact load caused by the asymmetric collapse of a single bubble in the cavitation flow field, Indicates the correction factor for the primary impact load, represents the secondary impact load correction factor, It represents the ratio of the distance from the center of a single bubble to the wall of the flow pipe in cavitation flow to the maximum radius of the single bubble;

[0062] ;

[0063] ;

[0064] The impact load of the current time step is obtained by adding up the impact loads generated by all single bubbles in the current time step on the wall of the flow pipe to be tested.

[0065] S9. Repeating steps S3 to S9 can obtain the impact loads of all time steps. The material cavitation incubation period of the flow pipe to be tested is calculated based on the impact loads in all time steps, which specifically includes: a. In one time step, the impact load generated by a single bubble on the wall of the flow pipe to be tested is compared with the yield stress of the material of the flow pipe to be tested, and the single bubble whose impact load reaches the yield stress of the material is retained and recorded as single bubble A; b. Use the Ludwig-type stress-strain formula of the material to calculate the material strain generated by the impact load of each single bubble A. The expression is as follows: ; in, It represents the impact load on the wall of the flow pipe to be tested. , represents the yield strength of the material, Represents the strength index of the material, represents material strain, n represents the hardening exponent of material strain; c. The material strain generated by the impact load of each single bubble A is calculated to obtain the energy absorbed by the material of the flow-through pipe to be tested during the strain process in the current time step. The expression is as follows: ; in, It represents the energy absorbed by the material during the material strain process. represents the strain caused by the ith impact load, represents the average impact load area, represents the maximum hardening thickness, Indicates that the material reaches the failure stress σ u The strain, l represents the length of the flow pipe to be measured, It represents the strain occurring at the position x where the length of the flow pipe to be measured is x. represents the shape factor of the material, ; d. Repeat a~d to obtain the energy absorbed by the flow pipe material to be tested during the strain process in all time steps. Add the energy absorbed by the flow pipe material to be tested during the strain process of single bubble A in all time steps to obtain the cumulative energy absorbed by the flow pipe material to be tested during the strain process. The expression is as follows: ; in, It represents the cumulative energy absorbed by the material of the flow pipe to be tested during the strain process, T represents the time the material is exposed to the cavitation flow, and m represents the number of impact loads that reach the yield stress of the material; e. The cavitation incubation period of the material of the flow pipe to be tested is calculated based on the cumulative energy absorbed by the material of the flow pipe to be tested during the strain process. The expression is as follows: ; in, Indicates the material cavitation incubation period of the flow pipe to be tested. It represents the total energy absorbed by the material during the cavitation incubation period. Indicates the material's failure stress σ u The absorbed energy.

[0066] The cavitation incubation period of the material of the flow pipe to be tested is the cavitation intensity.

[0067] like Figure 3 The figure shows the cumulative strain per unit time in different radial regions of the bottom plate of the flow pipe to be tested calculated by the cavitation prediction method (black line) of this embodiment. The distribution of Figure 3 It can be found that the calculation results of the cavitation prediction method of this embodiment are well consistent with the cavitation damage experimental data (red line) of the bottom plate of the flow pipe, which proves the effectiveness of the cavitation prediction method of this embodiment. Example 2

[0068] This embodiment provides a cavitation intensity prediction system coupled with a multi-scale material model, including: A memory for storing instructions; A processor is used to execute the instructions so that the system performs operations to implement the cavitation intensity prediction method of the coupled multi-scale material model as described in Example 1.

[0069] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for predicting cavitation intensity by coupling a multi-scale material model, characterized in that: include: S1. Grid the flow pipe to be tested to obtain the cavitation occurrence area; S2, calculating the transient non-cavitation flow field according to the cavitation occurrence area, and dividing the time when the flow pipe to be tested is exposed to the cavitation flow into multiple time steps; S3. In the current time step, the cavitation flow is simulated based on the flow field of the previous time step to obtain the cavitation flow field, wherein the cavitation flow field of the first time step is obtained based on the transient non-cavitation flow field; S4. Use the cavitation model to calculate the macroscopic evolution process of cavitation bubbles in the cavitation flow field; S5. According to the cavitation macro-evolution process, all cavitations in the cavitation flow field are identified and their macro-evolution information is calculated; S6. Convert all small cavitation bubbles in the cavitation flow field into single bubbles according to the macroscopic evolution information of all cavitation bubbles; S7, calculating the microscopic dynamic process of each single bubble to obtain the microscopic dynamic information of each single bubble; S8, calculating the impact load generated by each single bubble on the wall of the flow pipe to be measured according to the microscopic dynamic information of each single bubble, and adding the impact loads generated by all single bubbles on the wall of the flow pipe to be measured to obtain the impact load of the current time step; S9, repeat S3 to S9 to obtain the impact load of all time steps, and calculate the material cavitation incubation period of the flow pipe to be tested by comprehensively calculating the impact load of all time steps. The material cavitation incubation period is the cavitation intensity.

