Reduction and simulation verification method for flow-induced noise of unloading groove of closed axial plunger pump

Abstract

The invention discloses a reduction and simulation verification method for flow-induced noise of an unloading groove of a closed axial plunger pump. The method comprises a structure improvement method for reducing the flow-induced noise of a triangular unloading groove and a method for verifying the improved structure through simulation software. The method is different from an optimization method for establishing a mathematical model and finding an optimal structure parameter through an algorithm. Comprising the following steps: S1, providing an improved structure for a triangular unloading groove structure based on an unloading groove working principle; s2, calculating and comparing structure parameters before and after improvement; s3, establishing a flow field model and calculating flow field characteristics before and after improvement; s31, establishing a flow field model; s32, setting corresponding flow field boundary conditions; s33, flow field characteristics are calculated; s4, establishing a sound field model and calculating sound field characteristics before and after improvement; s41, establishing a sound field model; s42, setting corresponding sound field boundary conditions; s43, calculating sound field characteristics before and after improvement; and the effects before and after improvement are verified through the steps S3 and S4.

Description

Technical Field

[0001] The present invention relates to the technical field of noise reduction of closed axial piston pumps in the hydraulic component industry, and specifically to a method for reducing and verifying flow-induced noise in an unloading groove of a closed axial piston pump. Background Art

[0002] As one of the important equipment, the noise generated by the plunger pump has an important impact on the health and work efficiency of the operator. In order to protect the health of workers and the tranquility of the environment, many countries and regions have formulated strict regulations and standards to limit the noise level generated by industrial equipment. Plunger pumps usually work under high pressure and high speed conditions, and the noise they generate cannot be ignored. As one of the important sources of noise pollution, it is necessary to use simulation methods to study and verify the flow-induced noise of closed axial variable plunger pumps.

[0003] At present, the research on the flow-induced noise reduction technology of axial piston pumps is mainly focused on the structural improvement of the distribution pair, specifically, the research is carried out by influencing the flow field characteristics through the structure and then radiating them to the acoustic field characteristics. When the oil in the piston pump passes through the unloading groove, it is a throttling process. The oil flow through the unloading groove is directly related to the cross-sectional area of ​​the unloading groove, that is, the structure of the unloading groove will directly affect its flow field characteristics. The structure of the unloading groove plays an important role in the flow distribution process of the piston pump. The speed of the oil passing through, the flow rate of the oil passing through and the backflow of the oil will vary according to the different structures of the unloading groove. At the same time, the speed, flow rate and backflow of the oil affect the flow pulsation of the piston pump, which is the key factor causing the piston pump to generate vibration and noise. Therefore, how to determine a suitable unloading groove structure is a key method to reduce the flow-induced noise of the piston pump, and it is also a challenge faced by the technical field of the hydraulic component industry.

[0004] In order to further study and verify the relationship between the unloading tank structure and flow-induced noise, the simulation process of flow field characteristics and acoustic field characteristics is essential. Through simulation methods, the flow field characteristics and acoustic field distribution in the flow distribution process of the plunger pump are further studied to verify whether the unloading tank structure is reasonable and effective. At the same time, correct simulation methods can provide support for theory and experiment, reasonably reduce R&D costs, improve R&D efficiency, and promote the improvement of plunger pump structure, which has important application prospects. Summary of the invention

[0005] In order to solve the above problems, the present invention adopts the following technical solutions: a method for reducing and simulating the flow-induced noise of the unloading groove of a closed axial piston pump, including a structural improvement method for reducing the flow-induced noise of the triangular unloading groove, and a method for verifying the improved structure through simulation software. The present invention is different from the optimization method of building a mathematical model and finding the optimal structural parameters through an algorithm. Based on the working principle of the unloading groove, the present invention proposes an improved triangular groove structure to achieve the purpose of noise reduction.

[0006] To solve the above technical problems, the purpose of the present invention is achieved as follows: A method for reducing and simulating the flow-induced noise of a closed axial piston pump unloading groove comprises the following steps: S1: Based on the working principle of the unloading groove, an improved structure for the triangular unloading groove structure is proposed; the method for improving the triangular unloading groove structure in step S1 specifically includes: when the flow distribution waist-shaped window is aligned with the plunger hole of the cylinder body, a pressure difference is generated between the internal fluid in the plunger chamber and the fluid in the distribution area, thereby causing a throttling effect; S2: Calculate and compare the structural parameters before and after improvement; S3: Establish a flow field model and calculate the flow field characteristics before and after improvement; S31: Establish a flow field model; according to the assembly relationship of the internal parts of the closed axial piston pump, establish a flow domain model of the internal parts; S32: setting corresponding flow field boundary conditions; meshing the watershed model and setting boundary conditions; S33: Calculate the flow field characteristics; assign physical parameters to the flow medium, add the plunger pump flow component, start simulation, and obtain the flow field simulation results of the closed axial piston pump; S4: Establish a sound field model and calculate the sound field characteristics before and after improvement; S41: Establishing sound field model; S42: Setting the corresponding sound field boundary conditions; S43: Calculate the sound field characteristics before and after the improvement; verify the effects before and after the improvement through steps S3 and S4.

