Pump jet propeller rotor tip vortex cavitation high-precision calculation method
By performing local grid reconstruction and CFD calculation on the pump jet thruster rotor, the accurate prediction problem of vortex cavitation of the pump jet thruster rotor tip is solved, and the hydrodynamic and acoustic stealth performance of the thruster is improved.
Patent Information
- Application Number
- CN202510534517.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-27
- Publication Date
- 2025-08-08
AI Technical Summary
The prior art is difficult to accurately predict the vortex cavitation of the rotor tip of the pump jet thruster, resulting in rotor surface erosion and deterioration of the thruster performance, and it is difficult to measure complex devices and it is difficult to obtain flow field information.
Three-dimensional modeling software was used to establish a pump jet thruster model. Combined with the characteristics of tip vortex flow, the rotation domain of the pump jet thruster rotor was reconstructed locally. The LES turbulence model and SchnerrSauer cavitation model were used for CFD calculations, and the grid density was optimized to achieve high-precision prediction of tip vortex cavitation.
Accurate prediction of the vortex cavitation of the pump jet thruster tip is achieved, reducing rotor surface erosion and performance deterioration, and improving hydrodynamic performance and acoustic stealth performance.
Smart Images
Figure CN120449744A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of fluid mechanics analysis, and in particular relates to a high-precision calculation method for rotor tip vortex cavitation of a pump-jet propulsor. Background Art
[0002] As a new type of propulsion system with excellent performance, pump-jet propulsion undergoes flow separation at the rotor tip due to the pressure difference between the blade surface and the blade back during operation, which easily forms a complex vortex structure at the blade back. Due to the rotational characteristics of the vortex, the pressure at the vortex core is much lower than that of the surrounding fluid area. When the vortex core pressure falls below the saturated vapor pressure, cavitation occurs, which can cause erosion on the rotor surface, deteriorate the hydrodynamic performance of the propeller, and cause deformation of the rotor blades. Tip bleed vortex has the highest total pressure drop and the highest total pressure loss. Its impact on the propeller and propeller cannot be ignored, such as severe erosion near the blade tip, performance degradation, and unit vibration. The acoustic noise caused by tip bleed vortex has a very significant impact on the acoustic stealth performance of underwater vehicles at high speeds. Early studies generally used experimental observations. Although the experimental results were highly convincing, they placed high demands on the measurement equipment, economic costs, and time consumption. In addition, they were generally targeted at simpler models, and it was more difficult to measure the tip vortex cavitation flow field of complex devices. It was also difficult to obtain flow field information such as velocity, pressure, and acceleration at the cavitation position in order to quantitatively analyze tip vortex cavitation. Summary of the Invention
[0003] The purpose of this invention is to provide a high-precision calculation method for the tip vortex cavitation of a pump-jet propulsor rotor. Based on a commonly used multi-channel periodic structured grid and incorporating the characteristics of tip vortex flow, this method performs local mesh reconstruction within the rotating domain of the pump-jet propulsor rotor, ultimately achieving accurate prediction of the tip vortex cavitation of the pump-jet propulsor.
[0004] To achieve the above objectives, the present invention adopts the following technical solutions.
[0005] A high-precision calculation method for rotor tip vortex cavitation of a pump-jet propulsor comprises the following steps:
[0006] Step 1: Use 3D modeling software to establish a pump-jet propulsor model, wherein the pump-jet propulsor model includes a rotor model, a stator model, a hub model, and a duct model;
[0007] Step 2: Based on the structure of the pump-jet propulsor, the calculation area is divided into the outer domain of the duct, the stator domain, and the rotor domain;
[0008] The rotor domain is further divided into rotor domain 1, rotor domain 2 and rotor blade tip domain; rotor domain 1 is located on the front and rear side of the rotor close to the main shaft, including the area of rotor radius 0 to 0.92R0; rotor domain 2 is located on the side of the duct, on the front and rear sides of the rotor blade tip; the rotor blade tip domain is located in the rotor blade tip area; R0 is the rotor radius;
[0009] Step 3: Mesh the model and determine the specific mesh size and time step based on the LES turbulence model applicability evaluation criteria;
[0010] The outer domain of the duct and the stator domain use single-channel meshes, and the full-channel mesh is obtained by periodically rotating the meshes. The rotor domain 2 uses an unstructured mesh, while the rotor domain 1 and the rotor blade tip domain use a structured mesh.
