CN112896452A - Self-absorption performance prediction method for starting process of water-jet propeller - Google Patents

Self-absorption performance prediction method for starting process of water-jet propeller Download PDF

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CN112896452A
CN112896452A CN202110184717.6A CN202110184717A CN112896452A CN 112896452 A CN112896452 A CN 112896452A CN 202110184717 A CN202110184717 A CN 202110184717A CN 112896452 A CN112896452 A CN 112896452A
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water
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jet propeller
water jet
turbulence
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CN112896452B (en
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陈泰然
张富毅
鲁航
黄彪
王国玉
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Beijing Institute of Technology BIT
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
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Abstract

The invention relates to a self-absorption performance prediction method for a starting process of a water jet propeller, belongs to the technical field of ship industry and fluid machinery, and particularly belongs to the field of water jet propulsion. Based on a basic fluid mechanics equation, the invention divides the water inlet channel, the nozzle and the vehicle bottom water area model of the water jet propeller into grids by establishing a geometric model of the water jet propeller and establishing a corresponding flow field area, checks the independence of the grids, then carries out the setting of prediction parameters, and finally outputs the flow field information of the water jet propeller under the conditions of different water line heights or different starting time, thereby obtaining the lowest water line height for the normal starting of the water jet propeller. The method can reveal the evolution law of the gas phase, the vapor phase and the liquid phase in the starting process of the water-jet propeller, predict the lowest waterline height of the normal starting of the water-jet propeller, provide reference for the starting of the water-jet propeller, and save the cost and time of experiments.

Description

Self-absorption performance prediction method for starting process of water-jet propeller
Technical Field
The invention relates to a self-absorption performance prediction method for a starting process of a water jet propeller, belongs to the technical field of ship industry and fluid machinery, and particularly belongs to the field of water jet propulsion.
Background
The water jet propeller is a propulsion device composed of water inlet flow passage, propulsion pump, nozzle and other flow passage components, generates thrust by using the reaction force of ejected high-speed water flow, has the advantages of high propulsion efficiency, strong cavitation resistance, low vibration noise, simple transmission mechanism and the like, and is widely applied to ships, amphibious vehicles and underwater robots. At present, the research on the design method, the propulsion performance, the optimization design and the like of the water jet propeller based on the design working condition is mature, and the cases on the hydrodynamic performance and the self-absorption performance of the water jet propeller in the starting process are few.
The amphibious vehicle is a special vehicle which adopts a water jet propulsion device and gives consideration to land and water navigation, and relates to the starting process of a water jet propeller in the process that the amphibious vehicle drives from land to water surface, but because the draught of the amphibious vehicle in a shoal zone is small, the inside of the water jet propeller in the starting process cannot be ensured to be full of water flow, the water flow needs to be sucked from the bottom of the vehicle to be full of a runner and gas is discharged through the rotation of a propulsion pump, and meanwhile, the inside of the water jet propeller can also generate cavitation phenomenon, namely, the runner is in a gas-vapor-liquid three-phase coexisting state in the starting process, the process has obvious transient characteristics and influences the normal operation of the water jet propeller along with the negative effects of hydraulic shock excitation, impact load, cavitation damage, vibration noise and the like. Therefore, the transient characteristic of the starting self-priming process of the water jet propeller is a key problem which needs to be solved urgently in the field of propulsion of amphibious vehicles.
Since the end of the last century, with the development of computer equipment and the progress of computing technology, the development of computational fluid dynamics has further promoted the research on the starting self-priming process of the water jet propeller. Meanwhile, the rapid development of high-speed amphibious vehicles requires that the waterjet be started in as short a time as possible and obtain a greater thrust, which results in a waterjet having higher efficiency and power density, and that the gas be completely discharged and the generation of cavitation bubbles be suppressed as quickly as possible during the starting process. The starting self-priming experiment of the amphibious vehicle water jet propeller has high cost, large danger coefficient and large operation difficulty, so that the feasibility of the experiment is low, and numerical calculation becomes a main method for researching the starting self-priming problem of the water jet propeller.