[0007] On the basis of the above scheme and as a preferred scheme of the above scheme: in step S1, the bottom of the triangular unloading groove is improved to an arc structure.

[0008] On the basis of the above scheme and as a preferred scheme of the above scheme: the throttling effect can be described by the following throttling formula: (1-1); in, Indicates the throttling flow in the high pressure area, Indicates the throttling flow in the low pressure area, is the throttling coefficient of the oil; Represents the flow area in the high-pressure region, Indicates the flow area of ​​the low-pressure area; , and They are the oil pressure in the high-pressure area, low-pressure area and plunger cavity; is the density of the oil.

[0009] On the basis of the above scheme and as a preferred scheme of the above scheme: in step S2, a geometric method is used to calculate the flow area of ​​the unloading slot, and the flow areas before and after the improvement are compared, as follows: The flow area of ​​the improved unloading trough structure can be expressed as follows: (2-5); Trapezoid The area can be expressed as: (2-6); sector The area can be expressed as: (2-7); And, the triangle The area can be expressed as: (2-8); In the above formula, (2-9); (2-10); (2-11); (2-12); (2-13); (2-14); Substituting equations (2-9) to (2-14) derived above into equation (2-5), the flow area of ​​the improved unloading tank can be obtained: (2-15); in, is the depth angle, is the width angle, R is the pitch circle of the valve plate, is the central angle of the arc tangent to the quadrilateral, is the ratio of line segment ab to line segment cd, R 1 is the radius of the arc tangent to the quadrilateral.

[0010] On the basis of the above scheme and as a preferred scheme of the above scheme: the step S3 specifically includes: (1) Establish the flow domain model of internal parts, including the flow domain of inlet and outlet flow channels, the flow domain inside the distribution plate, the flow domain inside the cylinder body, and the flow domain inside the plunger cavity; (2) Establishing a flow turbulence model: Based on the assumption of energy transfer and dissipation process of turbulent motion, the short-term turbulent structure in turbulent flow is modeled, and the transport equations of turbulent kinetic energy and turbulent dissipation rate are solved to estimate the length scale and turbulent dissipation rate of turbulence, thereby calculating the motion characteristics of turbulence; (3) Grid the watershed model and set boundary conditions: based on the rated operating conditions of the plunger pump, set the inlet and outlet pressures, speed, and swash plate inclination angle.

[0011] On the basis of the above scheme and as a preferred scheme of the above scheme: (2) in establishing a flow turbulence model: The transport equation of turbulent kinetic energy can be written as: (3-1); The transport equation for the dissipation rate can be written as: (3-2); in, represents the turbulent kinetic energy due to the mean velocity gradient; represents the turbulent kinetic energy due to the buoyancy effect; It represents the effect of compressible turbulent pulsation expansion on the total dissipation rate; represents the turbulent viscosity coefficient; the constant parameter value in the formula is: ; ; ; Turbulent kinetic energy and dissipation rate The turbulent Prandtl numbers are: ; .

[0012] On the basis of the above scheme and as a preferred scheme of the above scheme: the sound field characteristic simulation of step S4 specifically includes the following steps: (1) An acoustic model is constructed based on the internal flow domain of the plunger pump, including the sound source domain, the sound propagation domain, and the infinite element domain. The "hemispherical method" is used to arrange acoustic monitoring points 1#, 2#, and 3# to simulate the noise at a radius of 1 m with the plunger pump as the center; (2) The acoustic analogy method is selected as the Lighthill acoustic analogy method, and its mathematical model can be derived as follows: (4-1); In the formula, is the fluid density, is the undisturbed fluid density, is the speed of sound in the undisturbed fluid, is the fluid velocity component, is the velocity component of the solid boundary motion, is the fluid pressure, is the viscous stress tensor component, is the unit tensor component, f is a function related to the shape and motion of the solid boundary; (3) The acoustic model is meshed, and at least 6 acoustic meshes must be present within one wavelength to ensure the accuracy of the acoustic simulation, that is, ; In the formula, is the grid size, is the minimum wavelength, is the speed of sound propagation in the fluid medium, To calculate the maximum frequency required; (4) Add frequency response analysis and assign physical parameters to the flow medium and propagation medium, and set boundary conditions such as volume sound source and surface sound source; (5) Add the ICFD component, import the above flow field simulation results into the sound source domain as the flow induced noise source, add the sound source modeling component, select the interpolation method for calculation, and finally add the DFT component to convert the time domain signal into the frequency domain signal for frequency response analysis; (6) After the calculation is completed, the sound pressure levels of different frequencies are converted into the total sound pressure level according to the following method in order to evaluate the noise level.

[0013] Based on the above solution and as a preferred solution of the above solution: in step (1): the length, width and height of the test pump do not exceed 0.3m, and the radius of the sphere R At least twice the maximum size of the test pump and not less than 1m.

