CN114757120A - Method for predicting unsteady cavitation fluid-solid coupling performance of composite propeller - Google Patents

Abstract

The invention discloses a method for predicting unsteady cavitation fluid-solid coupling performance of a composite propeller, and belongs to the technical field of composite propeller performance prediction. The implementation method of the invention comprises the following steps: on the basis of a flow field calculation model, a blade structure of the composite propeller is subjected to layered modeling based on a laminated plate theory, numerical calculation of structural dynamics is embedded into flow field calculation, an accurate fluid-solid coupling interface is set, bidirectional coupling and transmission are performed on a flow field numerical calculation result and a structural field numerical calculation result through a data transmission interface based on a tight coupling algorithm, the applicability and the accuracy of the bidirectional coupling and transmission are analyzed, and the unsteady cavitation fluid-solid coupling performance of the composite propeller is obtained. The method is beneficial to deep analysis and prediction of the cavitation hydrodynamic performance of the composite material propeller, can be applied to prediction of the structure dynamic response performance of the composite material propeller, and solves the engineering problems related to the strength and stability of the composite material propeller. The method has the advantages of high prediction efficiency and high precision.

Description

A prediction method for unsteady cavitation fluid-structure interaction performance of composite propellers

technical field

The invention relates to a method for predicting the unsteady cavitation fluid-structure coupling performance of a composite material propeller, which is suitable for predicting the hydrodynamic performance and cavitation performance of a composite material propeller based on a two-way fluid-structure coupling algorithm, and belongs to the technical field of composite material propeller performance prediction.

Background technique

In order to improve the hydrodynamic performance and vibration and noise performance of the propeller and increase the service life of the propeller, many scholars at home and abroad have conducted various researches on the manufacturing materials of new hydraulic machinery. Because fiber reinforced composites have high specific strength and high specific stiffness similar to alloy materials, as well as anisotropy and superior damping properties, they are suitable for various hydrodynamic machinery serving in complex underwater environments. Compared with traditional metal propellers, the fluid-structure coupling characteristics of composite propellers under the action of cavitation hydrodynamic loads can change the pitch angle of the propellers and inhibit the generation of cavitation, thereby improving the hydrodynamic performance of the propellers. Due to the complex shape structure of composite propeller blades and the diversity of internal laminate structures, it is very difficult to predict the cavitation fluid-structure interaction performance of composite propellers. Due to the difficulty of processing large-scale propellers, the hydrodynamic performance experiments of the propellers often pass the model test, but the equipment for the model test is still expensive and has scale effects. Therefore, the development of theoretical methods to predict the cavitation hydrodynamic performance of composite propellers has important engineering significance.

Because the fiber reinforced composite propeller has a complex structure and shape, and the blade will produce a certain elastic deformation under the action of hydrodynamics, involving a large number of complex nonlinear problems, it is suitable for the numerical calculation method of the fluid-structure interaction performance of the traditional metal propeller It is no longer applicable, and although the numerical calculation of the two-way fluid-structure interaction performance of composite propellers has been studied by many scholars, it is still limited to the prediction of hydrodynamic performance of composite propellers and the prediction of steady cavitation performance, and cannot be directly applied to composite propellers. Prediction of unsteady cavitation fluid-structure interaction performance of material propellers. Therefore, the establishment of a prediction method for the unsteady cavitation fluid-structure coupling performance of composite propellers can calculate the structural deformation of composite propellers and analyze the unsteady flow field characteristics of composite propellers, which has important practical significance for the practical application of propellers.

SUMMARY OF THE INVENTION

The invention discloses a method for predicting the unsteady cavitation fluid-structure coupling performance of a composite material propeller, and the technical problem to be solved is to establish a general method for predicting the unsteady cavitation fluid-structure coupling performance of a composite material propeller, based on the numerical value of the flow field. The calculation model includes the multiphase flow model of the flow field, the RANS equation of the external flow field calculation, and the cavitation model to realize the establishment of the flow field calculation model. On the basis of the flow field calculation model, the blade structure of the composite propeller is calculated based on the laminate theory. Carry out hierarchical modeling, embed the numerical calculation of structural dynamics into the flow field calculation, and set up an accurate fluid-structure coupling interface. Based on the tight coupling algorithm, the numerical calculation results of the flow field and the numerical calculation results of the structure field are bidirectionally carried out through the data transfer interface. Coupling and transfer, analyze its applicability and accuracy, and obtain the unsteady cavitation fluid-structure interaction performance of composite propellers. The invention is helpful for in-depth analysis and prediction of the cavitation hydrodynamic performance of the composite material propeller, can be applied to the prediction of the structural dynamic response performance of the composite material propeller, and solves engineering problems related to the strength and stability of the composite material propeller.

