A method for reducing and simulating the flow-induced noise of the unloading groove of a closed axial piston pump

Abstract

The present invention discloses a method for reducing and simulating the flow-induced noise of a closed axial piston pump unloading groove, including a structural 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 present invention is different from the optimization method of building a mathematical model and finding the optimal structural parameters through an algorithm. The following steps are included: S1: Propose an improved structure for the triangular unloading groove structure based on the working principle of the unloading groove; S2: Calculate and compare the structural parameters before and after the improvement; S3: Establish a flow field model and calculate the flow field characteristics before and after the improvement; S31: Establish a flow field model; S32: Set the corresponding flow field boundary conditions; S33: Calculate the flow field characteristics; S4: Establish an acoustic field model and calculate the acoustic field characteristics before and after the improvement; S41: Establish an acoustic field model; S42: Set the corresponding acoustic field boundary conditions; S43: Calculate the acoustic field characteristics before and after the improvement; Verify the effects before and after the improvement through the steps of S3 and S4.

Description

Technical Field

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

[0002] As one of the important equipment, the noise generated by the piston pump has an inestimable impact on the health and work efficiency of the operators. In order to protect the health of the workers and the tranquility of the environment, strict regulations and standards have been formulated in many countries and regions to limit the noise level generated by industrial equipment. Piston pumps usually work under high-pressure and high-speed conditions, and the noise generated by them is even more inestimable. 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 a closed axial variable piston pump.

[0003] At present, the research on the technology for reducing the flow-induced noise of axial piston pumps mainly focuses on the structural improvement of the valve plate pair. Specifically, it is studied by the structure affecting the flow field characteristics and then radiating to the sound field characteristics. The oil in the piston pump undergoes a throttling process when passing through the unloading groove. The oil flow rate through the unloading groove is directly related to the cross-sectional area of the unloading groove, that is to say, 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 valve plate matching process of the piston pump. The oil passing speed, the oil flow rate, and the oil backflow will vary according to the different structures of the unloading groove. At the same time, the oil speed, flow rate, and backflow affect the flow pulsation of the piston pump, which is the key factor causing the vibration and noise of the piston pump. Therefore, how to determine a suitable structure of the unloading groove is the key method for reducing the flow-induced noise of the piston pump and also a challenge faced by the technical field of hydraulic components.

[0004] In order to further study and verify the relationship between the structure of the unloading groove and the flow-induced noise, the simulation process of the flow field characteristics and the sound field characteristics is essential. By means of simulation, further in-depth study of the flow field characteristics and the sound field distribution during the valve plate matching process of the piston pump is carried out to verify whether the structure of the unloading groove is reasonable and effective. At the same time, the correct simulation means can provide support for theory and experiment, reasonably reduce the R & D cost, improve the R & D efficiency, and promote the structural improvement of the piston pump, which has important application prospects. Summary of the Invention

[0005] 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. Different from the optimization method of building a mathematical model and finding the optimal structural parameters through algorithms, the present invention proposes an improved triangular groove structure based on the working principle of the unloading groove to achieve the purpose of noise reduction.

[0006] To achieve the above object, the present invention is realized as follows for solving the above technical problems:

[0007] A method for reducing and simulating the flow-induced noise of the unloading groove of a closed axial piston pump, comprising the following steps:

[0008] S1: Based on the working principle of the unloading groove, an improved structure for the triangular unloading groove is proposed; the method for improving the triangular unloading groove structure in step S1 specifically includes: when the flow distribution kidney-shaped window aligns with the plunger hole of the cylinder block, a pressure difference will be generated between the internal fluid in the plunger chamber and the fluid in the distribution area, resulting in a throttling effect;

[0009] S2: Calculate and compare the structural parameters before and after the improvement;

[0010] S3: Establish a flow field model and calculate the flow field characteristics before and after the improvement;

[0011] S31: Establish a flow field model; according to the assembly relationship of the internal parts of the closed axial piston pump, establish the flow domain model of the internal parts;

[0012] S32: Set the corresponding flow field boundary conditions; perform mesh division on the flow domain model and set the boundary conditions;

[0013] S33: Calculate the flow field characteristics; at the same time, assign physical parameters to the flowing medium, add the flow components of the piston pump, start the simulation, and obtain the flow field simulation results of the closed axial piston pump;

[0014] S4: Establish a sound field model and calculate the sound field characteristics before and after the improvement;

[0015] S41: Establish a sound field model;

[0016] S42: Set the corresponding sound field boundary conditions;

[0017] S43: Calculate the sound field characteristics before and after the improvement; verify the effects before and after the improvement through the steps of S3 and S4.

