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

Method for predicting unsteady cavitation fluid-solid coupling performance of composite propeller Download PDF

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CN114757120A
CN114757120A CN202210373898.1A CN202210373898A CN114757120A CN 114757120 A CN114757120 A CN 114757120A CN 202210373898 A CN202210373898 A CN 202210373898A CN 114757120 A CN114757120 A CN 114757120A
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张丹丹
吴钦
董璐璐
黄彪
王国玉
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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

Method for predicting unsteady cavitation fluid-solid coupling performance of composite propeller
Technical Field
The invention relates to a method for predicting unsteady cavitation fluid-solid coupling performance of a composite propeller, which is suitable for predicting hydrodynamic performance and cavitation performance of the composite propeller based on a bidirectional fluid-solid coupling algorithm and belongs to the technical field of composite propeller performance prediction.
Background
In order to improve the hydrodynamic performance and the vibration noise performance of the propeller and prolong the service life of the propeller, numerous scholars at home and abroad research on manufacturing materials of novel hydraulic machinery in various aspects. The fiber reinforced composite material has high specific strength and high specific stiffness similar to those of alloy materials, and simultaneously has anisotropy and excellent damping performance, so that the fiber reinforced composite material is suitable for various hydrodynamic machines serving under complex underwater environments. Compare with traditional metal propeller, the fluid-solid coupling characteristic of the demonstration of combined material propeller under the effect of cavitation hydrodynamic load can make the pitch angle of propeller change, restraines the production of vacuole to promote the hydrodynamic force performance of propeller. Due to the complex appearance structure and the diversity of the internal layering structure of the propeller blade made of the composite material, the cavitation fluid-solid coupling performance of the propeller made of the composite material is difficult to predict. Due to the fact that the large-scale propeller is difficult to machine, the hydrodynamic performance of the propeller is often tested through a model test, equipment of the model test is still expensive in manufacturing cost, and a scale effect exists, so that the theoretical method for developing and predicting the cavitation hydrodynamic performance of the composite propeller has important engineering significance.
Because the fiber reinforced composite propeller has a complex structural shape, and the blades can generate certain elastic deformation under the action of hydrodynamic force, and a large number of complex nonlinear problems are involved, the numerical calculation method suitable for the fluid-solid coupling performance of the traditional metal propeller is not suitable any more, but the numerical calculation of the bidirectional fluid-solid coupling performance of the composite propeller is still limited in the hydrodynamic force performance prediction and the steady cavitation performance prediction of the composite propeller although being concerned and researched by many scholars, and cannot be directly applied to the unsteady cavitation fluid-solid coupling performance prediction of the composite propeller. Therefore, the method for predicting the unsteady cavitation fluid-solid coupling performance of the composite material propeller is established, the structural deformation of the composite material propeller can be calculated, the unsteady flow field characteristic of the composite material propeller can be analyzed, and the method has important practical significance for the practical application of the propeller.
Disclosure of Invention
The invention discloses a method for predicting unsteady cavitation fluid-solid coupling performance of a composite propeller, which aims to solve the technical problems that: a universal method for predicting unsteady cavitation fluid-solid coupling performance of a composite propeller is established, the establishment of a flow field calculation model is realized based on a flow field numerical calculation model comprising a flow field multiphase flow model, an RANS equation of outflow field calculation and a cavitation model, on the basis of the flow field calculation model, a blade structure of the composite propeller is subjected to layered modeling based on a laminated plate theory, the numerical calculation of structural dynamics is embedded into the flow field calculation, an accurate fluid-solid coupling interface is arranged, the flow field numerical calculation result and the structural field numerical calculation result are subjected to bidirectional coupling and transmission through a data transmission interface based on a tight coupling algorithm, the applicability and the accuracy of the bidirectional coupling and the transmission are analyzed, and the unsteady cavitation fluid-solid coupling performance of the composite propeller is obtained. The method is beneficial to deeply analyzing and predicting the cavitation hydrodynamic performance of the composite material propeller, can be applied to predicting the structure dynamic response performance of the composite material propeller, and solves the engineering problems related to the strength and the stability of the composite material propeller.
The application fields of the method for predicting the unsteady cavitation fluid-solid coupling characteristic of the composite material propeller comprise the fields of fluid-solid coupling characteristic prediction, propeller cavitation hydrodynamic performance prediction and composite material propeller optimization design. The method can effectively predict the hydrodynamic deformation generated by the composite propeller, and has the advantages of high prediction efficiency and high precision.