The application fields of the method for predicting the unsteady cavitation fluid-structure interaction characteristics of the composite propeller include the prediction of the fluid-structure interaction characteristics, the prediction of the hydrodynamic performance of the cavitation of the propeller, and the field of optimal design of the composite material propeller. The invention can effectively predict the hydrodynamic deformation generated by the composite material propeller, and has the advantages of high prediction efficiency and high precision.

A method for predicting the unsteady cavitation fluid-solid coupling performance of a composite material propeller disclosed in the present invention includes the following steps:

Step 1: Calculate the initial value of the steady-state flow field for the rigid propeller.

The steady initial value calculation is performed for the flow field of the rigid propeller, and the propeller rotation speed and the incoming flow speed of the propeller are set to obtain the initial value data of the steady flow field. The governing equations for the fluid steady state solution are expressed by the mass conservation equation and the momentum conservation equation:

where the subscripts i and j represent the coordinate directions, u is the velocity vector, ρ is the fluid density, p is the flow field pressure, v is the kinematic viscosity coefficient, fi is the mass force per unit volume, and δ _ij is the Kronecker function.

Step 2: Establish a finite element model of the composite propeller structure.

Based on the geometric parameters of the rigid propeller, the geometric model of the composite propeller is established. The fiber layup of the composite material is constrained by the geometric contour of the rigid propeller. Based on the finite element software, according to the layup sequence of the composite material propeller, the thickness and material properties of the layup material of the composite material propeller are set layer by layer, and the density ρ of each layer of fiber cloth is input. , elastic modulus E, shear modulus G, Poisson's ratio υ, establish the finite element model of the composite propeller. The in-plane force, bending moment, in-plane strain and curvature of the composite propeller section satisfy the following relationship:

In the formula: [N] represents the in-plane force, [M] is the bending moment, ε° and κ are the mid-plane strain and mid-plane curvature, and the [A], [B], and [D] matrices are the in-plane stiffness matrix, the coupling Stiffness Matrix and Bending Stiffness Matrix.

Preferably, the finite element software is implemented by using the ACP module in ANSYS Workbench.

Step 3: The initial value data of the steady flow field is transferred to the structure field through the fluid-solid coupling interface, and the finite element structure deformation is solved to obtain the mesh deformation of the structure field.

Through the fluid-solid coupling interface between the composite propeller and the flow field, the initial value data of the steady flow field is transferred to the structural field. According to the finite element model of the composite propeller established in step 2 and the obtained initial value data of the flow field, the composite material is completed. The finite element structural deformation of the material propeller is solved, and the mesh deformation of the structural field is obtained. The finite element method is used to conduct transient analysis of the propeller structure under the action of hydrodynamic load. The control equation of the dynamic structure is as follows:

和

分别为结构位移、结构速度和结构加速度，{F_EX}代表流固耦合作用下结构所受外部激励力，{F_HE}代表流固耦合作用下结构所受流场力。where [M _s ], [C _s ] and [K _s ] are the structural mass matrix, the structural damping matrix and the structural stiffness matrix, respectively, {X},

and

are the structural displacement, structural velocity and structural acceleration, respectively, {F _EX } represents the external excitation force on the structure under the action of fluid-structure interaction, and {F _HE } represents the flow field force on the structure under the action of fluid-structure interaction.

Step 4: Establish a turbulence model for the calculation of the flow field of the composite propeller.

In order to better capture the turbulent structure of the multi-scale unsteady flow field and the phenomenon of flow in the near-wall region, the eddy viscosity model is used, and the turbulent viscosity coefficient μ _t is introduced to establish a relationship between the Reynolds stress and the average velocity gradient. The calculation to determine the eddy viscosity coefficient uses the two-equation k-ωSST turbulence model to close the Reynolds time-averaged equation:

为系踪平均，速度G_k和G_w分别是由平均速度梯度和浮力影响引起的湍动能产生项，Y_k和Y_M分别是由平均速度梯度和可压缩湍流脉动膨胀对总的耗散率的影响，D_w为横向扩散项。式中，σ_w和σ_k分别为湍动能和湍流频率的普朗特数：where k is the turbulent kinetic energy, ω is the turbulent frequency, ρ is the fluid density, μ is the dynamic viscosity coefficient,

is the tethered average, the velocities G _k and G _w are the turbulent kinetic energy generation terms caused by the mean velocity gradient and buoyancy effects, respectively, and Y _k and Y _M are the total dissipation rate caused by the mean velocity gradient and the compressible turbulent pulsation expansion, respectively , _Dw is the lateral diffusion term. where _σw and _σk are Prandtl numbers of turbulent kinetic energy and turbulent frequency, respectively:

The formula for calculating the turbulent viscosity coefficient μ _t is as follows:

where S is the shear strain rate, and F ₁ and F ₂ are mixing functions.

Step 5: Establish a cavitation model for the calculation of the flow field of the composite propeller.

The cavitation model for the calculation of the flow field of the composite propeller adopts the transport equation based on cavitation dynamics proposed on the basis of the Ralyleigh-Plesset (R-P) equation:

where R _B is the bubble radius, p _v is the saturated vapor pressure in the environment, S is the surface tension coefficient, ρ _l is the liquid density, T _∞ is the far-field fluid temperature, and p _∞ is the far-field ambient pressure.

Ignoring the second derivative of the bubble radius and the interaction of surface tension, the rate of change of the bubble radius R _B , the bubble mass m _B and the bubble volume V _B with time is simplified respectively:

N _B is the density of cavitation vapor nucleus in water (that is, there are N _B cavities in unit volume), then the vapor phase volume ratio ɑ _v is:

Then the interphase mass exchange rate m per unit volume is:

The above formula is the evaporation term. According to the above relationship, the expressions of the evaporation rate and condensation rate between the vapor and liquid phases are respectively:

where α _nuc is the cavitation gas core volume fraction, C _d and C _p are the liquid phase evaporation rate when the partial pressure is lower than the saturated vapor pressure and the vapor phase condensation rate when the partial pressure is greater than the saturated vapor pressure, respectively, and R _B is the empty Bubble radius, P _v is p _v (T _∞ ).

Step 6: Transfer the deformation information of the structure field obtained in Step 3 to the flow field through the fluid-solid coupling interface, update the flow field grid and solve the flow field, and obtain the numerical calculation result of the flow field.

Through the fluid-structure coupling interface between the composite propeller and the flow field, the deformation data of the structure field is transmitted to the flow field, the flow field grid is updated, and the cavitation number of the propeller cavitation condition is set. Fourth, the established turbulence model and cavitation model are used to solve the flow field, and the numerical calculation results of the flow field are obtained. In the cavitation flow of the propeller, the flow field can be regarded as a continuous homogeneous medium fully mixed by gas, vapor and liquid, and the homogeneous flow model is used to solve the flow field of the propeller. The continuity equation and momentum equation are:

where u is the velocity vector, ρ _m is the density of the mixed medium, μ _m is the dynamic viscosity coefficient of the mixed medium, μ _t is the turbulent viscosity coefficient, and p is the flow field pressure. The definition of the medium density ρ _m and the medium dynamic viscosity coefficient μ _m of the mixing term are:

ρ _m =ρ _v α _v +ρ _l α _l (20)

μ _m = μ _v α _v + μ _l α _l (21)

where ρ _l , α _l and μ _l are the fluid density of the liquid phase, respectively, and ρ _v , α _v and μ _v are the fluid density, volume fraction and fluid kinematic viscosity of the vapor phase, respectively.

Step 7: Given the convergence criteria for the unsteady cavitation fluid-structure interaction calculation of the composite propeller, the calculation results meet the convergence criteria at the same time and the number of sub-iterations is not less than the maximum number of iteration steps, so as to realize the convergence of the fluid-structure interaction calculation method.

In each coupling step, the structure field and the flow field are continuously cross-solved in sub-iteration steps to achieve that the calculation results meet the convergence criteria, complete the fluid-structure coupling calculation at this time step, and enter the calculation of the next time step; if the convergence criteria are not met, the judgment The size of the number of iteration steps. If the number of sub-iteration steps is less than the maximum number of iteration steps, continue to perform the sub-iteration convergence solution calculation. If the number of sub-iteration steps is not less than the maximum number of iteration steps, enter the next iteration calculation. After continuous cross-solving of sub-iteration steps in each time step, the results of the fluid-structure interaction calculation method are converged, and the unsteady cavitation fluid-structure interaction calculation of the composite propeller is completed.