[0014] On the basis of the above scheme and as a preferred scheme of the above scheme: in step (2): The first term on the right side of the equal sign in the formula is the quadrupole sound source term caused by turbulent motion, the second term is the dipole sound source term excited by the solid wall pressure pulsation, and the third term is the monopole sound source term caused by the fluid pressure pulsation; ①Perform strong variation on equation (4-1) and consider density and speed They are all functions of space and time, introducing variational notation To represent small changes in these quantities, and in the spatial domain Integrate on; that is: (4-2); ②At the border Perform partial integration on the above, and we get the expression after weak variation: (4-3); ③ Consider boundaries and express it using the stress tensor: (4-4); ④Let , and expand it to get: (4-5); On the right side of the equation, the first term represents the contribution of the volume integral, while the second term reflects the effect of the surface integral; both terms include the effects of monopole, dipole, and quadrupole sound sources.

[0015] On the basis of the above scheme and as a preferred scheme of the above scheme: in step (6): ①Convert the sound pressure level of each frequency band into a linear energy value: For each octave, the sound pressure level , first calculate the corresponding energy ratio: (4-6); ②Add the energy values ​​of all the multiple frequencies: Add the converted linear energy values ​​to get the total energy value: (4-7); ③Convert the total energy value back to the total sound pressure level: (4-8).

[0016] Compared with the prior art, the present invention has the following outstanding and beneficial technical effects: (1) Compared with the traditional triangular unloading groove, the improved method provided by the present invention increases the flow area of ​​the unloading groove without changing the structural parameters of the triangular unloading groove, thereby increasing the flow rate passing through the unloading groove per unit time, reducing the flow backflow of the plunger pump during operation, and reducing the flow and pressure pulsation of the plunger pump.

[0017] (2) Through acoustic simulation, it is easier to observe the specific size of the flow-induced noise of the plunger pump at different frequencies, thereby improving the efficiency of structural improvement design, shortening the product development and maintenance cycle, and saving R&D costs.

[0018] (3) After appropriate parameter adjustment, this method can also be used to study closed axial piston pumps of different models and specifications, and has a certain degree of universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a flowchart of a method for reducing and simulating the flow-induced noise in the unloading groove of a closed axial piston pump according to an embodiment of the present invention.

[0020] Figure 2 Schematic diagram of a method for improving a triangular unloading groove according to an embodiment of the present invention.

[0021] Figure 3 Schematic diagram of the improved front triangular groove structure according to an embodiment of the present invention.

[0022] Figure 4 It is a schematic cross-sectional view of the improved unloading groove according to an embodiment of the present invention.

[0023] Figure 5 It is a comparison diagram of the flow area of ​​the unloading groove before and after the improvement of the embodiment of the present invention.

[0024] Figure 6 Schematic diagram of a flow field model according to an embodiment of the present invention.

[0025] Figure 7 This is the flow field grid parameter setting of an embodiment of the present invention.

[0026] Figure 8 This is the flow field rotor grid template setting of an embodiment of the present invention.

[0027] Fig. 9 4 is a flow field characteristic curve obtained by calculation according to an embodiment of the present invention.

[0028] Fig.10 Schematic diagram of an acoustic model according to an embodiment of the present invention.

[0029] Fig.11 It is a monitoring point set in the sound field of the embodiment of the present invention.

[0030] Fig.12 1# monitoring point frequency response curves before and after the improvement of the embodiment of the present invention.

[0031] Fig.13 2# monitoring point frequency response curves before and after the improvement of the embodiment of the present invention.

[0032] Fig.14 3# monitoring point frequency response curves before and after the improvement of the embodiment of the present invention.

[0033] Fig.15 It is the total sound pressure level of each monitoring point before and after the improvement of the embodiment of the present invention. DETAILED DESCRIPTION

[0034] The present invention will be further described below with reference to specific embodiments in conjunction with the accompanying drawings; In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] like Figure 1 The flowchart of the method for reducing the flow-induced noise of the unloading groove of the closed axial piston pump and the simulation verification is shown. In an embodiment of the present invention, a method for reducing the flow-induced noise of the unloading groove of the closed axial piston pump and the simulation verification is provided, and the method includes: Step 1: As a key component of the plunger pump, the unloading groove plays a role in balancing the oil pressure during the operation of the pump, thereby protecting the hydraulic system from possible damage caused by hydraulic shock. By adjusting the flow direction and flow rate of the oil, the unloading groove ensures that the hydraulic system maintains a stable pressure during operation.

[0036] Determine the working principle of the plunger pump unloading groove, and determine the improvement plan for reducing the flow induced noise of the unloading groove based on the working principle; its working principle is based on the throttling characteristics in fluid mechanics, and plays the role of pre-pressurization and pre-pressure reduction to avoid cavitation damage and vibration noise caused by excessive pressure difference in the distribution pair.

