High-efficiency and high-precision numerical simulation method for diesel engine air cooling field

Abstract

The present invention discloses a method for high-efficiency and high-precision numerical simulation of a diesel engine air cooling field. The present invention is carried out according to the following steps: (1) Based on the porous medium model theory: a three-dimensional radiator simplified model containing a porous medium region is established by using a defined porous medium model to replace the internal structure of the original radiator; (2) According to the dimensionless similarity of the velocity distribution of the main section of the fan swirl, the dissipation rate generation and diffusion term coefficients of the turbulent kinetic energy dissipation equation in the standard k-ε turbulence model are adjusted; (3) The standard k-ε turbulence model is used for the forced convection-dominated area, and the k-ε turbulence model corrected by the turbulent viscosity coefficient is used for the natural convection-dominated area. For the transition area between forced convection and natural convection, a k-ε turbulence model corrected by the linear interpolation of the turbulent viscosity coefficient is used to ensure a smooth and stable transition of the turbulent viscosity; (4) Numerical simulation technology for diesel engine air cooling field based on partition processing. The present invention realizes high-precision numerical simulation based on a small number of grids.

Description

Technical Field

[0001] The invention relates to the technical field of numerical simulation of diesel engine air cooling field, and more specifically, to a high-efficiency and high-precision numerical simulation method of diesel engine air cooling field. Background Art

[0002] Air-cooled diesel engines have the advantages of simple structure, reliable use, and strong environmental adaptability. Due to military needs and promotion before and after World War II, air-cooled diesel engines have developed rapidly. Since my country introduced various models of air-cooled diesel engines from Germany in the 1980s, air-cooled diesel engines have been widely used in large automobiles, engineering machinery, power generation equipment, ships, special vehicles and other occasions. However, the heat load of air-cooled diesel engines is relatively high. In air-cooled diesel engines, especially in some air-cooled diesel engines with mechanical transmission fans, overheating is prone to occur when working at low speed and heavy load. In addition, air-cooled diesel engines have high requirements for air duct layout. When arranging air ducts in the car, especially in the car with the diesel engine at the rear, it is necessary to pay attention to the correct air induction and exhaust, otherwise the diesel engine will be overheated and damaged. The above problems seriously restrict the further improvement of the performance of air-cooled diesel engines. Therefore, how to achieve high-precision numerical simulation of the diesel engine air-cooling field is crucial to explore the flow and heat transfer mechanism of the diesel engine air-cooling field, improve the cooling effect of the diesel engine air-cooling field, reduce the heat load of the air-cooled diesel engine, and improve the power of the air-cooled diesel engine.

[0003] However, the air-cooled diesel engine has a very complex geometric structure, a relatively large geometric scale, and both dynamic and static domains. The full-domain high-precision numerical simulation of the air-cooled field faces problems such as a huge number of grids, huge consumption of computing resources, and long computing time. At the same time, different components in the air-cooled diesel engine have different requirements for simulation strategies and simulation accuracy. Different choices of simulation strategies are also accompanied by viscous dissipation problems, which pose huge challenges to the choice of simulation strategies. At present, a method for efficient numerical simulation of the air-cooled field while maintaining high accuracy has not yet been proposed. Summary of the invention

[0004] In order to overcome the deficiencies in the prior art, the present invention provides a high-efficiency and high-precision numerical simulation method for the air cooling field of a diesel engine.

[0005] The present invention provides a high-efficiency and high-precision numerical simulation method for the air cooling field of a diesel engine, which is carried out according to the following steps:

[0006] (1) Radiator modeling technology based on porous media model theory. A periodic local single-layer model with the same internal structure as the radiator is established, and different inlet velocities are set to perform flow-heat coupling calculations on the local model. The calculation results are fitted into a velocity-pressure difference relationship using a quadratic polynomial. The viscous loss coefficient and inertial loss coefficient of the defined porous media model are obtained based on the improved Darcy's law and the fitted quadratic polynomial. A simplified three-dimensional radiator model containing a porous media area is established by using the defined porous media model to replace the original internal structure of the radiator.

[0007] (2) Numerical simulation technology of fan swirl based on numerical dissipation and viscous dissipation equivalent compensation method. First, a fine grid is used to perform a more detailed numerical simulation of the fan monomer to obtain the swirl field of the fan monomer. Secondly, in the air-cooled field, a coarse grid is used for the main section of the fan swirl. Finally, in order to reduce the numerical viscous dissipation caused by the coarse grid, according to the dimensionless similarity of the velocity distribution of the main section of the fan swirl, the dissipation rate generation and diffusion term coefficients of the turbulent kinetic energy dissipation equation in the standard k-ε turbulence model are adjusted, so that the dimensionless velocity distribution of the main section of the fan swirl numerically simulated by the coarse grid is basically consistent with the dimensionless velocity distribution under the fine grid, forming a numerical dissipation compensation k-ε turbulence model suitable for coarse grid numerical simulation.

[0008] (3) Cylinder liner / cylinder head numerical simulation technology based on thermal plume feature capture and viscosity compensation balance method. First, a three-dimensional flow-heat coupling numerical simulation is performed on the cylinder liner / cylinder head model using a fine grid to obtain the thermal flow field distribution near the cylinder liner / cylinder head. Secondly, based on the thermal flow field distribution results near the cylinder liner / cylinder head model, different flow structures of the flow field are partitioned. Finally, based on different partitions, under a coarse grid, the standard k-ε turbulence model is used for the forced convection-dominated area, the k-ε turbulence model corrected by the turbulent viscosity coefficient is used for the natural convection-dominated area, and the k-ε turbulence model corrected by the turbulent viscosity coefficient is used for the transition area between forced convection and natural convection to ensure a smooth and stable transition of turbulent viscosity. This forms a partitioned corrected k-ε turbulence model suitable for numerical simulation of thermal plumes under a coarse grid.

[0009] (4) Numerical simulation technology of diesel engine air cooling field based on partition processing. The whole air cooling field is numerically simulated by the steady Reynolds average method. According to the partition method in steps (1), (2) and (3), the flow field in the heat exchanger is simplified by the porous medium model and the laminar model is used in the porous medium model area. The turbulence model of the non-main section of the fan swirl and the cylinder liner / cylinder head forced convection area adopts the standard k-ε turbulence model. The turbulence model of the main section of the fan swirl adopts the numerical dissipation compensation k-ε turbulence model. The turbulence model of the natural convection area of ​​the cylinder liner / cylinder head adopts the turbulent viscosity coefficient corrected k-ε turbulence model. The diesel engine air cooling field model is partitioned to generate grids. The fan area adopts a structured grid, and the other areas of the air cooling field adopt an unstructured grid. The interface between the fan area and other areas adopts a sliding grid. The inlet boundary conditions of the computational domain are total temperature, total pressure, and axial intake. The outlet boundary condition is the mass flow outlet. The wall boundary condition of the heat-generating solid domain is a fixed temperature boundary. The interface between the fluid domain and the solid domain is a thermal coupling surface. The momentum equation and energy equation are discretized based on the finite volume method. The spatial discretization format adopts the second-order upwind format. The pressure-velocity coupling uses the SIMPLE algorithm to obtain the steady flow field of the diesel engine air cooling field.

[0010] Compared with the prior art, the present invention has the following beneficial effects:

[0011] 1. The high-efficiency and high-precision numerical simulation method for the diesel engine air-cooling field of the present invention simplifies the radiator components in the diesel engine air-cooling field by using a porous medium model method, numerically simulates the fan swirl by using a numerical dissipation and turbulent viscosity equivalent compensation correction method, and numerically simulates the heat flow field near the cylinder liner / cylinder head by using a thermal plume feature capture and viscosity compensation balance method, thereby reducing the calculation cost while ensuring accuracy.

[0012] 2. The efficient and high-precision numerical simulation method for the diesel engine air-cooling field of the present invention adopts the numerical simulation technology of partition processing for the diesel engine air-cooling field, thereby realizing high-precision numerical simulation based on a small number of grids. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Shown is a flow chart of a high-efficiency and high-precision numerical simulation method for diesel engine air cooling field;

[0014] Figure 2 The figure shows the simplified geometric structure diagram of the diesel engine air cooling field;

[0015] Figure 3 Shown is a cloud diagram of the velocity magnitude of the steady flow field in the diesel engine air cooling field. DETAILED DESCRIPTION

[0016] The efficient and high-precision numerical simulation method for the air cooling field of a diesel engine of the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0017] The specific process of this method is as follows:

[0018] (1) Radiator modeling technology based on porous media model theory. A periodic local single-layer model with the same internal structure as the radiator is established, and different inlet velocities are set to perform flow-heat coupling calculations on the local model. The calculation results are fitted into a velocity-pressure difference relationship using a quadratic polynomial. The viscous loss coefficient and inertial loss coefficient of the defined porous media model are obtained based on the improved Darcy's law and the fitted quadratic polynomial. The defined porous media model is used to replace the original internal structure of the radiator to establish a three-dimensional radiator model containing a porous media area.

[0019] (2) Numerical simulation technology of fan swirl based on numerical dissipation and viscous dissipation equivalent compensation method. First, a fine grid is used to perform a more detailed numerical simulation of the fan unit to obtain the swirl field of the fan unit. Secondly, in the air-cooled field, the grid is locally encrypted in the inlet section and transition section of the fan swirl where the flow changes dramatically, and a coarse grid is used for the main section of the fan swirl. Finally, in order to reduce the numerical viscous dissipation caused by the coarse grid, according to the dimensionless similarity of the velocity distribution of the main section of the fan swirl, the dissipation rate generation and diffusion term coefficients of the turbulent kinetic energy dissipation equation in the standard k-ε turbulence model are adjusted, so that the dimensionless velocity distribution of the main section of the fan swirl numerically simulated by the coarse grid is basically consistent with the dimensionless velocity distribution under the fine grid, forming a numerical dissipation compensation k-ε turbulence model suitable for coarse grid numerical simulation.

[0020] (3) Cylinder liner / cylinder head numerical simulation technology based on thermal plume feature capture and viscosity compensation balance method. First, a three-dimensional flow-heat coupling numerical simulation is performed on the cylinder liner / cylinder head model using a fine grid to obtain the thermal flow field distribution near the cylinder liner / cylinder head. Secondly, based on the thermal flow field distribution results near the cylinder liner / cylinder head model, different flow structures of the flow field are partitioned. Finally, based on different partitions, under a coarse grid, the standard k-ε turbulence model is used for the forced convection-dominated area, the k-ε turbulence model corrected by the turbulent viscosity coefficient is used for the natural convection-dominated area, and the k-ε turbulence model corrected by the turbulent viscosity coefficient is used for the transition area between forced convection and natural convection to ensure a smooth and stable transition of turbulent viscosity. This forms a partitioned corrected k-ε turbulence model suitable for numerical simulation of thermal plumes under a coarse grid.

[0021] (4) Numerical simulation technology of diesel engine air cooling field based on partition processing. The whole air cooling field is numerically simulated by the steady Reynolds average method. According to the partition method in steps (1), (2) and (3), the flow field in the heat exchanger is simplified by the porous medium model and the laminar model is used in the porous medium model area. The turbulence model of the non-main section of the fan swirl and the cylinder liner / cylinder head forced convection area adopts the standard k-ε turbulence model. The turbulence model of the main section of the fan swirl adopts the numerical dissipation compensation k-ε turbulence model. The turbulence model of the natural convection area of ​​the cylinder liner / cylinder head adopts the turbulent viscosity coefficient corrected k-ε turbulence model. The diesel engine air cooling field model is partitioned to generate grids. The fan area adopts a structured grid, and the other areas of the air cooling field adopt an unstructured grid. The interface between the fan area and other areas adopts a sliding grid. The inlet boundary conditions of the computational domain are total temperature, total pressure, and axial intake. The outlet boundary condition is the mass flow outlet. The wall boundary condition of the heat-generating solid domain is a fixed temperature boundary. The interface between the fluid domain and the solid domain is a thermal coupling surface. The momentum equation and energy equation are discretized based on the finite volume method. The spatial discretization format adopts the second-order upwind format. The pressure-velocity coupling uses the SIMPLE algorithm to obtain the steady flow field of the diesel engine air cooling field.

[0022] Example:

[0023] (1) This example is a certain type of air-cooled diesel engine. The process of the high-efficiency and high-precision numerical simulation method for the air-cooling field is as follows: Figure 1 The method introduced in step (1) is used to simplify the geometric structure of the radiator. Taking the intercooler as an example, the porous medium model parameters are calculated according to step (1) and formula (1). Table 1 shows the necessary parameters required to simplify the intercooler using the porous medium model.

[0024]

[0025] Where: is the pressure gradient in the i direction, Pa / m; is the viscous loss coefficient of the porous medium model, m -2 ; 2β is the inertia loss coefficient of the porous medium model, m -1 ; ρ is the fluid density, kg / m 3 .

[0026] Table 1 Parameters of the simplified porous media model for intercooler

[0027]

[0028] (2) Combining the method introduced in step (2) and formula (2), numerical viscosity dissipation compensation is performed on the turbulent kinetic energy dissipation equation of the fan swirl under the coarse grid, forming a numerical dissipation compensation k-ε turbulence model suitable for coarse grid numerical simulation. The compensation coefficients are shown in Table 2.

[0029]

[0030] Where: κ is the turbulent kinetic energy, m 2 / s 2 ;x i is the coordinate component, m; μ is the fluid dynamic viscosity, kg / (m·s); μ t is the turbulent viscosity, kg / (m·s); G κ is the generation term of turbulent kinetic energy κ caused by the average velocity gradient; ε is the turbulent kinetic energy dissipation rate; C1 and C2 are compensation coefficients.

[0031] Table 2 Compensation coefficients of fan swirl dissipation equation

[0032]

[0033] (3) Combined with the method introduced in step (3) and formula (3), the turbulent viscosity coefficient in the discrete equation of the thermal flow field near the cylinder liner / cylinder head is corrected under the coarse grid to form a modified k-ε turbulence model suitable for numerical simulation of thermal plumes under coarse grids. The compensation coefficients are shown in Table 3.

[0034]

[0035] Where: D μ is the dimensionless empirical coefficient of the standard k-ε turbulence model; D1 is the dimensionless correction coefficient in the transition zone; D2 is the dimensionless correction coefficient in the natural convection zone.

[0036] Table 3 Compensation coefficients of discrete equations for thermal flow field near the cylinder liner / cylinder head

[0037]

[0038] In the table: u g is the flow velocity in the transition zone, m / s.

[0039] (4) The simplified geometric structure of the air cooling field of this type of diesel engine is as follows Figure 2 As shown, the mesh generation method in step (4) is used to generate the mesh of the air cooling field of this type of diesel engine, and the numerical simulation method in step (4) is used to perform a steady numerical simulation of the air cooling field of this type of diesel engine to obtain the steady flow field result as shown in FIG. Figure 3 shown.

[0040] The above is only an introduction to the preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several modifications and substitutions can be made without departing from the principle of the present invention, and these modifications and substitutions should also be regarded as the protection scope of the present invention.

Claims

1. A high-efficiency and high-precision numerical simulation method for diesel engine air cooling field, characterized in that: The following steps are involved: (1) Based on the radiator modeling technology of porous medium model theory, a periodic local single-layer model with the same internal structure as the radiator is established, and different inlet velocities are set to perform flow-heat coupling calculation on the local model; the calculation results are fitted into a velocity-pressure difference relationship using a quadratic polynomial, and the viscous loss coefficient and inertial loss coefficient of the defined porous medium model are obtained according to the improved Darcy's law and the fitted quadratic polynomial. The above-defined porous medium model is used to replace the original internal structure of the radiator, and a simplified three-dimensional radiator model containing a porous medium area is established; (2) Numerical simulation technology of fan swirl based on numerical dissipation and viscous dissipation equivalent compensation method: First, a fine grid is used to perform a more detailed numerical simulation of the fan monomer to obtain the swirl field of the fan monomer; second, in the air-cooled field, a coarse grid is used for the main section of the fan swirl; finally, in order to reduce the numerical viscous dissipation caused by the coarse grid, according to the dimensionless similarity of the velocity distribution of the main section of the fan swirl, the dissipation rate generation and diffusion term coefficients of the turbulent kinetic energy dissipation equation in the standard k-ε turbulence model are adjusted, so that the dimensionless velocity distribution of the main section of the fan swirl simulated by the coarse grid is consistent with the dimensionless velocity distribution under the fine grid, forming a numerical dissipation compensation k-ε turbulence model suitable for coarse grid numerical simulation; (3) Cylinder liner / cylinder head numerical simulation technology based on thermal plume feature capture and viscosity compensation balance method: First, a three-dimensional flow-heat coupling numerical simulation is performed on the cylinder liner / cylinder head model using a fine grid to obtain the thermal flow field distribution near the cylinder liner / cylinder head; second, based on the thermal flow field distribution results near the cylinder liner / cylinder head model, different flow structures of the flow field are partitioned; finally, based on different partitions, under a coarse grid, a standard k-ε turbulence model is used for the forced convection-dominated area, and a k-ε turbulence model modified by the turbulent viscosity coefficient is used for the natural convection-dominated area. In order to ensure a smooth and stable transition of turbulent viscosity in the transition area between forced convection and natural convection, a k-ε turbulence model modified by the linear interpolation of the turbulent viscosity coefficient is used, thus forming a partitioned modified k-ε turbulence model suitable for numerical simulation of thermal plumes under a coarse grid; (4) A numerical simulation technology for the air cooling field of a diesel engine based on partition processing, wherein the entire air cooling field is numerically simulated using a steady Reynolds average method; according to the partitioning method in the above steps (1), (2) and (3), the flow field in the heat exchanger is simplified using a porous medium model and a laminar flow model is used in the porous medium model area; the turbulence model for the non-main section of the fan swirl and the cylinder liner / cylinder head forced convection area uses a standard k-ε turbulence model; the turbulence model for the main section of the fan swirl uses a numerical dissipation compensation k-ε turbulence model; and the turbulence model for the natural convection area of ​​the cylinder liner / cylinder head uses a turbulent viscosity coefficient corrected k-ε turbulence model; The diesel engine air-cooling field model is partitioned and grids are generated. Structured grids are used in the fan area, unstructured grids are used in other areas of the air-cooling field, and sliding grids are used at the interface between the fan area and other areas. The inlet boundary conditions of the calculation domain use total temperature, total pressure, and axial air intake, the outlet boundary condition is the mass flow outlet, the wall boundary condition of the heat-generating solid domain is a fixed temperature boundary, and the interface between the fluid domain and the solid domain is a thermal coupling surface. The momentum equation and the energy equation are discretized based on the finite volume method, the second-order upwind format is used in the spatial discretization format, and the SIMPLE algorithm is used for pressure-velocity coupling to obtain the steady flow field of the diesel engine air-cooling field.

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