Step 8, applying the methods described in Steps 1 to 7 to the field of numerical simulation of the optimal design of the composite propeller to achieve the predictability of the unsteady cavitation hydrodynamic performance of the composite propeller, which is conducive to the establishment of a rapid evaluation of the pros and cons of the flow field The method and the method for establishing the dynamic characteristics of cavitation and cavitation erosion of the composite propeller; Hydrodynamic performance prediction, composite propeller optimization design field.

When the method described in steps 1 to 8 is applied to the optimal design of the composite propeller and the prediction of the cavitation performance, the cavitation hydrodynamic performance of the composite propeller is obtained, and the effect of the composite material layering method on the cavitation hydrodynamic performance of the propeller is obtained. It can predict the structural dynamic response performance of composite propellers and solve engineering problems related to the strength and stability of composite propellers.

Beneficial effects:

1. A method for predicting the unsteady cavitation fluid-structure coupling performance of a composite propeller disclosed in the present invention, based on a tight coupling algorithm, bidirectionally couples and transfers the numerical calculation results of the flow field and the numerical calculation results of the structure field, and completes the iteration of the time step Convergence, the formation of unsteady cavitation fluid-structure interaction numerical calculation method.

2. A method for predicting the unsteady cavitation fluid-structure coupling performance of a composite propeller disclosed in the present invention, the unsteady cavitation fluid-structure coupling performance prediction method adopted in this method is more in line with the actual operation of the composite propeller. For in-depth and accurate analysis and prediction of the cavitation hydrodynamic performance of composite propellers, it can be applied to the prediction of structural dynamic response performance of composite propellers to solve engineering problems related to the strength and stability of composite propellers.

Description of drawings

1 is a flowchart of a method for predicting unsteady cavitation fluid-structure coupling performance of a composite propeller provided by the present invention;

2 is a schematic diagram of the incoming flow velocity of the large skew HSP composite material propeller provided by the embodiment of the present invention;

3 is a schematic diagram of a finite element model of a large skew HSP composite propeller provided by an embodiment of the present invention;

Fig. 4 is the unsteady cavitation shape of the large skew HSP composite propeller and the rigid propeller calculated by the embodiment of the present invention;

Fig. 5 is the unsteady cavitation cavitation volume comparison between the large skew HSP composite propeller and the rigid propeller calculated by the embodiment of the present invention;

FIG. 6 is a comparison of the propulsion efficiency changes between the large skew HSP composite propeller and the rigid propeller calculated by the embodiment of the present invention.

Detailed ways

With reference to the accompanying drawings, the prediction of the cavitation fluid-structure coupling characteristics of a single-material single-layer angle composite material high-slope HSP marine propeller is taken as an example. As shown in FIG. 1 , a method for predicting the unsteady cavitation fluid-structure coupling performance of a composite propeller disclosed in this embodiment, the specific implementation steps are as follows:

Step 1: Calculate the initial value of the steady-state flow field for the rigid propeller.

The steady initial value calculation is carried out for the flow field of the large-skew HSP marine rigid propeller with a diameter of 0.22m. The governing equations for the fluid steady state solution can be expressed by the mass conservation equation and the momentum conservation equation:

In the formula: the subscripts i and j represent the coordinate directions, u is the velocity vector, ρ is the fluid density, p is the flow field pressure, v is the kinematic viscosity coefficient, f _i is the mass force per unit volume, and δ _ij is the Kronecker function .

Step 2: Establish a finite element model of the composite propeller structure.

Based on the geometric parameters of the rigid propeller, the geometric model of the composite propeller is established. The fiber layup of the composite material is constrained with the geometric profile of a rigid propeller. The carbon fiber reinforced composite propeller with a single material and single layup angle is taken as the calculation object, and the stacking sequence of the propeller of the composite material is [-45] ₂₅ , and the material parameters of the composite material are shown in Table 1.

Table 1 Composite material parameters

The finite element model of the composite propeller is established based on the ACP module in ANSYS Workbench. The in-plane force, bending moment, in-plane strain and curvature of the composite propeller section satisfy the following relationship:

In the formula: [N] represents the in-plane force, [M] is the bending moment, ε° and κ are the mid-plane strain and mid-plane curvature, and the [A], [B], and [D] matrices are the tensile stiffness matrix, the coupling Stiffness Matrix and Bending Stiffness Matrix.

