Simulation analysis method of airplane air circulation refrigeration system based on CFD technology
Technical Field
The invention relates to the technical field of refrigeration, in particular to a simulation analysis method of an aircraft air circulation refrigeration system based on a CFD (computational fluid dynamics) technology.
Background
The air conditioning system on an aircraft is divided into four subsystems: a refrigeration system, a temperature control system, an air distribution system, and a pressurization control system. The most important of them is the refrigeration system, and the core of the refrigeration system is the air circulation refrigerator. The two companies that are currently most competitive in aircraft manufacture and development in the world are the united states boeing company and the european airbus company, respectively. Table 1 summarizes the air cycle chiller versions employed by boeing and airbus aircraft. The air circulation refrigerator of the airplane which is most widely applied at present adopts a three-wheel or four-wheel boosting type high-pressure water removal circulation system, has stronger ground refrigerating capacity, and keeps the advantages of small air supply pressure and power saving. The latest Boeing 787 aircraft air circulation refrigerator adopts an electrically-driven four-wheel boosting high-pressure water removal refrigeration system, engine air entraining is omitted, and energy consumption of civil aircraft is greatly saved, so that fuel consumption of the engine is reduced.
TABLE 1 air circulation refrigerator form for the cockpit of a civil aircraft in the world
For China, the air circulation refrigerator can only adopt two-stage bleed air and three-wheel boosting high-pressure water removal systems of an engine according to the development level of the current environment control accessories in China. As the first civil aircraft ARJ21-700 with independent intellectual property rights in China, the air refrigerating machine of the civil aircraft adopts the circulating refrigerating system. For the main line civil aircraft C919 with independent intellectual property rights according to the latest international airworthiness standard in the first money of China, the air entraining system still adopts an engine air entraining mode, and a certain gap still exists compared with the most advanced technology in foreign countries.
Disclosure of Invention
The invention overcomes the defects of the prior art and provides a simulation analysis method and a simulation analysis system of an aircraft air circulation refrigeration system based on a CFD technology.
The method adopts commercial calculation fluid software Fluent to establish a two-dimensional calculation model of the air circulation refrigeration system of the airplane, performs numerical simulation and predicts the refrigeration performance of the refrigeration system. Furthermore, the distribution of a temperature field, a pressure field and a flow field in the refrigerating system is analyzed, and theoretical and practical application basis is provided for the design of a practical and efficient refrigerating system.
The invention relates to a simulation analysis method of an aircraft air circulation refrigeration system based on a CFD technology, which comprises the following steps:
the method comprises the following steps: establishing a geometric model of an air circulation refrigeration system of the airplane;
step two: dividing and setting a control area;
step three: setting a boundary condition;
step four: dividing grids;
step five: establishing an unsteady state control equation, and respectively establishing a control equation for a gas area and a porous medium area by taking working medium gas air in a refrigeration system as an object;
step six: carrying out numerical solution;
step seven: and analyzing the simulation result and predicting the refrigeration performance of the air circulation refrigeration system of the airplane.
In the invention, further, the distribution of the temperature field, the pressure field and the flow field in the aircraft air circulation refrigeration system is observed, so that the operation mechanism of the refrigeration system and the flow state of the fluid can be analyzed.
The simulation analysis method comprises the following specific steps:
the first step is as follows: a geometric model of the air circulation refrigeration system of the airplane is established, and the model is a two-dimensional CFD model and comprises a precooler 1, a regulating valve 2, a primary heat exchanger 3, a compressor 4, a secondary heat exchanger 5, an expansion machine 6, a water separator 7, a one-way valve 8 and a mixing chamber 9.
The second step is as follows: the control regions are divided and set, and the internal control region where the precooler 1, the primary heat exchanger 3, and the secondary heat exchanger 5 are located is set as a porous medium region, the internal control region where the water separator 7 is located is set as a gas-liquid mixing region, and the other internal control regions are set as gas regions.
The third step is that: setting boundary conditions, setting the left end boundary of the precooler 1 as a speed inlet boundary, and setting the outer boundaries of the regulating valve 2, the compressor 4, the expander 6, the water separator 7, the one-way valve 8 and the mixing chamber 9 as isothermal boundaries; the outer boundaries of the primary heat exchanger 3 and the secondary heat exchanger 5 are set as adiabatic boundaries.
The fourth step is that: and dividing grids, adopting structured grids for all control domains of the model, and simultaneously carrying out local grid refinement near the boundary.
The fifth step is as follows: and establishing an unsteady state control equation, and establishing a control equation for a gas area and a porous medium area respectively by taking working medium gas air in the refrigerating system as an object.
First, a governing equation is established for the gas region:
continuity equation:
in the formula (1), ρ
fAnd
respectively the density and velocity of the gas.
The momentum equation:
in the formula (2), p is a static pressure,
is the pressure tensor;
energy equation:
in the formula (3), kfIs gas thermal conductivity, T is temperature, EfThe total energy of the gas;
then, a control equation is established for the porous medium region:
continuity equation:
the momentum equation:
in the formula (4), ε represents the porosity of the porous medium, and the porous medium region is filled with the screen, so that the porosity ε is determined by the mesh number m and the diameter d of the screenwDetermining:
hydraulic diameter d of the wire meshhCan be calculated by equation (7):
in the formula (5), SiIs a source term in the momentum equation and consists of two parts of viscous loss term and inertial loss term, and for isotropic media, SiCan be expressed as:
in the formula (8), μ is the dynamic viscosity of the gas, α is the degree of permeability, C2Coefficient of inertial resistance, α and C2Can be calculated by the following method:
the axial pressure drop of a region of porous media can be expressed as:
in the formula (9), foscFor the friction factor, according to empirical formula:
in equation (10), Re is the reynolds number of the fluid in the porous medium region and can be expressed as:
by combining the formula (9), the formula (10) and the formula (11), the degree of penetration α and the coefficient of inertial resistance C can be determined2:
Energy equation:
in the formula (14), psAnd EsDensity and total energy, k, respectively, of the solideffEffective thermal conductivity for porous media;
effective thermal conductivity k of porous media due to the effect of thermal contact resistanceeffMuch less than its average thermal conductivity, the following modifications can be made:
in formula (15), ksAnd kfThe thermal conductivity of the solid and gas respectively.
The sixth step: and (4) carrying out numerical solution, setting solver control parameters, a discrete format and a residual convergence standard according to the CFD model of the aircraft air circulation refrigeration system established in the steps, initializing a flow field, and starting to carry out numerical solution.
The seventh step is as follows: and analyzing the simulation result, and predicting the refrigeration performance of the air circulation refrigeration system of the airplane through analyzing the simulation result after the calculation is stable.
In addition, further, by observing the distribution conditions of the temperature field, the pressure field and the flow field inside the refrigeration system, the operation mechanism of the refrigeration system and the flow state of the fluid can be further analyzed.
The invention also provides a simulation analysis system of the aircraft air circulation refrigeration system based on the CFD technology, which comprises: the device comprises a temperature simulation analysis module, a pressure simulation analysis module and a speed simulation analysis module. The temperature simulation analysis module is used for simulating and analyzing a temperature field in the model, the pressure simulation analysis module is used for analyzing a pressure field in the model, and the speed simulation analysis module is used for simulating and analyzing a flow field in the model.
The model establishing module is used for establishing a geometric model of the aircraft air circulation refrigeration system;
the area setting module is used for dividing and setting a control area;
the boundary setting module is used for setting boundary conditions;
the grid division module is used for dividing grids;
the equation establishing module is used for establishing an unsteady state control equation, and respectively establishing control equations for a gas area and a porous medium area by taking working medium gas air in the refrigerating system as an object;
the numerical solving module is used for carrying out numerical solving;
and the result analysis module is used for analyzing the simulation result and predicting the refrigeration performance of the air circulation refrigeration system of the airplane.
Wherein the result analysis module comprises: the device comprises a temperature simulation analysis module, a pressure simulation analysis module and a speed simulation analysis module; the temperature simulation analysis module is used for simulating a temperature field in the analysis model, the pressure simulation analysis module is used for analyzing a pressure field in the model, and the speed simulation analysis module is used for simulating a flow field in the analysis model.
The simulation analysis system is used for realizing the simulation analysis method of the airplane air circulation refrigeration system based on the CFD technology.
The invention has the following beneficial effects and advantages: by the simulation analysis method and the simulation analysis system, the refrigeration performance of the air circulation refrigeration system of the airplane can be predicted in a short time, and a large amount of test time is saved; by the simulation analysis method and the system, a series of simulation results such as a temperature field, a pressure field, a flow field and the like in the air circulation refrigeration system of the airplane can be visually displayed, and the operation mechanism and the fluid characteristics in the refrigeration system can be deeply understood. The invention greatly reduces the research and development cost of the air circulation refrigeration system of the airplane and shortens the research and development period. The method and the device realize the rapid prediction of the refrigeration performance of the aircraft air circulation refrigeration system, deeply understand the operation mechanism and the fluid characteristic in the refrigeration system, and have important significance for the design optimization of the aircraft air circulation refrigeration system.
Drawings
Fig. 1 is a schematic view of a geometric model of an aircraft air cycle refrigeration system according to the present invention, wherein: 1-precooler, 2-regulating valve, 3-primary heat exchanger, 4-compressor, 5-secondary heat exchanger, 6-expander, 7-water separator, 8-one-way valve and 9-mixing chamber.
FIG. 2 is a schematic flow chart of the simulation analysis method of the present invention.
FIG. 3 is a schematic flow chart of a simulation analysis method according to the present invention.
FIG. 4 is a diagram of a result analysis module according to the present invention.
Fig. 5 is a temperature field profile inside a heat exchanger.
Fig. 6 is a pressure field profile inside a heat exchanger.
Fig. 7 is a flow field profile inside a heat exchanger.
FIG. 8 is a schematic diagram of a simulation analysis system according to the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following specific examples and the accompanying drawings. The procedures, conditions, experimental methods and the like for carrying out the present invention are general knowledge and common general knowledge in the art except for the contents specifically mentioned below, and the present invention is not particularly limited. The following detailed description of the embodiments of the present invention is provided in connection with the accompanying drawings and the examples, but not limited thereto, and it is to be understood that the present invention is not limited to the modifications and equivalents, and that the modifications and equivalents may be made without departing from the spirit and scope of the invention.
In order to overcome the defects of the prior art, the invention provides a simulation analysis method and a simulation analysis system of an aircraft air circulation refrigeration system based on a CFD technology, wherein the method comprises the following steps: establishing a geometric model of an air circulation refrigeration system of the airplane; dividing and setting a control area; setting a boundary condition; dividing grids; establishing a control equation; carrying out numerical solution; and analyzing the simulation result and predicting the refrigeration performance of the air circulation refrigeration system of the airplane. The two-dimensional calculation simulation of the air circulation refrigeration system of the airplane is realized through the commercial calculation fluid software Fluent, the refrigeration performance of the refrigeration system can be predicted in a short time, and the research and development cost is greatly reduced; and the operation mechanism and the fluid characteristics in the refrigeration system are deeply understood by analyzing the distribution of a temperature field, a pressure field and a flow field in the refrigeration system, and the method has important significance for the design optimization of the air circulation refrigeration system of the airplane.
The method adopts commercial calculation fluid software Fluent to establish a two-dimensional calculation model of the air circulation refrigeration system of the airplane, performs numerical simulation, predicts the refrigeration performance of the refrigeration system, analyzes the distribution of a temperature field, a pressure field and a flow field in the refrigeration system, and provides a theoretical basis for the design of the practical and efficient refrigeration system.
As shown in fig. 3, the simulation analysis method of the present invention includes the following steps:
the method comprises the following steps: establishing a geometric model of an air circulation refrigeration system of the airplane;
step two: dividing and setting a control area;
step three: setting a boundary condition;
step four: dividing grids;
step five: establishing an unsteady state control equation, and respectively establishing a control equation for a gas area and a porous medium area by taking working medium gas air in a refrigeration system as an object;
step six: carrying out numerical solution;
step seven: analyzing the simulation result and predicting the refrigeration performance of the air circulation refrigeration system of the airplane
In this embodiment, the object of the simulation analysis is a three-wheel boost air cycle refrigeration system.
Specifically, as shown in fig. 2, the simulation analysis method of the present invention includes the following steps:
the method comprises the following steps: the geometric model of the three-wheel boosting type air circulation refrigeration system is established, and is a two-dimensional CFD model and comprises a precooler 1, a regulating valve 2, a primary heat exchanger 3, a compressor 4, a secondary heat exchanger 5, an expander 6, a water separator 7, a one-way valve 8 and a mixing chamber 9, and is shown in figure 1.
Step two: dividing and setting control areas, setting the internal control areas where the precooler 1, the primary heat exchanger 3 and the secondary heat exchanger 5 are located as porous medium areas, setting the internal control area where the water separator 7 is located as a gas-liquid mixing area, and setting the other internal control areas as gas areas;
step three: the boundary condition is set, and the left end boundary of the precooler 1 is set as the velocity inlet boundary, and in the present embodiment, the velocity is set to 30 m/s. The outer boundaries of the regulating valve 2, the compressor 4, the expander 6, the water separator 7, the one-way valve 8 and the mixing chamber 9 are set as isothermal boundaries; setting the outer boundaries of the primary heat exchanger 3 and the secondary heat exchanger 5 as heat insulation boundaries;
step four: dividing grids, adopting structured grids for all control domains of the model, and simultaneously carrying out local grid refinement near the boundary;
step five: establishing an unsteady state control equation, taking working medium gas air in a refrigerating system as an object, and respectively establishing control equations for a gas area and a porous medium area:
firstly, a control equation is established for a gas area:
continuity equation:
in the formula: rho
fAnd
respectively the density and velocity of the gas.
The momentum equation:
in the formula: p is the static pressure of the molten steel,
is the pressure tensor;
energy equation:
in the formula: k is a radical offIs gas thermal conductivity, T is temperature, EfThe total energy of the gas;
and then establishing a control equation for the porous medium region:
continuity equation:
the momentum equation:
in the formula: epsilon is the porosity of the porous medium, and the porous medium area is filled with the silk screen, so that the porosity epsilon is formed by the mesh number m and the silk diameter d of the silk screenwDetermining:
hydraulic diameter d of the wire meshhCan be calculated by the following formula:
Siis a source term in the momentum equation and consists of two parts of viscous loss term and inertial loss term, and for isotropic media, SiCan be expressed as:
wherein μ is the dynamic viscosity of the gas, α is the degree of permeability, C2Coefficient of inertial resistance, α and C2Can be calculated by the following method:
the axial pressure drop of a region of porous media can be expressed as:
in the formula: f. ofoscFor the friction factor, according to empirical formula:
in the formula: re is the Reynolds number of the fluid in the region of porous media and can be expressed as:
by combining the formula (9), the formula (10) and the formula (11), the degree of penetration α and the coefficient of inertial resistance C can be determined2:
Energy equation:
in the formula: rhosAnd EsDensity and total energy, k, respectively, of the solideffEffective thermal conductivity for porous media;
effective thermal conductivity k of porous media due to the effect of thermal contact resistanceeffMuch less than its average thermal conductivity, the following modifications can be made:
in this embodiment, the porous medium region inside the precooler 1 is filled with a 635-mesh stainless steel wire mesh, and the porous medium regions inside the primary heat exchanger 3 and the secondary heat exchanger 5 are filled with a 100-mesh copper wire mesh. Table 1 summarizes the various parameters of the web obtained by the above calculations.
TABLE 1 internal Screen parameters of porous Medium zone
| Region(s)
|
Material
|
m
|
dw(μm)
|
ε
|
dh(μm)
|
α(m2)
|
C2(m-1)
|
| Precooler 1
|
SS304
|
635
|
20
|
0.607
|
31.4
|
1.5×10-11 |
81460
|
| Primary heat exchanger 3
|
Copper (Cu)
|
100
|
100
|
0.691
|
222.6
|
7.7×10-10 |
12173
|
| Secondary heat exchanger 5
|
Copper (Cu)
|
100
|
100
|
0.691
|
222.6
|
7.7×10-10 |
12173 |
Step six: performing numerical solution, setting solver control parameters, a discrete format and a residual convergence standard according to the CFD model of the aircraft air circulation refrigeration system established in the step, initializing a flow field, and starting to perform numerical solution;
in the embodiment, a laminar flow model is selected for calculation, a solver selects a PISO algorithm of pressure and speed coupling, and discrete format sampling is performedWith a second order windward format, the residual convergence standard energy term is 10-6All other parameters are 10-3The initial temperature was 300K.
Step seven: and analyzing the simulation result, and predicting the refrigeration performance of the air circulation refrigeration system of the airplane through analyzing the simulation result after the calculation is stable.
As shown in fig. 8, the present invention further provides a simulation analysis system of an aircraft air cycle refrigeration system based on CFD technology, where the system adopts a simulation analysis method of an aircraft air cycle refrigeration system based on CFD technology, and the method includes:
the model establishing module is used for establishing a geometric model of the aircraft air circulation refrigeration system;
the area setting module is used for dividing and setting a control area;
the boundary setting module is used for setting boundary conditions;
the grid division module is used for dividing grids;
the equation establishing module is used for establishing an unsteady state control equation, and respectively establishing control equations for a gas area and a porous medium area by taking working medium gas air in the refrigerating system as an object;
the numerical solving module is used for carrying out numerical solving;
the result analysis module is used for analyzing the simulation result and predicting the refrigeration performance of the air circulation refrigeration system of the airplane; the temperature simulation analysis module is used for simulating a temperature field in an analysis model, the pressure simulation analysis module is used for analyzing a pressure field in the model, and the speed simulation analysis module is used for simulating a flow field in the analysis model.
Furthermore, by observing the distribution of the temperature field, the pressure field and the flow field inside the refrigeration system, the operation mechanism of the refrigeration system and the flow state of the fluid can be further analyzed.
As shown in fig. 5, the temperature field distribution inside the primary heat exchanger was simulated.
As shown in FIG. 6, the pressure field distribution inside the primary heat exchanger was simulated
As shown in fig. 7, the flow field distribution inside the primary heat exchanger was simulated.
The protection of the present invention is not limited to the above embodiments. Variations and advantages that may occur to those skilled in the art may be incorporated into the invention without departing from the spirit and scope of the inventive concept, which is set forth in the following claims.