A method for calculating oil friction torque of a wet-type motor considering flow state and roughness

Abstract

The application provides a kind of oil friction torque calculation method of wet-type motor considering flow state and roughness, determines the surface morphology parameters of motor rotor by physical property parameter testing equipment, and combines the existing literature data, proposes an equivalent roughness height model considering kurtosis.According to the flow characteristics between motor stator and rotor gap, an analytical method of oil friction torque based on four typical flow states of Taylor-Couette flow system is constructed.CFD method is used to model the flow field of motor stator and rotor gap, and the above equivalent roughness height model is added to the wall boundary layer calculation.Based on the numerical calculation results, the undetermined coefficients in the analytical formula of oil friction torque are determined, forming a complete and efficient oil friction torque calculation method.The application can effectively improve the calculation accuracy of oil friction torque of wet-type motor.

Description

Technical Field

[0001] This invention relates to the field of wet motor technology, and in particular to a method for calculating the oil friction torque of a wet motor that takes into account flow state and roughness. Background Technology

[0002] Wet-type motors possess advantages such as lubrication compensation, thermal conductivity, and pressure balance. Their applications continue to expand in fields like aerospace and deep-sea development. However, because wet-type motors are filled with an oil-based medium, the viscosity of which is higher than that of a gaseous medium. This results in significant oil friction torque due to shear stress on the rotor walls within the gaps, leading to a substantial increase in the proportion of oil friction torque in mechanical losses under high-speed operating conditions. Therefore, predicting and mitigating this friction torque based on the motor's structure and operating parameters has become a critical challenge in the field of motor design and operation.

[0003] Currently, there are numerous reference models for calculating the torque or loss of oil friction in wet-type motors, mainly focusing on motor structural parameters and drive parameters. However, current research on the Taylor-Couette flow pattern in fluid mechanics and on the morphology of objects in materials science introduces errors into these models. Firstly, existing models generally classify flow states into laminar and turbulent flows. However, cutting-edge research in fluid mechanics reveals that the evolution of actual Taylor-Couette flows involves rich flow structures, which can introduce errors. Secondly, existing models often rely on a surface roughness height coefficient, determined based on empirical values. However, cutting-edge research in materials science shows that different surface roughness heights alter the boundary layer hydraulic flow state, and this equivalent roughness height is determined by the surface morphology parameters. Therefore, considering the evolution of flow structures and obtaining the equivalent roughness height is crucial in calculating oil friction torque. Furthermore, CFD numerical calculation methods for the stator-rotor clearance of motors do not yield highly accurate results. Therefore, boundary layer mesh generation and rotation of the turbulence model are essential. Summary of the Invention

[0004] The purpose of this invention is to provide a method for calculating the oil friction torque of a wet motor that takes into account the flow state and roughness, which can effectively improve the calculation accuracy of the oil friction torque of a wet motor.

[0005] To achieve the above-mentioned invention, the present invention adopts the following technical solution:

[0006] A method for calculating the oil friction torque of a wet-type electric motor that takes into account flow regime and roughness includes the following steps:

[0007] S1: Establish a modeling method for the equivalent roughness height of the motor gap surface;

[0008] S2: Establish a CFD-based method for calculating the flow domain of motor gaps;

[0009] S3: Establish an analytical modeling method for oil friction torque based on flow regime and roughness;

[0010] Step S1 includes the following steps:

[0011] S10: Measurement of motor surface morphology parameters;

[0012] S11: Statistics on surface morphology parameters of motor types;

[0013] S12: Introducing kurtosis S ku Construct an equivalent rough height basic model;

[0014] S13: Determine the undetermined coefficients of the model to obtain the complete form of the equivalent roughness height model;

[0015] Step S2 includes the following steps:

[0016] S20: Based on the motor structure and operating parameters, determine the structural characteristics and parameters of the CFD numerical calculation model for the motor gap flow domain;

[0017] S21: Determine the near-wall boundary layer mesh thickness;

[0018] S22: Design a mesh node partitioning scheme and verify mesh independence;

[0019] S23: Based on accuracy and economy, select a turbulence model suitable for calculating the flow domain of the motor gap;

[0020] Step S3 includes the following steps:

[0021] S30: A basic analytical model for oil friction torque is derived based on four typical flow states during motor operation;

[0022] S31: Introduce roughness to correct the original parameters;

[0023] S32: Correct the basic analytical model of oil friction torque based on the corrected parameters;

[0024] S33: Using the results of the CFD numerical calculation model established in S2, the undetermined coefficients in the basic analytical model are fitted to obtain a complete analytical model of oil friction torque.