Step 3: Transfer the pressure, velocity and other data of the initial value of the steady flow field to the structure field through the fluid-solid coupling interface, and solve the finite element structure deformation to obtain the mesh deformation of the structure field.

Through the fluid-structure coupling interface between the composite propeller and the flow field, the pressure, velocity and other data of the initial value of the steady flow field are transferred to the structural field. According to the finite element model of the composite propeller established in step 2 and the obtained flow field pressure, Speed and other data, complete the finite element structural deformation solution of the composite propeller, and obtain the mesh deformation of the structural field. The finite element method is used to conduct transient analysis of the propeller structure under the action of hydrodynamic load. The control equation of the dynamic structure is as follows:

和

分别为结构位移、结构速度和结构加速度，{F_EX}代表流固耦合作用下结构所受外部激励力，{F_HE}代表流固耦合作用下结构所受流场力。where [M _s ], [C _s ] and [K _s ] are the structural mass matrix, the structural damping matrix and the structural stiffness matrix, respectively, {X},

and

are the structural displacement, structural velocity and structural acceleration, respectively, {F _EX } represents the external excitation force on the structure under the action of fluid-structure interaction, and {F _HE } represents the flow field force on the structure under the action of fluid-structure interaction.

Step 4: Establish a turbulence model for the calculation of the flow field of the composite propeller.

In order to better capture the turbulent structure of the multi-scale unsteady flow field and the phenomenon of flow in the near-wall region, the eddy viscosity model is used, and the turbulent viscosity coefficient μ _t is introduced to establish a relationship between the Reynolds stress and the average velocity gradient. The calculation to determine the eddy viscosity coefficient uses the two-equation k-ωSST turbulence model to close the Reynolds time-averaged equation:

为系踪平均，G_k和G_w分别是由平均速度梯度和浮力影响引起的湍动能产生项，Y_k和Y_M分别是由平均速度梯度和可压缩湍流脉动膨胀对总的耗散率的影响，D_w为横向扩散项。式中，σ_w和σ_k分别为湍动能和湍流频率的普朗特数：where k is the turbulent kinetic energy, ω is the turbulent frequency, ρ is the fluid density, μ is the dynamic viscosity coefficient,

is the tethered average, G _k and G _w are the turbulent kinetic energy generation terms caused by the average velocity gradient and buoyancy effects, respectively, and Y _k and Y _M are the total dissipation rate caused by the average velocity gradient and the compressible turbulent pulsation expansion, respectively. influence, _Dw is the lateral diffusion term. where _σw and _σk are Prandtl numbers of turbulent kinetic energy and turbulent frequency, respectively:

The formula for calculating the turbulent viscosity coefficient μ _t is as follows:

where S is the shear strain rate, and F ₁ and F ₂ are mixing functions.

Step 5: Establish a cavitation model for the calculation of the flow field of the composite propeller.

The cavitation model for the calculation of the flow field of the composite propeller adopts the transport equation based on cavitation dynamics proposed on the basis of the Ralyleigh-Plesset (R-P) equation:

where R _B is the bubble radius, p _v is the saturated vapor pressure at 25°C (p _v =3169Pa), S is the surface tension coefficient, ρ _l is the liquid density, T _∞ is the far-field fluid temperature, p _∞ is the far-field ambient pressure.

Ignoring the second derivative of the bubble radius and the interaction of surface tension, the rate of change of the bubble radius R _B , the bubble mass m _B and the bubble volume V _B with time is simplified respectively:

The density of cavitation vapor nucleus in water N _B (that is, there are N _B cavities in unit volume), then the vapor phase volume ratio ɑ _v is:

Then the interphase mass exchange rate m per unit volume is:

The above formula is the evaporation term. According to the above relationship, the expressions of the evaporation rate and condensation rate between the vapor and liquid phases can be calculated as:

where α _nuc is the volume fraction of the cavitation gas nucleus, Cd and C _p are the evaporation rate of the liquid phase when the partial pressure is lower than the saturated vapor pressure and the condensation rate of the vapor phase when the partial pressure is greater than the saturated vapor pressure, respectively, and R _B is the cavitation Radius, P _v is p _v (T _∞ ).

Step 6: Transfer the structural field deformation and other information obtained in Step 2 to the flow field through the fluid-solid coupling interface, update the flow field grid and solve the flow field, and obtain data such as the hydrodynamic load and velocity of the flow field.

