Tiny structure control method for drag reduction of higher-speed-level train

Abstract

The invention provides a micro structure control method for resistance reduction of a higher-speed-level train. The micro structure control method specifically comprises the steps that a closely-arranged micro ridge-shaped two-dimensional structure with ridge lines parallel to the length direction of the train is designed; performing CFD numerical experiment based on the k-omega SST turbulence model and the microstructure numerical modeling boundary, and analyzing the flow characteristics of different sizes of microstructure surfaces on the high-speed train at the operation speed of 400km / h to obtain the optimal bionic microstructure cross section size; by analyzing a flow field of a simplified model of the high-speed train, summarizing flow characteristics of streaming of the high-speed train and combining flow control characteristics of the bionic microstructures, the bionic microstructures are arranged in a straight section area of the train, and the bionic microstructures are not arranged in streamline areas of a head train and a tail train. The method is reasonable in conception, can be applied to a high-speed train with the speed of 400 km / h, optimizes flow characteristics and reduces aerodynamic resistance by arranging microstructures with specific shapes and sizes on the surface of the train, and therefore the running efficiency and stability of the train are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of high-speed trains, and in particular to a micro-structure control method for reducing drag on higher-speed trains. Background Art

[0002] As a vital component of modern transportation systems, high-speed trains, with their high speed, low energy consumption, and high efficiency, have become a key component of infrastructure development worldwide. However, as train speeds continue to increase, aerodynamic drag has become a key factor affecting high-speed train performance. Against this backdrop, optimizing train aerodynamic characteristics to reduce aerodynamic drag, particularly frictional drag, has become a hot topic of research.

[0003] In recent years, bionic microstructure flow control technology, as an effective means of controlling aerodynamic drag, has achieved remarkable results in many fields. Specifically in the field of high-speed trains, bionic microstructures have the potential to improve the flow characteristics of airflow on the surface of the vehicle body, reduce frictional resistance, and enhance the energy efficiency and stability of the train. The principle is to arrange microstructures on the surface of the train to suppress pseudo-streamwise vortices and other pseudo-ordered structures, weaken the jet behavior of the inner layer of the turbulent boundary layer, and thereby reduce the momentum and energy exchange in the boundary layer, reduce friction and achieve the drag reduction effect. However, the application of microstructures on high-speed trains faces many challenges, including the selection of microstructure shape and size, and layout position. Therefore, the present invention has determined a microstructure flow control system suitable for high-speed trains and its application method through a large number of numerical experiments, which can optimize the aerodynamic performance of the train and reduce aerodynamic drag. Summary of the Invention

[0004] In response to the technical problems existing in the above-mentioned background technology, the present invention proposes a micro-structure control method for reducing drag on higher-speed trains. The method has a reasonable concept and can be applied to high-speed trains with a speed of 400 km / h. By arranging micro-structures of specific shapes and sizes on the surface of the train, the flow characteristics are optimized, the aerodynamic drag is reduced, and thus the operating efficiency and stability of the train are improved.

[0005] To solve the above technical problems, the present invention provides a microstructure control method for drag reduction of higher-speed trains, which specifically includes the following steps:

[0006] 1) Bionic microstructure shape design

[0007] Design a densely packed two-dimensional micro-ridge structure with ridge lines parallel to the length of the train;

[0008] 2) Acquisition of bionic microstructure dimensions

[0009] CFD numerical experiments were conducted based on the k-ωSST turbulence model and the numerical modeling boundary of the bionic microstructure. The flow characteristics of microstructure surfaces of different sizes on a high-speed train running at a speed of 400 km / h were analyzed, and the optimal cross-sectional dimensions of the bionic microstructure were obtained.

[0010] 3) Bionic microstructure layout design

[0011] By analyzing the flow field of a simplified high-speed train model that ignores the bogie, pantograph and windshield components, the flow characteristics of the flow around the high-speed train are summarized. Combined with the flow control characteristics of the bionic microstructure, the bionic microstructure is arranged in the straight section of the train, while the bionic microstructure is not arranged in the streamlined areas of the head and tail cars.

[0012] The microstructure control method for drag reduction of higher speed trains, wherein: the cross-sectional shape of a single bionic microstructure unit of the micro-ridged two-dimensional structure in step 1) is an isosceles triangle with a vertex angle of 53.13°, that is, a V-shaped structure with an aspect ratio of 1.

