Phase-change-based cavitation simulation calculation method and device for pressure pipeline

Abstract

The invention relates to the technical field of fluid calculation, and discloses a phase-change-based cavitation simulation calculation method and device for a pressure pipeline, and the method comprises the steps: building a constant flow initial model of the pressure pipeline; setting initial conditions of the gas-liquid two-phase flow, and calculating parameters of the gas-liquid two-phase flow by using a bubble uniform distribution model; establishing a gas-containing gas-liquid two-phase flow finite volume method calculation equation; establishing a gas-liquid two-phase phase change cavitation mathematical model, and determining a model coefficient; when the pressure intensity of the pressure pipeline is reduced below the vaporization pressure intensity, the pressure pipeline parameters are substituted into a cavitation equation to calculate the steam mass; substituting into a cavitation equation and a water hammer bridging boosting equation to calculate cavitation bridging time and bridging pressure when the pressure is recovered to be higher than the vaporization pressure; according to the method, the cavitation and water hammer bridging pressure boosting equation is introduced, the method is suitable for cavitation and liquid column bridging phenomena, the application conditions are extended to the absolute air pressure close to zero, liquid is vaporized, and the application scenes of simulation calculation are increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fluid mechanics, in particular to a phase change based cavitation simulation calculation method and device for a pressurized pipeline. BACKGROUND

[0002] In a water delivery system, cavitation refers to a phase change process in which cavitation bubbles are generated, developed and collapsed due to the fact that the local pressure of the liquid is lower than the saturated vapor at the same state and temperature, and a series of physical and chemical changes are triggered. The simulation of cavitation in a pressurized pipeline is of great practical significance to ensure the safe operation of the water delivery system. However, most existing cavitation models are used for local three-dimensional numerical simulation experiments, but in actual engineering, the application of three-dimensional numerical simulation to the entire hydropower station or water diversion project hydraulic system requires a large number of modeling grids, and the calculation amount is extremely large. Moreover, the grid characteristic length of such a grid is usually several meters, which cannot be used for microscopic three-dimensional cavitation simulation calculation. SUMMARY

[0003] Therefore, the present application provides a phase change based cavitation simulation calculation method and device for a pressurized pipeline to solve the problem of the existing cavitation model requiring a large number of modeling networks and a large amount of calculation.

[0004] In a first aspect, the present application provides a phase change based cavitation simulation calculation method for a pressurized pipeline, which comprises:

[0005] establishing a constant flow initial model of the pressurized pipeline;

[0006] setting initial conditions of gas-liquid two-phase flow, and calculating gas-liquid two-phase flow parameters under the initial conditions by using a uniform bubble distribution model;

[0007] establishing a gas-liquid two-phase flow finite volume method calculation equation;

[0008] establishing a gas-liquid two-phase phase change cavitation mathematical model, and determining cavitation mathematical model coefficients;

[0009] when the pressure of the pressurized pipeline drops below the vaporization pressure, substituting the parameters of the pressurized pipeline into the cavitation equation to calculate the steam quality;

[0010] when the pressure of the pressurized pipeline recovers above the vaporization pressure, substituting the cavitation equation and the water hammer healing pressure equation to calculate the cavitation healing time and the healing pressure;

[0011] substituting the calculation results into the finite volume model for iterative calculation, and outputting the calculation results.

[0012] The application considers the influence of cavitation, liquid column separation and healing on the transient process of gas-liquid two-phase flow, proposes a cavitation model of a pressurized pipeline, and proposes to determine the value of the cavitation model coefficient, which is suitable for one-dimensional cavitation simulation calculation of a pressurized pipeline, realizes the transformation from three-dimensional modeling to one-dimensional simulation, reduces the calculation amount, introduces the cavitation equation and the water hammer healing pressure equation, so that the simulation process is suitable for cavitation and liquid column healing phenomena that occur when the pressure is below the vaporization pressure, and the application conditions of simulation calculation are extended to the absolute pressure close to zero, the liquid vaporization, and the increase of the application scene of simulation calculation.

[0013] In an alternative embodiment, a constant flow initial model of a pressurized pipeline is established, comprising:

[0014] Extracting hydraulic data of a water delivery system of a water conservancy and hydropower project;

[0015] According to the hydraulic data, a constant flow initial model of a pressurized pipeline is established by using Bernoulli's formula.

[0016] The application establishes a constant flow initial model of a pressurized pipeline according to the hydraulic data in a water delivery system of a water conservancy and hydropower project, and provides a data basis for subsequent simulation.

[0017] In an alternative embodiment, a gas-liquid two-phase phase change cavitation mathematical model is established, comprising:

[0018] According to the one-dimensional gas-liquid two-phase flow parameters and the bubble uniform distribution model, the gas-liquid two-phase phase change cavitation mathematical model is established as follows:

[0019]

[0020] Wherein, F vap is the empirical correction coefficient of the evaporation process, F cond is the empirical correction coefficient of the condensation process, Q ch is the unit volume flow rate, p v is the steam density, N is the current unit volume bubble number, R is the current bubble radius, N b is the initial bubble number, k is the attenuation coefficient, a0 is the initial void fraction, a is the current void fraction, Vx is the segment length, and A is the pipe segment cross-sectional area.

[0021] The application proposes a one-dimensional pressurized pipeline cavitation model, so that the simulation process is suitable for one-dimensional cavitation simulation calculation of a pressurized pipeline.