The invention discloses a method for predicting unsteady cavitation fluid-solid coupling performance of a composite propeller, which comprises the following steps of:
the method comprises the following steps: and (4) performing initial value calculation of a steady-state flow field on the rigid propeller.
And performing steady initial value calculation aiming at the flow field of the rigid propeller, setting the rotating speed and the incoming flow speed of the propeller working by the propeller, and obtaining initial value data of the steady flow field. The governing equation for fluid steady state solution is expressed by a mass conservation equation and a momentum conservation equation:
Figure BDA0003589517480000021
Figure BDA0003589517480000022
in the formula: subscripts i, j represent coordinate directions, u is a velocity vector, ρ is a fluid density, p is a flow field pressure, v is a kinematic viscosity coefficient, fi is a unit volume mass force, and δijIs a kronecker function.
Step two: and establishing a finite element model of the composite propeller structure.
And establishing a geometric model of the composite propeller based on the geometric dimension parameters of the rigid propeller. The method comprises the steps of constraining fiber layering of a composite material by the geometric profile of a rigid propeller, setting the thickness and the material property of the layering material of the composite material propeller layer by layer according to the layering sequence of the composite material propeller based on finite element software, inputting the density rho, the elastic modulus E, the shear modulus G and the Poisson ratio upsilon of each layer of fiber cloth, and establishing a finite element model of the composite material propeller. The composite material propeller section plane internal force, bending moment, plane internal strain and curvature satisfy the following relational expressions:
Figure BDA0003589517480000023
In the formula: the [ N ] is surface internal force, the [ M ] is bending moment, the [ epsilon ] degree and the [ kappa ] are middle surface strain and middle surface curvature, and the [ A ], [ B ] and [ D ] matrixes are an in-plane rigidity matrix, a coupling rigidity matrix and a bending rigidity matrix respectively.
Preferably, the finite element software is realized by an ACP module in ANSYS Workbench.
Step three: and transmitting the initial value data of the steady flow field to the structural field through a fluid-solid coupling interface, and solving the finite element structural deformation to obtain the grid deformation of the structural field.
And (4) transmitting initial value data of the steady flow field to the structural field through a fluid-solid coupling interface between the composite propeller and the flow field, and according to the composite propeller finite element model established in the step two and the obtained initial value data of the flow field, completing the finite element structure deformation solving of the composite propeller to obtain the grid deformation of the structural field. Transient analysis is carried out on the propeller structure under the action of hydrodynamic load by using a finite element method, and the control equation of the dynamic structure is as follows:
Figure BDA0003589517480000031
in the formula [ Ms]、[Cs]And [ K ]s]Respectively a structural mass matrix, a structural damping matrix and a structural rigidity matrix, { X }, respectively,
Figure BDA0003589517480000032
And
Figure BDA0003589517480000033
respectively, structural displacement, structural velocity and structural acceleration, { FEXRepresents the external excitation force applied to the structure under the action of fluid-solid coupling, { F HEDenotes fluid and solidThe structure is subjected to the flow field force under the coupling action.
Step four: and (4) establishing a turbulence model for the composite material propeller flow field calculation.
In order to better capture the phenomenon of a multi-scale unsteady flow field turbulence structure and near-wall region flow, a vortex viscosity model is adopted, and a turbulence viscosity coefficient mu is introducedtThe reynolds stress is correlated with the mean velocity gradient. The calculation for determining the vortex viscosity coefficient adopts a two-equation k-omega SST turbulence model to close the mean square process of Reynolds:
Figure BDA0003589517480000034
Figure BDA0003589517480000035
where k is the turbulent kinetic energy, ω is the turbulent frequency, ρ is the fluid density, μ is the kinetic viscosity coefficient,
Figure BDA0003589517480000036
for tracking average, velocity GkAnd GwRespectively, the turbulent kinetic energy producing term, Y, due to the influence of the mean velocity gradient and buoyancykAnd YMThe influence of the mean velocity gradient and the compressible turbulent pulsating expansion on the total dissipation ratio, DwIs a lateral diffusion term. In the formula, σwAnd σkPrandtl numbers for turbulence energy and turbulence frequency, respectively:
Figure BDA0003589517480000037
Figure BDA0003589517480000038
coefficient of turbulent viscosity mutIs calculated as follows:
Figure BDA0003589517480000039
wherein S is a shear strain rate, F1、F2Is a mixing function.
Step five: and establishing a cavitation model for the flow field calculation of the composite propeller.