[0011] Step 4: Data is transferred between the rotor domains using interfaces, keeping the meshes of the duct outer domain, stator domain, rotor domain 1, and rotor domain 2 unchanged, and only changing the mesh density of the rotor blade tip domain;
[0012] Set the rotor boundary layer and adjust the grid thickness near the rotor wall to meet the calculation requirements of the LES model;
[0013] Step 5: Establish cross sections perpendicular to the rotor axis at different axial distances from the trailing edge of the rotor blade tip, with the diameter of each cross section being consistent with the diameter of the inner wall of the duct at that location, so as to monitor the pressure distribution characteristics of each cross section;
[0014] Step 6: Perform CFD calculations and import the mesh into CFD software capable of handling complex flow problems. After importing, set boundary conditions based on the actual operating conditions. Calculate the minimum vortex core pressure monitoring results for each cross-section of the rotor blade tip at different mesh densities under a specific operating condition. Monitor the convergence and stability of the simulation process to ensure the reliability of the simulation results. Plot the time-averaged curve and obtain a comparison curve of the time-averaged vortex core pressure after adjusting the maximum mesh unit size.
[0015] Step 7: By analyzing and comparing the time-averaged vortex core pressure comparison curves in Step 6, an optimal blade tip domain grid size is selected; the selection rule is to make the vortex core pressure change tend to be stable, and the maximum change rate of the vortex core pressure on each cross section does not exceed 3%;
[0016] Step 8. Based on the blade tip domain mesh size selected in step 7, the final mesh is imported into the CFD software, and the established numerical calculation model is solved using the CFD solver. The Schnerr-Sauer cavitation model is introduced to obtain the tip vortex cavitation results.
[0017] A further improvement or preferred implementation of the aforementioned high-precision calculation method for pump-jet propulsor rotor tip vortex cavitation, in step one, the model should include: the size and shape of the duct, stator and rotor, the position and size of the rotor and stator, the number of blades of the rotor and stator, and the gap between the inner wall of the duct and the cross-section of the rotor tip.
[0018] A further improvement or preferred embodiment of the aforementioned high-precision calculation method for rotor tip vortex cavitation of a pump-jet propulsor is as follows: in step three, a single-channel grid is constructed using ICEM 16.0 for the duct outer domain and the stator domain, and a full-channel grid is obtained by periodically rotating the grid; an unstructured grid is constructed using STARCCM+ for rotor domain 2; and a structured grid constructed by ICEM 16.0 is used for rotor domain 1 and the rotor blade tip domain.
[0019] A further improvement or preferred embodiment of the aforementioned high-precision calculation method for pump-jet propulsor rotor tip vortex cavitation, wherein step four specifically includes:
[0020] According to the tip vortex track, the rotor blade tip domain shape and interval, axial length, and circumferential angle are set. The circumferential section is unfolded into a two-dimensional graph, and the computational domains of various densities are obtained by adjusting the maximum size of the grid on the edge of the computational domain block.
[0021] The rotor boundary layer is set by the O-cut method near the rotor wall, and the thickness of the first layer of grid near the wall is set, which is the rotor wall y + Meet the calculation requirements of the LES model, and the rotor tip area above 0.9R is 40≤x + ≤80,10≤z + ≤25, in the subsequent mesh adjustment process, the mesh thickness inside the boundary layer remains unchanged, and only the mesh size outside the boundary layer is changed; set the unit time step, the rotation angle within the unit time step, and the maximum number of internal iterations to ensure that the time solution meets the calculation requirements of the LES model.
