A numerical simulation method and device for the collapse of a single cavitation bubble near a wall coupled with boundary motion

Abstract

The present invention discloses a method and device for numerical simulation of near-wall single cavitation collapse coupled with boundary motion, comprising: step 1, introducing a physical model of a near-wall single cavitation into a pre-constructed external flow field to obtain a corresponding flow field physical model; step 2, meshing the flow field physical model; setting initial conditions and flow field boundary conditions, and setting a time step that meets the calculation requirements; step 3, setting specific calculation parameters for solving the flow field process, and introducing a fluid volume method to capture the gas-liquid interface; step 4, applying wall vibration in the form of a user-defined function to simulate the cavitation dynamics behavior under vibration impact. The present invention takes into account the influence of wall vibration in the numerical simulation process by coupling boundary motion, and realizes the simulation of the dynamics behavior of near-wall single cavitation under vibration impact conditions. On this basis, the influence of conditions such as vibration frequency on the cavitation collapse process can be further explored, providing theoretical guidance for optimized cavitation suppression design.

Description

Technical Field

[0001] The present invention relates to the field of computational fluid dynamics, and in particular to a method and device for numerically simulating the collapse of a near-wall single cavitation bubble coupled with boundary motion. Background Art

[0002] When cavitation bubbles collapse near a solid wall, they generate enormous impact pressure. This pressure wave and high-speed jet can severely damage the wall, affecting the performance and life of the equipment. In practical applications, the generation, development, and collapse of cavitation bubbles are influenced by a variety of factors, such as vibration and shock. These factors can significantly affect the dynamic behavior of the bubbles, and thus the occurrence and development of cavitation erosion. Therefore, in-depth research on the dynamic behavior of cavitation bubbles under vibration and shock conditions is of great engineering significance.

[0003] Existing numerical simulation methods can well simulate the generation and collapse process of cavitation near solid walls. However, considering the wall deformation caused by vibration impact in actual application scenarios of engineering machinery, the cavitation collapse process near solid walls cannot be well matched to reality. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a numerical simulation method and device for near-wall single cavitation collapse coupled with boundary motion. The method further couples boundary motion on the basis of fixed wall working conditions, which helps to further explore the influence of vibration impact on the near-wall cavitation generation and collapse process, and provides a theoretical basis for the development of more effective cavitation suppression technology.

[0005] The object of the present invention is achieved through the following technical solutions: a numerical simulation method for the collapse of a single cavitation bubble near a wall coupled with boundary motion, comprising:

[0006] Step 1: Introduce the near-wall single cavitation physical model into the pre-constructed external flow field to obtain the corresponding flow field physical model;

[0007] Step 2: Mesh the flow field physical model in step 1 according to the calculation accuracy requirements, set the initial conditions and flow field boundary conditions, and set the time step that meets the calculation requirements according to the generated mesh quality;

[0008] Step 3: Set the specific calculation parameters for solving the flow field process and introduce the fluid volume method to capture the gas-liquid interface;

[0009] Step 4. Based on step 3, apply wall vibration using a user-defined function to simulate the cavitation dynamics under vibration impact. By varying parameters such as dimensionless wall distance and vibration frequency, the dynamic evolution of cavitation under vibration impact is determined.

[0010] The method further includes step 5: analyzing the cavitation generation and collapse mechanism under different working conditions according to the numerical simulation results obtained in step 4, so as to solve the problem of suppressing cavitation erosion of the diesel engine cylinder liner.

[0011] The present invention simulates the wall vibration impact in the actual working scene of engineering machinery by coupling boundary motion, which can provide a deeper understanding of the generation, development and collapse process of cavitation bubbles under complex conditions, provide a more accurate theoretical basis for studying the cavitation mechanism, and provide theoretical guidance for the further development of cavitation suppression technology.

[0012] Specifically, in step 1, the near-wall single cavitation physical model includes a rigid wall, a dimensionless distance from the wall of The flow field physical model includes a two-dimensional rectangular calculation domain and a distance from the bottom surface center to the bottom surface center. Two-dimensional single cavitation bubble.

[0013] Specifically, in step 2, the grid division refers to discretizing the computational domain of step 1 with a structured grid and encrypting the area around the cavitation bubble to generate a high-quality grid; the minimum grid size is less than 2 μm.