At present, in the conventional numerical calculation of the water jet propeller, the gas phase is not considered, the interaction between the gas phase and the liquid phase is lacked, and the change trend of the gas phase in the self-priming process cannot be obtained, so that a self-priming performance prediction method considering the gas phase is necessary to be developed and perfected for the starting self-priming problem of the water jet propeller.
Disclosure of Invention
The invention aims to solve the problems that the existing water jet propeller numerical calculation does not consider the gas phase, and the self-priming problem of the starting of the water jet propeller cannot be researched. The invention can be applied to the technical field of ship industry and fluid machinery, and particularly belongs to the field of water jet propulsion.
A self-absorption performance prediction method for a starting process of a water jet propeller comprises the following steps:
1. a self-absorption performance prediction method for a starting process of a water jet propeller is characterized by comprising the following steps: the method comprises the following steps:
the method comprises the following steps: the water-jet propeller model comprises a water inlet flow channel, an impeller, a guide vane, a nozzle and a vehicle bottom water area; generating an impeller and guide vane model of the water jet propulsion pump according to the flow and the lift parameters, and generating a water inlet flow channel, a nozzle and a vehicle bottom water area model of the water jet propulsion pump by using three-dimensional modeling software, thereby finally realizing the establishment of the water jet propulsion pump model;
step two: carrying out structured grid division on the water inlet flow channel, the nozzle and the vehicle bottom water area model of the water jet propeller in the step one, wherein the grid division is for a discrete flowing area, and guiding the impeller and the guide vane model of the water jet propeller pump obtained in the step one into turbine blade grid channel grid division software to complete the structured grid division of the impeller and the guide vane area, so as to finally realize the grid division of the water jet propeller model;
step three: in the water jet model and the grid of the first step and the second step, a computational fluid dynamics model is established as follows:
Figure BDA0002942602320000021
Figure BDA0002942602320000022
wherein ρ is density; t is time; i. j is 1, 2, 3; u. ofi、ujIs the velocity component; x is the number ofi、xjIs a coordinate component; p is pressure; mu.sl、μtLaminar flow viscosity coefficient and turbulent flow viscosity coefficient;
step four: the shear stress transmission SSTk-omega turbulence model (k is turbulence kinetic energy, and omega is turbulence frequency) integrates the advantages of a k-epsilon model (epsilon is turbulence kinetic energy dissipation) and a k-omega model, and the k-omega model is adopted in a near-wall region, so that the turbulence dissipation rate is small, and the convergence is good; a k-epsilon model is adopted in a turbulent flow full development area, so that the calculation efficiency is high, and the adaptability to a complex flow field is better; the turbulence energy k equation and the turbulence frequency ω equation are respectively:
Figure BDA0002942602320000023
Figure BDA0002942602320000024
in the formula, PkGenerating a term for turbulence; dkIs a turbulent dissipation term; sigmak、σω2Prandtl numbers for turbulence energy and turbulence frequency, respectively; f1Is a mixing function; s is the shear strain rate; cω、βωIs a constant number of times, and is,
Figure BDA0002942602320000025
βω＝0.075；
the water-jet propeller is a rotary impeller machine, the interior of the propeller has a strong rotating curvature effect due to high-speed rotation of an impeller, and in order to better predict the flow phenomenon in the water-jet propeller, the rotating curvature is corrected on the basis of an SSTk-omega turbulence model to obtain an SST-CC turbulence model, wherein the expression is as follows:
Figure BDA0002942602320000031
Figure BDA0002942602320000032
P′k＝Pkfr (7)
Figure BDA0002942602320000033
Figure BDA0002942602320000034
Figure BDA0002942602320000035
Figure BDA0002942602320000036
Figure BDA0002942602320000037
Figure BDA0002942602320000038
Figure BDA0002942602320000039
S2＝2SijSij (15)
Ω2＝2ΩijΩij (16)
D2＝max(S2,0.09ω2) (17)
of formula (II) to (III)'kGenerating a term for the modified turbulence; f. ofrThe dynamic correction coefficient of the turbulent flow generation term is selected, and the value range is 0-1.25;
Figure BDA00029426023200000310
the original dynamic correction coefficient is obtained; f. ofrotationAs a function of the intensity of rotation; cr1、Cr2And Cr3The values of the model constants are 1.0, 2.0 and 1.0 respectively; cscaleThe scale empirical coefficient is taken as 1; sijAnd ΩijRespectively, deformation rate and rotation rate; r is*Is the ratio of the deformation rate and the rotation rate;