[0025] Preferably, step S10 specifically includes:

[0026] To reduce measurement error, multiple areas of the surface involved in the gap formed by the motor stator and rotor were measured using an object surface topography measurement device. The arithmetic mean height was obtained using a probability density distribution method. Sa Root mean square height S q Maximum peak and valley S z skewness S sk and kurtosis S ku ;

[0027] Step S11 specifically includes:

[0028] Using profile shape parameters such as skewness S sk and kurtosis S ku As characteristic parameters, we statistically analyzed the relevant experimental parameters with motor-like surface profile shape parameters in existing literature.

[0029] Preferably, step S12 specifically includes:

[0030] Propose a method to introduce kurtosis S ku Equivalent rough height basic analytic function model: k s = f 1( S q , S sk , S ku )= aS q ( b + cS sk ) d ( S ku / 3) e ,

[0031] in a , b , c , d , e For the undetermined coefficients of the motor clearance surface;

[0032] This model introduces kurtosis. S ku This will allow the function model to incorporate the effect of surface sharpness on equivalent roughness into the calculation results.

[0033] Preferably, step S13 specifically includes:

[0034] Based on an iterative optimization algorithm, experimental measurements and relevant parameters of the motor-like surface from the references are substituted into the basic analytical model of the equivalent roughness height for fitting, and the undetermined coefficients are determined.a , b , c , d , e By taking values ​​of , we can obtain an accurate analytical function model of the equivalent roughness height applicable to the stator and rotor clearance surfaces of the motor.

[0035] Preferably, step S20 specifically includes:

[0036] Based on the integrity of the motor structural parameters, periodic characteristics, and Taylor-Couette flow characteristics, the structural features and parameters of the CFD numerical calculation model are determined; rotating and stationary walls are set, and the equivalent roughness height proposed in S1 is set for the walls using a user-defined function.

[0037] Preferably, step S21 specifically includes:

[0038] To ensure the efficiency of the numerical computation model in solving near-wall problems, the first layer of mesh near the wall must satisfy 1 ≤ y + ≤5, y + The dimensionless height near the wall; and according to the flow channel contraction theory, the mesh thickness Δ needs to be... h > k s + / 2, k s + The equivalent roughness height Reynolds number;

[0039] Step S22 specifically includes:

[0040] In the axial direction N z Zhou Xiang N θ and radial N r In terms of the number of nodes, multiple grid-independent schemes are designed using an incremental sequence. Dimensionless local transport parameters or global response parameters are used as evaluation parameters. When the rate of change between two adjacent evaluation parameters is less than 0.5%, the former is adopted as the optimal grid partitioning scheme for subsequent calculations.

[0041] Preferably, step S23 specifically includes:

[0042] Based on existing literature regarding experimental or direct numerical simulation results of Taylor-Couet flow systems with similar characteristics, the computational accuracy and economy of turbulence models were compared and screened to select the turbulence model most suitable for numerical calculation of the flow between the stator and rotor of the motor.

[0043] Preferably, step S30 specifically includes:

[0044] Based on the evolution of the Taylor-Couet flow pattern, a method for calculating the oil friction torque in the stator-rotor gap of an electric motor is proposed. T AC Basic analytical model:

[0045]

[0046] Among them, the stator inner diameter R s Rotor outer diameter R r Gap width d g = R s - R r Circumferential length L a radius ratio or = R r / R s Length-to-diameter ratio Г= L a / d g Dynamic viscosity μ oh r The angular velocity of the rotor, f , g , h For the undetermined coefficients that need to be solved using a CFD numerical calculation model, The c1 , The c2 and The c3 , respectively, are the critical Taylor numbers for flow regime transition.