[0022] In an alternative embodiment, the cavitation mathematical model coefficient is determined according to the following formula:

[0023]

[0024] Wherein, p max is the pressure extreme value when the water column healing occurs, pv Pv is the vaporization pressure, and ζ is a proportional coefficient.

[0025] The application determines the value of the cavitation model coefficient, so that the simulation process is applicable to one-dimensional cavitation simulation calculation of the pressurized pipeline, and the simulation accuracy is improved.

[0026] In an alternative embodiment, when the pressure of the pressurized pipeline drops below the vaporization pressure, the parameters of the pressurized pipeline are substituted into the cavitation equation to calculate the steam quality, including:

[0027] When the pressure of the pressurized pipeline drops below the vaporization pressure, the cavitation equation is as follows:

[0028]

[0029] Where, Δm v is the steam quality.

[0030] The application introduces the cavitation equation, so that the simulation process is applicable to cavitation and liquid column coalescence phenomena occurring when the pressure drops below the vaporization pressure.

[0031] In an alternative embodiment, after substituting the parameters of the pressurized pipeline into the cavitation equation to calculate the steam quality, the method further includes:

[0032] Calculate the cavitation volume and the void fraction, and determine whether the void fraction is greater than a preset void fraction threshold;

[0033] If the void fraction is greater than or equal to the preset void fraction threshold, the steps of calculating the cavitation coalescence time and the coalescence pressure are performed;

[0034] If the void fraction is less than the preset void fraction threshold, the step of substituting the calculation results into the finite volume model for iterative calculation is performed.

[0035] The application considers that the bubbles in the pressurized pipeline change at different void fractions, and uses the value of the void fraction as a critical condition for whether cavitation occurs. When liquid column separation occurs, the coalescence time and the coalescence pressure are calculated to provide data support for avoiding accidents. When there is no risk of liquid column separation, iterative calculation is performed to avoid over-treatment of low-risk conditions.

[0036] In an alternative embodiment, when the pressure of the pressurized pipeline recovers above the vaporization pressure, the cavitation coalescence time and the coalescence pressure are calculated by substituting into the cavitation equation and the water hammer coalescence pressure equation, including:

[0037] When the pressure of the pressurized pipeline recovers above the vaporization pressure, the cavitation equation is as follows:

[0038]

[0039] The water hammer coalescence pressure equation is as follows:

[0040]

[0041] Wherein, a1, a2 are wave speeds of liquid column before and after separation and closure respectively, and AV is the flow velocity difference between the two sections;

[0042] The sum of the pressure at the previous time and the water hammer closure pressure rise is determined as the closure pressure.

[0043] The present application introduces a cavitation model and a water hammer closure model to calculate the cavitation closure time and closure pressure, thereby improving the cavitation simulation calculation accuracy.

[0044] In the second aspect, the present application provides a phase change based cavitation simulation calculation device for a pressurized pipeline, which comprises:

[0045] A first model establishing module is configured to establish a constant flow initial model of the pressurized pipeline.

[0046] A first calculation module is configured to set initial conditions of gas-liquid two-phase flow and calculate gas-liquid two-phase flow parameters under the initial conditions by using a bubble uniform distribution model.

[0047] A second model establishing module is configured to establish a gas-containing type gas-liquid two-phase flow finite volume method calculation equation.

[0048] A determining module is configured to establish a gas-liquid two-phase phase change cavitation mathematical model and determine coefficients of the cavitation mathematical model.

[0049] A second calculation module is configured to, when the pressure of the pressurized pipeline drops below the vaporization pressure, substitute parameters of the pressurized pipeline into the cavitation equation to calculate steam quality.

[0050] A third calculation module is configured to, when the pressure of the pressurized pipeline recovers above the vaporization pressure, substitute into the cavitation equation and the water hammer closure pressure rise equation to calculate cavitation closure time and closure pressure.

[0051] A fourth calculation module is configured to substitute the calculation results into the finite volume model for iterative calculation and output the calculation results.

[0052] In the third aspect, the present application provides a computer device, which comprises a memory and a processor, the memory and the processor are communicatively connected, the memory stores computer instructions, and the processor executes the computer instructions to perform the phase change based cavitation simulation calculation method for a pressurized pipeline according to the first aspect or any one of the corresponding embodiments.

[0053] In a fourth aspect, the present application provides a computer readable storage medium, having stored thereon computer instructions for causing a computer to execute the simulation calculation method for phase change based cavitation of a pressurized pipeline according to the first aspect or any of the corresponding embodiments thereof. BRIEF DESCRIPTION OF DRAWINGS

[0054] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings required to be used in the specific embodiments or prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0055] Figure 1 is a flowchart of the simulation calculation method for phase change based cavitation of a pressurized pipeline according to an embodiment of the present application;

[0056] Figure 2 is a calculation flowchart of fluid pressure falling below the vaporization pressure according to an embodiment of the present application;

[0057] Figure 3 is a schematic diagram of the interface variable of the finite volume unit according to an embodiment of the present application;

[0058] Figure 4 is a calculation flowchart of fluid pressure recovering above the vaporization pressure according to an embodiment of the present application;

[0059] Figure 5 is a structural block diagram of the simulation calculation device for phase change based cavitation of a pressurized pipeline according to an embodiment of the present application;

[0060] Figure 6 is a hardware structure schematic diagram of the computer device according to an embodiment of the present application. DETAILED DESCRIPTION

[0061] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0062] First, the terms appearing in the embodiments of the present application are explained:

[0063] Cavitation: a kind of phase transition process caused by the appearance of cavitation inception, development and even collapse due to the local pressure of the liquid being lower than the saturation vapor pressure under the same state and temperature, and a series of physical and chemical reaction changes caused thereby. The decompression wave caused by the water hammer phenomenon in the transient process of the hydraulic system can cause cavitation at the elbow point of the tail pipe, the diversion tunnel and the tail tunnel.