Figure BDA00029426023200000311
the rotation rate is 0 in the case of a non-rotating system; DS (direct sequence)ijDt is the lagrangian derivative of the deformation rate tensor;
step five: predicting the internal cavitation of the water jet propeller by adopting a Zwart cavitation model, and obtaining an evaporation term
Figure BDA00029426023200000312
Coagulation item
Figure BDA00029426023200000313
Respectively as follows:
Figure BDA00029426023200000314
Figure BDA0002942602320000041
in the formula, pvThe saturated vapor pressure is 3169 Pa; rBThe diameter of the cavitation bubbles is 1 × 10-6m；αnucThe cavitation nuclear volume fraction is 5 × 10-4；CdestAnd CprodEvaporation coefficient and condensation coefficient are respectively 50 and 0.01;
step six: gas and liquid phases exist in the self-suction process, a free liquid level model method is adopted to capture a gas-liquid interface, and the gas-liquid interface is tracked to obtain free liquid level deformation;
step seven: in computational fluid mechanics software, three phases of liquid water, water vapor and air are set as material attributes as computational media; a free surface model is arranged between the interphase interaction air and the liquid water, a cavitation model is arranged between the liquid water and the water vapor, and no interaction exists between the air and the water vapor; the boundary condition of the inflow surface of the water area at the bottom of the train is set as a speed inlet, the outflow surface of the water area at the bottom of the train is set as a pressure outlet, the side surface and the bottom surface of the water area at the bottom of the train are set as open inlets, the top surface of the water area at the bottom of the train is set as a non-slip wall surface, the spout outlet is set as a pressure outlet, the surfaces of a pump shaft, an impeller and a guide vane are set as non-slip wall surfaces, and a dynamic-static interface is arranged among a;
the change rule of the rotating speed of the impeller region along with time is established through an expression, the rotating speed is linearly increased to a rated rotating speed, and the specific expression is as follows:
Figure BDA0002942602320000042
wherein T is time, TstartIs the starting time; n is the rotation speed;
the height of the waterline is defined by taking the central line of the pump shaft as a zero datum line through an expression, air is above the waterline at the initial moment, and liquid water is below the waterline; monitoring the variation trend of the flow, the lift, the torque, the power, the efficiency, the axial force and the thrust parameter of the water-jet propeller along with time in real time;
step eight: through the arrangement of the first step to the seventh step, on the basis of the fluid mechanics model calculated in the third step, a fourth SST-CC turbulence model, a fifth Zwart cavitation model and a sixth free liquid level model are added, the numerical calculation of a gas-liquid three-phase unsteady flow field is carried out, the pressure, the speed, the vorticity and a gas-liquid integral digital cloud chart of the flow field are read, and the variation trend of flow, lift, power, efficiency, axial force and thrust parameters along with time is extracted;
step nine: modifying the height of the waterline or the starting time, repeating the seventh step to the eighth step, obtaining the flow field information of the water jet propeller and the variation trend of each parameter under the conditions of different waterline heights or different starting times, and determining the lowest waterline height of the water jet propeller in normal starting;
step ten: flow field information of the water jet propeller and the variation trend of each parameter under the conditions of different water line heights or different starting time can be obtained based on the steps from the first step to the ninth step, the lowest water line height of the normal starting of the water jet propeller can also be obtained, and the final self-priming performance prediction is completed; the self-absorption performance prediction result can monitor the change of main parameters in real time, obtain the dynamic change of flow, lift, power, efficiency and thrust parameters, obtain the lowest waterline height for normal starting of the water jet propeller, provide reference for starting of the water jet propeller and save the cost and time of experiments; the invention can be applied to the technical field of ship industry and fluid machinery, in particular to the field of water jet propulsion;
advantageous effects
1. The invention relates to a self-absorption performance prediction method for a water-jet propeller in a starting process, which considers gas, steam and liquid phases and can obtain an evolution law of the gas, the steam and the liquid phases in the starting process of the water-jet propeller.