[0047] Preferably, step S31 specifically includes:

[0048] Based on the flow channel contraction theory and the equivalent surface roughness model of the motor proposed in S1, the relevant parameters are corrected: stator inner radius. R se Rotor outer radius R se ; Gap width d ge radius ratio or e Aspect ratio Г e Reynolds number Re re Taylor number The e ;

[0049] Step S32 specifically includes:

[0050] Based on the corrected parameters, the oil friction torque T AC The analytical model was modified.

[0051] Preferably, step S33 specifically includes:

[0052] Based on the CFD numerical calculation model in S2, the local transport parameters and global response parameters of the Taylor-Couet flow system with different rotational speeds and surface morphologies are calculated, and these parameters are then incorporated into the oil friction torque. T AC In the analytical model, fitting is performed to determine the undetermined coefficients, thereby obtaining a complete analytical model of oil friction torque.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] This invention proposes an equivalent roughness height calculation model based on kurtosis. The model parameters are fitted with experimental measurements and literature parameters to obtain an accurate calculation model of equivalent roughness height applicable to different motor rotor surfaces.

[0055] This invention establishes a CFD numerical solution domain based on motor structural parameters, determines the boundary layer meshing scheme based on driving strength parameters, explores a computational model with high efficiency and economy, incorporates an equivalent roughness height model into the boundary layer calculation, and constructs a flow domain solution model suitable for the stator and rotor clearance of the motor.

[0056] Based on the development law of Taylor-Couet flow, this invention divides the motor operating range into four classical flow regimes, derives a semi-analytical model of oil friction torque based on the flow regimes, and determines the undetermined coefficients in the analytical model based on CFD numerical calculation results, thereby obtaining an accurate calculation method for oil friction torque applicable to different motor rotor surfaces and their entire speed range. Attached Figure Description

[0057] Figure 1 This is a flowchart of a method according to an embodiment of the present invention;

[0058] Figure 2 This is a schematic diagram of the CFD numerical calculation model of the motor gap flow domain in an embodiment of the present invention;

[0059] Figure 3 This is a schematic diagram comparing the accuracy and economy of the turbulence model in this embodiment of the invention.

[0060] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the invention. To better illustrate this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings. Detailed Implementation

[0061] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0062] This embodiment provides a method for calculating the oil friction torque of a wet-type motor that considers flow regime and roughness. It takes into account four typical flow regimes of the Taylor-Cooette flow regime existing in the stator-rotor gap region of the motor and incorporates a new model for establishing equivalent roughness heights for the stator and rotor. The establishment of the analytical model includes 3 main steps and 12 sub-steps, such as... Figure 1 As shown. The three main steps include: S1, a modeling method for the equivalent roughness height of the motor gap surface; S2, a CFD-based method for calculating the flow domain of the motor gap; and S3, an analytical modeling method for oil friction torque based on flow regime and roughness.

[0063] The method S1 for modeling the equivalent roughness height of the motor clearance surface includes four sub-steps:

[0064] Step S10:

[0065] A three-dimensional white light interferometer was used to measure the surface morphology of multiple regions of typical rotors of wet-type motors (internal motors: carbon fiber sheath, metal sheath; internal motors: silicon steel laminated core rotor) and perform probability density distribution statistics to reduce errors, obtaining the arithmetic mean height. S a Root mean square height S q Maximum peak and valley S z skewness S sk and kurtosis S ku See Table 1.

[0066] Table 1. Results of surface morphology parameter measurement of the prototype stator and rotor

[0067]

[0068] Step S11:

[0069] Since the rotor provides driving force for the Taylor-Couet flow system of the motor clearance, relevant parameters with similar morphological features to the motor rotor surface are statistically analyzed. S ku <0 and Sku >3, as shown in Table 2.