[0064] If the cavitation space is large, water column separation may occur. The subsequent water column healing not only causes the cavity pressure to rise with the pulse, but also superimposes the impact force of the upstream and downstream water flow. In a relatively closed pipe, it may cause a pipe explosion accident, and if it occurs in the tail pipe of the pump turbine, it may cause a serious lifting accident.

[0065] In the related art, the following problems exist:

[0066] 1. The difficulty of cavitation simulation lies in calculating the volume of the cavity and the time of cavity healing. In the traditional cavitation numerical simulation experiment, the mathematical models such as DVCM and DGCM are based on the condition that the flow difference between the flow before and after the node is reached when the fluid pressure reaches the cavitation pressure and the segmentation point to determine whether cavitation occurs. This equation considers the speed difference before and after the node at the previous two times, and essentially still determines whether the cavity occurs and calculates the size of the cavity through the flow before and after the node, which does not conform to the actual physical law, and the simulation accuracy is also low.

[0067] 2. The existing cavitation model is mostly used in local three-dimensional numerical simulation experiment, but in actual engineering, the application of three-dimensional numerical simulation to the entire hydropower station or diversion water engineering hydraulic system requires extremely large modeling grid, and also brings about extremely large calculation amount, and the calculation of one working condition often lasts for several days or even dozens of days, which obviously cannot meet the engineering requirements. Moreover, the grid unit characteristic length of such grid is generally several meters, which cannot perform relatively microscopic three-dimensional cavitation simulation calculation. In the case where the specific position of cavitation occurrence cannot be determined, the local encryption method cannot be used for calculation.

[0068] According to the embodiment of the present application, a phase change-based cavitation simulation calculation method for a pressurized pipeline is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although the logical order is shown in the flowchart, in some cases, the steps shown or described herein can be executed in an order different from that shown herein.

[0069] In this embodiment, a phase change-based cavitation simulation calculation method for a pressurized pipeline is provided, Figure 1 is a flowchart of the phase change-based cavitation simulation calculation method for a pressurized pipeline according to the embodiment of the present application, as Figure 1As shown, the flow includes the following steps:

[0070] Step S101, establish a constant flow initial model of the pressurized pipeline.

[0071] In the embodiment of the present application, according to the design scheme of the pressurized pipeline, a constant flow initial model of the pressurized pipeline is established to provide initial conditions for subsequent gas-liquid two-phase flow analysis and gas release simulation.

[0072] Step S102, set the initial conditions of the gas-liquid two-phase flow, and calculate the gas-liquid two-phase flow parameters under the initial conditions by using a bubble uniform distribution model.

[0073] In the embodiment of the present application, the initial conditions of the gas-liquid two-phase flow are set in advance, the fluid in the pressurized pipeline is regarded as bubble-shaped gas-liquid two-phase flow by using the bubble uniform distribution model, and the gas-liquid two-phase flow parameters under the initial conditions are calculated.

[0074] Step S103, establish a finite volume method calculation equation of the gas-containing type gas-liquid two-phase flow.

[0075] In the embodiment of the present application, the calculated gas-liquid two-phase flow parameters are substituted into the linear equation set to establish a finite volume method calculation equation of the gas-containing type gas-liquid two-phase flow, and the pressurized pipeline under the gas-containing working condition is simulated.

[0076] Step S104, establish a gas-liquid two-phase phase change cavitation mathematical model, and determine the cavitation mathematical model coefficient.

[0077] In the embodiment of the present application, when the fluid pressure is less than the vaporization pressure, cavitation occurs in the pressurized pipeline, that is, the liquid rapidly evaporates into gas, at this time, the cavitation model is introduced for calculation, a gas-liquid two-phase phase change cavitation mathematical model is established, and the cavitation mathematical model coefficient value is determined.

[0078] Step S105, when the pressure of the pressurized pipeline drops below the vaporization pressure, substitute the pressurized pipeline parameters into the cavitation equation to calculate the steam quality.

[0079] In the embodiment of the present application, as shown in Figure 2 When the pressure of the pressurized pipeline drops below the vaporization pressure, the steam quality is calculated by using the cavitation equation.

[0080] Step S106, when the pressure of the pressurized pipeline recovers above the vaporization pressure, substitute into the cavitation equation and the water hammer healing pressure equation to calculate the cavitation healing time and the healing pressure.

[0081] In the embodiment of the present application, when the pressure of the pressurized pipeline recovers above the vaporization pressure, a cavitation cycle is formed, the cavitation equation and the water hammer healing pressure equation are substituted, and the cavitation healing time and the healing pressure are calculated.

[0082] Step S107, the calculation result is substituted into the finite volume model for iterative calculation, and the calculation result is output.

[0083] In the embodiment of the application, the physical quantity calculated in the above step is input into the finite volume model (FVM) for iterative calculation, and the total calculation time is generally 300 s. After the transition process gradually stabilizes, the iterative calculation is stopped, and the calculation result of 300 s is output.