2. The invention discloses a self-absorption performance prediction method for a starting process of a water-jet propeller, which monitors the change of main parameters in real time and can obtain the dynamic change of parameters such as flow, lift, power, efficiency, thrust and the like.
3. The invention relates to a self-priming performance prediction method for a starting process of a water jet propeller.
Drawings
FIG. 1 is a flow chart of a self-priming performance prediction method for a water jet startup process of the present invention;
FIG. 2 is a three-dimensional model diagram of a self-priming performance prediction method for a water jet starting process according to the present invention;
FIG. 3 is a calculated watershed graph of a self-priming performance prediction method for a water jet starting process according to the present invention;
FIG. 4 is a grid-divided graph of a self-priming performance prediction method for a water jet startup process of the present invention; wherein, the graph a is a water inlet flow passage grid, and the graph b is a propulsion pump grid;
fig. 5 is a water line height diagram of the self-priming performance prediction method during the starting process of the water jet propeller according to the invention.
Detailed Description
For a better understanding of the objects and advantages of the present invention, reference should be made to the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings.
Example 1
As shown in fig. 1, the main process of the self-priming performance prediction method for the starting process of the water jet propeller according to the embodiment includes the following specific steps:
the turbine blade design software adopts ANSYS Bladegen, the three-dimensional modeling software adopts Solidworks, the CAE pretreatment software adopts ANSYS ICEM software, the turbine blade grid channel grid division software adopts ANSYS Turbogrid software,
the method comprises the following steps: the model of the water jet propeller comprises a water inlet flow channel, an impeller, a guide vane and a nozzle, and further comprises a vehicle bottom water area, as shown in figure 2, the impeller and the guide vane of the water jet propeller pump are modeled by adopting ANSYS Bladegen software, and main hydraulic parameters of the propeller pump are shown in table 1. Modeling a water inlet flow channel, a nozzle and a vehicle bottom water area of the water-jet propeller by using Solidworks, wherein the water inlet flow channel is in a flat inlet type, a water inlet is in an oval shape, and finally, establishing a water-jet propeller model is realized as shown in figure 2. The performance of the water jet propeller is closely related to the structure of a vehicle body, the inflow conditions and the operation conditions, so that the flow field area around a water inlet is fully considered when the water jet propeller is subjected to numerical simulation, the length, the width and the height of the selected vehicle bottom flow field are respectively 30D, 10D and 8D, wherein D is the diameter of an impeller, as shown in figure 3.
TABLE 1 main Hydraulic parameters of water jet propulsion pump
Figure BDA0002942602320000061
Step two: in order to improve the grid quality and reduce the grid quantity, the water inlet channel, the nozzle and the vehicle bottom water area model of the water jet propeller in the step one are led into ANSYS ICEM software for structural grid division, as shown in fig. 4(a), by adjusting the grid size and the node distribution, boundary layer grids are adopted in a near-wall surface area, and grids are encrypted in an area near the water inlet channel; and (3) introducing the impeller and guide vane model of the water jet propulsion pump obtained in the step one into ANSYS turbo grid software to perform structured grid division on the impeller and guide vane regions, as shown in fig. 4(b), finally determining that the number of the impeller region grids is 178 ten thousand and the number of the guide vane region grids is 202 thousand through the operations of establishing a topological structure, setting blade top gaps, adjusting blade placement angles, editing grid sizes, arranging boundary layers and the like through the verification of grid independence, and finally realizing the grid division of the water jet propulsion pump model.