[0013] The microstructure control method for drag reduction of higher-speed trains, wherein the specific process of performing CFD numerical experiments based on the k-ωSST turbulence model and the bionic microstructure numerical modeling boundary in step (2) is as follows:

[0014] The Reynolds average method is used to decompose the mean and pulsating parts of the flow variables, velocity u and pressure p, and the time-averaged control equation is obtained:

[0015]

[0016] Where t is time, ρ is the fluid density, μ is the fluid dynamic viscosity, and are the average velocity and average pressure respectively, u' is the velocity pulsation term, is the Reynolds stress term introduced additionally to reflect the effect of turbulence on momentum transport;

[0017] Used to solve Reynolds stress in flow field The transport equations for the turbulent kinetic energy k and the turbulent specific dissipation rate ω are as follows:

[0018]

[0019] Where ρ is the fluid density; x j is the spatial coordinate, j represents the direction index, j = 1, 2, 3 corresponds to the x, y, z directions respectively; u j is the velocity component, k is the turbulent kinetic energy; μ t is the turbulent viscosity, which reflects the additional viscous effect of turbulence on fluid motion; σ k is the turbulent Prandtl number of the turbulent kinetic energy transport equation, τtij is the turbulent stress tensor, S ij is the strain rate tensor, β * is the empirical coefficient, ω is the specific turbulence dissipation rate; F1 is the mixing function;

[0020] From the perspective of velocity field, the drag reduction mechanism of the microstructure causes the velocity profile in the logarithmic law region to shift. The boundary condition of the microstructure numerical simulation is modified based on the k-ωSST turbulence model to simulate the velocity profile in the logarithmic law region on the bionic microstructure surface:

[0021]

[0022] Wherein, the Karman constant κ = 0.41; the constant B is determined by smooth wall experiments; ΔU + The logarithmic velocity offset caused by the wall properties. A negative offset corresponds to an increase in wall friction, and a positive offset corresponds to a decrease in wall friction. + The superscript “+” indicates the dimensionless physical quantity in the inner region of the boundary layer.

[0023] The microstructure control method for drag reduction of higher-speed trains, wherein the cross-sectional dimensions of the bionic microstructure are: width 70.7 microns, height 70.7 microns.

[0024] By adopting the above technical solution, the present invention has the following beneficial effects:

[0025] The present invention's microstructure control method for drag reduction on higher-speed trains is well-conceived and applicable to high-speed trains traveling at speeds of 400 km / h. By arranging microstructures of specific shapes and sizes on the train surface, the method optimizes flow characteristics and reduces the aerodynamic drag of the entire vehicle by 2.3%, thereby improving the train's operating efficiency and stability. The bionic microstructures of the present invention are simple in structure, require no energy input, and can effectively reduce wall aerodynamic friction resistance. The size and shape of the bionic microstructures designed in the present invention are suitable for each carriage, reducing the resistance of all carriages, effectively avoiding increases in train resistance caused by a mismatch between the size and shape of the bionic microstructures and local flow conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1A schematic diagram of a bionic microstructure surface involved in the microstructure control method for drag reduction of higher-speed trains according to the present invention;

[0028] Figure 2 Schematic cross-sectional view of a preferred bionic microstructure involved in the microstructure control method for drag reduction of higher-speed trains according to the present invention;

[0029] Figure 3 This is a microstructure layout diagram of a 400km / h high-speed train involved in the microstructure control method for drag reduction of higher-speed trains according to the present invention. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0031] The present invention will be further explained below with reference to specific embodiments.

[0032] like Figure 1 As shown, this embodiment provides a micro-structure control method for reducing drag on higher-speed trains, specifically comprising the following steps:

[0033] S100, bionic microstructure shape design

[0034] The bionic microstructure surface is a passive drag reduction technology that is inspired by the unique microstructure of shark skin. Inspired by shark skin, the present invention designs a closely arranged two-dimensional micro-ridge structure with ridges parallel to the length of the train. The cross-section of a single bionic microstructure unit is an isosceles triangle with a vertex angle of 53.13°, i.e. a V-shaped structure with an aspect ratio of 1. This shape can effectively guide airflow and reduce friction. The arrangement of the microstructure is as follows: Figure 1 shown.

[0035] S200, bionic microstructure size acquisition

[0036] After conducting a large number of CFD numerical experiments based on the k-ωSST turbulence model and the numerical modeling boundary of the bionic microstructure, the flow characteristics of microstructure surfaces of different sizes on a high-speed train running at a speed of 400 km / h were analyzed. The optimal cross-sectional dimensions of a single bionic microstructure unit were obtained as follows: width 70.7 microns, height 70.7 microns. The shape and size of the preferred bionic microstructure unit are as follows: Figure 2 As shown; a single bionic microstructure unit is stretched along the length of the vehicle to obtain ridge-like protrusions. The surface of the bionic microstructure is composed of parallel arranged ridge-like protrusions, and its overall shape is similar to the fan surface of a folding fan.