[0018] On the basis of the above solution and as the preferred solution of the above solution: In step S1, the bottom of the triangular unloading groove is improved to an arc structure.

[0019] Based on the above solution and as an optimized solution of the above solution: The throttling effect can be described by the following throttling formula:

[0020]

[0021] Wherein, q t represents the throttling flow rate in the high-pressure area, q n represents the throttling flow rate in the low-pressure area, C v is the throttling coefficient of the hydraulic oil; A hp represents the flow-through area of the high-pressure area, A lp represents the flow-through area of the low-pressure area; p h , p l and p f are the oil pressures in the high-pressure area, low-pressure area and plunger cavity respectively; ρ is the density of the oil.

[0022] Based on the above solution and as an optimized solution of the above solution: In step S2, the flow-through area of the unloading groove will be calculated using a geometric method, and the flow-through areas before and after the improvement will be compared, as follows:

[0023] The flow-through area of the improved unloading groove structure can be expressed as follows:

[0024] S 2 = S quadrilateral·abcd + S Arc·abo - S Triangular·abo (2-5);

[0025] The area of trapezoid abcd can be expressed as:

[0026]

[0027] The area of sector abo can be expressed as:

[0028]

[0029] And, the area of triangle abo can be expressed as:

[0030]

[0031] In the above formula,

[0032]

[0033] Substitute the equations (2-9) to (2-14) derived above into equation (2-5), and the flow-through area of the improved unloading groove can be obtained:

[0034]

[0035] Wherein, θ 1is the depth angle, θ 2 is the width angle, R is the pitch circle of the port plate, β is the central angle of the quadrilateral tangent arc, k 1 is the ratio of line segment ab to line segment cd, R 1 is the radius of the quadrilateral tangent arc.

[0036] Based on the above scheme and as an optimized scheme of the above scheme: The specific steps of step S3 include:

[0037] (1) Establish the flow domain model of the internal parts, including: the inlet and outlet flow channel domain, the internal domain of the port plate, the internal domain of the cylinder block, and the internal domain of the plunger cavity;

[0038] (2) Establish a flow turbulence model: Based on the assumptions of the energy transfer and dissipation processes of turbulent motion, by modeling the short-term turbulent structures in turbulent flow, solve the transport equations of turbulent kinetic energy and turbulent dissipation rate to estimate the length scale and turbulent dissipation rate of turbulence, so as to calculate the motion characteristics of turbulence;

[0039] (3) Mesh the flow domain model and set boundary conditions: Based on the rated operating conditions of the piston pump, set the inlet and outlet pressures, rotational speed, and swash plate angle.

[0040] Based on the above scheme and as an optimized scheme of the above scheme: In (2) establishing the flow turbulence model:

[0041] The transport equation of turbulent kinetic energy can be written as:

[0042]

[0043] The transport equation of dissipation rate can be written as:

[0044]

[0045] Among them, G k represents the turbulent kinetic energy caused by the average velocity gradient; G b represents the turbulent kinetic energy caused by the buoyancy effect; Y M represents the influence of the compressible turbulent pulsation expansion on the total dissipation rate; μ t represents the turbulent viscosity coefficient; the values of the constant parameters in the formula are: C 1ε = 1.44; C 2ε = 1.92; C 3ε = 0.09; the turbulent Prandtl numbers of turbulent kinetic energy k and dissipation rate ε are respectively: σ k = 1.0; σ ε = 1.3.

[0046] Based on the above scheme and as an optimized scheme of the above scheme: The specific steps of the sound field characteristic simulation in step S4 are as follows:

[0047] (1) Construct an acoustic model based on the internal flow domain of the plunger pump, including: the sound source domain, the sound propagation domain, and the infinite element domain. Use the "hemisphere method" to arrange the acoustic monitoring points 1#, 2#, and 3# to simulate the noise at a distance of 1 m from the center of the plunger pump.