[0014] Specifically, in step 2, the initial conditions refer to the dimensionless wall distance γ, the initial cavitation radius D0, and the initial pressure P0 within the bubble. The flow field boundary conditions refer to the pressure outlet boundary and the wall boundary. A time step that meets the computational requirements refers to a time step that meets the CFL (Courant-Friedrichs-Lewy) criterion.

[0015] Specifically, in step 3, the specific calculation parameter settings of the flow field solution process include discretizing the control equation using the finite volume method, using the pressure implicit operator splitting algorithm (PISO) for coupled solution, the gradient term using the least squares format based on the grid unit, the fluid volume fraction discretization format using the Compressive format, the density term, momentum term and energy term using the second-order upwind format, the pressure term using the body force weighted format, and the time term using the first-order implicit format.

[0016] Specifically, in step 3, the volume of fluid method refers to the VOF (volume of fluid) method, which introduces a scalar function to represent the fluid occupancy, usually denoted as α, whose value ranges from 0 to 1. For a certain calculation cell, α = 0 indicates that the cell is completely occupied by the gas phase; α = 1 indicates that the cell is completely occupied by the liquid phase; if 0 < α < 1, it means that the cell contains an interface.

[0017] Specifically, in step 4, applying wall vibration in the form of a user-defined function refers to simulating the actual near-wall working conditions of engineering machinery. In Ansys Fluent software, the DEFINE_GRID_MOTION macro is used to load the wall with an amplitude-time response function, dividing the wall into twenty regions. The motion equation of each node is:

[0018] A=A max sin(2πft)

[0019] Among them, A is the actual displacement of each point, A max is the peak amplitude at each node, and f is the vibration frequency.

[0020] Specifically, in step 4, changing the vibration frequency refers to changing the vibration frequency f in the motion equation of each node.

[0021] On the other hand, the present invention also provides a numerical simulation device for the collapse of a single cavitation bubble near the wall coupled with boundary motion, comprising a memory and one or more processors, wherein the memory stores executable code, and when the processor executes the executable code, it implements the numerical simulation method for the collapse of a single cavitation bubble near the wall coupled with boundary motion.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention takes into account the influence of wall vibration in the numerical simulation process by coupling boundary motion, which is more consistent with the actual operating conditions of engineering machinery.

[0024] (2) The present invention simulates the dynamic behavior of a single cavitation bubble near the wall under vibration impact conditions through a numerical simulation method of coupled boundary motion, and can further explore the influence of conditions such as vibration frequency on the cavitation collapse process, providing theoretical guidance for the optimized cavitation suppression design. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A flowchart of a numerical simulation method for the collapse of a single cavitation bubble near a wall coupled with boundary motion provided by the present invention;

[0026] Figure 2 A schematic diagram of the flow field physical model provided in this embodiment;

[0027] Figure 3 A schematic diagram of a grid provided for this embodiment;

[0028] Figure 4 Schematic diagram of the liquid phase volume fraction in the flow field when γ=1 and the wall is stationary, provided for this embodiment. Red corresponds to the liquid phase and blue to the gas phase;

[0029] Figure 5Schematic diagram of the liquid phase volume fraction in the flow field when γ=1 and the wall vibration frequency is 2000 Hz provided in this embodiment, with red corresponding to the liquid phase and blue corresponding to the gas phase;

[0030] Figure 6 Pressure contours of a single cavitation bubble at the moment of secondary collapse near a vibrating and stationary wall when γ = 1 provided for this embodiment, (a) corresponds to the result for the vibrating wall, (b) corresponds to the result for the stationary wall;

[0031] Figure 7 Schematic diagram of the change of cavitation volume and maximum wall pressure over time at different vibration frequencies provided in this embodiment.

[0032] Figure 8 This is a structural diagram of a numerical simulation device for the collapse of a near-wall single cavitation bubble coupled with boundary motion according to the present invention. DETAILED DESCRIPTION

[0033] The present invention is described in detail below with reference to the embodiments and accompanying drawings. It should be noted that the description of specific parameters is only exemplary and is not intended to limit the scope of the present invention.

[0034] like Figure 1 As shown, the present invention provides a numerical simulation method for the collapse of a single cavitation bubble near the wall coupled with boundary motion, which specifically includes the following steps:

[0035] Step 1: Introduce the near-wall single cavitation physical model into the pre-built external flow field to obtain Figure 2 The two-dimensional flow field physical model shown in the figure has a rectangular calculation domain with a length of 140D0 and a width of 80D0. D0 is the diameter of the cavitation bubble, which is taken as 0.05 mm. l is the distance from the initial cavitation center to the wall. The dimensionless distance of the initial cavitation bubble from the wall is The left and right sides of the computational domain are solid wall boundaries, the upper boundary is the pressure outlet with an outlet pressure of one atmosphere, and the lower boundary is a wall boundary, but wall vibration can be applied in the form of a user-defined function.