A cavitation model for calculating the composite propeller flow field adopts a transport equation based on cavitation dynamics, which is provided on the basis of a Ralyleigh-Plesset (R-P) equation:
Figure BDA00035895174800000310
In the formula, RBIs the cavitation radius, pvIs the saturated vapor pressure under the environment, S is the surface tension coefficient, rholIs the liquid density, T∞Is far field fluid temperature, p∞Is the far field ambient pressure.
Neglecting the interaction of the second derivative of the cavity radius and the surface tension, respectively simplifying the cavity radius RBCavitation mass mBAnd a cavitation volume VBRate of change with time:
Figure BDA0003589517480000041
Figure BDA0003589517480000042
Figure BDA0003589517480000043
NBis the cavitation steam core density (namely N in unit volume)BOne void), the vapor phase volume ratio alphavComprises the following steps:
Figure BDA0003589517480000044
the mass exchange rate m between phases per unit volume is:
Figure BDA0003589517480000045
the above formula is an evaporation term, and the expressions of the evaporation rate and the condensation rate between the vapor and the liquid phases are respectively found according to the relational expression:
Figure BDA0003589517480000046
Figure BDA0003589517480000047
in the formula, alphanucIs cavitation gas core volume fraction, CdAnd CpRespectively, the liquid phase evaporation rate when the local pressure is lower than the saturated vapor pressure and the vapor phase condensation rate when the local pressure is higher than the saturated vapor pressure, RBIs the cavitation radius, PvIs pv(T∞)。
Step six: and transmitting the structural field deformation information obtained in the step three to the flow field through a fluid-solid coupling interface, and updating a flow field grid and solving the flow field to obtain a numerical calculation result of the flow field.
And (4) transmitting the structural field deformation data to the flow field through a fluid-solid coupling interface between the composite material propeller and the flow field, updating a flow field grid, setting the cavitation number of the propeller under the cavitation condition, and solving the flow field based on the turbulence model and the cavitation model established in the third step and the fourth step to obtain a numerical calculation result of the flow field. In the cavitation flow of the propeller, the flow field can be regarded as a continuous uniform medium formed by fully mixing gas, steam and liquid, and the flow field of the propeller is solved by adopting a homogeneous phase flow model. Wherein the continuity equation and the momentum equation are:
Figure BDA0003589517480000048
Figure BDA0003589517480000049
In the formula: u is the velocity vector, ρmDensity of mixed medium, mumIs the dynamic viscosity coefficient of the mixing medium, mutFor the turbulent viscosity coefficient, p is the flow field pressure. Medium density p of mixed termmAnd coefficient of dynamic viscosity of medium mumAre defined as follows:
ρm＝ρvαv+ρlαl (20)
μm＝μvαv+μlαl (21)
in the formula: rhol、αlAnd mulDensity of the fluid, p, respectively in the liquid phasev、αvAnd muvThe fluid density, volume fraction and fluid kinematic viscosity of the vapor phase, respectively.
Step seven: and giving a convergence criterion of unsteady cavitation fluid-solid coupling calculation of the composite material propeller, so that the calculation result simultaneously meets the convergence criterion and the number of sub-iterations is not less than the maximum iteration step number, and realizing convergence of the fluid-solid coupling calculation method.
Continuously crossing solving of the structural field and the flow field in each coupling step through the sub-iteration step to achieve that a calculation result meets a convergence standard, completing fluid-solid coupling calculation of the time step, and entering next time step calculation; and if the convergence standard is not met, judging the size of the sub-iteration step number, if the sub-iteration step number is smaller than the maximum iteration step number, continuing to perform sub-iteration convergence solving calculation, and if the sub-iteration step number is not smaller than the maximum iteration step number, entering the next step of iterative calculation. And (4) continuously intersecting and solving the sub-iteration steps in each time step to realize the result convergence of the fluid-solid coupling calculation method and finish the unsteady cavitation fluid-solid coupling calculation of the composite material propeller.
Step eight, applying the method in the steps one to seven to the field of the optimized design numerical simulation of the composite material propeller, realizing the predictability of the unsteady cavitation hydrodynamic performance of the composite material propeller, and being beneficial to establishing a flow field quality rapid evaluation method and establishing a cavitation dynamic characteristic and cavitation erosion branching evaluation method of the composite material propeller; and eighthly, the application fields of the method for predicting the unsteady cavitation fluid-solid coupling performance of the composite material propeller comprise the fields of fluid-solid coupling characteristic prediction, propeller cavitation hydrodynamic performance prediction and composite material propeller optimization design.