[0048] (2) Select the acoustic analogy method as the Lighthill acoustic analogy method, and its mathematical model can be derived as follows:

[0049]

[0050] In the formula, ρ is the fluid density, ρ 0 is the density of the undisturbed fluid, c 0 is the speed of sound in the undisturbed fluid, u i is the fluid velocity component, U n is the solid boundary motion velocity component, p is the fluid pressure, τ in is the viscous stress tensor component, δ in is the unit tensor component, and f is a function related to the shape and motion of the solid boundary;

[0051] (3) Mesh the acoustic model. It is necessary to ensure that there are at least 6 acoustic meshes within 1 wavelength to guarantee the accuracy of the acoustic simulation, that is

[0052] In the formula, L is the mesh size, λ min is the minimum wavelength, c 0 is the speed of sound propagation in the fluid medium, f max is the maximum frequency required for the calculation;

[0053] (4) Add frequency response analysis and assign the physical parameters of the flowing medium and the propagation medium. At the same time, set the boundary conditions of the volume sound source and the surface sound source;

[0054] (5) Add the ICFD component, import the above flow field simulation results into the sound source domain as the flow-induced noise source. At the same time, 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 a frequency-domain signal for frequency response analysis;

[0055] (6) After the calculation, convert the sound pressure levels of different octaves into the total sound pressure level according to the following method to evaluate the noise level.

[0056] Based on the above scheme and as the preferred scheme of the above scheme: In step (1): The dimensions of the length, width, and height of the test pump do not exceed 0.3 m, and the radius R of the sphere is at least 2 times the maximum dimension of the test pump and not less than 1 m.

[0057] Based on the above - mentioned solution and as an optimized solution of the above - mentioned solution: In step (2):

[0058] The first term on the right - hand side of 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 fluctuation, and the third term is the monopole sound source term caused by the fluid pressure fluctuation;

[0059] ① Strongly vary equation (4 - 1). Considering that both the density ρ and the velocity u are functions of space and time, introduce the variation symbol δ to represent the small changes of these quantities, and at the same time integrate over the spatial domain Ω; that is:

[0060]

[0061] ② Perform integration by parts on the boundary Γ to obtain the expression after weak variation:

[0062]

[0063] ③ Consider the surface integral on the boundary and represent it using the stress tensor:

[0064]

[0065] ④ Let in the above formula and expand it to obtain:

[0066]

[0067] On the right - hand side of the equation, the first term represents the contribution of the volume integral, while the second term reflects the influence of the surface integral; both of these two terms cover the influences of monopole, dipole, and quadrupole sound sources.

[0068] Based on the above - mentioned solution and as an optimized solution of the above - mentioned solution: In step (6):

[0069] ① Convert the sound pressure level of each frequency band into a linear energy value:

[0070] For the sound pressure level SPL of each octave i , first calculate its corresponding energy ratio:

[0071]

[0072] ② Add up the energy values of all octaves:

[0073] Add up the converted linear energy values to obtain the total energy value:

[0074]

[0075] ③ Convert the total energy value back to the total sound pressure level:

[0076] SPL total = 10 × log 10 (L total )(4 - 8).

[0077] The prominent and beneficial technical effects of the present invention compared with the prior art are as follows:

[0078] (1) Compared with the traditional triangular unloading groove, the improvement 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 reverse flow of the plunger pump during operation, and reducing the flow rate and pressure pulsation of the plunger pump.

[0079] (2) Through acoustic simulation, it is more convenient to observe the specific magnitude 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.

[0080] (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 universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1 It is a flowchart of a method for reducing and simulating the flow-induced noise of the unloading groove of a closed axial piston pump according to an embodiment of the present invention.

[0082] Figure 2 It is a schematic diagram of the improved method of the triangular unloading groove according to an embodiment of the present invention.

[0083] Figure 3 It is a schematic diagram of the triangular groove structure before improvement according to an embodiment of the present invention.

[0084] Figure 4 It is a schematic cross-sectional view of the improved unloading groove according to an embodiment of the present invention.

[0085] Figure 5 It is a comparison diagram of the flow area of the unloading groove before and after improvement according to an embodiment of the present invention.

[0086] Figure 6 It is a schematic diagram of the flow field model according to an embodiment of the present invention.

[0087] Figure 7 It is the flow field grid parameter setting according to an embodiment of the present invention.

[0088] Figure 8 It is the flow field rotor grid template setting according to an embodiment of the present invention.

[0089] Figure 9 It is the flow field characteristic curve obtained by calculation according to an embodiment of the present invention.