Through the fluid-structure coupling interface between the composite propeller and the flow field, data such as the deformation of the structure field are transferred to the structure field, and the flow field grid is updated. And the cavitation model is used to solve the flow field, and the data such as the hydrodynamic load and velocity of the flow field cavitation are obtained. In the cavitation flow of the propeller, the flow field can be regarded as a continuous homogeneous medium fully mixed by gas, vapor and liquid, and the homogeneous flow model is used to solve the flow field of the propeller. The continuity equation and momentum equation are:

where u is the velocity vector, ρ _m is the density of the mixed medium, μ _m is the dynamic viscosity coefficient of the mixed medium, μ _t is the turbulent viscosity coefficient, and p is the flow field pressure. The definition of the medium density ρ _m and the medium dynamic viscosity coefficient μ _m of the mixing term are:

ρ _m =ρ _v α _v +ρ _l α _l (20)

μ _m = μ _v α _v + μ _l α _l (21)

where ρ _l , α _l and μ _l are the fluid density of the liquid phase, respectively, and ρ _v , α _v and μ _v are the fluid density, volume fraction and fluid kinematic viscosity of the vapor phase, respectively.

Step 7: Given the convergence criteria for the unsteady cavitation fluid-structure interaction calculation of the composite propeller, the calculation results meet the convergence criteria at the same time and the number of sub-iterations is not less than the maximum number of iteration steps, so as to realize the convergence of the fluid-structure interaction calculation method.

In each coupling step, the structure field and the flow field are continuously cross-solved in sub-iteration steps to achieve that the calculation results meet the convergence criteria, complete the fluid-structure coupling calculation at this time step, and enter the calculation of the next time step; if the convergence criteria are not met, the judgment The size of the number of iteration steps. If the number of sub-iteration steps is less than the maximum number of iteration steps, continue to perform the sub-iteration convergence solution calculation. If the number of sub-iteration steps is not less than the maximum number of iteration steps, enter the next iteration calculation. After continuous cross-solving of sub-iteration steps in each time step, the results of the fluid-structure interaction calculation method are converged, and the unsteady cavitation fluid-structure interaction calculation of the composite propeller is completed. The unsteady cavitation fluid-structure interaction performance prediction method of composite propeller can obtain the propulsion performance, instantaneous cavitation shape, flow field and blade pulsating pressure characteristics of composite materials when cavitation occurs under different wakes. The development curves of the propulsion efficiency and the cavitation volume of the composite propeller obtained by calculation are consistent with a uniform sinusoidal curve with five peaks. The propulsion efficiency of the composite propeller is higher than that of the rigid propeller, and the cavitation volume is significantly smaller than that of the rigid propeller. The results show that the laminated composite propeller has the advantages of delaying cavitation and improving the hydrodynamic performance of cavitation compared with the rigid propeller, which satisfies the practical application in this watershed and is superior to the traditional rigid propeller. The calculation results show that the prediction of the unsteady cavitation performance of the composite propeller has important engineering significance, which can be applied to the prediction of the cavitation performance of the composite propeller under different wake conditions, and it is possible to quickly evaluate the pros and cons of the flow field. At the same time, through the numerical simulation prediction of the cavitation performance of composite propellers and rigid propellers with different layup structures, a rapid evaluation of the performance of composite propellers can be achieved.

Step 8, applying the methods described in Steps 1 to 7 to the field of numerical simulation of the optimal design of the composite propeller to achieve the predictability of the unsteady cavitation hydrodynamic performance of the composite propeller, which is conducive to the establishment of a rapid evaluation of the pros and cons of the flow field The method and the method for establishing the dynamic characteristics of cavitation and cavitation erosion of the composite propeller; Hydrodynamic performance prediction, composite propeller optimization design field.

When the method described in steps 1 to 8 is applied to the optimal design of the composite propeller and the prediction of the cavitation performance, the cavitation hydrodynamic performance of the composite propeller is obtained, and the effect of the composite material layering method on the cavitation hydrodynamic performance of the propeller is obtained. It can predict the structural dynamic response performance of composite propellers and solve engineering problems related to the strength and stability of composite propellers.