[0070] Table 2. References: Stator and rotor surface parameters and their calculated values ​​and errors.

[0071]

[0072] References for parameters of sandblasted surfaces: KA Flack, MP Schulz, JM Barros, and YC Kim, “Surface friction behavior under transitional roughness”, International Journal of Heat and Fluids, Vol. 61, pp. 21–30, 2016, Digital Object Identifier: 10.1016 / j.ijheatfluidflow.2016.05.008.

[0073] References for parameters of the polished surface: MP Schultz and K.K. Flack, “Turbulent boundary layer of rough walls from hydraulically smooth to fully rough states”, Journal of Fluid Mechanics, Vol. 580, pp. 381–405, 2007, Digital Object Identifier: 10.1017 / S0022112007005502.

[0074] References for parameters of pipe grinding: MA Shockling, JJ Allen, and AJ Smitz, “Roughness effect in turbulent pipe flow”, Journal of Fluid Mechanics, Vol. 564, pp. 267–285, 2006, Digital Object Identifier: 10.1017 / S0022112006001467.

[0075] Step S12:

[0076] Due to the cliff S ku It characterizes the sharpness of peaks and valleys in the morphology and incorporates it into the existing formula for calculating equivalent roughness height:

[0077]

[0078] Step S13:

[0079] Based on the references, it has a similar degree of skewness to the typical rotor surface of the motor. S sk and kurtosis S ku The data was then iteratively fitted using the Levenberg-Marquardt optimization algorithm to finally obtain the result considering the surface kurtosis. S ku Mathematical model of equivalent roughness height ks :

[0080]

[0081] Where the fitting coefficient in the above equation R 2 =0.99241, proving the accuracy of the fit. This formula is applicable to surfaces involved in the stator and rotor clearance of the motor. The absolute error is obtained by comparing this formula with the experimental values ​​measured in the references, as shown in Table 2. k sa The fitted value is the equivalent roughness height model from the literature. k sp The values ​​represent the experimental roughness values ​​from the literature. The maximum absolute error of this model is 7.20%, demonstrating its accuracy.

[0082] When users expect to obtain accurate equivalent roughness height k s At this time, the surface morphology parameters can be determined first using a three-dimensional white light interferometer: root mean square height. S q skewness S sk and kurtosis S ku Then, it is substituted into the above formula for calculation. This patent provides the measurement of typical surfaces of the prototype and k s Calculation results: The stator core with 0.1mm silicon steel sheets is 20.897μm, the rotor core with 0.1mm silicon steel sheets is 17.470μm, the metal sheath is 1.899μm, and the carbon fiber sheath is 6.376μm.

[0083] The CFD-based method S2 for calculating the motor gap flow domain includes four sub-steps:

[0084] Step S20:

[0085] Based on the actual stator inner diameter of the motor R s Rotor outer diameter R r Gap width d g = R s - R r Circumferential length L a radius ratio or = R r / R s , length-to-diameter ratio Г= La / d g A computational fluid dynamics (CFD) model was established to represent the gap between the stator and rotor of the motor. Based on the characteristics of the complete Taylor vortex pattern, translational boundary conditions were set in the axial direction (with the number of periods consistent with the existing DNS value of Г=3.1), and rotational boundary conditions were set in the circumferential direction (with 20 periods). Figure 2 As shown. The boundary conditions are set as follows: rotor rotating wall 100, stator stationary wall 101, rotational period boundary 102, and translational period boundary 103. The equivalent roughness height model proposed in this invention is set on the rotor rotating wall 100 and the stator stationary wall 101 using a user-defined function.

[0086] Step S21:

[0087] During radial mesh generation, the flow channel contraction theory is adopted, and the virtual wall displacement method is used to move the wall to half of the equivalent roughness height. y + = y + + k s + / 2, where k s + This is the equivalent roughness height Reynolds number. Therefore, the thickness of the first mesh layer is Δ. h Need to be greater than k s + / 2. To ensure that the first mesh layer is located in the viscous sublayer of boundary layer 104, the height of the first mesh layer of boundary layer 104 between the rotor rotating wall 100 and the stator stationary wall 101 must satisfy 1 ≤ y + ≤5.