[0090] Figure 10 Schematic diagram of the acoustic model according to an embodiment of the present invention

[0091] Figure 11 Monitoring points set for the sound field according to an embodiment of the present invention

[0092] Figure 12 Frequency response curves of Monitoring Point 1 before and after improvement according to an embodiment of the present invention

[0093] Figure 13 Frequency response curves of Monitoring Point 2 before and after improvement according to an embodiment of the present invention

[0094] Figure 14 Frequency response curves of Monitoring Point 3 before and after improvement according to an embodiment of the present invention

[0095] Figure 15 Overall sound pressure levels of each monitoring point before and after improvement according to an embodiment of the present invention Detailed implementation manners

[0096] The present invention will be further described below with specific embodiments in conjunction with the accompanying drawings;

[0097] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be 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.

[0098] As Figure 1 shown in the flowchart of the method for reducing and simulating the flow-induced noise of the unloading groove of a closed axial piston pump, in an embodiment of the present invention, a method for reducing and simulating the flow-induced noise of the unloading groove of a closed axial piston pump, the method includes:

[0099] Step 1: The unloading groove, as a key component of the piston pump, 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 oil flow direction and velocity, the unloading groove can ensure that the hydraulic system maintains a stable pressure during operation.

[0100] Determine the working principle of the unloading groove of the piston pump, and determine the improvement scheme for reducing the flow-induced noise of the unloading groove according to the working principle; its working principle is based on the throttling characteristics in fluid mechanics, playing a role in pre-boosting and pre-reducing pressure to avoid cavitation damage and vibration noise caused by excessive pressure difference of the flow distribution pair.

[0101] When the flow distribution kidney-shaped window aligns with the piston hole of the cylinder block, a pressure difference will be generated between the internal fluid in the piston chamber and the fluid in the distribution area, resulting in a throttling effect. This effect can be described by the following throttling formula:

[0102]

[0103] Among them, q t represents the throttling flow rate in the high-pressure region, and q n represents the throttling flow rate in the low-pressure region. C v is the throttling coefficient of the oil; A hp represents the flow-through area of the high-pressure region, and A lp represents the flow-through area of the low-pressure region. p h , p l and p f are the oil pressures in the high-pressure region, low-pressure region, and plunger cavity respectively; ρ is the density of the oil.

[0104] According to Equation (1-1), the flow-through areas A hp and A lp have a linear relationship with the throttling flow velocity, and the throttling flow velocity is an important parameter related to the flow velocity in the flow distribution process. The improved structure of the unloading groove can expand the flow-through area, thereby increasing the throttling flow velocity and reducing the backflow. Therefore, the amplitude of the flow pulsation of the plunger pump is effectively reduced, and the vibration and noise are also reduced accordingly.

[0105] When the structure of the unloading groove changes, it will affect the size of the flow-through area in the throttling characteristics, and ultimately the flow rate through the unloading groove will change. When the flow rate through the unloading groove increases within a reasonable range, the velocity of the flowing medium in the unloading groove increases, which will shorten the time required for pre-pressure increase and pre-pressure decrease. In this way, the flow rate backflow generated during this process can be reduced, and the flow pulsation can be suppressed.

[0106] Step 1.2: According to the above working principle, the present invention takes the standard triangular unloading groove as the object of improvement. Figure 2 shows the structure and parameters of the standard unloading groove, including the depth angle θ 1 , the width angle θ 2 , the pitch circle radius R of the distribution disk, and the central angle Δθ of the unloading groove. The new structure proposed by the present invention is derived from the triangular unloading groove and maintains the same structural parameters θ 1 , θ 2 and Δθ. Without changing the depth angle, width angle, and central angle of the original structure, the triangular bottom is improved to be circumscribed by an arc, as shown in Figure 2 . The improved unloading groove increases the flow-through area, thereby increasing the throttling flow velocity. Therefore, during the flow distribution process, the backflow rate is reduced, thereby suppressing the flow and pressure pulsations.

[0107] The advantages of improving the bottom of the triangular unloading groove into an arc structure are as follows: (a) The arc-shaped structure has less resistance and pressure loss during the fluid flow process. The fluid can pass through more smoothly, with a large flow capacity and high flow efficiency. (b) The arc-shaped structure can ensure that the fluid is evenly distributed across the entire pipe cross-section during the flow process, 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 the depth angle, width angle, and transition angle, by changing the cross-sectional area of the unloading groove and connecting the triangular bottom with an arc, the flow area is calculated and increased, changing its flow field characteristics. When the plunger cavity transitions from the oil suction area to the oil discharge area, the hydraulic oil in the plunger pump is pre-boosted and pre-depressurized, achieving the weakening of flow pulsation and pressure pulsation, and thus effectively reducing the noise of the plunger pump.