Step three: in order to calculate the calculation domains established in the first step and the second step, a computational fluid dynamics model needs to be established first, the basic control equation comprises a continuity equation and a momentum equation, and the specific expression is as follows:
Figure BDA0002942602320000062
Figure BDA0002942602320000063
wherein ρ is density; t is time; i. j is 1, 2, 3; u. ofi、ujIs the velocity component; x is the number ofi、xjIs a coordinate component; p is pressure; mu.sl、μtLaminar and turbulent viscosity coefficients, respectively.
Step four: the shear stress transmission SSTk-omega turbulence model (k is turbulence kinetic energy, and omega is turbulence frequency) integrates the advantages of a k-epsilon model (epsilon is turbulence kinetic energy dissipation) and a k-omega model, and the k-omega model is adopted in a near-wall region, so that the turbulence dissipation rate is small, and the convergence is good; and a k-epsilon model is adopted in a turbulent flow full development area, so that the calculation efficiency is high, and the adaptability to a complex flow field is better. The turbulence energy k equation and the turbulence frequency ω equation are respectively:
Figure BDA0002942602320000064
Figure BDA0002942602320000071
in the formula, PkGenerating a term for turbulence; dkIs a turbulent dissipation term; sigmak、σω2Prandtl numbers for turbulence energy and turbulence frequency, respectively; f1Is a mixing function; s is the shear strain rate; cω、βωIs a constant number of times, and is,
Figure BDA0002942602320000072
βω＝0.075。
the water-jet propeller is a rotary impeller machine, the interior of the propeller has a strong rotating curvature effect due to the high-speed rotation of an impeller, and in order to better predict the flow phenomenon in the water-jet propeller, the rotating curvature is corrected on the basis of an SSTk-omega turbulence model to obtain an SST-CC turbulence model, wherein the expression is as follows:
Figure BDA0002942602320000073
Figure BDA0002942602320000074
P′k＝Pkfr (7)
Figure BDA0002942602320000075
Figure BDA0002942602320000076
Figure BDA0002942602320000077
Figure BDA0002942602320000078
Figure BDA0002942602320000079
Figure BDA00029426023200000710
Figure BDA00029426023200000711
S2＝2SijSij (15)
Ω2＝2ΩijΩij (16)
D2＝max(S2,0.09ω2) (17)
of formula (II) to (III)'kGenerating a term for the modified turbulence; f. ofrThe dynamic correction coefficient of the turbulent flow generation term is selected, and the value range is 0-1.25;
Figure BDA00029426023200000712
the original dynamic correction coefficient is obtained; f. ofrotationAs a function of the intensity of rotation; cr1、Cr2And Cr3The values of the model constants are 1.0, 2.0 and 1.0 respectively; cscaleThe scale empirical coefficient is taken as 1; sijAnd ΩijRespectively, deformation rate and rotation rate; r is*Is the ratio of the deformation rate and the rotation rate;
Figure BDA0002942602320000081
the rotation rate is 0 in the case of a non-rotating system; DS (direct sequence)ijthe/Dt is the Lagrangian derivative of the deformation rate tensor.
Step five: in order to better predict the development process of the internal cavitation of the water jet propeller, a Zwart cavitation model is adopted, and an evaporation term
Figure BDA0002942602320000082
Coagulation item
Figure BDA0002942602320000083
Respectively as follows:
Figure BDA0002942602320000084
Figure BDA0002942602320000085
in the formula, pvThe saturated vapor pressure is 3169 Pa; rBThe diameter of the cavitation bubbles is 1 × 10-6m；αnucThe cavitation nuclear volume fraction is 5 × 10-4；CdestAnd CprodThe evaporation coefficient and the condensation coefficient are respectively 50 and 0.01.