[0084] The simulation calculation method for the phase change-based cavitation of the pressurized pipeline provided in the embodiment considers the influence of cavitation, liquid column separation and coalescence on the transient process of gas-liquid two-phase flow, proposes a cavitation model for the pressurized pipeline, and proposes a method for determining the value of the cavitation model coefficient, which is suitable for one-dimensional cavitation simulation calculation of the pressurized pipeline, realizes the transition from three-dimensional modeling to one-dimensional simulation, reduces the calculation amount, introduces the cavitation equation and the water hammer coalescence pressure rise equation, so that the simulation process is suitable for cavitation and liquid column coalescence phenomena occurring when the pressure is below the vaporization pressure, extends the applicable conditions of the simulation calculation to the case where the absolute pressure is close to zero and the liquid vaporizes, and increases the applicable scenarios of the simulation calculation.

[0085] In the embodiment, a simulation calculation method for the phase change-based cavitation of a pressurized pipeline is provided, and the flow includes the following steps:

[0086] Step S201, an initial model of a constant flow of a pressurized pipeline is established.

[0087] Specifically, the above step S201 includes:

[0088] Step S2011, hydraulic data of a water conveyance system of a water conservancy and hydropower project are extracted.

[0089] Step S2012, an initial model of a constant flow of a pressurized pipeline is established according to the hydraulic data and by using the Bernoulli formula.

[0090] In the embodiment of the application, based on the water conservancy and hydropower design drawings, the relevant data of the entire water conveyance system are extracted, including the head-related information of water conservancy facilities such as the pressure pipeline, the reservoir, the water inlet and outlet, the surge chamber, the valve, the unit and the water pump, and the initial model of the constant flow of the pressurized pipeline is established by using the Bernoulli formula:

[0091]

[0092] wherein, is the pressure head of the section i, j, Z i , Z j is the position head of the section i, j, is the velocity head of the section i, j, Δh i-jThe head loss between cross section i and cross section j includes local head loss and friction head loss.

[0093] By substituting the head information of the pressure pipeline, reservoir, inlet and outlet, pressure regulating chamber, valves, unit, pump, and head loss along the pipeline into the formula, the pressure and flow parameters along each segment of the entire pipeline system can be obtained.

[0094] An initial model of steady flow in a pressurized pipeline is established based on hydraulic data from the water supply system of the water conservancy and hydropower system, providing a data foundation for subsequent simulations.

[0095] Step S202: Set the initial conditions for gas-liquid two-phase flow and calculate the gas-liquid two-phase flow parameters under the initial conditions using a bubble uniform distribution model.

[0096] Specifically, step S202 includes:

[0097] Step S2021: Set the initial conditions for gas-liquid two-phase flow based on the pressure change along the water conveyance system of the water conservancy and hydropower project.

[0098] Step S2022: Calculate the initial gas phase density, number of bubbles per unit volume, and gas volumetric elastic modulus under the initial conditions using a bubble uniform distribution model.

[0099] In this embodiment of the invention, if the pressure change along the pipeline of the water conveyance system is small, the initial cavitation rate of the gas-liquid two-phase flow can be selected, that is, the initial gas volume of the gas in the gas-liquid two-phase flow can be selected, and the initial gas volume of the gas in the pressurized pipeline can be set as a fixed value as the initial condition.

[0100] If the pressure variation along the pipeline of the water conveyance system is large, the volume difference of the same mass of gas under different pressure conditions is large. Therefore, given the initial gas mass in the gas-liquid two-phase flow, the initial condition is set as the initial gas mass in the gas-liquid two-phase flow in the pressurized pipeline.

[0101] The initial gas phase density ρ is calculated using the following formula. g :

[0102]

[0103] Where, m g For gas phase mass, W g Let be the volume of the gas phase.

[0104] Calculate the number of bubbles N per unit volume using the following formula. b :

[0105] N b =n·AVx·α(3)

[0106] Wherein, n is the bubble amount, A is the pipe section cross-sectional area, Vx is the subsection length, and a is the gas volume, also known as the void fraction.

[0107] The gas elasticity modulus K is calculated according to the following formula g :

[0108] K g =rp g (4)

[0109] Wherein, r is a multi-party gas index, and under isothermal conditions, the value is 1.

[0110] The above parameters are substituted into the basic equation of the water hammer wave velocity to calculate the initial water hammer wave velocity, and the basic equation of the water hammer wave velocity is as follows:

[0111]

[0112] Wherein, p g is the gas density, p l is the liquid density, D is the diameter of the pressurized pipeline, C1 is the pipeline fixed mode coefficient, which can be generally taken as 1, E is the elastic modulus of the thin-walled elastic circular pipe, e is the pipe wall thickness, K g is the gas elasticity modulus, and K l is the liquid elasticity modulus.

[0113] By considering the change value of the water pressure along the water delivery system of the water conservancy and hydropower engineering when setting the initial conditions of the gas-liquid two-phase flow, the actual working condition scene is adapted, the physical quantity parameters under the initial conditions are calculated by using the bubble uniform distribution model, and data basis is provided for subsequent simulation analysis.

[0114] Step S203, a finite volume method calculation equation of the gas-containing type gas-liquid two-phase flow is established.

[0115] Specifically, the above step S203 includes:

[0116] Step S2031, substituting the gas-liquid two-phase flow parameters into the linear equation set to establish the finite volume method calculation equation of the gas-containing type gas-liquid two-phase flow.

[0117] In the embodiment of the application, the finite volume method calculation equation of the gas-containing type gas-liquid two-phase flow is established, and the basic equations of the gas-liquid two-phase transient flow are the momentum equation and the energy equation.