[0036] Step 2: Use Figure 3 The structured mesh shown discretizes the computational domain from step 1 and refines the area surrounding the cavitation bubble to a minimum mesh size of less than 2 μm. The cavitation bubble is specified using a patch, with an initial pressure of 0.5 MPa. The time step is set to 50e-8 seconds to ensure accurate simulation of the cavitation collapse process.

[0037] Step 3. In Ansys Fluent, the control equations are discretized using the finite volume method, and the pressure implicit operator splitting algorithm (PISO) is used for coupled solution. The gradient term adopts the least squares format based on the grid unit, the fluid volume fraction discretization format adopts the Compressive format, the density term, momentum term and energy term adopt the second-order upwind format, the pressure term adopts the body force weighted format, and the time term uses the first-order implicit format.

[0038] The two-phase flow model adopts the VOF model, and the main steps include:

[0039] 1. Initialize volume fraction function: Initialize the volume fraction in the computational domain and determine the fluid occupancy of each computational unit based on the initial conditions;

[0040] 2. Solve the fluid motion equations: Use the Navier-Stokes equations to solve the velocity and pressure fields of the fluid. This requires considering the differences in physical properties of the two fluids, such as density and viscosity.

[0041] 3. Interface tracking: Update the interface position by solving the volume fraction equation;

[0042] 4. Recalculate physical properties: Based on the updated volume fraction function, recalculate the effective physical properties of each calculation unit, such as density and viscosity, usually using linear interpolation:

[0043] ρ=α l ρ l +α g ρ g

[0044] μ=α l μ l +α g μ g

[0045] α l represents the liquid volume fraction, α g represents the gas phase volume fraction.

[0046] 5. Repeat iteration: Repeat the above steps until the convergence condition is reached or the simulation time ends.

[0047] Step 4. Based on step 3, to simulate the actual near-wall working conditions in construction machinery, use the FluentDEFINE_GRID_MOTION macro to load the amplitude response function over time, divide the wall surface into 20 regions, and the maximum amplitude at the center is 60μm. The motion equation of each node is:

[0048] A=A max sin(2πft)

[0049] A is the actual displacement of each point, A max is the peak amplitude at each node, and f is the vibration frequency.

[0050] Step 5: Based on the numerical simulation results obtained in step 4, analyze the cavitation generation and collapse mechanisms under different operating conditions and apply them to solve related engineering problems; related engineering problems include diesel engine cylinder liner cavitation suppression, etc.

[0051] like Figure 4 The following are the numerical simulation results of the cavitation generation and collapse process near the stationary wall when γ = 1. Figure 5 Shown are the numerical simulation results of the cavitation generation and collapse process when γ=1 and the wall vibration frequency is 2000Hz. The overall dynamic process of the cavitation can be roughly divided into four stages: growth, collapse, rebound, and collapse. In the growth stage, due to the restriction of the wall, the shape of the cavitation gradually changes from a uniform circle to an ellipsoid. The bottom of the cavitation is relatively flat in the early stage of collapse. Due to the existence of the pressure gradient, the upper end of the cavitation is relatively sharp, but it continues to shrink and sink inward in the late stage of collapse. At the end of collapse, the cavitation is directly impacted by the jet. At this time, there is a large pressure in the center of the cavitation accompanied by a large velocity gradient. After collapsing to the minimum volume, the cavitation enters the rebound stage, and the cavitation volume gradually increases. In the second collapse process after the rebound, unlike the previous gradual collapse, the cavitation at this time shows an overall collapse trend. In addition, the cavitation near the vibrating wall can grow to a larger volume. As Figure 6 The pressure contours at the moment of secondary collapse of a single cavity near a vibrating and stationary wall surface indicate that the collapse of a single cavity near a vibrating wall will lead to a more destructive secondary collapse process than that of a stationary wall. The peak pressure of the wall caused by the secondary collapse of a single cavity near a vibrating wall is close to 0.4 MPa, which is even much higher than the pressure value of the primary collapse. The peak pressure of the wall corresponding to the secondary collapse of a single cavity near a stationary wall is around 0.2 MPa. This suggests that the collapse process of a single cavity near a vibrating wall will cause a more severe impact on the wall surface, especially in the process of repeated cavitation collapse. The secondary collapse of a single cavity near a vibrating wall will even cause more serious wall damage than the primary collapse.