Step six: gas and liquid phases exist in the self-suction process, a free liquid level model method is adopted to capture a gas-liquid interface, and the gas-liquid interface is tracked to obtain free liquid level deformation;
step seven: in computational fluid mechanics software, three phases of liquid water, water vapor and air are set as material attributes as computational media; a free surface model is set between the interphase interaction air and the liquid water, water is a main phase, air is a secondary phase, and the surface tension coefficient is set to be 0.072N/m; a cavitation model is arranged between the liquid water and the water vapor, and the saturated vapor pressure is 3169 Pa; no interaction exists between air and water vapor;
setting the boundary condition of the inflow surface of the water area at the bottom of the vehicle as a speed inlet, and assuming that the navigational speed in the starting process is unchanged at 0m/s because the flow in the water jet propeller is focused; the outflow surface of the water area at the bottom of the vehicle is provided with a pressure outlet, and the pressure value is linearly increased along with the water depth; the side surface and the bottom surface of the water area at the bottom of the train are provided with open inlets, the top surface of the water area at the bottom of the train is provided with a non-slip wall surface, the outlet of the nozzle is provided with a pressure outlet, and the pressure value is atmospheric pressure; the surfaces of the pump shaft, the impeller and the guide vane are set to be non-slip wall surfaces; the inlet water flow channel and the impeller region, and the impeller region and the guide vane region are provided with dynamic-static interfaces, as shown in fig. 3.
The change rule of the rotating speed of the impeller region along with time is established through an expression, the rotating speed is linearly increased to a rated rotating speed, the acceleration time is 3s, and the specific expression is as follows:
Figure BDA0002942602320000086
the water line height takes the pump shaft center line as a zero datum line, the water line height h is defined as 0.25D through an expression, D is the impeller diameter, and the water line is an air phase above the initial time, and a liquid water phase and a water vapor-free phase below the initial time, as shown in fig. 5. And the variation trend of parameters such as flow, lift, torque, power, efficiency, axial force, thrust and the like of the water spraying propeller along with time is monitored in real time.
The reference pressure is 1atm, the gravity acceleration direction of the buoyancy model is the negative direction of the y axis, the flow field speed at the initial moment is 0m/s, and the pressure is 1 atm; transient solution, wherein the total calculation time is 5s, the time step is 0.0005s, the iteration times are 100 times, and the convergence precision is 0.0001; the momentum equation is in a High Resolution format, and the turbulence equation is in a First Order format.
Step eight: solving the calculation
And (4) calculating the numerical value of the gas-vapor-liquid three-phase unsteady flow field by setting the steps from the first step to the seventh step through computational fluid dynamics software. And (4) in post-processing software, performing result post-processing, reading cloud charts of the flow field such as pressure, speed, vorticity, gas-steam-liquid integral number and the like, and extracting the change trend of parameters such as flow, lift, power, efficiency, axial force, thrust and the like along with time.
Step nine: and modifying the height of the waterline, repeating the seventh step to the eighth step, calculating three working conditions of the height of the waterline, namely 0.35D, 0.20D and 0.10D, obtaining the flow field information of the water jet propeller and the variation trend of each parameter under the condition of different waterline heights, and determining the lowest waterline height for the normal starting of the water jet propeller.
Step ten: based on the steps from the first step to the ninth step, the flow field information of the water jet propeller and the variation trend of each parameter under the conditions of different water line heights or different starting time can be obtained, the lowest water line height of the normal starting of the water jet propeller can also be obtained, and the final self-priming performance prediction is completed. The change of main parameters can be monitored in real time according to the self-absorption performance prediction result, the dynamic change of parameters such as flow, lift, power, efficiency and thrust can be obtained, the lowest waterline height of normal starting of the water jet propeller is obtained, reference is provided for starting of the water jet propeller, and the cost and time of experiments are saved. The invention can be applied to the technical field of ship industry and fluid machinery, and particularly belongs to the field of water jet propulsion.