[0118] The linear equation set is as follows:

[0119]

[0120] In the formula, the flux value of the unit boundary can be obtained by approximate solution of the Riemann problem:

[0121]

[0122] where ''-'' represents the average value, Δx and Δt are the calculation space step and time step respectively, and subscript i indicates the unit cell space position, such as Figure 3 as shown, i-1 / 2 and i+1 / 2 respectively indicate the left boundary point and the right boundary point of the unit cell, f i+12 (u L,i+12 ,u R,i+12 ) is the numerical flux of the interface i+1 / 2, u L and u R are the variable values on the left and right of the interface respectively.

[0123] By establishing the finite volume method calculation equation of the gas-liquid two-phase flow containing gas, the simulation process and the actual working condition are improved by considering the gas-liquid two-phase characteristics in the simulation process.

[0124] Step S204, a gas-liquid two-phase phase change cavitation mathematical model is established, and a cavitation mathematical model coefficient is determined.

[0125] Specifically, the step S204 of establishing the gas-liquid two-phase phase change cavitation mathematical model comprises:

[0126] Step S2041, according to the one-dimensional gas-liquid two-phase flow parameter and the bubble uniform distribution model, a gas-liquid two-phase phase change cavitation mathematical model is established.

[0127] In the embodiment of the application, the gas-liquid two-phase phase change cavitation mathematical model is established, and when the fluid pressure p is less than the vaporization pressure p v , cavitation occurs in the pressurized pipeline, that is, the liquid rapidly evaporates into gas, and the vaporization pressure of water at different temperatures is shown in Table 1.

[0128] Table 1

[0129]

[0130]

[0131] Since the existing cavitation model is mostly a three-dimensional or two-dimensional simulation of cavitation occurring at solid edge parts such as water wings, underwater cylinders and flow above sharp edge orifices, it is not applicable to one-dimensional pressurized pipe flow. Based on preliminary analysis and judgment of physical laws, combined with a large number of cavitation models suitable for three-dimensional models based on the pressure flow state equation and mass transport, and according to the actual situation of one-dimensional gas-liquid two-phase pipe flow and the bubble uniform distribution model, the following cavitation model is proposed:

[0132]

[0133] where F vap is the empirical correction coefficient of the evaporation process, F cond is the empirical correction coefficient of the condensation process, and Qch is the unit volume flow, p is the density of the liquid v is the vapor density, N is the current number of bubbles per unit volume, and R is the current bubble radius.

[0134] During cavitation, small bubbles gradually aggregate into large bubbles, so the number of bubbles N is constantly changing, and the calculation formula is as follows:

[0135]

[0136] where N b is the initial number of bubbles, k is the decay coefficient, a0 is the initial cavitation rate, and a is the current cavitation rate.

[0137] The current bubble radius is calculated as follows:

[0138]

[0139] where Vx is the length of the segment, and A is the cross-sectional area of the pipe segment.

[0140] By proposing a one-dimensional pressure pipeline cavitation model, the simulation process is suitable for one-dimensional cavitation simulation calculation of pressure pipelines.

[0141] Specifically, the step S204 of determining the cavitation mathematical model coefficient to establish the gas-liquid two-phase phase change cavitation mathematical model includes the following steps:

[0142] According to the cavitation model, the mass exchange rate is proportional to the difference between the flow field pressure and the vaporization pressure to the power of 0.5. When the flow field pressure is less than the cavitation pressure, the liquid vaporizes, and the water molecules enter the vapor phase from the liquid phase. When the flow field pressure is greater than the cavitation pressure, the water vapor liquefies, and the water molecules enter the liquid phase from the vapor phase.

[0143] In fact, when cavitation occurs due to the limitation of absolute pressure, the flow field pressure will fluctuate around the vaporization pressure. In the numerical simulation process, the vapor phase partial pressure will be reduced to the minimum absolute pressure, which is generally around 2000 Pa, after being affected by a large numerical decompression wave. When the gas-liquid two-phase flow is affected by the reflected pressure-increasing wave and the water column is closed, the difference between the flow field pressure and the vaporization pressure will often reach hundreds of thousands or even millions of Pa. Therefore, in order to meet the requirement that the cavitation achieves a cycle from growth to closure within one water hammer cycle in the experiment, the evaporation coefficient should be much larger than the condensation coefficient in the cavitation equation.

[0144] The derivation formula of the time of existence of the vapor cavity is as follows:

[0145]

[0146] where ΔH inThe difference between the first water hammer wave valley after the cavity and the initial pressure can be obtained by the following formula:

[0147] ΔH in = H0 + p g / γ - p v / γ (12)

[0148] ΔH is the Joukowsky water hammer pressure rise:

[0149]

[0150] The above formula is combined to obtain the first steam cavity existence time T cs :

[0151]

[0152] After comparing a large number of water column separation test data, the cavitation coefficient is determined according to the following formula:

[0153]

[0154] Wherein, p max is the pressure extreme value when the water column closes, p v is the vaporization pressure, and ζ is the proportional coefficient.

[0155] By determining the cavitation model coefficient value method, the simulation process is suitable for one-dimensional cavitation simulation calculation of the pressurized pipeline, and the accuracy of the simulation is improved.

[0156] Step S205, when the pressure of the pressurized pipeline drops below the vaporization pressure, the parameters of the pressurized pipeline are substituted into the cavitation equation to calculate the steam quality.

[0157] Specifically, when the pressure of the pressurized pipeline drops below the vaporization pressure, the related parameters of the pressurized pipeline are brought into the following cavitation equation for calculation, and the steam quality can be obtained, and the cavitation equation is as follows:

[0158]

[0159] Wherein, Δm v is the steam quality.