[0088] Step S22:

[0089] Design 8 sets of mesh node division schemes, in the axial direction ( N z ), Zhou Xiang ( N θ ) and radial ( N r An increasing sequence is used, and dimensionless torque is selected. G = J ω / n 2 and Nusselt No ω = G / G lamThe criteria for evaluating grid independence are shown in Table 3. J ω = T r / (2π L a r ) represents the angular velocity flux. n The dynamic viscosity of the oil. r Given the density of the oil, the dynamic viscosity μ can be derived from this. n×r , T r To maintain the speed of the drive rotor n The torque required at that time G lam = J ω lam / n 2 The dimensionless torque under laminar flow conditions. J ω lam =2 nR s 2 R r 2 oh r / ( R s 2 - R r 2 ) represents the angular velocity flux under laminar flow conditions. oh r This represents the angular velocity of the rotor. Starting with scheme 7, G and No ω The volatility decreased to 0.47%, indicating that the scheme achieved a balance between computational efficiency and result accuracy. Therefore, scheme 7 was adopted for the mesh generation of subsequent numerical calculations.

[0090] Table 3. Mesh independence verification scheme

[0091]

[0092] Step S23:

[0093] To determine the applicability of the turbulence model while also considering the economics of numerical computation, Realizable... k-e Model, SST k-oh Models and Stress -ohThe RSM model is compared with Vent's experiments (see: F. Vent, "Turbulence between two rotating coaxial cylinders", Archives of Applied Mechanics, Vol. 4, No. 6, pp. 577–595, December 1933, Digital Object Identifier: 10.1007 / BF02084936) and Scheupp's direct numerical simulation results (see: A. Scheupp, E. Clement, D. Legendre, and C. Gabier, "Numerical simulation of bubble dispersion in turbulent Taylor-Couette flow", Physical Fluids, Vol. 26, No. 4, p. 043304, April 2014, Digital Object Identifier: 10.1063 / 1.4871728), as follows: Figure 3 As shown. The supercomputing node used for computation is configured with an AMD EPYC 7452 @ 2.35GHz 64-core 256GB processor. Realizable. k-e The model requires a minimum average kernel time of 1.44 × 10⁻⁶. 4 However, its calculations G The average error between the test and DNS reached a maximum of 11.56%. SST k-oh Models and Stress -oh The RSM model yielded smaller average errors of 5.75% and 3.49%, respectively, but the RSM model had the highest average kernel time of 1.82 × 10⁻⁶. 4 In summary, SST k-oh The model has good accuracy and low computational cost, so it is the best choice for calculation of the object under study.

[0094] The S3 method for analytical modeling oil friction torque based on flow regime and roughness includes four sub-steps:

[0095] Step S30:

[0096] For a TC system with a smooth surface and constant temperature, the driving intensity of the system gradually increases with the continuous increase of the inner rotor speed. During this process, the flow state within the TC system changes from Couet flow to a turbulent state containing Taylor-Couet flows of varying development stages. Based on the flow characteristics, the flow states during this development process can be divided into four categories, and the rotor friction torque derived from this also has four forms:

[0097] ① Kuet flow

[0098] when The When the velocity is sufficiently small, the flow is in a purely azimuthal laminar state. At this point, due to the conservation of radial angular momentum, the tangential velocity... u φ ( r Radial position only rThe function, independent of f and z And the other two velocity components u r ( r )and u z ( r All are 0. Substituting the above conditions into the three-dimensional incompressible Navier-Stokes equations yields a second-order linear differential equation, the solution of which is:

[0099]

[0100] Simultaneously, by incorporating the boundary conditions of the Taylor-Couet system and applying Newton's law of internal friction, the frictional torque on the infinitesimal element of the rotor surface is obtained. t r Integrating this value over the rotor surface, the total frictional torque on the rotor surface under laminar flow conditions is obtained. T CFR :

[0101]