The prediction result shows that the pump shaft central line is taken as a zero reference line, when the height of a waterline is more than or equal to 0.15 times of the diameter of the impeller, the water-jet propeller can completely discharge internal gas in a short time, and the smaller the height of the waterline is, the more serious the lift and flow lag is.
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 within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (1)

1. A self-absorption performance prediction method for a starting process of a water jet propeller is characterized by comprising the following steps: the method comprises the following steps:
the method comprises the following steps: the water-jet propeller model comprises a water inlet flow channel, an impeller, a guide vane, a nozzle and a vehicle bottom water area; generating an impeller and a guide vane model of the water jet propulsion pump according to the flow and the lift parameters, and generating a water inlet runner, a nozzle and a vehicle bottom water area model of the water jet propulsion pump by using three-dimensional modeling software to finally realize the establishment of the water jet propulsion pump model;
step two: carrying out structured grid division on the water inlet flow channel, the nozzle and the vehicle bottom water area model of the water jet propeller in the step one, wherein the grid division is for a discrete flowing area, and guiding the impeller and guide vane model of the water jet propeller pump obtained in the step one into turbine blade grid channel grid division software to complete the structured grid division of the impeller and guide vane area, so as to finally realize the grid division of the water jet propeller model;
step three: in the water jet model and the grid of the first step and the second step, a computational fluid dynamics model is established as follows:
Figure FDA0002942602310000011
Figure FDA0002942602310000012
wherein ρ is density; t is time; i. j is 1, 2, 3; u. ofi、ujIs the velocity component; x is the number ofi、xjIs a coordinate component; p is pressure; mu.sl、μtLaminar flow viscosity coefficient and turbulent flow viscosity coefficient;
step four: the shear stress transmission SSTk-omega turbulence model (k is turbulence kinetic energy, and omega is turbulence frequency) integrates the advantages of a k-epsilon model (epsilon is turbulence kinetic energy dissipation) and a k-omega model, and the k-omega model is adopted in a near-wall region, so that the turbulence dissipation rate is small, and the convergence is good; a k-epsilon model is adopted in a turbulent flow full development area, so that the calculation efficiency is high, and the adaptability to a complex flow field is better; the turbulence energy k equation and the turbulence frequency ω equation are respectively:
Figure FDA0002942602310000013
Figure FDA0002942602310000014
in the formula, PkGenerating a term for turbulence; dkIs a turbulent dissipation term; sigmak、σω2Prandtl numbers for turbulence energy and turbulence frequency, respectively; f1Is a mixing function; s is the shear strain rate; cω、βωIs a constant number of times, and is,
Figure FDA0002942602310000015
βω＝0.075；
the water-jet propeller is a rotary impeller machine, the interior of the propeller has a strong rotating curvature effect due to the high-speed rotation of an impeller, and in order to better predict the flow phenomenon in the water-jet propeller, the rotating curvature is corrected on the basis of an SSTk-omega turbulence model to obtain an SST-CC turbulence model, wherein the expression is as follows:
Figure FDA0002942602310000016
Figure FDA0002942602310000021
P′k＝Pkfr (7)
Figure FDA0002942602310000022
Figure FDA0002942602310000023
Figure FDA0002942602310000024
Figure FDA0002942602310000025
Figure FDA0002942602310000026
Figure FDA0002942602310000027
Figure FDA0002942602310000028
S2＝2SijSij (15)
Ω2＝2ΩijΩij (16)
D2＝max(S2,0.09ω2) (17)
of formula (II) to (III)'kGenerating a term for the modified turbulence; f. ofrThe dynamic correction coefficient of the turbulent flow generation term is selected, and the value range is 0-1.25;
Figure FDA0002942602310000029
is a primary motionA state correction factor; f. ofrotationAs a function of the intensity of rotation; cr1、Cr2And Cr3The values of the model constants are 1.0, 2.0 and 1.0 respectively; cscaleThe scale empirical coefficient is taken as 1; sijAnd ΩijRespectively, deformation rate and rotation rate; r is*Is the ratio of the deformation rate and the rotation rate;
Figure FDA00029426023100000210