When the method in the first step to the eighth step is applied to the optimization design and cavitation performance prediction of the composite propeller, the cavitation hydrodynamic performance of the composite propeller is obtained, the influence of a composite material layering mode on the cavitation hydrodynamic performance of the propeller is obtained, the structure dynamic response performance prediction of the composite propeller is realized, and the engineering problems related to the strength and the stability of the composite propeller are solved.
Has the beneficial effects that:
1. the invention discloses a method for predicting unsteady cavitation fluid-solid coupling performance of a composite propeller.
2. The method for predicting the unsteady cavitation fluid-solid coupling performance of the composite material propeller disclosed by the invention is more in line with the flow field environment of the actual operation of the composite material propeller, is favorable for deeply and accurately analyzing and predicting the cavitation hydrodynamic performance of the composite material propeller, can be applied to predicting the structural dynamic response performance of the composite material propeller, and solves the engineering problems related to the strength and the stability of the composite material propeller.
Drawings
FIG. 1 is a flow chart of a method for predicting unsteady cavitation fluid-solid coupling performance of a composite propeller provided by the invention;
fig. 2 is a schematic diagram of the incoming flow speed of a large-side-inclined HSP composite propeller provided by an embodiment of the invention;
FIG. 3 is a schematic diagram of a finite element model of a large-side-bias HSP composite propeller provided by an embodiment of the invention;
FIG. 4 is a graph of unsteady cavitation patterns calculated for a large sideslope HSP composite propeller and a rigid propeller in accordance with an embodiment of the present invention;
FIG. 5 is a comparison of unsteady cavitation bubble volumes of a large laterally skewed HSP composite propeller and a rigid propeller calculated in accordance with an embodiment of the invention;
Fig. 6 is a comparison of the calculated change in propulsion efficiency of a large sideslope HSP composite propeller compared to a rigid propeller according to an embodiment of the invention.
Detailed Description
With reference to the attached drawings, cavitation fluid-solid coupling characteristic prediction of a single-material single-layering-angle composite material large-side-inclination HSP marine propeller is taken as an embodiment. As shown in fig. 1, the method for predicting unsteady cavitation fluid-solid coupling performance of a composite propeller disclosed in this embodiment includes the following specific implementation steps:
the method comprises the following steps: and calculating the initial value of the steady-state flow field of the rigid propeller.
And (3) performing fixed initial value calculation on the flow field of the rigid propeller with the diameter of 0.22m and the large-side-inclination HSP for the ship, setting the incoming flow speed of the propeller at 1050r/min, and acquiring initial value data such as pressure, speed and the like of the fixed flow field. The governing equation for the steady state solution of the fluid can be expressed by the mass conservation equation and the momentum conservation equation:
Figure BDA0003589517480000061
Figure BDA0003589517480000062
in the formula: subscripts i, j represent coordinate directions, u is a velocity vector, ρ is a fluid density, p is a flow field pressure, v is a kinematic viscosity coefficient, fiIs a mass force per unit volume, δijIs the kronecker function.
Step two: and establishing a finite element model of the composite propeller structure.
And establishing a geometric model of the composite propeller based on the geometric dimension parameters of the rigid propeller. The fiber lay-up of the composite material is constrained by the geometric profile of the rigid propeller. Taking a single-material single-layer-angle carbon fiber reinforced composite propeller as a calculation object, wherein the stacking sequence of the composite propeller is [ -45 ]]25The material parameters of the composite material are shown in Table 1.
TABLE 1 composite parameters
Figure BDA0003589517480000063
And establishing a finite element model of the composite material propeller based on an ACP module in the ANSYS Workbench. The composite material propeller cross-section plane internal force and bending moment, and the plane internal strain and curvature satisfy the following relational expressions:
Figure BDA0003589517480000064
in the formula: the [ N ] generation surface internal force, [ M ] is bending moment, epsilon DEG and kappa are mid-plane strain and mid-plane curvature, and the [ A ], [ B ] and [ D ] matrixes are respectively a tensile stiffness matrix, a coupling stiffness matrix and a bending stiffness matrix.
Step three: and transmitting the pressure, speed and other data of the initial value of the steady flow field to the structural field through a fluid-solid coupling interface, and carrying out finite element structural deformation solving to obtain the grid deformation of the structural field.