[0108] Step 2: Calculate the flow area of the unloading groove using geometric methods, specifically as follows:

[0109] The flow area A of the triangular groove 0 is related to the specific cross-sectional area of the triangular prism, as Figure 3 shown by Δbcd in, where Δfgh represents the working surface in contact with the kidney-shaped window of the cylinder block, and the angle formed with the straight line af is the depth angle θ of the triangular groove 1 ; O is the center of the distribution circle of the valve plate, and cd is the arc generated when the plunger hole contacts the triangular groove. Since the radius of the distribution circle is much larger than the arc length of cd, the arc cd can be regarded as a straight line. The angle formed by ac and ad represents the width angle of the triangular groove, i.e., θ 2 ; the opening angle of the triangular groove is represented by Δθ, and the radius of the distribution circle of the valve plate is represented by R; Δacd is the cross-section perpendicular to ef, and its area is the flow area A in engineering calculations 0 .

[0110]

[0111] Among them

[0112] ae = ef·tanθ 1 = R·θtanθ 1 (2-2);

[0113]

[0114] Therefore, the relationship between the flow area S between the kidney-shaped groove and the unloading groove and the cylinder block rotation angle θ can be calculated by the following formula:

[0115]

[0116] Similarly, the flow area of the improved unloading groove can also be obtained through geometric calculation. Figure 4Shows the cross-section of the improved unloading groove. The flow area of this part can be approximated as the sum of the areas of quadrilateral abcd and sector abo (excluding triangle abo). In addition, the radius R of circle afb 1 is a function of the rotation angle θ.

[0117] Therefore, the flow area of the improved unloading groove structure can be expressed as follows:

[0118] S 2 = S quadrilateral·abcd + S Arc·abo - S Triangular·abo (2 - 5);

[0119] The area of trapezoid abcd can be expressed as:

[0120]

[0121] The area of sector abo can be expressed as:

[0122]

[0123] And the area of triangle abo can be expressed as:

[0124]

[0125] In the above formula,

[0126]

[0127]

[0128] Substitute the equations (2 - 9) to (2 - 14) derived above into equation (2 - 5), and the flow area of the improved unloading groove can be obtained:

[0129]

[0130] where, θ 1 is the depth angle, θ 2 is the width angle, R is the pitch circle of the distributor disk, β is the central angle of the quadrilateral tangent arc, k 1 is the ratio of line segment ab to line segment cd, R 1 is the radius of the quadrilateral tangent arc.

[0131] 2.1 Plot the flow areas of the unloading grooves before and after improvement using drawing software, as shown in Figure 5 shown.

[0132] These two flow field curves are parabolic in shape, and the flow field is a quadratic function of the cylinder block rotation angle. In addition, the flow field variation of the improved unloading groove is similar to that of the triangular groove. Finally, during the entire flow rate distribution process, it is observed that the flow-through area of the improved unloading groove is larger than that of the triangular unloading groove. Specifically, when the width angle θ 1 and the depth angle θ 2 remain unchanged, the maximum flow-through area increases from 0.606 mm 2 to 0.813 mm 2 . The improved unloading groove effectively increases the flow-through area during the entire distribution process, with a maximum increase of 34.15%.

[0133] Step 3: Establish a flow field mathematical model and calculate the flow field characteristics before and after improvement

[0134] 3.1 Establish a flow field mathematical model

[0135] Based on the working principle of the swash plate axial piston pump, the internal flow domain of the piston pump is extracted using CAD software to obtain the fluid domain model as shown Figure 6 . It includes the suction and discharge oil flow channels, the cylinder block piston empty flow channel, the piston flow channel, and the port plate kidney-shaped window flow channel of the piston pump.

[0136] Establish a flow turbulence model: Based on the assumptions of the energy transport and dissipation processes of turbulent motion, by modeling the short-term turbulent structures in turbulent flow, the transport equations of turbulent kinetic energy and turbulent dissipation rate are solved to estimate the turbulent length scale and turbulent dissipation rate, thereby calculating the motion characteristics of turbulence.

[0137] The transport equation of turbulent kinetic energy can be written as:

[0138]

[0139] The transport equation of the dissipation rate can be written as:

[0140]

[0141] Among them, G k represents the turbulent kinetic energy caused by the average velocity gradient; G b represents the turbulent kinetic energy caused by the buoyancy effect; Y M represents the influence of the compressible turbulent pulsation expansion on the total dissipation rate; μ t represents the turbulent viscosity coefficient. The values of the constant parameters in the formula are: C 1ε = 1.44; C 2ε = 1.92; G 3ε = 0.09; The turbulent Prandtl numbers of the turbulent kinetic energy k and the dissipation rate ε are respectively: σ k = 1.0; σ ε = 1.3.