[0022] A further improvement or preferred implementation of the aforementioned high-precision calculation method for tip vortex cavitation of a pump-jet propulsor rotor, wherein step five also includes: defining the distance between each axial section in units of the rotor radius R0, wherein the axial position of the cross section Δx=0.00R0 corresponds to the position of the rotor trailing edge, and when Δx / R0 is a negative value, the pressure value on the monitoring surface is the vortex core pressure before the rotor trailing edge, and when Δx / R0 is a positive value, it is the vortex core pressure in the wake.
[0023] In a further improvement or preferred embodiment of the aforementioned high-precision calculation method for pump-jet rotor tip vortex cavitation, the turbulence model in step 3 can be expressed as:
[0024]
[0025] Where: are the filtered velocity and pressure respectively; ρ is the density of the fluid; μ is the dynamic viscosity of the fluid; μ t is the subscale eddy viscosity; and is the component of velocity in different directions after filtering; t is time; x i and x j Indicators representing different spatial coordinates; t refers to time; refers to The product of is filtered.
[0026] In a further improvement or preferred embodiment of the aforementioned high-precision calculation method for the tip vortex cavitation of a pump-jet propulsor, in step eight, the Schnerr-Sauer cavitation model can be expressed as:
[0027]
[0028] Where P v is the vapor pressure; P is the local pressure; ρ v and ρ m are the steam density and the mixture density respectively; r b is the bubble radius; ρ l is the liquid density;
[0029] In the above formula, α is specifically:
[0030]
[0031] Where α is the gas volume fraction, n b is the number of cavitation bubbles per unit volume.
[0032] Cavitation radius R c It is defined by the following formula:
[0033] BRIEF DESCRIPTION OF THE DRAWINGS
[0034] Figure 1 It is a schematic diagram of the geometric model of the computational domain;
[0035] Figure 2 This is a schematic diagram of the rotor blade tip area grid division;
[0036] Figure 3 It is a schematic diagram of the rotor blade tip area outline and mesh encryption boundary position;
[0037] Figure 4 is the wall y + Schematic diagram;
[0038] Figure 5 is a schematic diagram of the Courant number;
[0039] Figure 6 Schematic diagram of monitoring section location
[0040] Figure 7 This is a schematic diagram of the outer domain grid of the catheter and its boundary conditions;
[0041] Figure 8 The average curve of the lowest pressure of the vortex core obtained by adjusting the maximum size of the mesh unit of the encrypted edge 1
[0042] Figure 9 The average curve of the lowest pressure of the vortex core obtained by adjusting the maximum size of the mesh unit of the encrypted edge 2
[0043] Figure 10 The average curve of the lowest pressure of the vortex core obtained by adjusting the maximum size of the mesh unit of the encrypted edge 3
[0044] Figure 11 It is the numerical calculation result of tip vortex cavitation when the working condition is 1100rpm. DETAILED DESCRIPTION
[0045] The present invention will be further described below with reference to the accompanying drawings. This embodiment is combined with a front stator pump-jet propulsor model to explain the invention in detail.
[0046] Step 1: Use 3D modeling software (such as SolidWorks, Catia, etc.) to establish a pump-jet propulsor model, wherein the pump-jet propulsor model includes a rotor, a stator, a hub, and a duct;
[0047] The model should have high precision and be able to accurately reflect the size, shape, position and size of the vehicle and the rotor and stator. In this embodiment, the specific parameters are shown in Table 1. The calculation domain geometry model is as follows: Figure 1 shown.