And D, transmitting the initial value of the pressure, the speed and other data of the steady flow field to the structural field through a fluid-solid coupling interface between the composite propeller and the flow field, and completing the finite element structure deformation solution of the composite propeller according to the finite element model of the composite propeller established in the step two and the obtained pressure, speed and other data of the flow field to obtain the grid deformation of the structural field. Transient analysis is carried out on the propeller structure under the action of hydrodynamic load by using a finite element method, and the control equation of the dynamic structure is as follows:
Figure BDA0003589517480000071
In the formula [ M ]s]、[Cs]And [ K ]s]Respectively a structural mass matrix, a structural damping matrix and a structural rigidity matrix, { X }),
Figure BDA0003589517480000072
And
Figure BDA0003589517480000073
respectively, structural displacement, structural velocity and structural acceleration, { FEXDenotes the external excitation force applied to the structure by fluid-solid coupling, { FHEAnd represents the fluid field force of the structure under the fluid-solid coupling effect.
Step four: and (4) establishing a turbulence model for the composite material propeller flow field calculation.
In order to better capture the phenomena of multi-scale unsteady flow field turbulence structure and near-wall region flow, a vortex viscosity model is adopted to introduce a turbulence viscosity coefficient mutThe reynolds stress is correlated with the mean velocity gradient. The calculation for determining the vortex viscosity coefficient adopts a two-equation k-omega SST turbulence model to close the mean square range of Reynolds:
Figure BDA0003589517480000074
Figure BDA0003589517480000075
wherein k is the turbulent kinetic energy, ω is the turbulent frequency, ρ is the fluid density, μ is the kinetic viscosity coefficient,
Figure BDA0003589517480000076
for trace average, GkAnd GwRespectively by mean speed stepsTurbulence energy producing term, Y, caused by influence of gravity and buoyancykAnd YMThe influence of the mean velocity gradient and the compressible turbulent pulsating expansion on the total dissipation ratio, DwIs a lateral diffusion term. In the formula, σwAnd σkPrandtl numbers for turbulence energy and turbulence frequency, respectively:
Figure BDA0003589517480000077
Figure BDA0003589517480000078
coefficient of turbulent viscosity mu tIs calculated as follows:
Figure BDA0003589517480000079
wherein S is a shear strain rate, F1、F2Is a mixing function.
Step five: and establishing a cavitation model for the composite material propeller flow field calculation.
A cavitation model for calculating the composite propeller flow field adopts a transport equation based on cavitation dynamics, which is provided on the basis of a Ralyleigh-Plesset (R-P) equation:
Figure BDA0003589517480000081
in the formula, RBIs the cavitation radius, pvIs saturated vapor pressure (p) at 25 deg.Cv3169Pa), S is the surface tension coefficient, rholIs a liquid density, T∞For far field fluid temperature, p∞Is the far field ambient pressure.
Neglecting the second derivative of the cavitation radius and the interaction of the surface tension, respectively simplifying the cavitation radius RBMass of cavitation mBAnd the cavitation volume VBRate of change with time:
Figure BDA0003589517480000082
Figure BDA0003589517480000083
Figure BDA0003589517480000084
cavitation in water steam nucleus density NB(i.e., N in unit volume)BOne void), the vapor phase volume ratio alphavComprises the following steps:
Figure BDA0003589517480000085
the mass exchange rate m between phases per unit volume is:
Figure BDA0003589517480000086
the above expression is an evaporation term, and the expressions of the evaporation rate and the condensation rate between vapor and liquid phases are respectively found from the above relation:
Figure BDA0003589517480000087
Figure BDA0003589517480000088
in the formula, alphanucIs cavitation gas core volume fraction, Cd and CpRespectively, the liquid phase evaporation rate when the local pressure is lower than the saturated vapor pressure and the vapor phase condensation rate when the local pressure is higher than the saturated vapor pressure, R BIs the cavitation radius, PvIs pv(T∞)。
Step six: and (4) transmitting the structural field deformation and other information obtained in the step two to the flow field through a fluid-solid coupling interface, updating a flow field grid and solving the flow field, and obtaining data of hydrodynamic load, speed and the like of the flow field.