[0037] When the flow distribution waist window is aligned with the plunger hole of the cylinder body, a pressure difference is generated between the internal fluid in the plunger chamber and the fluid in the distribution area, resulting in a throttling effect. This effect can be described by the following throttling formula: (1-1); in, q t Indicates the throttling flow in the high pressure area, q n Indicates the throttling flow in the low pressure area. C v is the throttling coefficient of the oil; A hp Represents the flow area in the high-pressure region, A lp Indicates the flow area in the low pressure area. p h , p l and p f They are the oil pressure in the high-pressure area, low-pressure area and plunger cavity; ρ is the density of the oil.

[0038] According to formula (1-1), the flow area A hp and A lpIt is linearly related to the throttling flow rate, which is an important parameter related to the flow rate in the flow distribution process. The improved structure of the unloading groove can expand the flow area, thereby increasing the throttling flow rate and reducing backflow. Therefore, the flow pulsation amplitude of the plunger pump is effectively reduced, and vibration and noise are also reduced.

[0039] When the structure of the unloading slot changes, it affects the size of the flow area in the throttling characteristics, and ultimately changes the flow through the unloading slot. When the flow through the unloading slot increases within a reasonable range, the speed of the flowing medium in the unloading slot increases, which shortens the time required for pre-pressurization and pre-pressure reduction. In this way, the flow backflow generated in this process can be reduced and the flow pulsation can be suppressed.

[0040] Step 1.2: According to the above working principle, the present invention takes the standard triangular unloading groove as the improvement object. Figure 2 Shows the structure and parameters of a standard unloading trough, including the depth angle θ 1 , Width Angle θ 2 , the pitch circle radius of the distribution plate R and the center angle of the unloading groove The new structure proposed in this invention is derived from the triangular unloading groove, maintaining the same structural parameters. θ 1 , θ 2 and Without changing the depth angle, width angle and center angle of the original structure, the bottom of the triangle is improved to be an arc circumscribed, such as Figure 2 As shown in the figure. The improved unloading groove increases the flow area, thereby increasing the throttling flow rate. Therefore, during the flow distribution process, the reverse flow rate is reduced, thereby suppressing the flow and pressure pulsation.

[0041] The advantages of improving the bottom of the triangular unloading groove to an arc structure are as follows: (a) The arc structure has less resistance and pressure loss during fluid flow. The fluid can pass more smoothly, with large flow capacity and high flow efficiency. (b) The arc structure can ensure that the fluid is evenly distributed over the entire pipe cross section during the flow, which helps to achieve a more uniform stress distribution and cooling effect. At the same time, without changing the original structural parameters of the triangular unloading groove, such as depth angle, width angle, and transition angle, by changing the cross-sectional area of ​​the unloading groove, the bottom of the triangle is changed to an arc connection, and its flow area is calculated and increased, and its flow field characteristics are changed. When the plunger cavity transitions from the oil suction area to the oil discharge area, the hydraulic oil in the plunger pump is pre-pressurized and pre-depressurized to achieve the weakening of flow pulsation and pressure pulsation, thereby effectively reducing the noise of the plunger pump.

[0042] Step 2: Use the geometric method to calculate the flow area of ​​the unloading tank as follows: Flow area of ​​triangular slot A 0 is related to the specific cross-sectional area of ​​the triangular prism, e.g. Figure 3 In As shown, Indicates the working surface in contact with the waist-shaped window of the cylinder body, and the straight line af The angle formed is the depth angle of the triangular groove θ 1 ; O is the center of the distribution plate dividing circle, cd The arc produced when the plunger hole contacts the triangular groove. cd The arc length can therefore be cd Treated as a straight line. ac and ad The angle formed represents the width angle of the triangular groove, that is θ 2 ; The opening angle of the triangular slot is The radius of the distribution plate pitch circle is expressed as R express; is perpendicular to ef The cross section, whose area is the flow area in engineering calculations A 0 .

[0043] (2-1); in (2-2); (2-3); Therefore, the flow area between the waist-shaped groove and the unloading groove is S Rotation angle with cylinder θ The relationship between can be calculated by the following formula: (2-4); Similarly, the flow area of ​​the improved unloading trough can also be obtained through geometric calculation. Figure 4 The cross section of the improved unloading trough is shown. The flow area of ​​this part can be approximated as a quadrilateral abcd and fan-shaped abo (Except the triangle abo ). In addition, the circle afb Radius R 1 is the rotation angle θ function.

[0044] Therefore, the flow area of ​​the improved unloading trough structure can be expressed as follows: (2-5); Trapezoid The area can be expressed as: (2-6); sector The area can be expressed as: (2-7); And, the triangle The area can be expressed as: (2-8); In the above formula, (2-9); (2-10); (2-11); (2-12); (2-13); (2-14); Substituting equations (2-9) to (2-14) derived above into equation (2-5), we can obtain the flow area of ​​the improved unloading tank: (2-15); in, is the depth angle, is the width angle, R is the pitch circle of the valve plate, is the central angle of the arc tangent to the quadrilateral, Is a line segment ab With line segment cd The ratio of R 1 is the radius of the arc tangent to the quadrilateral.