[0048] Table 1 Model parameters of front stator pump-jet propulsor
[0049]
[0050] Step 2: Based on the structure of the pump-jet propulsor, the calculation area is divided into the outer domain of the duct, the stator domain and the rotor domain; the rotor domain is further divided into rotor domain 1, rotor domain 2 and rotor blade tip domain; the rotor domain is further subdivided into three regions (taking a single rotor domain blade as an example, the specific Figure 2 ), which are rotor domain 1 (the area below 0.92R), rotor blade tip domain (the blade tip area above 0.92R and its tip vortex area), and rotor domain 2 (the area outside the rotor blade tip area above 0.92R);
[0051] Step 3: Use CFD pre-processing software to mesh the model. The specific mesh size and time step are determined based on the LES turbulence model applicability evaluation criteria. Single-channel meshes are used for the duct outer domain and stator domain, and the full-channel mesh is obtained by periodically rotating the mesh. Unstructured meshes are used for rotor domain 2, and structured meshes are used for rotor domain 1 and the rotor blade tip domain.
[0052] In this example, ICEM 16.0 was used to construct a single-channel mesh for the duct outer domain and the stator domain, and a full-channel mesh was obtained by periodically rotating the mesh. Due to its asymmetric shape, STARCCM+ was used to construct an unstructured mesh for rotor domain 2. For rotor domain 1 and the rotor blade tip domain, structured meshes constructed using ICEM 16.0 were used to ensure mesh consistency near the wall.
[0053] Step 4: Data is transferred between the rotor domains using interfaces, keeping the meshes of the duct outer domain, stator domain, rotor domain 1, and rotor domain 2 unchanged, and only changing the mesh density of the rotor blade tip domain;
[0054] The shape and range of the rotor blade tip domain are set according to the tip vortex track. The axial length of the rotor blade tip domain is about 100 mm, and the circumferential angle is about 120°. The circumferential section is unfolded into a two-dimensional graph, and the calculation domains of various densities are obtained by adjusting the maximum size of the grid on the edge of the calculation domain block. The adjustment edge definition is as follows: Figure 3 , its size definition is always the same as that of refined edge 1.
[0055] The rotor boundary layer is set by the O-cut method near the rotor wall. The thickness of the first layer of mesh near the wall is 0.005mm. + like Figure 4 As shown, the rotor wall y + Basically meet the calculation requirements of the LES model, and the rotor tip area above 0.9R is 40≤x + ≤80,10≤z + ≤25, in the subsequent mesh adjustment process, the mesh thickness inside the boundary layer remains unchanged, and only the mesh size outside the boundary layer is changed. The unit time step is 1×10 -4 s, corresponding to a rotation angle of 0.66° per unit time step, and the Courant number is Figure 5 As shown, at the same time, the maximum internal iteration is 10 steps, and the time solution meets the calculation requirements of the LES model;
[0056] Step 5: Establish cross sections perpendicular to the rotor axis at different axial distances Δx from the trailing edge of the rotor blade tip, with the diameter of each cross section being consistent with the diameter of the duct at that location, so as to monitor the pressure distribution characteristics of each cross section;
[0057] The distance between each axial section is defined in units of rotor radius R, where the axial position of the cross section Δx = 0.00R corresponds exactly to the position of the rotor trailing edge. When Δx / R is negative, the pressure value on the monitoring surface is the vortex core pressure before the rotor trailing edge. When Δx / R is positive, it is the vortex core pressure in the wake, as shown in the figure. Figure 6 ;
[0058] Step 6: Perform CFD calculations and import the mesh into CFD software (such as ANSYS Fluent, STARCCM+, etc.). The software should be able to handle complex flow problems. After importing, set boundary conditions according to the actual working conditions, such as Figure 7 Calculate the monitoring results of the minimum vortex core pressure of each cross section in the rotor blade tip area at different grid densities under a certain working condition, monitor the convergence and stability of the simulation process to ensure the reliability of the simulation results, and draw the time-averaged value curve to obtain the time-averaged vortex core pressure comparison curve after adjusting the maximum size of the grid unit;
[0059] The monitoring results of the lowest pressure of the vortex core in each cross section within 6 cycles after the calculation is stable are taken to draw the time-average curve. The time-average comparison curves of the vortex core pressure after adjusting the maximum size of the grid unit on the three boundaries of the encrypted edge 1 and the encrypted edge 3 are obtained as follows: Figures 8 to 10 , the mesh size parameters of each boundary mesh are shown in Table 2.