And (4) transmitting data such as structural field deformation to the structural field through a fluid-solid coupling interface between the composite material propeller and the flow field, updating a flow field grid, setting the cavitation number to be 2.99, and performing flow field solution based on the turbulence model and the cavitation model established in the third step and the fourth step to obtain data such as flow field cavitation hydrodynamic load, speed and the like. In the cavitation flow of the propeller, a flow field can be regarded as a continuous uniform medium formed by fully mixing gas, steam and liquid, and the flow field of the propeller is solved by adopting a homogeneous phase flow model. Wherein the continuity equation and the momentum equation are:
Figure BDA0003589517480000089
Figure BDA0003589517480000091
in the formula: u is the velocity vector, ρmIs the density of the mixed medium, mumIs the kinetic viscosity coefficient of the mixing medium, mutFor the turbulent viscosity coefficient, p is the flow field pressure. Medium density p of the mixing termmAnd coefficient of dynamic viscosity of medium mumAre defined as follows:
ρm＝ρvαv+ρlαl (20)
μm＝μvαv+μlαl (21)
in the formula: rhol、αlAnd mulDensity of the fluid, p, respectively in the liquid phasev、αvAnd muvThe fluid density, volume fraction and fluid kinematic viscosity of the vapor phase, respectively.
Step seven: and giving a convergence criterion of unsteady cavitation fluid-solid coupling calculation of the composite material propeller, so that the calculation result simultaneously meets the convergence criterion and the number of sub-iterations is not less than the maximum iteration step number, and realizing convergence of the fluid-solid coupling calculation method.
Continuously crossing solving of the structural field and the flow field in each coupling step through the sub-iteration step to achieve that a calculation result meets a convergence standard, completing fluid-solid coupling calculation of the time step, and entering next time step calculation; and if the convergence standard is not met, judging the size of the sub-iteration step number, if the sub-iteration step number is smaller than the maximum iteration step number, continuing to perform sub-iteration convergence solving calculation, and if the sub-iteration step number is not smaller than the maximum iteration step number, entering the next step of iterative calculation. And (4) continuously intersecting and solving the sub-iteration steps in each time step to realize the result convergence of the fluid-solid coupling calculation method and finish the unsteady cavitation fluid-solid coupling calculation of the composite material propeller. The method for predicting the unsteady cavitation fluid-solid coupling performance of the composite propeller can obtain the propulsion performance, the instantaneous cavitation form, the flow field and the blade pulsating pressure characteristic of the composite material when cavitation occurs under different wake flows. The calculated propulsion efficiency and cavitation volume development curves of the composite propeller are consistent to a uniform sinusoidal curve accompanied by 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 compared with the rigid propeller, the composite propeller with the layers has the advantages of delaying cavitation and improving the hydrodynamic performance of cavitation, meets the practical application under the condition of the watershed and is superior to the traditional rigid propeller. The calculation result shows that the method has important engineering significance for the prediction and research of the unsteady cavitation performance of the composite propeller, can be suitable for predicting the cavitation performance of the composite propeller under different wake conditions, and realizes the possibility of rapidly evaluating the quality of a flow field; meanwhile, the performance of the composite propeller can be quickly evaluated through numerical simulation prediction of cavitation performance of the composite propeller and the rigid propeller with different layering structures.
Step eight, applying the method in the steps one to seven to the field of the optimized design numerical simulation of the composite propeller, realizing the predictability of the unsteady cavitation hydrodynamic performance of the composite propeller, and being beneficial to establishing a flow field quality rapid evaluation method and establishing a cavitation dynamic characteristic and cavitation erosion branching evaluation method of the composite propeller; and eighthly, the application fields of the method for predicting the unsteady cavitation fluid-solid coupling performance of the composite propeller comprise the fields of fluid-solid coupling characteristic prediction, propeller cavitation hydrodynamic performance prediction and composite propeller optimization design.
When the method in the first step to the eighth step is applied to the optimization design and cavitation performance prediction of the composite propeller, the cavitation hydrodynamic performance of the composite propeller is obtained, the influence of a composite material layering mode on the cavitation hydrodynamic performance of the propeller is obtained, the structure dynamic response performance prediction of the composite propeller is realized, and the engineering problems related to the strength and the stability of the composite propeller are solved.