[0160] By introducing the cavitation equation, the simulation process is suitable for cavitation and liquid column closing phenomenon occurring when the pressure reaches below the vaporization pressure.

[0161] In some optional embodiments, the method further comprises:

[0162] Step S206, calculating the cavitation volume and the cavitation rate, and determining whether the cavitation rate is greater than a preset cavitation rate threshold.

[0163] Step S207: If the cavitation rate is greater than or equal to the preset cavitation rate threshold, then the steps of calculating the cavitation closure time and closure pressure are executed.

[0164] Step S208: If the hole rate is less than the preset hole rate threshold, then perform the step of substituting the calculation result into the finite volume model for iterative calculation.

[0165] In this embodiment of the invention, the essence of cavitation in pressurized pipelines is that water undergoes a phase change in a low-pressure region, forming a group of cavitation bubbles. When the degree of cavitation is small, the gas produced by liquid vaporization exists in the pipeline in the form of cavitation bubbles and vapor cavities. As the cavities further grow into larger cavities, they adhere to the top of the pipe. In horizontal pipelines, for liquid column separation to occur, a low-pressure state needs to be maintained for a relatively long time, allowing the liquid to continuously vaporize and the cavities to continue expanding. When the cavitation rate reaches a certain critical value, the bubbles will no longer flow with the liquid. In vertical pipelines, pipelines with a large degree of inclination, and at bends, the pipeline will be filled with large cavities, resulting in liquid column separation. Therefore, determining the critical cavitation rate at which liquid column separation occurs in the pipeline becomes extremely important. A cavitation rate of 15% is used as the critical condition for cavitation to occur.

[0166] Given the free gas in water and the mass m of the gas obtained from the release of the gas. g The cavitation volume is calculated using the following formula:

[0167] W v =ρ v (m v +m g (17)

[0168] Where, ρ v The density of holes during cavitation.

[0169] The hole rate is calculated using the following formula:

[0170]

[0171] Whether liquid-column separation occurs at a certain point can be determined by whether the critical condition vacancy rate α reaches 15%.

[0172] like Figure 4 As shown, if the cavitation rate is greater than or equal to 15%, the cavitation closing time and closing pressure are calculated. If the cavitation rate is less than 15%, the calculated results are directly substituted into the finite volume model for iterative calculation.

[0173] Considering the changes in air bubbles within pressurized pipelines under different cavitation rates, the cavitation rate is used as the critical condition for whether cavitation occurs. When liquid column separation occurs, the healing time and healing pressure are calculated to provide data support to avoid accidents. When there is no risk of liquid column separation, iterative calculations are performed to avoid over-processing low-risk operating conditions.

[0174] Step S209, when the pressure of the pressurized pipeline is restored to above the vaporization pressure, the cavitation equation and the water hammer healing pressure equation are substituted to calculate the cavitation healing time and the healing pressure.

[0175] Specifically, the pressure of the pressurized pipeline is restored to above the vaporization pressure, forming a cavitation cycle, and the cavitation equation and the water hammer healing pressure equation are used to calculate the cavitation healing time and the healing pressure.

[0176] If the void fraction a is less than 15% of the liquid column separation critical value, cavitation does not occur, and if the void fraction is greater than 15%, liquid column separation occurs, and the liquid column healing pressure needs to be considered.

[0177] By the condensation equation in the cavitation model equation, the time point t1 when the steam mass is small enough can be obtained, and the water hammer healing pressure formula is as follows, given the cross-section flow velocity difference AV before and after the point:

[0178]

[0179] Wherein, a1 and a2 are respectively the wave speeds before and after the liquid column separation healing, and here the wave speeds of the unit front and rear interfaces are taken.

[0180] At this moment, the pressure of the point is the sum of the pressure calculated at the last moment and the water hammer healing pressure, and the pressure p of the point is:

[0181]

[0182] The simulation calculation method for cavitation based on phase change for a pressurized pipeline provided in this embodiment introduces a cavitation model and a water hammer healing model to calculate the cavitation healing time and the healing pressure, thereby improving the simulation calculation precision of cavitation.

[0183] In this embodiment, a simulation calculation device for cavitation based on phase change for a pressurized pipeline is also provided, which is used to implement the above-mentioned embodiments and preferred embodiments, and will not be described again. As used below, the term "module" can be a combination of software and / or hardware that implements a predetermined function. Although the device described in the following embodiments is preferably implemented in software, hardware, or a combination of software and hardware is also possible and is contemplated.

[0184] This embodiment provides a simulation calculation device for cavitation based on phase change for a pressurized pipeline, as shown in Figure 5 , comprising:

[0185] The first model establishment module 501 is configured to establish an initial model of the constant flow of the pressurized pipeline.

[0186] The first calculation module 502 is configured to set initial conditions of the gas-liquid two-phase flow and calculate parameters of the gas-liquid two-phase flow under the initial conditions by using a uniform bubble distribution model.

[0187] The second model establishing module 503 is configured to establish a finite volume method calculation equation of the gas-liquid two-phase flow.

[0188] The determining module 504 is configured to establish a gas-liquid two-phase phase change cavitation mathematical model and determine coefficients of the cavitation mathematical model.

[0189] The second calculation module 505 is configured to substitute parameters of the pressurized pipeline into the cavitation equation to calculate steam mass when the pressure of the pressurized pipeline drops below the vaporization pressure.

