Prediction method and device for gas-liquid phase change energy source item of unstructured grid

Abstract

The invention discloses a method and a device for predicting a gas-liquid phase change energy source item of an unstructured grid, relates to the technical field of liquid rocket engines, and aims to solve the problem that an energy source item prediction method in the prior art is low in prediction precision of the energy source item of the unstructured grid. The method comprises the following steps: acquiring fluid data of a plurality of grid units in a non-uniform structure grid; based on the fluid data of the plurality of grid units, obtaining phase interface grid units; performing phase change energy source item construction on the phase interface grid units to obtain phase change energy source items of the non-uniform Cartesian grid units; obtaining a phase change energy source item of the unstructured grid unit according to the characteristic length of the unstructured grid unit and the phase change energy source item of the non-uniform Cartesian grid unit; wherein the form of the phase change energy source item of the non-uniform Cartesian grid is consistent with that of the phase change energy source item of the structural grid; therefore, the prediction precision of the non-structural network energy source item is improved.

Description

Technical Field

[0001] The invention relates to the technical field of liquid rocket engines, and in particular to a method and a device for predicting an energy source term of a non-structured grid gas-liquid phase change. Background Art

[0002] Gas-liquid phase change is widely present in the field of liquid rocket engines. Since it is difficult to quickly, accurately and comprehensively grasp the phase change process through theoretical and experimental methods, designers need to use numerical calculations to deeply understand the phase change mechanism and optimize equipment design. This places high demands on numerical methods, which not only need to capture the complex topological structure of the gas-liquid interface, but also need to accurately calculate the heat and mass transfer near the interface. In addition, industrial equipment often has complex internal geometric configurations, which makes it difficult to use structured grid division, which requires the phase change model to be expanded to unstructured grids.

[0003] In the prior art, the energy jump model is divided into two types according to the construction form. One is to construct the phase change function by the dot product of the phase fraction gradient and the temperature gradient, and write the phase change energy source term as S h =λ eff (▽α l ·▽T), the gradient term is calculated using the central difference, so the phase change source term is non-zero only near the phase interface. Another model assumes that the phase interface temperature is the saturation temperature (T int =T s ), by calculating the temperature gradient between the phase interface grid and the adjacent grid cells, the discrete energy jump is directly simulated, that is, a discrete energy jump model that directly simulates the discrete energy jump. Through verification, the discrete energy jump model corresponding to the direct simulation method has a high degree of consistency with the theoretical value; however, the discrete energy jump model is currently only applicable to structured grids. If the discrete energy jump method is used to predict the energy jump differential of unstructured grids, its prediction accuracy is low, resulting in the designer being unable to grasp the real data of the phase change process of unstructured grids.

[0004] In view of this, in order to improve the prediction accuracy of energy source terms in unstructured grid phase change processes, a prediction method suitable for energy source terms in gas-liquid phase change processes in unstructured grids is urgently needed to solve the problem of low prediction accuracy of energy jump differential predictions on unstructured networks in energy jump prediction methods in the existing technology. Summary of the invention

[0005] The purpose of the present invention is to provide a method and device for predicting gas-liquid phase change energy source items of unstructured grids, so as to solve the problem of low prediction accuracy of energy jump prediction methods for unstructured network energy source items in the prior art.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] In a first aspect, the present invention provides a method for predicting an unstructured grid gas-liquid phase change energy source term, which may include:

[0008] Obtain fluid data for multiple grid cells in a non-uniform structured grid;

[0009] Based on the fluid data of the plurality of grid cells, a phase interface grid cell is obtained;

[0010] Constructing a phase change energy source term for the phase interface grid unit to obtain a phase change energy source term for a non-uniform Cartesian grid unit; the phase change energy source term for the non-uniform Cartesian grid has the same discrete form in each orthogonal direction;

[0011] According to the characteristic length of the unstructured grid unit and the phase change energy source term of the non-uniform Cartesian grid unit, the phase change energy source term of the unstructured grid unit is obtained; the form of the non-uniform Cartesian grid phase change energy source term is consistent with the form of the structured grid phase change energy source term.

[0012] Preferably, the step of constructing the phase change energy source term for the phase interface grid unit to obtain the phase change energy source term for the non-uniform Cartesian grid unit may include:

[0013] Using the formula:

[0014]

[0015] Determine the equivalent thermal conductivity of the unstructured grid in the i direction; where λ′ eff，(i±1，int) is the equivalent thermal conductivity of the unstructured grid in the i direction, λ i±1 is the thermal conductivity at the i±1 grid, λ g is the gas thermal conductivity, λ l is the thermal conductivity of the liquid, c i is the adaptive coefficient in the i direction, α g is the gas volume fraction, α l is the liquid volume fraction, m i±1 =δ i / δ i±1 =V i / V i±1 is the ratio of adjacent characteristic lengths, δ i is the length of the i grid and the i±1 grid in the i direction, δ i±1 is the length of the i±1 grid in the i direction, V i and V i±1 are the volumes of the i grid and the i±1 grid in the i direction respectively.

[0016] Preferably, the step of constructing the phase change energy source term for the phase interface grid unit to obtain the phase change energy source term for the non-uniform Cartesian grid unit may include:

[0017] Using the formula:

[0018]

[0019] Determine the phase change energy source term in the direction of the non-uniform Cartesian grid unit i; wherein, is the phase change energy source term in the i direction of the non-uniform Cartesian grid unit, λ eff，(i±1，int) is the equivalent thermal conductivity, T i±1 is the temperature at the i±1 grid, T s is the saturation temperature, λ i±1 is the thermal conductivity at the i±1 grid, λ g is the gas thermal conductivity, λ l is the thermal conductivity of the liquid, c i is the adaptive coefficient, δ i is the characteristic length in the i direction, α g，i+1 is the gas volume fraction of the positive adjacent grid in the direction of grid cell i, α g，i-1 is the gas volume fraction of the negative adjacent grid in the direction of grid cell i.

[0020] Preferably, in any direction of the phase interface grid unit, the heat flux in the positive direction of the grid unit is equal to the heat flux from the phase interface of the phase interface grid unit to the boundary surface of the grid adjacent to the positive direction or equal to the heat flux from the boundary surface of the phase interface grid unit to the center of the grid adjacent to the positive direction;

[0021] The heat flux of the grid unit in the negative direction is equal to the heat flux from the interface of the phase interface grid unit to the boundary surface of the grid adjacent to the negative direction or equal to the heat flux from the boundary surface of the phase interface grid unit to the center of the grid adjacent to the negative direction.

[0022] Preferably, obtaining the phase change energy source term of the unstructured grid unit according to the characteristic length of the unstructured grid unit and the phase change energy source term of the non-uniform Cartesian grid unit may include:

[0023] Using the formula:

[0024]

[0025] Get the characteristic length of the unstructured grid unit in the i direction; where δ i ′ is the characteristic length of the unstructured grid unit in the i direction, is the characteristic area, is the unknown coefficient, V is the volume, and n is the dimension.

[0026] Preferably, obtaining the phase change energy source term of the unstructured grid unit according to the characteristic length of the unstructured grid unit and the phase change energy source term of the non-uniform Cartesian grid unit may include:

[0027] The characteristic length of the unstructured grid unit in the i direction is substituted into the formula corresponding to the phase change energy source term of the non-uniform Cartesian grid unit to obtain the phase change energy source term of the unstructured grid unit in the i direction.

[0028] Preferably, the product of the characteristic lengths of the unstructured grid unit in each direction is equal to the volume of the unstructured grid unit.

[0029] Preferably, obtaining the phase interface grid unit based on the fluid data of the plurality of grid units may include:

[0030] Determine whether the fluid in the target grid unit is in a saturated state, and determine whether the target grid unit is in a same-phase or mixed-phase fluid; the target grid unit is any one of the multiple grid units;

[0031] If the fluid in the target grid cell is in a saturated state and the target grid cell is not inside a same-phase or mixed-phase fluid, the target grid cell is determined as a phase interface grid cell;

[0032] If the fluid in the target grid cell is in an unsaturated state, or the target grid cell is inside a same-phase or mixed-phase fluid, the target grid cell is determined as a non-phase interface grid cell.

[0033] Preferably, the method for obtaining a non-structured grid gas-liquid phase change energy source term provided by the present invention may further include: constructing a phase change energy source term for the phase interface grid unit to obtain a phase change energy source term for a uniform Cartesian grid unit.

[0034] In a second aspect, the present invention provides a prediction device for an unstructured grid gas-liquid phase change energy source term, which may include:

[0035] An acquisition module, the acquisition module is used to acquire fluid data of multiple grid cells in a non-uniform structure grid;

[0036] A first obtaining module, the first obtaining module is used to obtain a phase interface grid unit based on the fluid data of the plurality of grid units;

[0037] A construction module, wherein the construction module is used to construct a phase change energy source term for the phase interface grid unit to obtain a phase change energy source term for a non-uniform Cartesian grid unit; the phase change energy source term for the non-uniform Cartesian grid has the same discrete form in each orthogonal direction;

[0038] The second obtaining module is used to obtain the phase change energy source term of the unstructured grid unit according to the characteristic length of the unstructured grid unit and the phase change energy source term of the non-uniform Cartesian grid unit; the form of the non-uniform Cartesian grid phase change energy source term is consistent with the form of the phase change energy source term of the structured grid.

[0039] Compared with the prior art, the present invention provides a prediction method for a non-structured grid gas-liquid phase change energy source term, which obtains fluid data of multiple grid cells in a non-uniform structured grid; obtains a phase interface grid cell based on the fluid data of the multiple grid cells; constructs a phase change energy source term for the phase interface grid cell to obtain a phase change energy source term for a non-uniform Cartesian grid cell; the phase change energy source term of the non-uniform Cartesian grid has the same discrete form in each orthogonal direction; and obtains the phase change energy source term of the non-structured grid cell according to the characteristic length of the non-structured grid cell and the phase change energy source term of the non-uniform Cartesian grid cell. Phase change energy source term; the form of the non-uniform Cartesian grid phase change energy source term is consistent with the form of the phase change energy source term of the structured grid; because the phase interface in the present invention is in a saturated state and the phase change source term is decomposed along the orthogonal direction, an orthogonal component with a unified form is constructed to obtain the phase change energy source term of the non-uniform Cartesian grid unit; and a characteristic length is introduced to predict the phase change energy source term of the non-structured grid unit, thereby improving the prediction accuracy of the energy source term of the non-structured network; the discrete energy jump model in the prior art can be applied to the non-structured network, and the energy source term of the non-structured network is accurately predicted. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0041] Figure 1 A schematic flow chart of a method for predicting an energy source term of a gas-liquid phase change in an unstructured grid provided by the present invention;

[0042] Figure 2 A schematic structural diagram of a prediction device for an unstructured grid gas-liquid phase change energy source term provided by the present invention. DETAILED DESCRIPTION

[0043] In order to clearly describe the technical solutions of the embodiments of the present invention, in the embodiments of the present invention, words such as "first" and "second" are used to distinguish the same items or similar items with basically the same functions and effects. For example, the first threshold and the second threshold are only used to distinguish different thresholds, and their order is not limited. Those skilled in the art can understand that words such as "first" and "second" do not limit the quantity and execution order, and words such as "first" and "second" do not necessarily limit them to be different.

[0044] It should be noted that, in the present invention, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0045] In the present invention, "at least one" means one or more, and "plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, the combination of a and b, the combination of a and c, the combination of b and c, or the combination of a, b and c, where a, b, c can be single or multiple.

[0046] The discrete energy jump model in the prior art is applicable to various phase change processes, such as single-phase saturation, two-phase saturation and two-phase unsaturation phase change processes, and it is in good agreement with the theoretical value; however, the differential discrete energy jump is currently only applicable to structured grids, and faces many difficulties when extended to unstructured grids; for example: (1) unstructured grids such as tetrahedrons and polyhedrons are non-uniform, and the grid length, grid area and grid volume are inconsistent, which makes it difficult to construct the differential format on the unstructured grid; (2) unstructured grids such as tetrahedrons and polyhedrons are anisotropic, which makes it difficult to determine the direction of the phase interface and which adjacent grid to select for differential calculation, which makes it difficult to select the differential grid on the unstructured grid; (3) unstructured grids such as tetrahedrons and polyhedrons have poor orthogonality, which will affect the differential accuracy on the unstructured grid. These problems lead to the low prediction accuracy of the existing discrete energy jump model for unstructured grids, and it cannot be applied to predict energy source terms in unstructured grids, limiting its application in industrial simulation.

[0047] In view of this, the present invention provides a prediction method and device for gas-liquid phase change energy source terms in an unstructured grid. By constructing orthogonal components with a unified form and introducing the concept of characteristic length of the unstructured grid, the existing discrete energy jump model is optimized, and the prediction accuracy is improved. The discrete energy jump model can be applied to the prediction of phase change energy source terms in unstructured grids and the calculation of gas-liquid two-phase flow with phase change, thereby broadening the scope of application of the discrete energy jump model.

[0048] Next, the technical solution of the present invention is described in detail with reference to the accompanying drawings:

[0049] See also Figure 1 , Figure 1 The present invention provides a flow chart of a method for predicting the energy source term of gas-liquid phase change in an unstructured grid. The execution subject is a server or terminal device equipped with the technical solution disclosed in the embodiment of the present invention, such as a simulation service platform or iPad.

[0050] exist Figure 1 In, the method may include:

[0051] Step 110: Obtain fluid data of multiple grid cells in the non-uniform structured grid.

[0052] Step 120: Obtaining a phase interface grid unit based on the fluid data of the plurality of grid units.

[0053] In step 110 to step 120, the phase interface is identified by acquiring the fluid data of multiple grid cells in the non-uniform structure grid, and the phase interface grid cells are obtained. The phase interface can be understood as an interface in a saturated state in the model.

[0054] It should be noted that the judgment of the phase interface is based on two principles: first, the fluid of the interface unit must reach a supersaturated state and have a phase change potential; second, the interface unit cannot be inside the same phase or mixed phase fluid. Based on this principle, the following judgment method is used for gas-liquid two-phase flow: If a grid unit has supercooled gas (i.e., the gas volume fraction is greater than zero α g >0 and the temperature is lower than the saturation temperature T<T s ), and there is pure liquid in the adjacent grid (the liquid volume fraction is α l =1), condensation occurs at the grid unit; if there is superheated liquid in a grid unit (i.e., the liquid volume fraction is greater than zero α l >0 and the temperature is higher than the saturation temperature T>T s ), and there is pure gas in the adjacent grid (the gas volume fraction is α g =1), evaporation occurs at this grid unit.

[0055] Step 130: constructing phase change energy source terms for the phase interface grid unit to obtain phase change energy source terms for the non-uniform Cartesian grid unit; the phase change energy source terms for the non-uniform Cartesian grid have the same discrete form in each orthogonal direction.

[0056] In step 130, after obtaining the phase interface, it is first necessary to construct a phase change source term on the non-uniform structure grid. The phase change energy source term is the difference in heat flux on both sides of the phase interface. According to the principle of energy conservation, the heat flux on both sides of the phase interface is discretized and equivalently processed, and the equivalent thermal conductivity inside the grid is further calculated. Finally, the phase change energy source term of the non-uniform Cartesian grid unit is obtained by combining the equivalent thermal conductivity. The orthogonal directions of the non-uniform Cartesian grid can be divided into three orthogonal directions, such as: i, j, k orthogonal directions; the discrete form in each orthogonal direction is the same; thus, based on the energy jump model, the phase change energy source term of the non-uniform Cartesian grid unit is constructed through the equivalent thermal conductivity, and the non-uniform grid has a uniform form of phase change energy source term.

[0057] Step 140: Obtain the phase change energy source term of the unstructured grid unit according to the characteristic length of the unstructured grid unit and the phase change energy source term of the non-uniform Cartesian grid unit; the form of the non-uniform Cartesian grid phase change energy source term is consistent with the form of the structured grid phase change energy source term.

[0058] In step 140, the concept of characteristic length of unstructured grids is introduced, so that the phase change energy source term of unstructured grid cells can be predicted using the model corresponding to the phase change energy source term of the predicted non-uniform Cartesian grid cells, for example, a discrete energy jump model. Because the phase change energy source term of the non-uniform Cartesian grid cell is consistent with the form of the phase change energy source term of the structured grid, the discrete energy jump model can be generalized and applied to unstructured grids to achieve the prediction of the phase change energy source term of the unstructured grid and meet the accuracy requirements; in other words, because the method provided by the present invention can improve the prediction accuracy of the discrete energy jump model in unstructured grids, the discrete energy jump model can be generalized and applied to unstructured grids.

[0059] Based on this, the present invention provides a prediction method for gas-liquid phase change energy source terms in an unstructured grid, which obtains fluid data of multiple grid cells in a non-uniform structured grid; obtains a phase interface grid cell based on the fluid data of the multiple grid cells; constructs a phase change energy source term for the phase interface grid cell to obtain a phase change energy source term for the non-uniform Cartesian grid cell; obtains the phase change energy source term for the unstructured grid cell according to the characteristic length of the unstructured grid cell and the phase change energy source term of the non-uniform Cartesian grid cell; because based on the energy jump, a phase change source term with a unified form on the non-uniform grid is constructed through the equivalent thermal conductivity; and the characteristic length of the unstructured grid is introduced to improve the prediction accuracy of the discrete energy jump model in the unstructured grid, so that the application scope of the discrete energy jump model can be extended from the structured grid to the unstructured grid, and the gas-liquid two-phase flow with phase change in the unstructured grid is calculated, which is of great significance for the accurate prediction of the phase change of complex flow fields in industrial equipment.

[0060] Preferably, in step 120, obtaining the phase interface grid unit based on the fluid data of the plurality of grid units may include:

[0061] The determination of the phase interface should be based on two principles: first, the unit fluid must reach a supersaturated state and have a phase change potential; second, the unit cannot be inside the same phase or mixed phase fluid.

[0062] Determine whether the fluid in the target grid unit is in a saturated state, and determine whether the target grid unit is in a same-phase or mixed-phase fluid; the target grid unit is any one of the plurality of grid units;

[0063] If the fluid in the target grid cell is in a saturated state and the target grid cell is not inside a same-phase or mixed-phase fluid, the target grid cell is determined as a phase interface grid cell;

[0064] If the fluid in the target grid cell is in an unsaturated state, or the target grid cell is inside a same-phase or mixed-phase fluid, the target grid cell is determined as a non-phase interface grid cell.

[0065] Based on this, multiple grid cells in the non-uniform structure grid are screened to obtain multiple phase interface grid cells. Data processing is performed on each phase interface grid cell according to the method described in the first aspect of the present invention, so as to construct the phase change energy source term of the non-uniform Cartesian grid cell.

[0066] Preferably, in step 130, after the phase interface is identified, a phase change source term is first constructed on the inhomogeneous structure grid, and a phase change energy source term is is the difference in heat flow on both sides of the phase interface; the formula can be used:

[0067]

[0068] The phase change energy source term on the non-uniform structure grid is calculated; among them, is the phase change energy source term, is the heat flux jump on both sides of the phase interface, is the heat flux in the positive direction near the phase interface, is the heat flux in the negative direction near the phase interface, A i is the projection of the phase interface in the i direction, V is the mesh volume of the phase interface, λ is the thermal conductivity, T is the temperature, and x i is the coordinate in the i direction.

[0069] Furthermore, according to the law of energy conservation, the heat flow on both sides of the phase interface Equal to the heat flux q from the phase interface int to the adjacent mesh boundary surface i±1 / 2 i±1 / 2,int , which is also equal to the heat flux q from the boundary surface i±1 / 2 of the phase interface to the adjacent grid center i±1 i±1,i±1 / 2 That is, in any direction of the phase interface grid unit, the heat flux in the positive direction of the grid unit is equal to the heat flux from the phase interface of the phase interface grid unit to the boundary surface of the grid adjacent to the positive direction, or equal to the heat flux from the boundary surface of the phase interface grid unit to the center of the grid adjacent to the positive direction; the heat flux in the negative direction of the grid unit is equal to the heat flux from the phase interface of the phase interface grid unit to the boundary surface of the grid adjacent to the negative direction, or equal to the heat flux from the boundary surface of the phase interface grid unit to the center of the grid adjacent to the negative direction.

[0070] Furthermore, assuming that the thermal conductivity of the i±1 grid is uniform, the heat flux q from the boundary surface i±1 / 2 of the phase interface to the center of the adjacent grid i±1 is i±1,i±1 / 2 The formula can be used:

[0071]

[0072] Discrete processing is performed; where λ i±1 is the thermal conductivity at the i±1 grid, T i±1 is the temperature at the i±1 grid, T i±1 / 2 is the temperature at i±1 / 2 of the i±1 boundary surface, and δ is the characteristic length of the uniform Cartesian grid.

[0073] Furthermore, assuming that inside the i grid unit, one side of the phase interface is pure liquid phase, and the other side is pure gas phase, an adaptive coefficient c can be used i To automatically identify, the phase interface temperature can be the saturation temperature, that is: T int =T s .

[0074] Further, the formula can be used:

[0075]

[0076] Heat flux q from the phase interface int to the adjacent mesh boundary surface i±1 / 2 i±1 / 2,int Discrete processing is performed; among them, is the adaptive coefficient, λ g is the thermal conductivity of gas, λ l is the thermal conductivity of the liquid, α g is the gas volume fraction, α l is the liquid volume fraction, T s is the saturation temperature and δ is the characteristic length of the uniform Cartesian grid.

[0077] It should be noted that the adaptive coefficient c i The corresponding formula can be obtained: i The direction of gas phase growth in the i direction is determined. When the gas phase fraction at i+1 is greater than that at i-1, the growth direction is the positive direction of i, c i =1, otherwise -1. i = 1, the interface close to i+1 is filled with pure gas phase; when c i When =-1, the phase interface close to i+1 is filled with pure liquid phase.

[0078] Furthermore, the boundary surface temperature T can be eliminated by combining the formula in the prior art: i±1 / 2 After that, the formula can be used:

[0079]

[0080] Get the heat flow q from the phase interface int to the adjacent grid center i±1 i±1,int ; Among them, λ eff,(i±1,int) For the equivalent thermal conductivity, the formula can be used:

[0081]

[0082] The equivalent thermal conductivity is calculated.

[0083] Furthermore, the prediction of an unstructured grid gas-liquid phase change energy source term provided by the present invention may include: constructing a phase change energy source term for the phase interface grid unit to obtain a phase change energy source term for a uniform Cartesian grid unit.

[0084] Preferably, the formula can be used:

[0085]

[0086] The phase change energy source term caused by the energy jump in the i direction on a uniform Cartesian grid is calculated.

[0087] In formulas (4) to (6), is the phase change energy source term caused by the energy jump in the i direction on the uniform Cartesian grid, T i±1 is the temperature from the interface to the center of the adjacent grid, T s is the saturation temperature, δ is the characteristic length of the uniform Cartesian grid, λ g is the thermal conductivity of gas, λ l is the thermal conductivity of the liquid, α g is the gas volume fraction, α l is the liquid volume fraction, λ i±1 is the thermal conductivity from the phase interface to the center of the adjacent grid.

[0088] It should be noted that the phase change energy source terms in each coordinate direction on the uniform Cartesian grid can be calculated using the methods shown in formulas (4) to (6), and then the calculation results are summed to obtain the total amount of phase change energy source terms caused by the energy jump on the uniform Cartesian grid, so as to evaluate the impact of the total energy jump.

[0089] Further, the constructing of the phase change energy source term of the phase interface grid unit to obtain the phase change energy source term of the non-uniform Cartesian grid unit may include:

[0090] Using the formula:

[0091]

[0092] Heat flux q from the adjacent grid boundary i±1 / 2 to the adjacent grid center i±1 i±1,i±1 / 2 Discrete processing; and use the formula:

[0093]

[0094] Heat flux q from the phase interface int to the adjacent grid boundary i±1 / 2 i±1 / 2,int Discrete processing is performed; among them, δ i and δ i±1 are the lengths q of the i grid and i±1 grid in the i direction respectively i±1 / 2,int .

[0095] Preferably, the formula in the prior art can be combined to eliminate T i±1 / 2 Afterwards, the phase change energy source term is constructed for the phase interface grid unit to obtain the phase change energy source term of the non-uniform Cartesian grid unit, which may include using the formula:

[0096]

[0097] Determine the equivalent thermal conductivity of the unstructured grid in the i direction; where λ'eff,(i±1,int) is the equivalent thermal conductivity of the unstructured grid in the i direction, λ i±1 is the thermal conductivity at the i±1 grid, λ g is the gas thermal conductivity, λ l is the thermal conductivity of the liquid, c i is the adaptive coefficient in the i direction, α g is the gas volume fraction, α l is the liquid volume fraction, m i±1 =δ i / δ i±1 =V i / V i±1 is the ratio of adjacent characteristic lengths, δ i is the length of the i grid and the i±1 grid in the i direction, δ i±1 is the length of the i±1 grid in the i direction, V i and V i±1 are the volumes of the i grid and the i±1 grid in the i direction respectively.

[0098] Preferably, for the phase interface density in the i direction of the non-uniform grid, the formula can be used:

[0099]

[0100] The phase interface density in the i direction of the non-uniform grid is calculated; where: ρ Ai is the phase interface density in the i direction of the non-uniform grid, A i is the characteristic area, V is the characteristic volume, α g,i+1 is the gas volume fraction of the positive adjacent grid in the direction of grid cell i, α g,i-1 is the gas volume fraction of the negative adjacent grid in the direction of grid cell i, δ i is the length of the i-grid in the i-direction.

[0101] Further, the step of constructing the phase change energy source term for the phase interface grid unit to obtain the phase change energy source term for the non-uniform Cartesian grid unit may include using the formula:

[0102]

[0103] The phase change energy source term caused by energy jump on the non-uniform Cartesian grid is calculated; among them, is the phase change energy source term in the i direction of the non-uniform Cartesian grid unit, λ eff,(i±1,int) is the equivalent thermal conductivity, T i±1 is the temperature at the i±1 grid, T s is the saturation temperature, λ i±1 is the thermal conductivity at the i±1 grid, λ g is the gas thermal conductivity, λl is the thermal conductivity of the liquid, c i is the adaptive coefficient, δ i is the characteristic length in the i direction, α g，i+1 is the gas volume fraction of the adjacent grid in the positive upward direction of grid cell i, α g，i-1 is the gas volume fraction of the negative adjacent grid in the direction of grid cell i.

[0104] Based on this, the present invention provides a prediction method for the gas-liquid phase change energy source term of an unstructured grid, which constructs the phase change source term of an inhomogeneous structured grid through the equivalent thermal conductivity. The phase change source term has a unified form in each orthogonal direction, which is convenient for extension to unstructured grids.

[0105] Furthermore, in order to facilitate numerical calculations and overcome the problem that the unstructured grid has a complex structure and is difficult to simply define the source term, the unstructured grid can be equivalent to a non-uniform Cartesian grid. Assuming that the characteristic length in the i direction is inversely proportional to the characteristic surface density in that direction, the formula can be used:

[0106]

[0107] Get the characteristic length of the unstructured grid unit in the i direction; where δ′ i is the characteristic length of the unstructured grid unit in the i direction, is the characteristic area, is the unknown coefficient, V is the volume, and n is the dimension.

[0108] It should be noted that the product of the characteristic lengths of the unstructured grid unit in each direction is equal to the volume of the unstructured grid unit, that is: Thus, the unknown coefficient S in formula (12) can be obtained; and for the three-dimensional grid coefficient is Therefore, the unstructured grid can be approximately equivalent to a grid with a characteristic length δ i The non-uniform Cartesian structured grid with ′ as the edge has the same phase change energy source term as the structured grid in form.

[0109] Preferably, in step 140, obtaining the phase change energy source term of the unstructured grid unit according to the characteristic length of the unstructured grid unit and the phase change energy source term of the non-uniform Cartesian grid unit may include: substituting the characteristic length of the unstructured grid unit in the i direction into the formula corresponding to determining the phase change energy source term of the non-uniform Cartesian grid unit to obtain the phase change energy source term in the i direction of the unstructured grid unit; that is, substituting the characteristic length calculated by formula (12) into formula (11), replacing δ in formula (11) i , the phase change energy source term in the i direction of the unstructured grid unit can be calculated.

[0110] It should be noted that the present invention only takes the i orthogonal direction of each grid coordinate as an example to explain in detail the technical solution of the present invention. The calculation method of the phase change energy source term in other orthogonal directions (such as j and k orthogonal directions) is the same as the calculation method of the phase change energy source term in the i orthogonal direction, and will not be repeated here.

[0111] Furthermore, the above technical solution can continue to be used to calculate the phase change energy source terms in the orthogonal directions of j and k, so as to calculate the phase change energy source terms of each coordinate in the unstructured grid unit using the discrete energy jump model corresponding to the direct simulation method.

[0112] Based on this, the method provided by the present invention can be used to approximately convert the unstructured grid into a grid with a characteristic length δ i The phase change energy source term of the non-uniform Cartesian structured grid with ′ as the edge is consistent with that of the structured grid in form. Through the concept of equivalent length, the prediction accuracy of the phase change model on the structured grid for the phase change energy source term of the unstructured grid is improved, so that the phase change model on the structured grid can be successfully extended to the unstructured grid.

[0113] In a second aspect, the present invention provides a prediction device for an unstructured grid gas-liquid phase change energy source term. Figure 2 , Figure 2 A schematic structural diagram of a prediction device for an unstructured grid gas-liquid phase change energy source term provided by the present invention.

[0114] The acquisition module 210 is used to acquire fluid data of multiple grid cells in the non-uniform structure grid.

[0115] The first obtaining module 220 is used to obtain the phase interface grid unit based on the fluid data of the plurality of grid units.

[0116] The construction module 230 is used to construct the phase change energy source term of the phase interface grid unit to obtain the phase change energy source term of the non-uniform Cartesian grid unit; the phase change energy source term of the non-uniform Cartesian grid has the same discrete form in each orthogonal direction.

[0117] The second obtaining module 240 is used to obtain the phase change energy source term of the unstructured grid unit according to the characteristic length of the unstructured grid unit and the phase change energy source term of the non-uniform Cartesian grid unit; the form of the non-uniform Cartesian grid phase change energy source term is consistent with the form of the structured grid phase change energy source term.

[0118] Based on this, the present invention provides a prediction device for a non-structured grid gas-liquid phase change energy source item, which obtains fluid data of multiple grid units in a non-uniform structured grid through an acquisition module, and obtains a phase interface grid unit based on the fluid data of the multiple grid units through a first acquisition module, and then constructs a phase change energy source item for the phase interface grid unit through a construction module to obtain a phase change energy source item of a non-uniform Cartesian grid unit; the phase change energy source item of the non-uniform Cartesian grid has the same discrete form in each orthogonal direction, and finally obtains the phase change energy source item of the non-structured grid unit according to the characteristic length of the non-structured grid unit and the phase change energy source item of the non-uniform Cartesian grid unit through a second acquisition module; the form of the non-uniform Cartesian grid phase change energy source item is consistent with the form of the phase change energy source item of the structured grid; thereby improving the prediction accuracy of the phase change energy source item prediction model for the structured grid in the non-structured grid, which is conducive to the promotion and application of the phase change energy source item prediction model for the structured grid to the prediction of the phase change energy source item for the non-structured grid, which is of great significance for the accurate prediction of the phase change of complex flow fields in industrial devices.

[0119] Although the present invention is described herein in conjunction with various embodiments, in the process of implementing the claimed invention, those skilled in the art may understand and implement other variations of the disclosed embodiments by viewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "one" or "an" does not exclude multiple situations. A single processor or other unit may implement several functions listed in the claims. Certain measures are recorded in different dependent claims, but this does not mean that these measures cannot be combined to produce good results.

[0120] Although the present invention has been described in conjunction with specific features and embodiments thereof, it is apparent that various modifications and combinations may be made thereto without departing from the spirit and scope of the present invention. Accordingly, this specification and the accompanying drawings are merely exemplary illustrations of the present invention as defined by the appended claims and are deemed to cover any and all modifications, variations, combinations or equivalents within the scope of the present invention. Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, the present invention is intended to include such modifications and variations if they fall within the scope of the claims of the present invention and their equivalents.

Claims

1. A method for predicting energy source terms of gas-liquid phase change in an unstructured grid, characterized in that: include: Obtain fluid data for multiple grid cells in a non-uniform structured grid; Based on the fluid data of the plurality of grid cells, a phase interface grid cell is obtained; Constructing a phase change energy source term for the phase interface grid unit to obtain a phase change energy source term for a non-uniform Cartesian grid unit; the phase change energy source term for the non-uniform Cartesian grid has the same discrete form in each orthogonal direction; According to the characteristic length of the unstructured grid unit and the phase change energy source term of the non-uniform Cartesian grid unit, the phase change energy source term of the unstructured grid unit is obtained; the form of the non-uniform Cartesian grid phase change energy source term is consistent with the form of the structured grid phase change energy source term.

2. The method according to claim 1, characterized in that The step of constructing a phase change energy source term for the phase interface grid unit to obtain a phase change energy source term for the non-uniform Cartesian grid unit includes: Using the formula: Determine the equivalent thermal conductivity of the unstructured grid in the i direction; where λ' eff,(i±1,int) is the equivalent thermal conductivity of the unstructured grid in the i direction, λ i±1 is the thermal conductivity at the i±1 grid, λ g is the gas thermal conductivity, λ l is the thermal conductivity of the liquid, c i is the adaptive coefficient in the i direction, α g is the gas volume fraction, α l is the liquid volume fraction, m i±1 =δ i / δ i±1 =V i / V i±1 is the ratio of adjacent characteristic lengths, δ i is the length of the i grid and the i±1 grid in the i direction, δ i±1 is the length of the i±1 grid in the i direction, V i and V i±1 are the volumes of the i grid and the i±1 grid in the i direction respectively.

3. The method according to claim 2, characterized in that The step of constructing a phase change energy source term for the phase interface grid unit to obtain a phase change energy source term for the non-uniform Cartesian grid unit includes: Using the formula: Determine the phase change energy source term in the direction of the non-uniform Cartesian grid unit i; wherein, is the phase change energy source term in the i direction of the non-uniform Cartesian grid unit, λ eff,(i±1,int) is the equivalent thermal conductivity, T i±1 is the temperature at the i±1 grid, T s is the saturation temperature, λ i±1 is the thermal conductivity at the i±1 grid, λ g is the gas thermal conductivity, λ l is the thermal conductivity of the liquid, c i is the adaptive coefficient, δ i is the characteristic length in the i direction, α g，i+1 is the gas volume fraction of the positive adjacent grid in the direction of grid cell i, α g，i-1 is the gas volume fraction of the negative adjacent grid in the direction of grid cell i.

4. The method according to claim 1, characterized in that In any direction of the phase interface grid unit, the heat flux in the positive direction of the grid unit is equal to the heat flux from the phase interface of the phase interface grid unit to the boundary surface of the grid adjacent to the positive direction or equal to the heat flux from the boundary surface of the phase interface grid unit to the center of the grid adjacent to the positive direction; The heat flux in the negative direction of the grid unit is equal to the heat flux from the interface of the phase interface grid unit to the boundary surface of the grid adjacent to the negative direction or equal to the heat flux from the boundary surface of the phase interface grid unit to the center of the grid adjacent to the negative direction.

5. The method according to claim 1, characterized in that The step of obtaining the phase change energy source term of the unstructured grid unit according to the characteristic length of the unstructured grid unit and the phase change energy source term of the non-uniform Cartesian grid unit comprises: Using the formula: Get the characteristic length of the unstructured grid unit in the i direction; where δ′ i is the characteristic length of the unstructured grid unit in the i direction, is the characteristic area, is the unknown coefficient, V is the volume, and n is the dimension.

6. The method according to claim 5, characterized in that The step of obtaining the phase change energy source term of the unstructured grid unit according to the characteristic length of the unstructured grid unit and the phase change energy source term of the non-uniform Cartesian grid unit comprises: The characteristic length of the unstructured grid unit in the i direction is substituted into the formula corresponding to the phase change energy source term of the non-uniform Cartesian grid unit to obtain the phase change energy source term of the unstructured grid unit in the i direction.

7. The method according to claim 5, characterized in that The product of the characteristic lengths of the unstructured grid unit in each direction is equal to the volume of the unstructured grid unit.

8. The method according to claim 1, characterized in that The step of obtaining a phase interface grid unit based on the fluid data of the plurality of grid units comprises: Determine whether the fluid in the target grid unit is in a saturated state, and determine whether the target grid unit is in a same-phase or mixed-phase fluid; the target grid unit is any one of the plurality of grid units; If the fluid in the target grid cell is in a saturated state and the target grid cell is not inside a same-phase or mixed-phase fluid, the target grid cell is determined as a phase interface grid cell; If the fluid in the target grid cell is in an unsaturated state, or the target grid cell is inside a same-phase or mixed-phase fluid, the target grid cell is determined as a non-phase interface grid cell.

9. The method according to claim 1, characterized in that The method further comprises: A phase change energy source term is constructed for the phase interface grid unit to obtain a phase change energy source term of a uniform Cartesian grid unit.

10. A prediction device for an unstructured grid gas-liquid phase change energy source term, characterized in that: include: An acquisition module, the acquisition module is used to acquire fluid data of multiple grid cells in a non-uniform structure grid; A first obtaining module, the first obtaining module is used to obtain a phase interface grid unit based on the fluid data of the plurality of grid units; A construction module, wherein the construction module is used to construct a phase change energy source term for the phase interface grid unit to obtain a phase change energy source term for a non-uniform Cartesian grid unit; the phase change energy source term for the non-uniform Cartesian grid has the same discrete form in each orthogonal direction; The second obtaining module is used to obtain the phase change energy source term of the unstructured grid unit according to the characteristic length of the unstructured grid unit and the phase change energy source term of the non-uniform Cartesian grid unit; the form of the non-uniform Cartesian grid phase change energy source term is consistent with the form of the phase change energy source term of the structured grid.

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