The above detailed description is intended to illustrate the objects, aspects and advantages of the present invention, and it should be understood that the above detailed description is only exemplary of the present invention and is not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (4)

1. A method for predicting unsteady cavitation fluid-solid coupling performance of a composite propeller is characterized by comprising the following steps: the method comprises the following steps:
the method comprises the following steps: calculating an initial value of a steady-state flow field of the rigid propeller;
calculating a steady initial value aiming at the flow field of the rigid propeller, setting the rotating speed and the incoming flow speed of the propeller working to obtain initial value data of the steady flow field; the governing equation for fluid steady state solution is expressed by a mass conservation equation and a momentum conservation equation:
Figure FDA0003589517470000011
Figure FDA0003589517470000012
in the formula: subscripts i, j represent coordinate directions, u is a velocity vector, ρ is a fluid density, p is a flow field pressure, v is a kinematic viscosity coefficient, fiMass per unit volume, deltaijIs a kronecker function;
step two: establishing a finite element model of the composite propeller structure;
establishing a geometric model of the composite propeller based on the geometric dimension parameters of the rigid propeller; constraining fiber layering of the composite material by using a geometric profile of the rigid propeller, setting the thickness and the material property of the layering material of the composite material propeller layer by layer according to the layering sequence of the composite material propeller based on finite element software, inputting the density rho, the elastic modulus E, the shear modulus G and the Poisson ratio upsilon of each layer of fiber cloth, and establishing a finite element model of the composite material propeller; the composite material propeller section plane internal force, bending moment, plane internal strain and curvature satisfy the following relational expressions:
Figure FDA0003589517470000013
In the formula: the [ N ] generation surface internal force, [ M ] is bending moment, epsilon DEG and kappa are middle surface strain and middle surface curvature, and matrixes [ A ], [ B ] and [ D ] are an in-plane rigidity matrix, a coupling rigidity matrix and a bending rigidity matrix respectively;
step three: transmitting initial value data of the steady flow field to the structural field through a fluid-solid coupling interface, and solving finite element structural deformation to obtain structural field grid deformation;
transmitting initial value data of the steady flow field to the structural field through a fluid-solid coupling interface between the composite propeller and the flow field, and completing finite element structure deformation solving of the composite propeller according to the composite propeller finite element model established in the step two and the obtained initial value data of the flow field to obtain grid deformation of the structural field; transient analysis is carried out on the propeller structure under the action of hydrodynamic load by using a finite element method, and the control equation of the dynamic structure is as follows:
Figure FDA0003589517470000014
in the formula [ M ]s]、[Cs]And [ K ]s]Respectively a structural mass matrix, a structural damping matrix and a structural rigidity matrix, { X }, respectively,
Figure FDA0003589517470000015
And
Figure FDA0003589517470000016
respectively, structural displacement, structural velocity and structural acceleration, { FEXRepresents the external excitation force applied to the structure under the action of fluid-solid coupling, { FHEThe power of the structure under the fluid-solid coupling action is represented by the flow field force;
Step four: establishing a turbulence model for flow field calculation of the composite material propeller;
in order to better capture the phenomena of multi-scale unsteady flow field turbulence structure and near-wall region flow, a vortex viscosity model is adopted to introduce a turbulence viscosity coefficient mutEstablishing a relation between the Reynolds stress and the average velocity gradient; the calculation for determining the vortex viscosity coefficient adopts a two-equation k-omega SST turbulence model to close the mean square range of Reynolds:
Figure FDA0003589517470000021
Figure FDA0003589517470000022
wherein k is the turbulent kinetic energy, ω is the turbulent frequency, ρ is the fluid density, μ is the kinetic viscosity coefficient,
Figure FDA0003589517470000023
for tracking average, velocity GkAnd GwRespectively, the turbulent kinetic energy producing term, Y, due to the influence of the mean velocity gradient and buoyancykAnd YMThe influence of the mean velocity gradient and the compressible turbulent pulsating expansion on the total dissipation ratio, DwIs a lateral diffusion term; in the formula, σwAnd σkPrandtl numbers for turbulence energy and turbulence frequency, respectively:
Figure FDA0003589517470000024
Figure FDA0003589517470000025
coefficient of turbulent viscosity mutIs calculated as follows:
Figure FDA0003589517470000026
wherein S is a shear strain rate, F1、F2Is a mixing function;
step five: establishing a cavitation model for flow field calculation of the composite propeller;
a cavitation model for calculating the composite propeller flow field adopts a transport equation based on cavitation dynamics, which is provided on the basis of a Ralyleigh-Plesset (R-P) equation:
Figure FDA0003589517470000027
In the formula, RBIs the cavitation radius, pvIs the saturated vapor pressure in the environment, S is the surface tension coefficient, ρ l is the liquid density, T∞Is far field fluid temperature, p∞Is far field environment pressure intensity;