[0052] Since the actual operating environment of construction machinery is complex and the operating conditions are non-constant, the vibration frequency of the wall is not fixed, but changes with time. Therefore, the vibration frequency can be changed to consider the influence of vibration conditions of different frequencies on the dynamic behavior of single cavitation near the vibrating wall. Figure 7The figure shows a schematic diagram of the change in cavitation volume and maximum wall pressure over time at different vibration frequencies (f = 1000 Hz, f = 2000 Hz, and f = 3000 Hz). The higher the wall vibration frequency, the shorter the corresponding collapse time. In particular, the cavitation collapse time decreases rapidly at f = 3000 Hz, suggesting that wall vibration accelerates the collapse process after rebound. Since the time is shortened and the collapse volume is similar, the faster the vibration, the higher the maximum wall pressure. The second peak at f = 3000 Hz is significantly higher than that of the other two operating conditions. The faster the frequency, the larger the peak. These phenomena indicate that the higher the wall vibration frequency, the greater the secondary damage to the wall caused by cavitation collapse.

[0053] It can be seen that the present invention realizes the simulation of the dynamic behavior of a single cavitation bubble near the wall under vibration impact conditions through the numerical simulation method of coupled boundary motion. On this basis, the influence of conditions such as vibration frequency on the cavitation collapse process can be further explored, providing theoretical guidance for the optimized cavitation suppression design that is closer to actual working conditions.

[0054] Corresponding to the aforementioned embodiment of a method for numerically simulating the collapse of a single cavitation bubble near a wall coupled with boundary motion, the present invention further provides an embodiment of a device for numerically simulating the collapse of a single cavitation bubble near a wall coupled with boundary motion.

[0055] See also Figure 8 An embodiment of the present invention provides a numerical simulation device for the collapse of a single cavitation bubble near the wall coupled with boundary motion, comprising a memory and one or more processors. The memory stores executable code, and when the processor executes the executable code, it is used to implement a numerical simulation method for the collapse of a single cavitation bubble near the wall coupled with boundary motion in the above embodiment.

[0056] The embodiment of the numerical simulation device for the collapse of a near-wall single cavitation bubble coupled with boundary motion provided by the present invention can be applied to any device with data processing capabilities, and the device with data processing capabilities can be a device or apparatus such as a computer. The device embodiment can be implemented through software, or through hardware or a combination of software and hardware. Taking software implementation as an example, as a device in a logical sense, it is formed by the processor of any device with data processing capabilities in which it is located reading the corresponding computer program instructions in the non-volatile memory into the memory for execution. From the hardware level, if Figure 8 As shown, it is a hardware structure diagram of any device with data processing capability for a numerical simulation device for near-wall single cavitation collapse coupled with boundary motion provided by the present invention, except Figure 8 In addition to the processor, memory, network interface, and non-volatile memory shown, any device with data processing capabilities in which the apparatus in the embodiment is located may also include other hardware, generally based on the actual functions of the device with data processing capabilities, which will not be described in detail.

[0057] The implementation process of the functions and effects of each unit in the above-mentioned device is specifically described in the implementation process of the corresponding steps in the above-mentioned method, and will not be repeated here.

[0058] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to the partial description of the method embodiments. The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the present invention. A person of ordinary skill in the art can understand and implement the present invention without inventive work.

[0059] An embodiment of the present invention further provides a computer-readable storage medium having a program stored thereon. When the program is executed by a processor, the method for numerical simulation of near-wall single cavitation collapse coupled with boundary motion in the above embodiment is implemented.

[0060] The computer-readable storage medium may be an internal storage unit of any device with data processing capabilities described in any of the aforementioned embodiments, such as a hard disk or memory. The computer-readable storage medium may also be an external storage device of any device with data processing capabilities, such as a plug-in hard disk, a smart media card (SMC), an SD card, a flash card, etc. equipped on the device. Furthermore, the computer-readable storage medium may also include both an internal storage unit and an external storage device of any device with data processing capabilities. The computer-readable storage medium is used to store the computer program and other programs and data required by any device with data processing capabilities, and may also be used to temporarily store data that has been output or is to be output.

[0061] The present invention also provides a computer program product, comprising a computer program, which, when executed by a processor, implements the method for numerical simulation of near-wall single cavitation collapse coupled with boundary motion.