[0142] 3.2 Set the corresponding flow field boundary conditions

[0143] For the piston pump with the model number SA10VG18, set the inlet and outlet pressures to 0.3 MPa and 30 MPa respectively, the rotational speed to 2600 RPM, and the swash plate angle to 18°. Through model establishment, mesh generation, template selection, setting of flowing medium parameters, and setting of the overall working conditions of the piston pump.

[0144] To improve the accuracy of mesh generation, different mesh generation techniques are applied in different flow channel regions to generate high-quality meshes. In regions such as the oil suction and discharge flow channels of the pump and the kidney-shaped windows of the flow distribution components, conventional mesh generation techniques are adopted. Refine the meshes in these regions by adjusting the mesh control parameters to ensure the accuracy of the simulation results. The specific settings are as Figure 7 shown.

[0145] When the piston pump is working, on the one hand, the piston in the piston hole of the cylinder block rotates around the main shaft as the cylinder block rotates, and on the other hand, it extends and retracts along the axis direction in the hole. This compound motion causes the flow domain in the piston hole of the cylinder block to change at all times. To accurately simulate this complex motion form, use the swash plate axial piston pump mesh template (SwashPlatePiston) built into the PumpLinx software to generate the mesh of the rotor. This mesh template integrates dynamic mesh and sliding mesh technologies, can fully meet the motion form of the piston during operation, and takes into account the characteristics of the rotation and expansion of the rotor, thus effectively simulating the working process of the piston pump. The generated mesh is as Figure 8 shown.

[0146] 3.3 Calculate the flow field characteristics before and after improvement

[0147] Carry out simulation and obtain the corresponding results, as Figure 9 shown.

[0148] Figure 9 In the figure a in , it shows the outlet flow rate of the piston pump at different load pressures within the working angles of two pistons. It can be seen from the figure that the outlet flow rate shows a similar trend at different load pressures. When the piston hole window is connected to the unloading groove of the cylinder block, since the pressure in the piston cavity has not yet risen to the load level, there is a pressure difference between the piston cavity and the high pressure at the discharge end, resulting in backflow of the oil, causing a significant drop in the flow rate. Subsequently, due to the rapid rise in pressure in the piston hole, the oil starts to be discharged through the top window, and the outlet flow rate continues to increase until it reaches the maximum point. This explains Figure 9The peaks and valleys in a of []. By comparing the simulation results of the improved groove and the triangular groove, it can be seen that the improved unloading groove can effectively reduce the flow reversal during the operation of the plunger pump under different load pressures. When the load pressure is 30 MPa, the flow reversal reaches the maximum reduction, and the maximum reduction of the flow reversal is 12.9%.

[0149] Figure 9 b in [] shows the change of the plunger chamber pressure under different load pressures when the plunger pump rotates one week. The change trend of the pressure in the plunger chamber remains consistent under different load pressures. At the same time, as the load pressure increases, the average pressure in the plunger chamber also increases. Because the flow reversal finally reaches the plunger chamber, causing a sudden change in the pressure in the plunger chamber. 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 chamber under various load pressures, and the maximum pressure fluctuation reduction can reach 10.6% at 30 MPa.

[0150] 3.4 Export the flow field calculation results

[0151] The output of the flow field calculation results requires identifying, reading the results of the flow field calculation, and converting the internal flow into a sound source term through the ICFD (Integral Interpolation Computational Fluid Dynamics Data Processing Module) component. The method for outputting the CFD (Computational Fluid Dynamics) flow field results is as follows: In the PumpLinx software, output and save the results of the unsteady calculation in the EnsightGold format. At the same time, after outputting the Ensight Gold file, the header file encas in it needs to be changed. In the "model (model)" column, select the last time step 1080 of the calculation. At the same time, add 4 * signs corresponding to the time step in the following "density (density)", "velocity (velocity)", and "pressure (pressure)". Only in this way can the exported Ensight Gold file be recognized by the subsequent acoustic simulation software Actran, enabling the subsequent sound field simulation to proceed normally.