[0045] 2.1 Use drawing software to draw the flow area of ​​the unloading slot before and after the improvement, such as Figure 5 shown.

[0046] The two flow field curves are parabolic in shape, and the flow field is a quadratic function of the cylinder rotation angle. In addition, the flow field change of the improved unloading groove is similar to the flow field change pattern of the triangular groove. Finally, in the whole flow distribution process, it is observed that the flow area of ​​the improved unloading groove is larger than that of the triangular unloading groove. Specifically, when the width angle θ 1 and depth angle θ 2When the flow rate remains unchanged, the maximum flow area increases from 0.606mm² to 0.813mm². The improved unloading slot effectively increases the flow area in the entire distribution process, with a maximum increase of 34.15%.

[0047] Step 3: Establish a mathematical model of the flow field and calculate the flow field characteristics before and after improvement 3.1 Establishing the mathematical model of flow field Based on the working principle of the inclined plate axial piston pump, the internal flow area of ​​the piston pump is extracted using CAD software to obtain the following Figure 6 The fluid domain model shown in the figure includes the suction and discharge channels of the plunger pump, the cylinder plunger air channel, the plunger channel, and the distribution waist window channel.

[0048] Establish a flow turbulence model: Based on the assumption of energy transfer and dissipation process of turbulent motion, by modeling the short-term turbulent structure in turbulent flow, solving the transport equations of turbulent kinetic energy and turbulent dissipation rate to estimate the length scale and turbulent dissipation rate of turbulence, the motion characteristics of turbulence are calculated.

[0049] The transport equation of turbulent kinetic energy can be written as: (3-1); The transport equation for the dissipation rate can be written as: (3-2); in, represents the turbulent kinetic energy due to the mean velocity gradient; represents the turbulent kinetic energy due to the buoyancy effect; It represents the effect of compressible turbulent pulsation expansion on the total dissipation rate; represents the turbulent viscosity coefficient. The constant parameter value is: ; ; ; Turbulent kinetic energy k and dissipation rate The turbulent Prandtl numbers are: ; .

[0050] 3.2 Setting the corresponding flow field boundary conditions For the plunger pump model SA10VG18, the inlet and outlet pressures are set to 0.3MPa and 30MPa respectively, the speed is set to 2600RPM, and the swash plate angle is set to 18°. Through model establishment, mesh division, template selection, flow medium parameter setting, and plunger pump working global condition setting.

[0051] In order to improve the accuracy of meshing, different meshing techniques are applied in different flow channel areas to generate high-quality meshes. Conventional meshing techniques are used in areas such as the pump suction and discharge channels and the kidney-shaped windows of the distribution components. The meshes in these areas are refined by adjusting the mesh control parameters to ensure the accuracy of the simulation results. The specific settings are as follows: Figure 7 shown.

[0052] When the plunger pump is working, the plunger in the plunger hole of the cylinder body rotates around the main axis as the cylinder body rotates, and on the other hand, it extends and retracts in the hole along the axial direction. This composite movement causes the flow field in the plunger hole of the cylinder body to change all the time. In order to accurately simulate this complex form of movement, the built-in swash plate axial piston pump grid template (SwashPlatePiston) of the PumpLinx software is used to generate the mesh of the rotor. This grid template integrates dynamic grid and sliding grid technology, which can fully meet the movement of the plunger during the working process, while taking into account the characteristics of rotor rotation and expansion and contraction, thereby effectively simulating the working process of the plunger pump. The generated grid is as follows Figure 8 shown.

[0053] 3.3 Calculation of flow field characteristics before and after improvement Carry out simulation and get corresponding results, such as Fig. 9 shown.

[0054] Fig. 9 Figure a shows the outlet flow of the plunger pump at different load pressures within the two plunger working angles. As can be seen from the figure, the outlet flow shows a similar trend under different load pressures. When the plunger hole window and the unloading groove of the cylinder body are connected, since the pressure in the plunger cavity has not yet risen to the load level, there is a pressure difference between the plunger cavity and the high pressure at the discharge end, which causes oil backflow and a significant drop in flow. Subsequently, due to the sharp increase in pressure in the plunger hole, the oil began to be discharged through the top window, and the outlet flow continued to increase until it reached the maximum point. This explains Fig. 9 The peak and valley values ​​in a in . By comparing the simulation results of the improved slot and the triangular slot, it can be seen that the improved unloading slot can effectively reduce the flow backflow when the plunger pump is working under different load pressures. When the load pressure is 30MPa, the flow backflow reaches the maximum reduction, and the maximum reduction of flow backflow is 12.9%.

[0055] Fig. 9Figure b shows the change in plunger cavity pressure under different load pressures when the plunger pump rotates one circle. The pressure change trend in the plunger cavity remains consistent under different load pressures. At the same time, as the load pressure increases, the average pressure in the plunger cavity also increases. Because the backflow of the flow eventually reaches the plunger cavity, it causes a sudden pressure change in the plunger cavity. By comparing the two structures, it can be seen that compared with the triangular unloading groove, the improved structure can reduce the pressure fluctuation amplitude in the plunger cavity under various load pressures, and the maximum pressure fluctuation reduction can reach 10.6% at 30MPa.