[0102] ②Laminar flow

[0103] When the driving force of the system is very small, energy transfer is limited by the laminar boundary layer. At this point, the boundary layer remains laminar, but the mainstream region becomes turbulent and exhibits spatiotemporally stable Taylor vortices. The and No ω The relationship between them satisfies the scaling power law ( α (Scaling factor for different TC systems under low-drive flow conditions) No ω -1~ The 1 / 3+α ,Right now No ω -1= aTa 1 / 3+α ( f (This refers to the offset coefficient of the function). Combining this with the parameters defined above, the oil friction torque under laminar flow conditions can be derived. T LR for:

[0104]

[0105] ③Classical Transient Flow

[0106] As the driving intensity is further increased, the flow regime within the boundary layer gradually changes from laminar to turbulent. At this point, the spatiotemporally stable Taylor vortices are disrupted, and the Taylor vortex flow state transitions to a modulated Taylor vortex state, resulting in its time dependence. In this transitional state, hairpin vortices (considered plumes in Rayleigh-Bénard flows) are ejected from the inner and outer cylinders, and these vortices contribute to the formation of large-scale mainstream structures. These structures, in turn, generate axial pressure gradients and couple back into the boundary layer, causing plumes to be ejected back to nearby locations. The and No ω The relationship between them satisfies the scaling power law ( β (Scaling factor for different Taylor-Couette flow systems under transitional flow conditions) No ω ~ The 1 / 3+β ,Right now No ω = bTa 1 / 3+β ( g (This refers to the offset coefficient of the function). Combining the parameters defined above, the oil friction torque under low-drive flow conditions can be derived. T CTR for:

[0107]

[0108] ④Limited turbulent flow state

[0109] When the driving force of the system is sufficiently large, the boundary layer becomes fully turbulent, and the system enters the so-called limiting flow state. The Taylor-Couet flow system with stator-rotor clearance in a motor exhibits... or →1 indicates a small gap characteristic, resulting in relatively less disruption to flow continuity. Therefore, the scaling exponent of the limiting flow state or the transitional flow state close to the limiting flow state has a significant impact on the flow's continuity. or The dependence on [the value of] is relatively weak, meaning that it exhibits a similar scaling power law under different stator and rotor size parameters. At this point... The and No ω The relationship between them satisfies the scaling power law ( c (Scaling factor for different Taylor-Couette flow systems under transitional flow conditions) No ω ~ The 0.39+γ ,Right now No ω = cTa 0.39+γ ( h (This refers to the offset coefficient of the function). Combining the parameters defined above, the oil friction torque under low-drive flow conditions can be derived. T UTR for:

[0110]

[0111] Because the critical Taylor number for flow regime transition varies among Taylor-Couette flow systems with different characteristics, studies have found that increasing the radius ratio will advance the flow regime transition. Therefore, the critical Taylor number for flow regime transition needs to be determined based on the system under study; here, we assume that they are respectively... The c1 , The c2 and The c3 .

[0112] Step S31:

[0113] When fluid flows over a series of densely distributed rough elements, most of the fluid between the rough elements is trapped, forming streamlined, closed, small vortices. A small portion of the fluid above the rough elements is trapped and added to these vortices. There is only a small amount of momentum exchange and virtually no mass exchange between the trapped fluid and the flowing fluid. The fluid trapped by the rough elements acts as a blockage in the flow, equivalent to reducing the cross-sectional area of ​​the flow channel. The flow channel contraction theory has been well proven, especially for flows with rough walls that satisfy… e / D h,cf Under the condition of ≤0.05 (which meets the condition of the motor stator-rotor gap flow channel characteristics), this theory has a more obvious modeling advantage (wherein, e For surface roughness, D h,cf (To reduce the hydraulic diameter). Therefore, this invention proposes a correction method for the analytical calculation of oil friction of the geometric parameters and driving parameters of the Taylor-Couet flow system based on the above-mentioned influencing factors: extending the actual wall surface in the direction of the flow domain. k s / 2 length, that is, the stator extends radially inward. k ss / 2 length and the rotor extends radially outward. k sr The length is 2 / 2 to account for the influence of the flow channel contraction theory caused by the combined effects of pressure and viscous forces. The existing parameters are corrected using the above method: a) Stator inner radius. R se =R s - k ss / 2; b) Rotor outer radius R se =R r - k sr / 2; c) Gap width d ge = Rse - R re d) Radius ratio or e = R re / R se e) Aspect ratio Г e = L a / d ge f) Reynolds number Re re = R re oh r d ge / ν;g) Taylor number The e =(1+ or e ) 4 (64 or e 2 ) -1 d ge 2 ( R se + R re ) 2 oh r 2 ν -2 .