[0152] Step 4: Establish a sound field model and calculate the sound field characteristics before and after improvement

[0153] 4.1 Establish a sound field model

[0154] Based on the internal flow domain of the plunger pump, an acoustic model is constructed, including: the sound source domain, the sound propagation domain, and the infinite element domain. In acoustic simulations, simplified boundary conditions or flow models (such as plane wave assumptions, simplified geometries, etc.) are often used to make the simulation more efficient and reduce the complexity of the model, such as Figure 10As shown in the figure; at the same time, referring to relevant standards, the "hemisphere method" is adopted to arrange the acoustic monitoring points 1#, 2#, and 3#. The length, width, and height of the test pump do not exceed 0.3 m, and the radius R of the sphere is at least twice the maximum size of the test pump and not less than 1 m. Due to the limitation of the test site size, finally R = 1 m is determined. Therefore, it is used to simulate the noise at a radius of 1 m with the plunger pump as the center, as Figure 11 shown;

[0155] The sound analogy method is selected as the Lighthill sound analogy method, and its mathematical model can be derived as follows:

[0156]

[0157] In the formula, ρ is the fluid density, ρ 0 is the density of the undisturbed fluid, c 0 is the speed of sound in the undisturbed fluid, u i is the fluid velocity component, U n is the solid boundary motion velocity component, p is the fluid pressure, τ in is the viscous stress tensor component, δ in is the unit tensor component, and f is a function related to the shape and motion of the solid boundary.

[0158] 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.

[0159] ① Strongly vary the equation (4-1). Considering that both the density ρ and the velocity u are functions of space and time, the variational symbol δ is introduced to represent the small changes in these quantities, and at the same time, an integral is performed over the spatial domain Ω. That is:

[0160]

[0161] ② Perform integration by parts on the boundary Γ to obtain the expression after weak variation:

[0162]

[0163] ③ Consider the surface integral on the boundary and represent it using the stress tensor:

[0164]

[0165] ④ Let in the above formula and expand it to obtain:

[0166]

[0167] On the right side of the equation, the first term represents the contribution of the volume integral, while the second term reflects the influence of the surface integral. Both terms cover the effects of monopole, dipole, and quadrupole sound sources.

[0168] 4.2 Set the corresponding acoustic field boundary conditions

[0169] The acoustic model will be meshed, and it is necessary to ensure that there are at least 6 acoustic meshes within 1 wavelength to guarantee the accuracy of the acoustic simulation, that is In the formula, L is the mesh size, λ min λ min is the minimum wavelength, c 0 c 0 is the sound propagation speed in the fluid medium, f max is the maximum frequency required for the calculation;

[0170] Set the material, add the physical parameters of 46# anti-wear hydraulic oil. The sound speed is 1380 m / s and the density is 875 kg / m 3 . At the same time, add the propagation medium air in the sound propagation domain. The sound speed is 340 m / s and the density is 1.225 kg / m 3 .

[0171] Add the frequency response analysis component, select the NFF format in the Format option, and locate the File file name as freq.nff. The maximum frequency is set to nine times the frequency 3510 Hz. Add acoustic1 (acoustic component No. 1) in Component (acoustic component), set the material to the above-mentioned 46# anti-wear hydraulic oil, and at the same time select Lighthill_Volume (volume sound source) and Lighthill_surface (surface sound source) for Domain Assignation (domain name assignment). Then add acoustic 2 (acoustic component No. 2), set the material to air, and select Transition (transition domain) for Domain Assignation (domain name assignment). Finally, add the infinite_acoustic (infinite element domain) acoustic component, set the material to air, set the Interpolation Order (interpolation order) to 10, and select Infinite (infinite element domain) for Domain Assignation (domain name assignment). Finally, click Compute center from scope (calculate the geometric center) and Automatic spherical system (automatic spherical generation).

[0172] The conversion between time-domain signals and frequency-domain signals, adding an ICFD (Integral Interpolation Computational Fluid Dynamics Data Processing Module) component, and adding a Caasource (Sound Source Modeling Component) to the ICFD component. Input the Ensight Gold file exported from the flow field simulation here, and 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 the interpolation method in Advances. Finally, add a DFT (Discrete Fourier Transform) component, and select the Hanning window for the window function.

[0173] Start the frequency response analysis. Export the above-set frequency response analysis components for the ICFD (Integral Interpolation Computational Fluid Dynamics Data Processing Module) component to successfully calculate the conversion between time-domain signals and frequency-domain signals, and then the frequency response analysis can be started to obtain the acoustic field characteristics.