[0056] 3.4 Exporting flow field calculation results The output of flow field calculation results requires the results of flow field calculation to be identified, read, and the internal flow to be converted into sound source terms through the ICFD (integral interpolation computational fluid dynamics data processing module) component. The method of outputting CFD (computational fluid dynamics) flow field results is as follows: In the PumpLinx software, the results of the unsteady calculation are output and saved in the EnsightGold format. At the same time, after outputting the Ensight Gold file, the header file encas needs to be changed. In the "model" column, select the last step of the calculation time step 1080, and at the same time, add 4 * signs corresponding to the time step in the "density", "velocity", and "pressure" below. At this point, the exported Ensight Gold file can be recognized by the subsequent acoustic simulation software Actran, so that the subsequent sound field simulation can proceed normally.

[0057] Step 4: Establish the sound field model and calculate the sound field characteristics before and after improvement 4.1 Establishing the sound field model The acoustic model is constructed based on the internal flow domain of the plunger pump, including the sound source domain, the sound propagation domain and the infinite element domain. In acoustic simulation, simplified boundary conditions or flow models (such as plane wave assumptions, simplified geometric shapes, etc.) are often used to make the simulation more efficient and reduce the complexity of the model. Fig.10 As shown; referring to relevant standards, the "hemispherical method" is used to arrange acoustic monitoring points 1#, 2#, and 3#. The length, width, and height of the test pump are no more than 0.3m, and the radius R of the sphere is at least twice the maximum size of the test pump and shall not be less than 1m. Due to the limitation of the size of the test site, it was finally determined R =1m. Therefore, it is used to simulate the noise at a radius of 1m with the plunger pump as the center. Fig.11 As shown; The acoustic analogy method is selected as the Lighthill acoustic analogy method, and its mathematical model can be derived by: (4-1); In the formula, is the fluid density, is the undisturbed fluid density, is the speed of sound in the undisturbed fluid, is the fluid velocity component, U n is the velocity component of the solid boundary motion, p is the fluid pressure, is the viscous stress tensor component, is the unit tensor component, f is a function related to the shape and motion of the solid boundary.

[0058] The first term on the right side of the equal sign in the formula is the quadrupole sound source term caused by turbulent motion, the second term is the dipole sound source term excited by the solid wall pressure pulsation, and the third term is the monopole sound source term caused by the fluid pressure pulsation.

[0059] ①Perform strong variation on equation (4-1) and consider density and speed They are all functions of space and time, introducing variational notation To represent small changes in these quantities, and in the spatial domain Integrate on . That is: (4-2); ②At the border Perform partial integration on the above, and we get the expression after weak variation: (4-3); ③ Consider boundaries and express it using the stress tensor: (4-4); ④Let , and expand it to get: (4-5); On the right side of the equation, the first term represents the contribution of the volume integral, while the second term reflects the effect of the surface integral. Both terms include the effects of monopole, dipole, and quadrupole sound sources.

[0060] 4.2 Set the corresponding sound field boundary conditions The acoustic model will be meshed, and it is necessary to have at least 6 acoustic meshes within 1 wavelength to ensure the accuracy of the acoustic simulation, that is, ; In the formula, is the grid size, is the minimum wavelength, is the speed of sound propagation in the fluid medium, To calculate the maximum frequency required; Set the material and add 46# anti-wear hydraulic oil physical parameters, where the speed of sound is 1380m / s and the density is 875kg / m 3 At the same time, the propagation medium of the sound propagation domain is added, the sound speed is 340 m / s, and the density is 1.225 kg / m 3 .

[0061] Add a frequency response analysis component and select NFF format in the Format option. Locate the File file named freq.nff and set the maximum frequency to 3510Hz. Add acoustic1 to the Component, set the material to the 46# anti-wear hydraulic oil, and select Lighthill_Volume and Lighthill_surface for Domain Assignment. Add acoustic 2, set the material to air, and select Transition for Domain Assignment. Finally, add the infinite_acoustic acoustic component, set the material to air, set the Interpolation Order to 10, select Infinite for Domain Assignment, and finally click Compute center from scope and Automatic spherical system.

[0062] To convert time domain signals into frequency domain signals, add the ICFD (Integral Interpolation Computational Fluid Dynamics Data Processing Module) component, and add the Caasource (Source Modeling Component) in the ICFD component. Input the Ensight Gold file exported from the flow field simulation here to convert the flow field information into time domain signals. At the same time, check Compute Lighthill volume and Compute Lighthill surface in Aerodynamic Sources. And change the conversion method to interpolation method in Advances. Finally, add the DFT (Discrete Fourier Transform) component and select the Hanning window as the window function.