2. The cavitation intensity prediction method of coupling multi-scale material model according to claim 1 is characterized in that: The meshing is achieved by using the blockMesh tool in the open source software OpenFOAM.

3. The method for predicting cavitation intensity by coupling a multi-scale material model according to claim 1, characterized in that: The calculation of the transient non-cavitation flow field according to the cavitation occurrence area and the simulation of the cavitation flow based on the flow field of the previous time step to obtain the cavitation flow field are both implemented by the open source software OpenFOAM, wherein the calculation of the transient non-cavitation flow field according to the cavitation occurrence area includes: PimpleFoam was used to calculate the transient non-cavitation flow field. The calculation parameters were set to 3 to 5 outer loops and 3 to 5 inner loops in each time step, and the variable residual was set to 10 -5 ~10 -4 ; The cavitation flow is simulated based on the flow field of the previous time step to obtain the cavitation flow field, including: Based on the flow field of the previous time step, interPhaseChangeFoam was used to simulate the cavitation flow. The simulation parameters were set to 2 to 3 external cycles and 3 to 5 internal cycles in each time step, and the pressure residual was set to 10 -8 ~10 -6 , the residuals of the other variables are set to 10 -7 ~10 -5 , and the cavitation flow field is obtained.

4. The method for predicting cavitation intensity by coupling a multi-scale material model according to claim 1, characterized in that: The calculation expression of the macroscopic evolution process of cavitation bubbles in the cavitation flow field is as follows: ； ； ； in, represents the density of the gas-liquid mixture, represents the flow velocity of the gas-liquid mixed fluid in the i direction, represents the flow velocity of the gas-liquid mixed fluid in the j direction, represents the component in the i direction, represents the component in the j direction, represents the pressure of gas-liquid mixed fluid, represents the viscosity of the gas-liquid mixture, represents the source term of the effect of bubbles on macroscopic cavitation, represents the water vapor volume fraction in cavitation flow, represents the cavitation flow calculation time, represents the component of the artificial compression velocity in the j direction, represents the condensation and evaporation rates in cavitation flow, which are calculated by the cavitation model; The cavitation models include the Schnerr-Sauer cavitation model, the Zwart-Gerbera-Belamni cavitation model and the Saito cavitation model.

5. The method for predicting cavitation intensity by coupling a multi-scale material model according to claim 1, characterized in that: According to the cavitation macro-evolution process, all cavitations in the cavitation flow field are identified and their macro-evolution information is calculated, including: According to the macroscopic evolution of cavitation, all cavitations in the cavitation flow field are identified using the three-dimensional space connected component labeling algorithm. The macroscopic evolution information contained in each cavitation is calculated, wherein the macroscopic evolution information includes the number of grid cells, the position of the cavitation center of mass, the cavitation volume, and the relative sphericity of the cavitation.

6. The method for predicting cavitation intensity by coupling a multi-scale material model according to claim 1, characterized in that: The method of converting all small cavitation bubbles in the cavitation flow field into single bubbles according to the macroscopic evolution information of all cavitation bubbles includes: According to the macroscopic evolution information of all cavities, it is judged whether each cavitation is a small cavitation. If the number of grid cells is greater than the preset threshold and the relative sphericity of the cavitation is less than 2, the cavitation is a small cavitation. Convert all small cavitation bubbles into single bubbles.

7. The method for predicting cavitation intensity by coupling a multi-scale material model according to claim 1, characterized in that: The microscopic dynamic process of each single bubble is calculated to obtain the microscopic dynamic information of each single bubble, including: Based on Newton's second law, the single bubble motion speed is obtained by calculating the single bubble motion process, and its expression is as follows: ； in, represents the mass of a single bubble, represents the velocity of a single bubble, represents the cavitation flow calculation time, represents the virtual mass force, represents the pressure gradient force, represents buoyancy, Indicates resistance, represents lift, Represents the volume change force; The modified Rayleigh-Plesset equation is used to calculate the single bubble growth process and the single bubble collapse process to obtain the single bubble radius, wherein the expression of the bubble growth process is: ； in, represents the radius of a single bubble, Represents the first derivative of the change in the radius of a single bubble, represents the second-order derivative of the change in the radius of a single bubble, represents the density of the gas-liquid mixture, represents the pressure inside a single bubble in the cavitation flow field, represents the Euler cavitation flow pressure at the center of a single bubble in the cavitation flow field, represents the surface tension of a single bubble in the cavitation flow field, Indicates the viscosity of gas-liquid mixed fluid; The expression of the single bubble collapse process is: ； in, It represents the relative ratio of gas density to liquid density. represents the speed of sound in pure water. represents the saturated vapor pressure of the liquid phase, represents the partial pressure of non-condensable gas in the cavitation flow field, It represents the radius when a single bubble in the cavitation flow field begins to shrink, and k represents the compression constant; The single bubble movement speed and the single bubble radius constitute the microscopic dynamic information of the single bubble.