[0190] The third calculation module 506 is configured to substitute into the cavitation equation and the water hammer healing pressure equation to calculate cavitation healing time and healing pressure when the pressure of the pressurized pipeline recovers above the vaporization pressure.

[0191] The fourth calculation module 507 is configured to substitute the calculation results into the finite volume model for iterative calculation and output the calculation results.

[0192] In some optional embodiments, the first model establishing module 501 comprises:

[0193] The extraction unit is configured to extract hydraulic data of a water conveyance system of a water conservancy and hydropower project.

[0194] The first model establishing unit is configured to establish an initial model of a pressurized pipeline constant flow by using Bernoulli's equation according to the hydraulic data.

[0195] In some optional embodiments, the determining module 504 comprises:

[0196] The second model establishing unit is configured to establish a gas-liquid two-phase phase change cavitation mathematical model according to one-dimensional gas-liquid two-phase flow parameters and a uniform bubble distribution model.

[0197] In some optional embodiments, the device further comprises:

[0198] The determining module is configured to calculate cavitation volume and cavitation rate and determine whether the cavitation rate is greater than a preset cavitation rate threshold.

[0199] The first execution module is configured to perform the step of calculating cavitation healing time and healing pressure if the cavitation rate is greater than or equal to the preset cavitation rate threshold.

[0200] The second execution module is configured to perform the step of substituting the calculation results into the finite volume model for iterative calculation if the cavitation rate is less than the preset cavitation rate threshold.

[0201] Further functional descriptions of the above modules and units are the same as those in the corresponding embodiments described above, and will not be repeated here.

[0202] In this embodiment, the phase-change-based cavitation simulation computing device for pressurized pipelines is presented in the form of functional units. Here, a unit refers to an ASIC (Application Specific Integrated Circuit) circuit, a processor and memory that execute one or more software or fixed programs, and / or other devices that can provide the above functions.

[0203] This invention also provides a computer device having the above-described features. Figure 5 The diagram shows a phase-change-based cavitation simulation apparatus for pressurized pipelines.

[0204] Please see Figure 6 , Figure 6 This is a schematic diagram of the structure of a computer device provided in an optional embodiment of the present invention, such as... Figure 6 As shown, the computer device includes one or more processors 10, memory 20, and interfaces for connecting the components, including high-speed interfaces and low-speed interfaces. The components communicate with each other via different buses and can be mounted on a common motherboard or otherwise installed as needed. The processors can process instructions executed within the computer device, including instructions stored in or on memory to display graphical information of a GUI on external input / output devices (such as display devices coupled to the interfaces). In some alternative implementations, multiple processors and / or multiple buses can be used with multiple memories and multiple memory modules, if desired. Similarly, multiple computer devices can be connected, each providing some of the necessary operations (e.g., as a server array, a group of blade servers, or a multiprocessor system). Figure 6 Take a processor 10 as an example.

[0205] Processor 10 may be a central processing unit, a network processor, or a combination thereof. Processor 10 may further include a hardware chip. The hardware chip may be an application-specific integrated circuit (ASIC), a programmable logic device (PLD), or a combination thereof. The programmable logic device may be a complex programmable logic device (CAMP), a field-programmable gate array (FPGA), a general-purpose array logic (GDA), or any combination thereof.

[0206] The memory 20 stores instructions executable by at least one processor 10 to cause at least one processor 10 to perform the method shown in the above embodiments.

[0207] The memory 20 can include a program storage area and a data storage area. The program storage area can store an operating system, application programs required for at least one function, and the like. The data storage area can store data created according to the use of the computer device, and the like. In addition, the memory 20 can include a high-speed random access memory, and can further include a non-transitory memory such as at least one of a magnetic disk storage device, a flash memory device, or other non-transitory solid state storage device. In some alternative embodiments, the memory 20 can optionally include a memory disposed remotely from the processor 10, which can be connected to the computer device through a network. Examples of the network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and a combination thereof.

[0208] The memory 20 can include a volatile memory such as a random access memory, and can further include a non-volatile memory such as a flash memory, a hard disk, or a solid state disk. The memory 20 can also include a combination of the above-mentioned types of memories.

[0209] The computer device further includes an input device 30 and an output device 40. The processor 10, the memory 20, the input device 30, and the output device 40 can be connected through a bus or other means, Figure 6 The connection through the bus is taken as an example.

[0210] The input device 30 can receive input digital or character information, and generate key signal input related to the user settings and function control of the computer device, such as a touch screen, and the like. The output device 40 can include a display device, and the like.

[0211] The embodiments of the present application also provide a computer readable storage medium. The above-mentioned method according to the embodiments of the present application can be implemented in hardware, firmware, or recorded in a storage medium, or stored in a remote storage medium or a non-transitory machine readable storage medium and downloaded from a network and stored in a local storage medium, so that the method described herein can be processed by such software on a storage medium using a general purpose computer, a special purpose processor, or programmable or special purpose hardware. The storage medium can be a magnetic disk, an optical disk, a read-only memory, a random access memory, a flash memory, a hard disk, or a solid state disk, and the like. Further, the storage medium can also include a combination of the above-mentioned types of memories. It can be understood that the computer, the processor, the microprocessor controller, or the programmable hardware includes a storage component that can store or receive software or computer code, which, when accessed and executed by the computer, the processor, or the hardware, implements the method shown in the above-mentioned embodiments.