[0063] Start frequency response analysis. Export the frequency response analysis component set up above to use the ICFD (Integral Interpolation Computational Fluid Dynamics Data Processing Module) component to smoothly calculate the conversion between time domain signals and frequency domain signals, and then start frequency response analysis to obtain the sound field characteristics.

[0064] After the calculation is completed, the sound pressure levels of different frequencies are converted into the total sound pressure level according to the following method to evaluate the noise level: ①Convert the sound pressure level of each frequency band into a linear energy value: For each octave, the sound pressure level , first calculate the corresponding energy ratio: (4-6); ②Add the energy values ​​of all the multiple frequencies: Add the converted linear energy values ​​to get the total energy value: (4-7); ③Convert the total energy value back to the total sound pressure level: (4-8); The simulated sound pressure curves at 1m outside the piston pump before and after the improvement are as follows: Fig.12 , 13 , as shown in 14. From the spectrum curves obtained at three different test points, it can be seen that the improved unloading groove structure can reduce the noise generated by the operation of the plunger pump at different frequencies. At each test point, the improved structure can reduce the flow noise by 5-8dB at different multiples, and the maximum noise reduction reaches 9.6%. The improved noise is generally distributed in the range of 60-80dB. In order to observe the effect of noise reduction more intuitively, the spectrum curves obtained from the above three monitoring points are calculated to obtain the corresponding total sound pressure level, as shown in Fig.15 The noise level was the highest and the noise reduction was the most significant at the 2# test point. The total sound pressure values ​​at the three points were 5.16dB, 6.53dB, and 4.65dB, respectively, and the noise reduction reached 6.33%, 7.41%, and 5.59%.

[0065] The method of the present invention can reduce the flow-induced noise of a closed axial piston pump and study the sound pressure of the fluid domain therein, and can improve the simulation efficiency compared with the traditional numerical simulation method.

[0066] In the description of the present invention, it should be understood that the terms "upper", "lower", "top", "bottom", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is conventionally placed when in use, or are the orientations or positional relationships conventionally understood by those skilled in the art. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0067] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for reducing and simulating the flow-induced noise of a closed axial piston pump unloading groove, characterized in that: The following steps are involved: S1: Based on the working principle of the unloading groove, an improved structure for the triangular unloading groove structure is proposed; the method for improving the triangular unloading groove structure in step S1 specifically includes: when the flow distribution waist-shaped window is aligned with the plunger hole of the cylinder body, a pressure difference is generated between the internal fluid in the plunger chamber and the fluid in the distribution area, thereby causing a throttling effect; S2: Calculate and compare the structural parameters before and after improvement; S3: Establish a flow field model and calculate the flow field characteristics before and after improvement; S31: Establish a flow field model; according to the assembly relationship of the internal parts of the closed axial piston pump, establish a flow domain model of the internal parts; S32: setting corresponding flow field boundary conditions; meshing the watershed model and setting boundary conditions; S33: Calculate the flow field characteristics; assign physical parameters to the flow medium, add the plunger pump flow component, start simulation, and obtain the flow field simulation results of the closed axial piston pump; S4: Establish a sound field model and calculate the sound field characteristics before and after improvement; S41: Establishing sound field model; S42: Setting the corresponding sound field boundary conditions; S43: Calculate the sound field characteristics before and after the improvement; verify the effects before and after the improvement through steps S3 and S4.

2. The method for reducing and simulating the flow-induced noise of the unloading groove of a closed axial piston pump according to claim 1 is characterized in that: In step S1, the bottom of the triangular unloading groove is improved to an arc structure.

3. The method for reducing and simulating the flow-induced noise of the unloading groove of a closed axial piston pump according to claim 2 is characterized in that: The throttling effect can be described by the following throttling formula: （1-1）； in, Indicates the throttling flow in the high pressure area, Indicates the throttling flow in the low pressure area, is the throttling coefficient of the oil; Represents the flow area in the high-pressure region, Indicates the flow area of ​​the low-pressure area; , and They are the oil pressure in the high-pressure area, low-pressure area and plunger cavity; is the density of the oil.

4. The method for reducing and simulating the flow-induced noise of the unloading groove of a closed axial piston pump according to claim 1 is characterized in that: In step S2, the flow area of ​​the unloading slot is calculated by a geometric method, and the flow areas before and after the improvement are compared, as follows: The flow area of ​​the improved unloading trough structure can be expressed as follows: (2-5)； Trapezoid The area can be expressed as: (2-6)； sector The area can be expressed as: (2-7)； And, the triangle The area can be expressed as: (2-8)； In the above formula, (2-9)； (2-10)； (2-11)； (2-12)； (2-13)； (2-14)； Substituting equations (2-9) to (2-14) derived above into equation (2-5), the flow area of ​​the improved unloading tank can be obtained: (2-15); in, is the depth angle, is the width angle, R is the pitch circle of the valve plate, is the central angle of the arc tangent to the quadrilateral, is the ratio of line segment ab to line segment cd, R 1 is the radius of the arc tangent to the quadrilateral.