[0114] Step S32:

[0115] The oil friction torque was derived based on the corrected relevant parameters. T AC subscript i , j and k The codes represent three types of rotor surfaces: 1 for metal sheath, 2 for carbon fiber sheath, and 3 for 0.1mm iron core.

[0116]

[0117] Step S33:

[0118] For the latter three types of Taylor-Couette turbulent flows within the stator-rotor gap of the motor, the scaling factor cannot be obtained analytically. Using the CFD numerical calculation method proposed in this invention, the aforementioned power-law relationship is fitted, as shown in Table 4. Based on the data in this table, the oil friction torque of the motor can be accurately calculated.

[0119] Table 4 Power-law fitting coefficients

[0120]

[0121] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for calculating the oil friction torque of a wet-type electric motor considering flow regime and roughness, characterized in that... Includes the following steps: S1: Establish a modeling method for the equivalent roughness height of the motor gap surface; S2: Establish a CFD-based method for calculating the flow domain of motor gaps; S3: Establish an analytical modeling method for oil friction torque based on flow regime and roughness; Step S1 includes the following steps: S10: Measurement of motor surface morphology parameters; S11: Statistics on surface morphology parameters of motor types; S12: Introducing kurtosis S ku Construct an equivalent rough height basic model; S13: Determine the undetermined coefficients of the model to obtain the complete form of the equivalent roughness height model; Step S2 includes the following steps: S20: Based on the motor structure and operating parameters, determine the structural characteristics and parameters of the CFD numerical calculation model for the motor gap flow domain; S21: Determine the near-wall boundary layer mesh thickness; S22: Design a mesh node partitioning scheme and verify mesh independence; S23: Based on accuracy and economy, select a turbulence model suitable for calculating the flow domain of the motor gap; Step S3 includes the following steps: S30: A basic analytical model for oil friction torque is derived based on four typical flow states during motor operation; S31: Introduce roughness to correct the original parameters; S32: Correct the basic analytical model of oil friction torque based on the corrected parameters; S33: Using the results of the CFD numerical calculation model established in S2, the undetermined coefficients in the basic analytical model are fitted to obtain a complete analytical model of oil friction torque. Step S12 specifically includes: Propose a method to introduce kurtosis S ku Equivalent rough height basic analytic function model: k s = f 1( S q , S sk , S ku )= aS q ( b + cS sk ) d ( S ku / 3) e , in a , b , c , d , e For the undetermined coefficients of the motor clearance surface; This model introduces kurtosis. S ku This will allow the function model to incorporate the influence of surface sharpness on equivalent roughness into the calculation results; Step S20 specifically includes: Based on the integrity of the motor structural parameters, periodic characteristics, and Taylor-Couet flow characteristics, the structural features and parameters of the CFD numerical calculation model are determined; rotating and stationary walls are set, and the proposed equivalent roughness height model is set on the rotating and stationary walls through the user-defined function interface.

2. The method for calculating the oil friction torque of a wet motor considering flow regime and roughness according to claim 1, characterized in that, Step S10 specifically includes: To reduce measurement error, multiple areas of the surface involved in the gap formed by the motor stator and rotor were measured using an object surface topography measurement device. The arithmetic mean height was obtained using a probability density distribution method. S a Root mean square height S q Maximum peak and valley S z skewness S sk and kurtosis S ku ; Step S11 specifically includes: Using the cross-sectional shape parameter as a characteristic parameter, we statistically analyzed the relevant experimental parameters of the cross-sectional shape parameter of the motor-like surface.