8. The method for predicting cavitation intensity by coupling a multi-scale material model according to claim 1, characterized in that: The impact load generated by each single bubble on the wall of the flow pipe to be measured is calculated according to the microscopic dynamic information of each single bubble, and the impact load generated by all single bubbles on the wall of the flow pipe to be measured is added to obtain the impact load in the current time step, including: According to the microscopic dynamic information of a single bubble, the ideal bubble symmetric collapse model is used to calculate the impact load on the wall of the flow pipe to be tested caused by the symmetric collapse of a single bubble. The expression is as follows: ； in, represents the impact load caused by the symmetrical collapse of a single bubble in the cavitation flow field, represents the far-field pressure of cavitation flow, r represents the distance from the center of a single bubble in the cavitation flow field to the wall of the flow pipe, , for The first derivative of represents the speed of sound in pure water. It represents the density of gas-liquid mixed fluid; The correction coefficient is introduced to consider the primary and secondary impact loads caused by the asymmetric collapse of a single bubble, and the impact load caused by the asymmetric collapse of a single bubble on the wall of the flow pipe to be measured is obtained, that is, the impact load caused by a single bubble on the wall of the flow pipe to be measured, and its expression is as follows: ； in, represents the impact load caused by the asymmetric collapse of a single bubble in the cavitation flow field, Indicates the correction factor for the primary impact load, represents the secondary impact load correction factor, It represents the ratio of the distance from the center of a single bubble to the wall of the flow pipe in cavitation flow to the maximum radius of the single bubble; ； ； The impact loads generated by all single bubbles on the wall of the flow pipe to be tested are added together to obtain the impact load in the current time step.

9. The method for predicting cavitation intensity by coupling a multi-scale material model according to claim 1, characterized in that: The material cavitation incubation period of the flow pipe to be tested is calculated based on the impact load of all time steps, including: a. In one time step, the impact load generated by a single bubble on the wall of the flow pipe to be tested is compared with the yield stress of the material of the flow pipe to be tested, and the single bubble whose impact load reaches the yield stress of the material is retained and recorded as single bubble A; b. Calculate the material strain caused by the impact load of each single bubble A. The expression is as follows: ； in, It represents the impact load on the wall of the flow pipe to be tested. , represents the yield strength of the material, Represents the strength index of the material, represents material strain, n represents the hardening exponent of material strain; c. The material strain generated by the impact load of each single bubble A is calculated to obtain the energy absorbed by the material of the flow-through pipe to be tested during the strain process in the current time step. The expression is as follows: ；； in, It represents the energy absorbed by the material during the material strain process. represents the strain caused by the ith impact load, represents the average impact load area, represents the maximum hardening thickness, Indicates that the material reaches the failure stress σ u The strain, l represents the length of the flow pipe to be measured, It represents the strain occurring at the position x where the length of the flow pipe to be measured is x. represents the shape factor of the material, ; d. Repeat a~d to obtain the energy absorbed by the flow pipe material to be tested during the strain process in all time steps. Add the energy absorbed by the flow pipe material to be tested during the strain process of single bubble A in all time steps to obtain the cumulative energy absorbed by the flow pipe material to be tested during the strain process. The expression is as follows: ； in, It represents the cumulative energy absorbed by the material of the flow pipe to be tested during the strain process, T represents the time the material is exposed to the cavitation flow, and m represents the number of impact loads that reach the yield stress of the material; e. The cavitation incubation period of the material of the flow pipe to be tested is calculated based on the cumulative energy absorbed by the material of the flow pipe to be tested during the strain process. The expression is as follows: ； in, Indicates the cavitation incubation period of the material of the flow pipe to be tested. It represents the total energy absorbed by the material during the cavitation incubation period. Indicates the material's failure stress σ u The absorbed energy.

10. A cavitation intensity prediction system coupled with a multi-scale material model, characterized in that: include: A memory for storing instructions; A processor is used to execute the instructions so that the system performs operations to implement the cavitation intensity prediction method of the coupled multi-scale material model as described in any one of claims 1 to 9.

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