5. The method for reducing and simulating the flow-induced noise of the unloading groove of a closed axial piston pump according to claim 1 is characterized in that: The step S3 specifically includes: (1) Establish the flow domain model of internal parts, including the flow domain of inlet and outlet flow channels, the flow domain inside the distribution plate, the flow domain inside the cylinder body, and the flow domain inside the plunger cavity; (2) Establishing a flow turbulence model: Based on the assumption of energy transfer and dissipation process of turbulent motion, the short-term turbulent structure in turbulent flow is modeled, and the transport equations of turbulent kinetic energy and turbulent dissipation rate are solved to estimate the length scale and turbulent dissipation rate of turbulence, thereby calculating the motion characteristics of turbulence; (3) Grid the watershed model and set boundary conditions: based on the rated operating conditions of the plunger pump, set the inlet and outlet pressures, speed, and swash plate inclination angle.

6. The method for reducing and simulating the flow-induced noise of the unloading groove of a closed axial piston pump according to claim 5 is characterized in that: (2) Establishing the flow turbulence model: The transport equation of turbulent kinetic energy can be written as: （3-1）; The transport equation for the dissipation rate can be written as: （3-2）； in, represents the turbulent kinetic energy due to the mean velocity gradient; represents the turbulent kinetic energy due to the buoyancy effect; It represents the effect of compressible turbulent pulsation expansion on the total dissipation rate; represents the turbulent viscosity coefficient; the constant parameter value in the formula is: ; ; ; Turbulent kinetic energy and dissipation rate The turbulent Prandtl numbers are: ; .

7. The method for reducing and simulating the flow-induced noise of the unloading groove of a closed axial piston pump according to claim 1 is characterized in that: The sound field characteristic simulation of step S4 specifically includes the following steps: (1) An acoustic model is constructed based on the internal flow domain of the plunger pump, including the sound source domain, the sound propagation domain, and the infinite element domain. The "hemispherical method" is used to arrange acoustic monitoring points 1#, 2#, and 3# to simulate the noise at a radius of 1 m with the plunger pump as the center; (2) The acoustic analogy method is selected as the Lighthill acoustic analogy method, and its mathematical model can be derived as follows: （4-1）; In the formula, is the fluid density, is the undisturbed fluid density, is the speed of sound in the undisturbed fluid, is the fluid velocity component, is the velocity component of the solid boundary motion, is the fluid pressure, is the viscous stress tensor component, is the unit tensor component, f is a function related to the shape and motion of the solid boundary; (3) The acoustic model is meshed, and at least 6 acoustic meshes must be present within one wavelength to ensure the accuracy of the acoustic simulation, that is, ; In the formula, is the grid size, is the minimum wavelength, is the speed of sound propagation in the fluid medium, To calculate the maximum frequency required; (4) Add frequency response analysis and assign physical parameters to the flow medium and propagation medium, and set boundary conditions such as volume sound source and surface sound source; (5) Add ICFD component, import the above flow field simulation results into the sound source domain as the flow induced noise source, add sound source modeling component, select interpolation method for calculation, and finally add DFT component to convert time domain signal into frequency domain signal for frequency response analysis; (6) After the calculation is completed, the sound pressure levels of different frequencies are converted into the total sound pressure level according to the following method in order to evaluate the noise level.

8. The method for reducing and simulating the flow-induced noise of the unloading groove of a closed axial piston pump according to claim 7 is characterized in that: In step (1): the length, width and height of the test pump shall not exceed 0.3m, and the radius R of the sphere shall be at least twice the maximum dimension of the test pump and shall not be less than 1m.

9. The method for reducing and simulating the flow-induced noise of the unloading groove of a closed axial piston pump according to claim 7, characterized in that: In step (2): The first term on the right side of the equal sign in the formula is the quadrupole sound source term caused by turbulent motion, the second term is the dipole sound source term excited by the solid wall pressure pulsation, and the third term is the monopole sound source term caused by the fluid pressure pulsation; ①Perform strong variation on equation (4-1) and consider density and speed They are all functions of space and time, introducing variational notation To represent small changes in these quantities, and in the spatial domain Integrate on; that is: （4-2）; ②At the border Perform partial integration on the above, and we get the expression after weak variation: （4-3）; ③ Consider boundaries and express it using the stress tensor: （4-4）; ④Let , and expand it to get: （4-5）; On the right side of the equation, the first term represents the contribution of the volume integral, while the second term reflects the effect of the surface integral; both terms include the effects of monopole, dipole, and quadrupole sound sources.

10. The method for reducing and simulating the flow-induced noise of the unloading groove of a closed axial piston pump according to claim 7, characterized in that: In step (6): ①Convert the sound pressure level of each frequency band into a linear energy value: For each octave the sound pressure level , first calculate the corresponding energy ratio: (4-6); ②Add the energy values ​​of all the multiple frequencies: Add the converted linear energy values ​​to get the total energy value: (4-7); ③Convert the total energy value back to the total sound pressure level: (4-8)。

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