3. The method for calculating the oil friction torque of a wet motor considering flow regime and roughness according to claim 2, characterized in that, Step S13 specifically includes: Based on an iterative optimization algorithm, experimental measurements and relevant parameters of the motor-like surface are fitted into the basic analytical model of the equivalent roughness height to determine the undetermined coefficients. a , b , c , d , e By taking values ​​of , we can obtain an accurate analytical function model of the equivalent roughness height applicable to the stator and rotor clearance surfaces of the motor.

4. The method for calculating the oil friction torque of a wet motor considering flow regime and roughness according to claim 3, characterized in that, Step S21 specifically includes: To ensure the efficiency of the numerical computation model in solving near-wall problems, the first layer of mesh near the wall must satisfy 1 ≤ y + ≤5, y + The dimensionless height near the wall; and according to the flow channel contraction theory, the mesh thickness Δ needs to be... h > k s + / 2, k s + The equivalent roughness height Reynolds number; Step S22 specifically includes: Number of axial nodes N z Number of circumferential nodes N θ and number of radial nodes N r The design employs an incremental sequence to create multiple grid-independent schemes, using dimensionless local transport parameters or global response parameters as evaluation parameters. When the rate of change between two adjacent evaluation parameters is less than 0.5%, the former is adopted as the optimal grid partitioning scheme for subsequent calculations.

5. The method for calculating the oil friction torque of a wet motor considering flow regime and roughness according to claim 4, characterized in that, Step S23 specifically includes: By referencing experimental or direct numerical simulation results of Taylor-Couet flow systems with similar characteristics, the computational accuracy and economy of turbulence models are compared and screened to select the turbulence model that is most suitable for numerical calculation of the flow between the stator and rotor of the motor.

6. The method for calculating the oil friction torque of a wet motor considering flow regime and roughness according to claim 5, characterized in that, Step S30 specifically includes: Based on the evolution of the Taylor-Couet flow pattern, a method for calculating the oil friction torque in the stator-rotor gap of an electric motor is proposed. T AC Basic analytical model: ； Among them, the stator inner diameter R s Rotor outer diameter R r Gap width δ g = R s - R r Circumferential length L a radius ratio η = R r / R s , length-to-diameter ratio Г= L a / δ g Dynamic viscosity μ ω r ω is the angular velocity of the rotor. f , g , h For the undetermined coefficients that need to be solved using a CFD numerical calculation model, Ta c1 , Ta c2 and Ta c3 These are the critical Taylor numbers for flow regime transition. α The scaling factor is the scaling factor for different Taylor-Couette flow systems under low-driving laminar flow conditions. β The scaling factor is the scaling factor for different Taylor-Couette flow systems in the classical transitional flow state. γ is the scaling factor for different Taylor-Couet flow systems in the transitional flow state within the limiting turbulent flow state.

7. The method for calculating the oil friction torque of a wet motor considering flow regime and roughness according to claim 6, characterized in that, Step S31 specifically includes: Based on the flow channel contraction theory and the equivalent surface roughness model of the motor proposed in S1, the relevant parameters are corrected: stator inner radius. R se Rotor outer radius R se ; Gap width δ ge radius ratio η e Aspect ratio Г e Reynolds number Re re Taylor number Ta e ; Step S32 specifically includes: Based on the corrected parameters, the oil friction torque T AC The analytical model was modified.

8. The method for calculating the oil friction torque of a wet motor considering flow regime and roughness according to claim 7, characterized in that, Step S33 specifically includes: Based on the CFD numerical calculation model in S2, the local transport parameters and global response parameters of the Taylor-Couet flow system with different rotational speeds and surface morphologies are calculated, and these parameters are then incorporated into the oil friction torque. T AC In the analytical model, fitting is performed to determine the undetermined coefficients, thereby obtaining a complete analytical model of oil friction torque.

Images