neglecting cavitation bubblesThe second derivative of the radius and the interaction of the surface tension respectively simplify the radius R of the hollow bubbleBMass of cavitation mBAnd the cavitation volume VBRate of change with time:
Figure FDA0003589517470000031
Figure FDA0003589517470000032
Figure FDA0003589517470000033
NBcavitation vapor nuclear density in water, vapor phase volume ratio alphavComprises the following steps:
Figure FDA0003589517470000034
the mass exchange rate m between phases per unit volume is:
Figure FDA0003589517470000035
the above formula is an evaporation term, and the expressions of the evaporation rate and the condensation rate between the vapor and the liquid phases are respectively found according to the relational expression:
Figure FDA0003589517470000036
Figure FDA0003589517470000037
in the formula, alphanucIs cavitation gas core volumeFraction, CdAnd CpRespectively, the liquid phase evaporation rate when the local pressure is lower than the saturated vapor pressure and the vapor phase condensation rate when the local pressure is higher than the saturated vapor pressure, RBIs the cavitation radius, PvIs pv(T∞)；
Step six: transmitting the structural field deformation information obtained in the step three to the flow field through a fluid-solid coupling interface, and performing flow field grid updating and flow field solving to obtain a flow field numerical calculation result;
transmitting the structural field deformation data to the flow field through a fluid-solid coupling interface between the composite material propeller and the flow field, updating a flow field grid, setting a cavitation number of the propeller under the cavitation condition, and performing flow field solution based on the turbulence model and the cavitation model established in the third step and the fourth step to obtain a numerical calculation result of the flow field; in the cavitation flow of the propeller, a flow field can be regarded as a continuous uniform medium formed by fully mixing gas, steam and liquid, and a homogeneous phase flow model is adopted to solve the flow field of the propeller; wherein the continuity equation and the momentum equation are:
Figure FDA0003589517470000038
Figure FDA0003589517470000039
In the formula: u is the velocity vector, ρmIs the density of the mixed medium, mumIs the kinetic viscosity coefficient of the mixing medium, mutIs the turbulent flow viscosity coefficient, and p is the flow field pressure; medium density p of the mixing termmAnd coefficient of dynamic viscosity of medium mumAre defined as follows:
ρm＝ρvαv+ρlαl (20)
μm＝μvαv+μlαl (21)
in the formula：ρl、αlAnd mulDensity of the fluid, p, respectively in the liquid phasev、αvAnd muvFluid density, volume fraction and fluid kinematic viscosity, respectively, of the vapor phase;
step seven: giving a convergence criterion of unsteady cavitation fluid-solid coupling calculation of the composite material propeller, so that the calculation result simultaneously meets the convergence criterion and the number of sub-iterations is not less than the maximum iteration step number, and realizing convergence of the fluid-solid coupling calculation method;
continuously crossing solving of the structural field and the flow field in each coupling step through the sub-iteration step to achieve that a calculation result meets a convergence standard, completing fluid-solid coupling calculation of the time step, and entering next time step calculation; if the convergence standard is not met, judging the size of the sub-iteration steps, if the sub-iteration steps are smaller than the maximum iteration steps, continuing to perform sub-iteration convergence solution calculation, and if the sub-iteration steps are not smaller than the maximum iteration steps, entering the next step of iterative calculation; and (4) continuously intersecting and solving the sub-iteration steps in each time step to realize the result convergence of the fluid-solid coupling calculation method and finish the unsteady cavitation fluid-solid coupling calculation of the composite material propeller.
2. The method for predicting the unsteady cavitation fluid-solid coupling performance of the composite propeller as recited in claim 1, wherein the method comprises the following steps: step eight, applying the method in the steps one to seven to the field of the optimized design numerical simulation of the composite propeller, realizing the predictability of the unsteady cavitation hydrodynamic performance of the composite propeller, and being beneficial to establishing a flow field quality rapid evaluation method and establishing a cavitation dynamic characteristic and cavitation erosion branching evaluation method of the composite propeller; and eighthly, the application fields of the method for predicting the unsteady cavitation fluid-solid coupling performance of the composite material propeller comprise the fields of fluid-solid coupling characteristic prediction, propeller cavitation hydrodynamic performance prediction and composite material propeller optimization design.
3. The method for predicting the unsteady cavitation fluid-solid coupling performance of the composite propeller as recited in claim 2, wherein the method comprises the following steps: when the method in the first step to the eighth step is applied to the optimization design and cavitation performance prediction of the composite propeller, the cavitation hydrodynamic performance of the composite propeller is obtained, the influence of a composite material layering mode on the cavitation hydrodynamic performance of the propeller is obtained, the structure dynamic response performance prediction of the composite propeller is realized, and the engineering problems related to the strength and the stability of the composite propeller are solved.
4. The method for predicting the unsteady cavitation fluid-solid coupling performance of the composite propeller as claimed in claim 1, 2 or 3, wherein the method comprises the following steps: the finite element software is realized by an ACP module in ANSYS Workbench.
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