[0060] Table 2 Total number of grids in different rotor blade tip areas
[0061]
[0062] Step 7: Select the optimal blade tip domain grid size by analyzing and comparing the time-averaged vortex core pressure comparison curves in step 6;
[0063] By analyzing and comparing the time-averaged vortex core pressure comparison curves in step 6, the maximum mesh sizes on Refinement Edge 1 and Refinement Edge 3 are adjusted, and the mesh sizes on each Refinement Edge are reduced based on MESH 2. The vortex core pressure change rate is less than 3% (the pressure obtained by monitoring in this paper is the difference between the actual pressure and the pressure at the pressure outlet. Therefore, the pressure at the pressure outlet should be included in the definition of the time-averaged vortex core pressure change rate.). It can be finally determined that the maximum size of the rotor blade tip domain mesh is 0.1mm on Refinement Edge 1, 0.4mm on Refinement Edge 2, and 0.2mm on Refinement Edge 3. In other words, MESH 2 can meet the calculation requirements.
[0064] Step 8. Based on the blade tip domain mesh size selected in step 7, the final mesh is imported into professional CFD software, and the established numerical calculation model is solved using a CFD solver. The Schnerr-Sauer cavitation model is introduced to obtain the tip vortex cavitation results.
[0065] The SchnerrSauer cavitation model is introduced and the numerical calculation model is solved using the solver. The isosurface of the gas volume fraction α = 0.1 is taken to display the tip vortex cavitation. The tip vortex cavitation results are as follows: Figure 11 .
[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.
Claims
1. A high-precision calculation method for pump-jet propulsor rotor tip vortex cavitation, characterized by: The steps include: Step 1: Use 3D modeling software to establish a pump-jet propulsor model, wherein the pump-jet propulsor model includes a rotor model, a stator model, a hub model, and a duct model; Step 2: Based on the structure of the pump-jet propulsor, the calculation area is divided into the outer domain of the duct, the stator domain, and the rotor domain; The rotor domain is further divided into rotor domain 1, rotor domain 2 and rotor blade tip domain; rotor domain 1 is located on the front and rear side of the rotor close to the main shaft, including the area of rotor radius 0 to 0.92R0; rotor domain 2 is located on the side of the duct, on the front and rear sides of the rotor blade tip; the rotor blade tip domain is located in the rotor blade tip area; R0 is the rotor radius; Step 3: Mesh the model and determine the specific mesh size and time step based on the LES turbulence model applicability evaluation criteria; The outer domain of the duct and the stator domain use single-channel meshes, and the full-channel mesh is obtained by periodically rotating the meshes. The rotor domain 2 uses an unstructured mesh, while the rotor domain 1 and the rotor blade tip domain use a structured mesh. Step 4: Data is transferred between the rotor domains using interfaces, keeping the meshes of the duct outer domain, stator domain, rotor domain 1, and rotor domain 2 unchanged, and only changing the mesh density of the rotor blade tip domain; Set the rotor boundary layer and adjust the grid thickness near the rotor wall to meet the calculation requirements of the LES model; Step 5: Establish cross sections perpendicular to the rotor axis at different axial distances from the trailing edge of the rotor blade tip, with the diameter of each cross section being consistent with the diameter of the inner wall of the duct at that location, so as to monitor the pressure distribution characteristics of each cross section; Step 6: Perform CFD calculations. Import the mesh into CFD software capable of handling complex flow problems. After importing, set boundary conditions based on the actual operating conditions. Calculate the minimum vortex core pressure monitoring results for each cross-section of the rotor blade tip at different mesh densities under a certain operating condition. Monitor the convergence and stability of the simulation process to ensure the reliability of the simulation results. Plot the time-averaged curve and obtain a comparison curve of the time-averaged vortex core pressure after adjusting the maximum mesh unit size. Step 7: By analyzing and comparing the time-averaged vortex core pressure comparison curves in Step 6, an optimal blade tip domain grid size is selected; the selection rule is to make the vortex core pressure change tend to be stable, and the maximum change rate of the vortex core pressure on each cross section does not exceed 3%; Step 8. Based on the blade tip domain mesh size selected in step 7, the final mesh is imported into the CFD software, and the established numerical calculation model is solved using the CFD solver. The Schnerr-Sauer cavitation model is introduced to obtain the tip vortex cavitation results.