The above-mentioned specific descriptions further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned descriptions are only specific embodiments of the present invention, and are not intended to limit the protection of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (4)

1. a composite propeller unsteady cavitation fluid-structure coupling performance prediction method, is characterized in that: comprise the steps: Step 1: Calculate the initial value of the steady flow field for the rigid propeller; Carry out the steady initial value calculation for the flow field of the rigid propeller, set the propeller rotation speed and the incoming flow speed for the propeller to work, and obtain the initial value data of the steady flow field; the control equation of the fluid steady state solution is expressed by the mass conservation equation and the momentum conservation equation :

In the formula: the subscripts i and j represent the coordinate directions, u is the velocity vector, ρ is the fluid density, p is the flow field pressure, v is the kinematic viscosity coefficient, f _i is the mass force per unit volume, and δ _ij is the Kronecker function ; Step 2: Establish a finite element model of the composite propeller structure; Based on the geometric parameters of the rigid propeller, the geometric model of the composite propeller is established; the fiber layup of the composite material is constrained by the geometric contour of the rigid propeller, and the layup of the composite propeller is set layer by layer according to the layup sequence of the composite propeller based on the finite element software. Layer material thickness and material properties, input the density ρ, elastic modulus E, shear modulus G, and Poisson’s ratio υ of each layer of fiber cloth to establish the finite element model of the composite propeller; the internal force and bending moment of the composite propeller section It satisfies the following relation with the in-plane strain and curvature:

In the formula: [N] represents the in-plane force, [M] is the bending moment, ε° and κ are the mid-plane strain and mid-plane curvature, and the [A], [B], and [D] matrices are the in-plane stiffness matrix, the coupling stiffness matrix and bending stiffness matrix; Step 3: Transfer the initial value data of the steady flow field to the structure field through the fluid-solid coupling interface, and solve the finite element structure deformation to obtain the mesh deformation of the structure field; Through the fluid-solid coupling interface between the composite propeller and the flow field, the initial value data of the steady flow field is transferred to the structural field. According to the finite element model of the composite propeller established in step 2 and the obtained initial value data of the flow field, the composite material is completed. The finite element structural deformation of the material propeller is solved, and the mesh deformation of the structural field is obtained; the finite element method is used to perform a transient analysis of the propeller structure under the action of hydrodynamic load, and the dynamic structure control equation is as follows:

where [M _s ], [C _s ] and [K _s ] are the structural mass matrix, the structural damping matrix and the structural stiffness matrix, respectively, {X},

and

are the structural displacement, structural velocity and structural acceleration, respectively, {F _EX } represents the external excitation force on the structure under the action of fluid-structure interaction, {F _HE } represents the flow field force on the structure under the action of fluid-structure interaction; Step 4: Establish a turbulence model for the calculation of the flow field of the composite propeller; In order to better capture the turbulent structure of the multi-scale unsteady flow field and the phenomenon of flow in the near-wall region, the eddy viscosity model is used, and the turbulent viscosity coefficient μ _t is introduced to establish a relationship between the Reynolds stress and the average velocity gradient; the calculation of the eddy viscosity coefficient is determined by using The two-equation k-ωSST turbulence model closes the Reynolds time-averaged equation:

where k is the turbulent kinetic energy, ω is the turbulent frequency, ρ is the fluid density, μ is the dynamic viscosity coefficient,

is the tethered average, the velocities G _k and G _w are the turbulent kinetic energy generation terms caused by the mean velocity gradient and buoyancy effects, respectively, and Y _k and Y _M are the total dissipation rate caused by the mean velocity gradient and the compressible turbulent pulsation expansion, respectively , D _w is the lateral diffusion term; in the formula, σ _w and σ _k are the Prandtl number of turbulent kinetic energy and turbulent frequency, respectively:

The formula for calculating the turbulent viscosity coefficient μ _t is as follows:

where S is the shear strain rate, F ₁ and F ₂ are the mixing functions; Step 5: Establish a cavitation model for the calculation of the flow field of the composite propeller; The cavitation model for the calculation of the flow field of the composite propeller adopts the transport equation based on cavitation dynamics proposed on the basis of the Ralyleigh-Plesset (R-P) equation:

where R _B is the bubble radius, p _v is the saturated vapor pressure in the environment, S is the surface tension coefficient, ρl is the liquid density, T _∞ is the far-field fluid temperature, and p _∞ is the far-field ambient pressure; Ignoring the second derivative of the bubble radius and the interaction of surface tension, the rate of change of the bubble radius R _B , the bubble mass m _B and the bubble volume V _B with time is simplified respectively:

N _B is the density of cavitation vapor nucleus in water, then the vapor phase volume ratio ɑ _v is:

Then the interphase mass exchange rate m per unit volume is:

The above formula is the evaporation term. According to the above relationship, the expressions of the evaporation rate and condensation rate between the vapor and liquid phases are respectively:

where α _nuc is the cavitation gas core volume fraction, C _d and C _p are the liquid phase evaporation rate when the partial pressure is lower than the saturated vapor pressure and the vapor phase condensation rate when the partial pressure is greater than the saturated vapor pressure, respectively, and R _B is the empty bubble radius, P _v is p _v (T _∞ ); Step 6: Transfer the information of the deformation of the structure field obtained in Step 3 to the flow field through the fluid-solid coupling interface, update the flow field grid and solve the flow field, and obtain the numerical calculation result of the flow field; Through the fluid-structure coupling interface between the composite propeller and the flow field, the deformation data of the structure field is transmitted to the flow field, the flow field grid is updated, and the cavitation number of the propeller cavitation condition is set. Fourth, the established turbulence model and cavitation model are used to solve the flow field, and the numerical calculation results of the flow field are obtained. The flow model is used to solve the flow field of the propeller; the continuity equation and momentum equation are:

where u is the velocity vector, ρ _m is the density of the mixed medium, μ _m is the dynamic viscosity coefficient of the mixed medium, μ _t is the turbulent viscosity coefficient, and p is the flow field pressure; the medium density ρ _m of the mixing term and the dynamic viscosity of the medium are The coefficients _μm are defined as: ρ _m =ρ _v α _v +ρ _l α _l (20) μ _m = μ _v α _v + μ _l α _l (21) where ρ _l , α _l and μ _l are the fluid density of the liquid phase, respectively, and ρ _v , α _v and μ _v are the fluid density, volume fraction and fluid kinematic viscosity of the vapor phase, respectively; Step 7: Given the convergence criterion of the unsteady cavitation fluid-structure interaction calculation of the composite propeller, make the calculation result satisfy the convergence criteria at the same time and the number of sub-iterations is not less than the maximum number of iteration steps, so as to realize the convergence of the fluid-structure interaction calculation method; In each coupling step, the structure field and the flow field are continuously cross-solved in sub-iteration steps to achieve that the calculation results meet the convergence criteria, complete the fluid-structure coupling calculation at this time step, and enter the calculation of the next time step; if the convergence criteria are not met, the judgment The size of the number of iteration steps. If the number of sub-iteration steps is less than the maximum number of iteration steps, continue the sub-iteration convergence solution calculation. If the number of sub-iteration steps is not less than the maximum number of iteration steps, enter the next iteration calculation; after the sub-iteration steps within each time step The continuous cross-solving of the composite material realizes the convergence of the results of the fluid-structure coupling calculation method, and completes the unsteady cavitation fluid-structure coupling calculation of the composite propeller. 2. The method for predicting the unsteady cavitation fluid-structure coupling performance of a composite propeller according to claim 1, wherein in step 8, the method described in steps 1 to 7 is applied to the optimal design value of the composite propeller In the field of simulation, realizing the predictability of the unsteady cavitation hydrodynamic performance of the composite propeller is conducive to the establishment of a rapid evaluation method for the pros and cons of the flow field and the establishment of a method for evaluating the dynamic characteristics of cavitation and cavitation erosion of the composite propeller; steps The application fields of the method for predicting the unsteady cavitation fluid-structure interaction performance of the composite propeller include the prediction of fluid-structure interaction characteristics, the prediction of the cavitation hydrodynamic performance of the propeller, and the optimization design of the composite material propeller. 3. A method for predicting the unsteady cavitation fluid-structure coupling performance of a composite propeller according to claim 2, wherein: when the method described in steps 1 to 8 is applied to the optimal design and cavitation of the composite propeller In the performance prediction, the cavitation hydrodynamic performance of the composite propeller is obtained, the influence of the composite material layering method on the cavitation hydrodynamic performance of the propeller is obtained, the structural dynamic response performance prediction of the composite propeller is realized, and the strength and stability of the composite propeller are solved. Sex-related engineering issues. 4. The method for predicting the unsteady cavitation fluid-structure coupling performance of a composite propeller according to claim 1, 2 or 3, wherein the finite element software is implemented by selecting the ACP module in ANSYS Workbench.

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