the rotation rate is 0 in the case of a non-rotating system; DS (direct sequence)ijDt is the lagrangian derivative of the deformation rate tensor;
step five: predicting the internal cavitation of the water jet propeller by adopting a Zwart cavitation model, and obtaining an evaporation term
Figure FDA00029426023100000211
Coagulation item
Figure FDA00029426023100000212
Respectively as follows:
Figure FDA00029426023100000213
Figure FDA00029426023100000214
in the formula, pvThe saturated vapor pressure is 3169 Pa; rBThe diameter of the cavitation bubbles is 1 × 10-6m；αnucThe cavitation nuclear volume fraction is 5 × 10-4；CdestAnd CprodEvaporation coefficient and condensation coefficient are respectively 50 and 0.01;
step six: gas and liquid phases exist in the self-suction process, a free liquid level model method is adopted to capture a gas-liquid interface, and the gas-liquid interface is tracked to obtain free liquid level deformation;
step seven: in computational fluid dynamics software, three phases of liquid water, water vapor and air are set as material attributes as computational media; a free surface model is arranged between the interphase interaction air and the liquid water, a cavitation model is arranged between the liquid water and the water vapor, and no interaction exists between the air and the water vapor; the boundary condition of the inflow surface of the water area at the bottom of the train is set as a speed inlet, the outflow surface of the water area at the bottom of the train is set as a pressure outlet, the side surface and the bottom surface of the water area at the bottom of the train are set as open inlets, the top surface of the water area at the bottom of the train is set as a non-slip wall surface, the outlet of the nozzle is set as a pressure outlet, the surfaces of the pump shaft, the impeller and the guide vane are set as non-slip wall surfaces, and dynamic-static interfaces are;
the change rule of the rotating speed of the impeller region along with time is established through an expression, the rotating speed is linearly increased to a rated rotating speed, and the specific expression is as follows:
Figure FDA0002942602310000031
wherein T is time, TstartIs the starting time; n is the rotation speed;
the height of the waterline is defined by taking the central line of the pump shaft as a zero datum line through an expression, and air is above the waterline at the initial moment and liquid water is below the waterline; monitoring the variation trend of the flow, the lift, the torque, the power, the efficiency, the axial force and the thrust parameter of the water-jet propeller along with time in real time;
step eight: through the arrangement of the first step to the seventh step, on the basis of the fluid mechanics model calculated in the third step, a fourth SST-CC turbulence model, a fifth Zwart cavitation model and a sixth free liquid level model are added, the numerical calculation of the gas-liquid three-phase unsteady flow field is carried out, the pressure, the speed, the vorticity and a gas-liquid integral cloud map of the flow field are read, and the change trends of flow, lift, power, efficiency, axial force and thrust parameters along with time are extracted;
step nine: modifying the height of the waterline or the starting time, repeating the seventh step to the eighth step to obtain the flow field information of the water jet propeller and the variation trend of each parameter under the conditions of different waterline heights or different starting times, and determining the lowest waterline height of the normal starting of the water jet propeller;
step ten: flow field information of the water jet propeller and the variation trend of each parameter under the conditions of different waterline heights or different starting time can be obtained based on the steps from the first step to the ninth step, the lowest waterline height of the water jet propeller in normal starting can also be obtained, and the final self-priming performance prediction is completed; the self-absorption performance prediction result can monitor the change of main parameters in real time, obtain the dynamic change of flow, lift, power, efficiency and thrust parameters, obtain the lowest waterline height for normal starting of the water jet propeller, provide reference for the starting of the water jet propeller and save the cost and time of experiments; the invention can be applied to the technical field of ship industry and fluid machinery, and particularly belongs to the field of water jet propulsion.
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