[0174] After the calculation is completed, convert the sound pressure levels at different octaves into the total sound pressure level according to the following method to evaluate the noise level:

[0175] ① Convert the sound pressure level of each frequency band into a linear energy value:

[0176] For the sound pressure level SPL of each octave i , first calculate its corresponding energy ratio:

[0177]

[0178] ② Add up the energy values of all octaves:

[0179] Add up the converted linear energy values to obtain the total energy value:

[0180]

[0181] ③ Convert the total energy value back to the total sound pressure level:

[0182] SPL total =10×log 10 (L total ) (4 - 8);

[0183] The sound pressure curves at 1 m outside the plunger pump before and after the improvement obtained by simulation are as Figure 12 、 13, as shown in Fig. 14. It can be known from the frequency spectrum curves obtained from 3 different test points that the improved unloading groove structure can reduce the noise generated by the operation of the plunger pump at different frequencies. Among each test point, the improved structure can reduce the flow noise by 5 - 8 dB at different octave frequencies, and the maximum noise reduction reaches 9.6%. The improved noise is generally distributed in the range of 60 - 80 dB. In order to more intuitively observe the effect of noise reduction, the corresponding overall sound pressure levels are calculated from the frequency spectrum curves obtained at the above 3 monitoring points, as Figure 15 shown. The maximum noise and the most significant noise reduction are both collected at the 2# test point. The overall sound pressure values reduced at the three points are 5.16 dB, 6.53 dB, and 4.65 dB respectively, and the noise reduction reaches 6.33%, 7.41%, and 5.59%.

[0184] Adopting the method of the present invention can achieve the reduction of the flow-induced noise of the closed axial piston pump and study the sound pressure in its fluid domain. Moreover, compared with the traditional numerical simulation method, it can improve the simulation efficiency.

[0185] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of this invention is usually placed during use, or the orientation or positional relationship commonly understood by those skilled in the art. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0186] The above embodiments are only preferred embodiments of the present invention, and do not limit the protection scope of the present invention accordingly. Therefore, all equivalent changes made according to the structure, shape, and principle of the present invention should be covered within 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: Among them, q t represents 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 Indicates the flow area of ​​the high-pressure region, A lp Indicates the flow area of ​​the low pressure area; p h 、p l and p f are the oil pressures in the high-pressure area, low-pressure area and plunger cavity respectively; ρ 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: S2=S quadrilateral·abcd +S Arc·abo -S Triangular·abo (2-5); The area of ​​trapezoid abcd can be expressed as: The area of ​​sector abo can be expressed as: And, the area of ​​triangle abo can be expressed as: In the above formula, Substituting equations (2-9) to (2-14) derived above into equation (2-5), the flow area of ​​the improved unloading tank can be obtained: Among them, θ1 is the depth angle, θ2 is the width angle, R is the pitch circle of the distribution plate, β is the central angle of the quadrilateral tangent arc, k1 is the ratio of line segment ab to line segment cd, and R1 is the radius of the quadrilateral tangent arc.

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: The transport equation for the dissipation rate can be written as: Among them, G k represents the turbulent kinetic energy due to the mean velocity gradient; G b represents the turbulent kinetic energy caused by buoyancy; Y M represents the effect of compressible turbulent pulsation expansion on the total dissipation rate; μ t represents the turbulent viscosity coefficient; the constant parameter value in the formula is: C 1ε =1.44; C 2ε =1.92; C 3ε =0.09; the turbulent Prandtl numbers of turbulent kinetic energy k and dissipation rate ε are: σ k =1.0;σ ε =1.

3.

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: Where ρ is the fluid density, ρ0 is the undisturbed fluid density, c0 is the speed of sound in the undisturbed fluid, and u i is the fluid velocity component, U n is the velocity component of the solid boundary motion, p is the fluid pressure, τ in is the viscous stress tensor component, δ in is the unit tensor component, and 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, Where L is the grid size, λ min is the minimum wavelength, c0 is the speed of sound propagation in the fluid medium, f max 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.

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. ① Perform strong variation on equation (4-1), considering that density ρ and velocity u are functions of space and time, introduce the variational symbol δ to represent the small changes of these quantities, and integrate them over the spatial domain Ω; that is: ②Performing partial integration on the boundary Γ, we obtain the expression after weak variation: ③ Consider boundaries and express it using the stress tensor: ④Let And expand it, we get: 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 SPL i , first calculate the corresponding energy ratio: ②Add the energy values ​​of all the multiple frequencies: Add the converted linear energy values ​​to get the total energy value: ③Convert the total energy value back to the total sound pressure level: SPL total =10×log 10 (L total ) (4-8)。

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