[0062] The above embodiments are used to illustrate the present invention rather than to limit the present invention. Any modifications and changes made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A numerical simulation method for the collapse of a single cavitation bubble near a wall coupled with boundary motion, characterized by: include: Step 1: Introduce the near-wall single cavitation physical model into the pre-constructed external flow field to obtain the corresponding flow field physical model; Step 2: Mesh the flow field physical model in step 1 according to the calculation accuracy requirements, set the initial conditions and flow field boundary conditions, and set the time step that meets the calculation requirements according to the generated mesh quality; Step 3: Set specific calculation parameters for solving the flow field process and capture the gas-liquid interface based on the fluid volume method; Step 4: Based on step 3, apply wall vibration in the form of a user-defined function to simulate the cavitation dynamics behavior under vibration impact; change the vibration frequency parameter to obtain the cavitation dynamics evolution law under vibration impact.

2. The method for numerically simulating the collapse of a single cavitation bubble near a wall coupled with boundary motion according to claim 1, characterized in that: The method further includes step 5: analyzing the cavitation generation and collapse mechanism under different working conditions according to the numerical simulation results obtained in step 4, so as to solve the problem of suppressing cavitation erosion of the diesel engine cylinder liner.

3. The method for numerical simulation of single cavitation collapse near a wall coupled with boundary motion according to claim 1 or 2, characterized in that: In step 1, the near-wall single cavitation physical model includes a rigid wall surface, and the dimensionless distance from the wall surface is A two-dimensional circular bubble, is the distance from the initial cavitation center to the wall, is the initial cavitation diameter; the flow field physical model includes a two-dimensional rectangular calculation domain and a distance from the bottom center Two-dimensional single cavitation bubble.

4. The method for numerical simulation of single cavitation collapse near a wall coupled with boundary motion according to claim 1 or 2, characterized in that: In step 2, the meshing refers to discretizing the computational domain of step 1 with a structured mesh, and encrypting the area around the cavitation bubble to produce a high-quality mesh with a minimum mesh size of less than 2 μm.

5. The method for numerical simulation of near-wall single cavitation collapse coupled with boundary motion according to claim 1 or 2, characterized in that: In step 2, the initial condition refers to the dimensionless wall distance , the initial radius of the cavitation bubble and the initial pressure inside the bubble ; The flow field boundary conditions refer to the pressure outlet boundary and the wall boundary; the time step that meets the calculation requirements refers to the time step that meets the CFL criterion.

6. The method for numerical simulation of near-wall single cavitation collapse coupled with boundary motion according to claim 1 or 2, characterized in that: In step 3, the specific calculation parameter settings for the flow field solution process include discretizing the control equation using the finite volume method, using the implicit operator splitting algorithm PISO of pressure for coupled solution, using the least squares format based on grid cells for the gradient term, using the Compressive format for the fluid volume fraction discretization format, using the second-order upwind format for the density term, momentum term and energy term, using the body force weighted format for the pressure term, and using the first-order implicit format for the time term.

7. The method for numerical simulation of near-wall single cavitation collapse coupled with boundary motion according to claim 1 or 2, characterized in that: In step 3, the volume of fluid method refers to the VOF method, which introduces a scalar function to represent the fluid occupancy rate, denoted as , whose value range is between 0 and 1; for a certain computing unit, , indicating that the unit is completely occupied by the gas phase; , indicating that the unit is completely occupied by the liquid phase; if , it means that the unit contains an interface.

8. The method for numerical simulation of near-wall single cavitation collapse coupled with boundary motion according to claim 1 or 2, characterized in that: In step 4, the application of wall vibration in the form of a user-defined function refers to simulating the actual near-wall working conditions in engineering machinery. In Ansys Fluent software, the DEFINE_GRID_MOTION macro is used to load the wall with an amplitude-time response function, dividing the wall into multiple regions. The motion equation of each node is: in, is the actual displacement of each point, is the peak amplitude at each node, is the vibration frequency.

9. The method for numerical simulation of single cavitation collapse near a wall coupled with boundary motion according to claim 8, characterized in that: In step 4, changing the vibration frequency means changing the vibration frequency in the motion equation of each node .

10. A numerical simulation device for the collapse of a single cavitation bubble near a wall coupled with boundary motion, comprising a memory and one or more processors, wherein the memory stores executable code, characterized in that: When the processor executes the executable code, a numerical simulation method for near-wall single cavitation collapse coupled with boundary motion according to any one of claims 1 to 9 is implemented.

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