2. The high-precision calculation method for pump-jet propulsor rotor tip vortex cavitation according to claim 1 is characterized in that: In the step 1, the model should include: the size and shape of the duct, stator and rotor, the position and size of the rotor and stator, the number of blades of the rotor and stator, and the gap between the inner wall of the duct and the cross section of the rotor tip.
3. The high-precision calculation method for pump-jet propulsor rotor tip vortex cavitation according to claim 1 is characterized in that: In step 3, ICEM 16.0 is used to construct a single-channel mesh for the duct outer domain and the stator domain, and a full-channel mesh is obtained by periodically rotating the mesh; STARCCM+ is used to construct an unstructured mesh for the rotor domain 2; and structured meshes constructed using ICEM 16.0 are used for the rotor domain 1 and the rotor blade tip domain.
4. The high-precision calculation method for pump-jet propulsor rotor tip vortex cavitation according to claim 1 is characterized in that: The step 4 specifically includes: According to the tip vortex track, the rotor blade tip domain shape and interval, axial length, and circumferential angle are set. The circumferential section is unfolded into a two-dimensional graph, and the computational domains of various densities are obtained by adjusting the maximum size of the grid on the edge of the computational domain block. The rotor boundary layer is set by the O-cut method near the rotor wall, and the thickness of the first layer of grid near the wall is set, which is the rotor wall y + Meet the calculation requirements of the LES model, and the rotor tip area above 0.9R is 40≤x + ≤80,10≤z + ≤25, in the subsequent mesh adjustment process, the mesh thickness inside the boundary layer remains unchanged, and only the mesh size outside the boundary layer is changed; set the unit time step, the rotation angle within the unit time step, and the maximum number of internal iterations to ensure that the time solution meets the calculation requirements of the LES model.
5. The high-precision calculation method for pump-jet propulsor rotor tip vortex cavitation according to claim 1 is characterized in that: The step five further includes: defining the distance between each axial section in units of the rotor radius R0, wherein the axial position of the cross section Δx=0.00R0 corresponds to the position of the rotor trailing edge, and when Δx / R0 is a negative value, the pressure value on the monitoring surface is the vortex core pressure before the rotor trailing edge, and when Δx / R0 is a positive value, it is the vortex core pressure in the wake.
6. The high-precision calculation method for pump-jet propulsor rotor tip vortex cavitation according to claim 1, characterized in that: The turbulence model in step 3 can be expressed as: Where: are the filtered velocity and pressure respectively; ρ is the density of the fluid; μ is the dynamic viscosity of the fluid; μ t is the subscale eddy viscosity; and is the component of velocity in different directions after filtering; t is time; x i and x j Indicators representing different spatial coordinates; t refers to time; refers to The product of is filtered.
7. The high-precision calculation method for pump-jet propulsor rotor tip vortex cavitation according to claim 1 is characterized in that: In step eight, the SchnerrSauer cavitation model can be expressed as: Where P v is the vapor pressure; P is the local pressure; ρ v and ρ m are the steam density and the mixture density respectively; r b is the bubble radius; ρ l is the liquid density; In the above formula, α is specifically: Where α is the gas volume fraction, n b is the number of cavitation bubbles per unit volume; Cavitation radius R c It is defined by the following formula: