CN111539069A - Method for simulating and calculating drag reduction of surface microstructure of high-speed train - Google Patents
Method for simulating and calculating drag reduction of surface microstructure of high-speed train Download PDFInfo
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Abstract
The invention discloses a method for simulating and calculating drag reduction of a microstructure on the surface of a high-speed train, which simplifies a complex three-marshalling model of the high-speed train, verifies the consistency of wall shear stress of the three-marshalling model and a scaled three-marshalling model in the same calculation domain by analyzing and comparing wall shear stress of the simplified model and the three-marshalling model, carries the microstructure on the simplified three-marshalling model, and replaces the shear stress of the actual three-marshalling model carrying the microstructure with the shear stress of the simplified three-marshalling model carrying the microstructure, thereby conveniently calculating the drag reduction efficiency of the surface of the microstructure carried by the high-speed train. The calculation method is simple and feasible; and the calculation speed, the calculation efficiency and the calculation precision are improved.
Description
Technical Field
The invention relates to the technical field of high-speed train pneumatic drag reduction, in particular to a method for simulating and calculating drag reduction of a high-speed train surface microstructure.
Background
The energy crisis in the 21 st century is becoming more severe, and saving energy consumption becomes a research direction in which people pay more attention, so that in the design process of high-speed trains, the energy consumption also becomes an important index for evaluation. Research shows that the pneumatic resistance of the train is in direct proportion to the square of the running speed of the train, and the pneumatic resistance of the train is smaller when the train runs at a low speed; along with the increase of the speed of the train, the aerodynamic resistance of the train during running is increased continuously, and the proportion of the aerodynamic resistance in the total resistance is increased continuously. When the speed of the high-speed train reaches 200km/h, the influence of the pneumatic resistance on the train exceeds the influence of the mechanical resistance on the train, particularly when the speed reaches 300km/h, the proportion of the pneumatic resistance in the total resistance is up to 85%, and the pneumatic resistance also becomes one of important factors for restricting the speed increase of the high-speed train. Therefore, the research on the pneumatic drag reduction technology of the high-speed train has important significance for saving energy consumption and accelerating the high-speed train.
CFD numerical simulation calculation shows that the drag reduction efficiency of the V-shaped microstructure is the best, the V-shaped microstructure has certain drag reduction efficiency within the speed range of 200-400km/h, the height h of the microstructure surface is the order of magnitude of 10-100 mu m, the size of a high-speed train is the order of magnitude of 10m, the size order of magnitude of a three-marshalling high-speed train model for performing dynamic analysis is 100m generally, the difference is 5 orders of magnitude, and if a microstructure geometric model is directly established on the surface of the train model and numerical simulation calculation is performed, the calculated amount is extremely large, and the result accuracy is low.
Disclosure of Invention
In view of the above problems, the present invention provides a method for calculating drag reduction efficiency of a high-speed train by using a simplified model, which can improve calculation speed, calculation efficiency and calculation accuracy. The technical scheme is as follows:
a method for simulating and calculating drag reduction of a microstructure on the surface of a high-speed train comprises the following steps:
step 1: determining the microstructure type and microstructure size for local drag reduction according to the preliminary simulation calculation of the smooth flat plate and the microstructure, wherein the microstructure type and the microstructure size comprise the height h and the vertex angle alpha of the microstructure;
step 2: establishing a three-marshalling scaling model of the high-speed train;
and step 3: establishing a three-marshalling simplified model of the high-speed train, selecting a calculation domain and boundary conditions, and dividing grids;
step 3.1: a rectangular flat plate with the length and the width similar to the three-grouping reduction model is used as a three-grouping simplified model; taking the middle area of the three-grouping simplified model along the length direction as a simplified model research area;
step 3.2: taking the length and the width of the rectangular flat plate as the length and the width of the calculation domain and the width of the rectangular flat plate as the height of the calculation domain; then determining the boundary condition of the calculation domain;
step 3.3: regulating and dividing the three-grouping simplified model integral grid according to the selected calculation domain and the boundary, wherein the three-grouping simplified model integral grid adopts a structured grid, and carrying out grid encryption near an inlet area and a bottom surface research area;
and 4, step 4: simplifying the drag reduction efficiency simulation calculation of the high-speed train carrying microstructure surface:
step 4.1: establishing a grid model: arranging a V-shaped microstructure surface with the height h and the vertex angle alpha in a simplified model research area; setting a microstructure surface near-wall area grid at a corresponding position of the three-grouping simplified model integral grid;
step 4.2: in FLUENT, carrying out numerical simulation calculation on the grid model to obtain a distribution rule of the shear stress of the surface wall of the microstructure, and comparing the distribution rule with the distribution rule of the shear stress of the surface wall of the flat plate surface to obtain the drag reduction benefit caused by the arrangement of the microstructure surface at a certain position in a simplified model research area.
Further, the boundary condition of the three-grouping simplified model calculation domain is selected according to the following steps: the air flow speed at the inlet, the pressure at the outlet, whether the side and top surfaces are symmetrical, the shear condition of the bottom surface of the calculation area as a wall surface, the joint surface of the grid, the head car body, the middle car body and the tail car body as smooth wall surfaces, and the shear condition of the car body ground.
The invention has the beneficial effects that: the method calculates the drag reduction efficiency of the microstructure of the high-speed train by simplifying the drag reduction efficiency of the model, and the calculation method is simple and feasible; the calculation speed, the calculation efficiency and the calculation precision are improved; the invention combines the national strategy of energy conservation and emission reduction, and has more important application value when the high-speed train runs at higher speed in the future.
Drawings
FIG. 1 is a flow chart of a method according to an embodiment of the present invention.
Fig. 2 is in the form of a microstructure.
Fig. 3 is a smooth three consist train model.
Fig. 4 is a smooth three-consist train calculation field Fluid.
Fig. 5 is an overall schematic view of the hexahedral mesh.
Fig. 6 is a side of a hexahedral mesh.
Fig. 7 is a train surface tetrahedral mesh.
FIG. 8 is a schematic view of the positions of the straight lines a, b, c.
FIG. 9 is a graph showing the distribution of wall shear stress along lines a, b, and c.
Fig. 10 is a schematic view of the location of the investigation region.
FIG. 11 is a simplified model diagram.
FIG. 12 is a simplified model computation domain diagram.
FIG. 13 is a simplified model overall mesh diagram.
FIG. 14 is a simplified comparative graph of shear stress distribution of a flat-faced wall surface in a model study region.
FIG. 15 is a simplified model study area microstructure surface mesh.
FIG. 16 is a graph comparing the shear stress distribution of the surface wall of the 80 μm microstructure.
Detailed Description
The invention is described in further detail below with reference to the figures and specific embodiments. The flow chart of the method of the embodiment of the method for simulating and calculating the drag reduction of the microstructure on the surface of the high-speed train is shown in figure 1. The following describes the details of the present invention for a high-speed train with a speed of 400 km/h:
step 1: according to the preliminary simulation calculation of the smooth flat plate and the microstructure, determining the microstructure type and the microstructure size for local resistance reduction:
determining the basic speed of the high-speed train to be simulated and calculated, analyzing the drag reduction efficiency of the surfaces of the V-shaped microstructures with different heights and different vertex angle angles by selecting a calculation domain and utilizing CFD simulation calculation software, screening out a microstructure form with good drag reduction efficiency by simulation analysis calculation, and primarily determining the geometric size of the microstructure.
The microstructure form aimed at by the present invention is shown in fig. 2, and the main geometrical parameters are the height and the apex angle of the microstructure.
Step 2: establishing a three-marshalling scaling model of the high-speed train and a finite element simulation calculation model:
(1) establishment of scaled geometric model of three-marshalling train
A1: 16 three-marshalling train scaling model is established, and areas such as a pantograph, a bogie and the like are simplified, so that a smooth three-marshalling train model is obtained as shown in figure 3. The model is divided into a head car, a middle car and a tail car. The total length is about 5m and the height is about 0.24 m.
(2) Selection of three-group scaling model calculation domain and boundary condition
As shown in fig. 4, the Fluid calculation domain of the smooth three-consist train is divided into two calculation domains: fluid1 and Fluid2, Fluid1 are calculation domains near the train, such as region a in fig. 4; the other region is Fluid2, shown as region B in fig. 4. The overall length of the computational domain was 20m, the width was 3.75m, and the height was 2.5 m. The boundary conditions of the calculation field Fluid are shown in table 1.
TABLE 1 smooth three-consist train calculation Domain Fluid boundary conditions
(3) Mesh model building
And establishing a smooth three-marshalling train model grid model through ICEM-CFD on the basis of the smooth three-marshalling train model geometric model. The grid model is divided into three layers:
1) hexahedral mesh: and the grid is positioned at the outermost layer and is a structured grid in the computational domain Fluid2, and the grid is good in quality and small in quantity.
2) Tetrahedral mesh: and the tetrahedral mesh is positioned in the middle layer, and in the calculation field Fluid1, the tetrahedral mesh can better fit the curved surface in the train model.
3) Prism grid: located at the innermost layer, in the computational domain Fluid1, the train surface boundary layer mesh can be finely expressed.
In the computational domain Fluid2, the hexahedral mesh is divided, as shown in fig. 5 and 6. And the grid is encrypted in the three directions of x, y and z and at the position close to the train.
In the computational domain Fluid1, tetrahedral mesh division is carried out, encryption is carried out in the area close to the surface of the train, the size of the grid on the surface of the train is 10mm, and hexahedral and tetrahedral mesh splicing is carried out on the INTER1 surface, wherein the grid size of each area is as follows:
BODY1:10mm
BODY2:10mm
BODY3:10mm
BOTTOM1:30mm
INTER1:30mm
the train surface mesh is shown in fig. 7, and it can be seen that the mesh is well attached to the train surface.
Prismatic meshing is performed in an area 15mm from the surface of the train, wherein:
height of first layer of prismatic grid: initial Height is 0.0125 mm.
Prism grid height growth rate: height Ratio is 1.2.
Number of prism grid layers: number of Layer 30.
Total height of prism lattice: total Height is 15 mm.
The division of the prism grids enables the flow field of the near-wall area on the surface of the train to be more finely expressed in the subsequent simulation calculation result.
(4) Numerical calculation results and analysis
And in FLUENT, carrying out simulation calculation on the established grid model, and carrying out post-processing analysis on a simulation calculation result. Three straight lines a (y is 0), b (z is 0.2m) and c (z is 0.1m) in the x direction are selected on the surface of the train, as shown in fig. 8, the wall shear stress distribution on the three straight lines is shown in fig. 8, wherein the abscissa is the distance from the most front end of the train model.
As can be seen from fig. 9, the wall shear stress decreases as x increases. Under the influence of the shape of the vehicle head, the variation range of the wall shear stress is large within 1m to 1.5m, when x is the same, the wall shear stress on three straight lines has large difference, and when x is within 1.5m to 6m, the variation of the wall shear stress is gentle, and the distribution difference of the wall shear stress on the three straight lines is small. Therefore, both sides and the top of the vehicle body are selected, and the area with 1.5m < x <6m is the research area, and the area is shown as the dark area in fig. 9.
The shear stress of the downstream wall surface of the region is on the top and the side surface of the front end of the region, the shear stress of the wall surface is larger, the shear stress of the rear end is smaller, and the shear stress is between 17Pa and 19 Pa.
And analyzing the stress condition of the train model to obtain the results shown in the table 2, and displaying data, wherein the research area is positioned in the middle of the train and has extremely low differential pressure resistance in the x direction, and the resistance in the x direction mainly comes from friction resistance. The resistance of the whole model in the x direction is 100.00N, and the total resistance of the research area in the x direction is 25.40N, which accounts for 25.4% of the total resistance. Thus, reducing the frictional resistance of the area of investigation by applying a microstructured surface will contribute to a reduction of the overall resistance of the train model.
TABLE 2 stress analysis chart for smooth train model
And step 3: the method comprises the steps of establishing a simplified model of the high-speed train with three groups, selecting a calculation domain and boundary conditions, dividing a grid model, and verifying the distribution rule and comparison of the wall shear stress of the smooth high-speed train.
(1) Establishment of simplified model of three marshalling of high-speed train
The simplified model is a rectangular flat plate with the length of 6m and the width of 0.2m, the length and the width of the model are similar to those of a train model, as shown in fig. 11, the middle part (a transverse line region in the figure) of the model is a research region, a smooth plane and a microstructure surface are sequentially arranged in the research region, and the resistance is obtained through numerical simulation calculation, so that the drag reduction efficiency of the microstructure surface applied to the simplified model is obtained.
(2) Selection of three-grouping simplified model calculation domain and boundary condition
The simplified model computational domain size is shown in FIG. 12, and the boundary conditions are shown in Table 3.
TABLE 3 simplified model boundary conditions
(3) Mesh model building of three-grouping simplified model
Mesh model of the triple-grouping simplified model as shown in fig. 13, a structured mesh is used to perform mesh encryption near the entrance area and near the bottom study area.
(4) Numerical calculation and verification
In FLUENT, the numerical simulation calculation was performed on the mesh model, and the wall shear stress distribution was obtained as shown in fig. 14. A smoother line is a research area flat plate surface wall surface shear stress distribution rule, and the abscissa is a distance from an inlet; the rest three lines are wall shear stress distribution rules on three straight lines of the train surface a, b and c respectively.
At the front end of the simplified model research area, the flow is not developed into turbulent flow, and the boundary layer is thin, so the wall shear stress is large. With the increase of the distance x from the front end, the flow gradually develops into turbulent flow, the thickness of the boundary layer gradually increases, the wall surface shear stress gradually decreases, and finally the wall surface shear stress tends to be stable. As can be seen from fig. 14, the simplified model research area wall shear stress is relatively similar to the train model research area wall shear stress after the wall shear stress tends to be stable. Therefore, the drag reduction benefits brought by the application of the microstructure surface to the train model research area can be reflected by the drag reduction benefits brought by the application of the microstructure surface to the smooth part of the simplified model research area.
And 4, step 4: the simulation calculation of the drag reduction efficiency of the surface of the simplified microstructure carried by the high-speed train comprises the grid model division of the simplified model carrying the microstructure and the drag reduction efficiency calculation of the microstructure carried by the high-speed train model.
(1) Mesh model building
The V-shaped microstructure surface r with the height of 80 μm and the vertex angle of 40 degrees is arranged in the simplified model study area, the whole grid is similar to the grid shown in FIG. 13, and the grid of the microstructure surface near-wall area is shown in FIG. 15.
(2) Simulation calculation results and analysis
In FLUENT, a grid model is subjected to numerical simulation calculation to obtain a distribution rule of the shear stress of the surface wall of the microstructure, and the distribution rule is compared with the distribution rule of the shear stress of the surface wall of the flat plate, so that the resistance reduction benefit brought by the arrangement of the microstructure surface at a certain position in a simplified model research area is obtained. As shown in table 4 and fig. 16, it can be seen that the microstructured surface has a drag reduction efficiency of about 16%, and the closer to the front end of the flat plate, the higher the drag reduction efficiency.
TABLE 480 μm microstructure surface wall shear stress distribution contrast table
The numerical simulation calculation result shows that the wall shear stress of a train model research area is between 17.2Pa and 18.6Pa, the area corresponding to a simplified model is obtained according to a table 4, the distance between the simplified model and an entrance is between 1.4m and 2.8m, and the drag reduction efficiency of the microstructure surface of the area is between 15.6 percent and 15.8 percent, so that the microstructure surface is arranged in the train model research area, the brought local drag reduction benefit is between 15.6 percent and 15.8 percent, and the area resistance accounts for 25.4 percent of the total resistance of the train model, and the brought total drag reduction benefit is 4.0 percent.
Claims (2)
1. A method for simulating and calculating drag reduction of a microstructure on the surface of a high-speed train is characterized by comprising the following steps:
step 1: according to the preliminary simulation calculation of the smooth flat plate and the microstructure, the microstructure type and the microstructure size for local resistance reduction are determined, including the height of the microstructurehAnd top angleα；
Step 2: establishing a three-marshalling scaling model of the high-speed train;
and step 3: establishing a three-marshalling simplified model of the high-speed train, selecting a calculation domain and boundary conditions, and dividing grids;
step 3.1: a rectangular flat plate with the length and the width similar to the three-grouping reduction model is used as a three-grouping simplified model; taking the middle area of the three-grouping simplified model along the length direction as a simplified model research area;
step 3.2: taking the length and the width of the rectangular flat plate as the length and the width of the calculation domain and the width of the rectangular flat plate as the height of the calculation domain; then determining the boundary condition of the calculation domain;
step 3.3: dividing the three-grouping simplified model integral grid according to the selected calculation domain and the boundary condition, wherein the three-grouping simplified model integral grid adopts a structured grid, and carrying out grid encryption near an inlet area and a bottom surface research area;
and 4, step 4: simplifying the drag reduction efficiency simulation calculation of the high-speed train carrying microstructure surface:
step 4.1: establishing a grid model: in the simplified model study area, the arrangement height ishAt a vertex angle ofαThe V-shaped microstructured surface of (a); setting a microstructure surface near-wall area grid at a corresponding position of the three-grouping simplified model integral grid;
step 4.2: in FLUENT, carrying out numerical simulation calculation on the grid model to obtain a distribution rule of the shear stress of the surface wall of the microstructure, and comparing the distribution rule with the distribution rule of the shear stress of the surface wall of the flat plate surface to obtain the drag reduction benefit caused by the arrangement of the microstructure surface at a certain position in a simplified model research area.
2. The method for simulating and calculating drag reduction of the surface microstructure of the high-speed train as claimed in claim 1, wherein the boundary conditions of the three-consist simplified model calculation domain are selected according to: the air flow speed at the inlet, the pressure at the outlet, whether the side and top surfaces are symmetrical, the shear condition of the bottom surface of the calculation area as a wall surface, the joint surface of the grid, the head car body, the middle car body and the tail car body as smooth wall surfaces, and the shear condition of the car body ground.
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Application publication date: 20200814 |