[0212] Part of the present application can be applied as a computer program product, for example, computer program instructions, when executed by a computer, through the operation of the computer, the method and / or technical solutions according to the present application can be called or provided. Those skilled in the art should understand that the form of computer program instructions in computer readable medium includes but is not limited to source file, executable file, installation package file and the like, and accordingly, the way of computer program instructions executed by computer includes but is not limited to: the computer directly executes the instructions, or the computer compiles the instructions and then executes the corresponding compiled program, or the computer reads and executes the instructions, or the computer reads and installs the instructions and then executes the corresponding installed program. Here, the computer readable medium can be any available computer readable storage medium or communication medium accessible to the computer.

[0213] Although the embodiments of the present application are described in conjunction with the drawings, various modifications and changes can be made by those skilled in the art without departing from the spirit and scope of the present application, and such modifications and changes fall within the scope of the present application.

Claims

1. A phase change based cavitation simulation calculation method for a pressurized pipe, characterized by, The method comprises: establishing a constant flow initial model of the pressurized pipeline; setting initial conditions of gas-liquid two-phase flow, and calculating parameters of the gas-liquid two-phase flow under the initial conditions by using a bubble uniform distribution model; establishing a finite volume method calculation equation of the gas-liquid two-phase flow containing gas; establishing a gas-liquid two-phase phase change cavitation mathematical model, and determining coefficients of the cavitation mathematical model; when the pressure of the pressurized pipeline drops below the vaporization pressure, substituting parameters of the pressurized pipeline into the cavitation equation to calculate steam quality; when the pressure of the pressurized pipeline recovers above the vaporization pressure, substituting into the cavitation equation and a water hammer healing pressure boosting equation to calculate cavitation healing time and healing pressure; substituting the calculation results into the finite volume model for iterative calculation, and outputting the calculation results.

2. The method of claim 1, wherein, The establishment of the constant flow initial model of the pressurized pipeline comprises: extracting hydraulic data of a water conveyance system of a water conservancy and hydropower project; establishing the constant flow initial model of the pressurized pipeline by using Bernoulli's formula according to the hydraulic data.

3. The method of claim 1, wherein, The establishment of the gas-liquid two-phase phase change cavitation mathematical model comprises: according to one-dimensional gas-liquid two-phase flow parameters and a bubble uniform distribution model, the gas-liquid two-phase phase change cavitation mathematical model is established as follows: where F vap is an empirical correction factor for the evaporation process, F cond is an empirical correction factor for the condensation process, Q ch is the volumetric flow rate, p v is the steam density, N is the current number of bubbles per unit volume, R is the current bubble radius, N b is the initial number of bubbles, k is the decay coefficient, a0 is the initial void fraction, a is the current void fraction, Vx is the length of the segment, and A is the cross-sectional area of the pipe segment.

4. The method of claim 3, wherein, the coefficients of the cavitation mathematical model are determined according to the following formula: where p max is the pressure extremum at the moment of water column closure, p v is the vaporization pressure, and ζ is a proportionality coefficient.

5. The method of claim 4, wherein, when the pressure of the pressurized pipeline drops below the vaporization pressure, the cavitation equation is as follows: after substituting the parameters of the pressurized pipeline into the cavitation equation to calculate the steam quality, the method further comprises: where Δm v is the mass of steam.

6. The method of claim 1, wherein, calculating cavitation volume and cavitation rate, and determining whether the cavitation rate is greater than a preset cavitation rate threshold; if the cavitation rate is greater than or equal to the preset cavitation rate threshold, the step of calculating the cavitation healing time and the healing pressure is performed; if the cavitation rate is less than the preset cavitation rate threshold, the step of substituting the calculation results into the finite volume model for iterative calculation is performed. when the pressure of the pressurized pipeline recovers above the vaporization pressure, the cavitation equation is as follows:

7. The method of claim 5, wherein, when the pressure of the pressurized pipeline recovers above the vaporization pressure, the cavitation equation is as follows: the water hammer healing pressure boosting equation is as follows: wherein a1 and a2 are respectively wave velocities of two points before and after separation and healing of a liquid column, and ΔV is a flow velocity difference between the two cross sections; the sum of the pressure of the last time and the water hammer healing pressure boosting is determined as the healing pressure. The device comprises:

8. A phase change based cavitation simulation computing device for a pressurized pipe, characterized by, a first model establishing module, configured to establish a constant flow initial model of the pressurized pipeline; a first calculation module, configured to set initial conditions of gas-liquid two-phase flow, and calculate parameters of the gas-liquid two-phase flow under the initial conditions by using a bubble uniform distribution model; a second model establishing module, configured to establish a finite volume method calculation equation of the gas-liquid two-phase flow containing gas; a determining module, configured to establish a gas-liquid two-phase phase change cavitation mathematical model, and determine coefficients of the cavitation mathematical model; a second calculation module, configured to, when the pressure of the pressurized pipeline drops below the vaporization pressure, substitute parameters of the pressurized pipeline into the cavitation equation to calculate steam quality; a third calculation module, configured to, when the pressure of the pressurized pipeline recovers above the vaporization pressure, substitute into the cavitation equation and a water hammer healing pressure boosting equation to calculate cavitation healing time and healing pressure; ​ A fourth calculation module is configured to substitute the calculation result into the finite volume model for iterative calculation and output the calculation result.

9. A computer device, comprising: The application further provides a computer readable storage medium having stored computer instructions for causing a computer to execute the simulation calculation method for phase change based cavitation of a pressurized pipeline according to any one of claims 1 to 7. The computer readable storage medium has stored computer instructions for causing a computer to execute the simulation calculation method for phase change based cavitation of a pressurized pipeline according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, ​

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