[0037] The specific process of conducting a large number of CFD numerical experiments based on the k-ωSST turbulence model and the bionic microstructure numerical modeling boundary is as follows:

[0038] In turbulence simulation, the Reynolds-Averaged Navier-Stokes (RANS) method is often used to reduce the computational cost of turbulence simulation. By decomposing the mean and pulsating parts of the flow variables velocity u and pressure p, the time-averaged governing equations are obtained. Taking the momentum equation as an example, after Reynolds averaging, we can obtain:

[0039]

[0040] Where t is time, ρ is the fluid density, μ is the fluid dynamic viscosity, and are the average velocity and average pressure respectively, u' is the velocity pulsation term, and the additional Reynolds stress term is It reflects the influence of turbulence on momentum transport. Since the Reynolds stress term cannot be solved directly, it needs to be solved closed by means of a turbulence model. The k-ωSST (Shear Stress Transport) model used in this embodiment is a hybrid turbulence model developed by Menter based on the standard k-ω model. Its core idea is to use the k-ω model in the near-wall region to accurately capture the characteristics of the turbulent boundary layer, and to use the k-ε model in the free shear flow region far away from the wall to reduce the sensitivity to far-field turbulence.

[0041] Used to solve Reynolds stress in flow field The transport equations of turbulent kinetic energy k and turbulent specific dissipation rate ω are:

[0042]

[0043] Where ρ is the fluid density, x j is the spatial coordinate (j represents the direction index, j = 1, 2, 3 corresponds to the x, y, z directions), u j is the velocity component, k is the turbulent kinetic energy; μ t is the turbulent viscosity, which reflects the additional viscous effect of turbulence on fluid motion; σ k is the turbulent Prandtl number of the turbulent kinetic energy transport equation, τ tij is the turbulent stress tensor, S ij is the strain rate tensor, β * is the empirical coefficient, ω is the specific turbulence dissipation rate; F1 is the mixing function used to switch between the k-ω model and the k-ε model;

[0044] From the perspective of velocity field, the drag reduction mechanism of the microstructure can be explained as the displacement of the velocity profile in the logarithmic law region. The boundary condition of the microstructure numerical simulation is modified based on the existing k-ωSST turbulence model to simulate the velocity profile in the logarithmic law region above the bionic microstructure surface:

[0045]

[0046] Offset ΔU + In this paper, the superscript “+” represents the dimensionless physical quantity in the inner region of the boundary layer (the reference speed is the friction speed where τ w represents the wall shear stress, and ρ represents the fluid density); in the above formula, the Karman constant κ = 0.41; the constant B is determined by smooth wall experiments and is usually taken as 5.0; ΔU + It is the velocity offset in the logarithmic region caused by the wall properties. A negative offset corresponds to an increase in wall friction, and a positive offset corresponds to a decrease in wall friction.

[0047] S300, bionic microstructure layout design

[0048] By analyzing the flow field of a simplified model of a high-speed train that ignores components such as bogies, pantographs, and windshields, summarizing the flow characteristics of the flow around high-speed trains, and combining the flow control characteristics of bionic microstructures, the present invention arranges bionic microstructures in the straight section of the train, while not arranging bionic microstructures in the streamlined areas of the head and tail cars; in the straight section of the train, aerodynamic resistance is mainly dominated by friction resistance, and pressure difference resistance accounts for a very small proportion; arranging bionic microstructures in the straight section of the train can directly have a positive impact on friction resistance, thereby improving the overall aerodynamic performance. The specific location is as follows Figure 3 As shown in the purple area, the small picture shows the cross-sectional shape of the microstructure. The width of the microstructure unit is equal to the speed, that is, s = h = 70.7 μm, and the unit cross-sectional area A g =2500μm 2 .

[0049] In order to compare the drag reduction effect before and after installing the microstructure, the aerodynamic drag coefficient C of the high-speed train is defined as D ,as follows:

[0050]

[0051] In the above formula, F x is the integral of the aerodynamic force on the train surface in the flow direction; ρ is the air density, which is 1.225 kg / m 3 ;S x is the area of ​​the train's maximum cross-section; V is the train's running speed, which is 400km / h.

[0052] CFD numerical calculations based on the k-ωSST turbulence model and the numerical modeling boundary of the bionic microstructure revealed the aerodynamic drag of the entire train and each carriage of a 400 km / h high-speed train after installing a bionic microstructure surface with a cross-sectional height and width equal to 70.7 microns, as shown in Table 1. According to specific numerical experimental data, the bionic microstructure of the present invention can reduce the overall aerodynamic drag of the train by 2.3%. After installing a microstructure of this size, the drag of each carriage decreased, demonstrating the effective drag reduction effect of the microstructure across the entire train. The second carriage achieved the greatest drag reduction, achieving a drag reduction rate of 2.9%.

[0053] Table 1 Aerodynamic resistance of high-speed trains equipped with the patented microstructure

[0054]

[0055]

[0056] The invention has a reasonable concept and can be applied to high-speed trains with a speed of 400 km / h. By arranging microstructures of specific shapes and sizes on the surface of the train, the flow characteristics are optimized, the aerodynamic resistance is reduced, and thus the operation efficiency and stability of the train are improved.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A microstructure control method for reducing drag on higher speed trains, characterized in that: The specific steps include: 1) Bionic microstructure shape design Design a densely packed two-dimensional micro-ridge structure with ridge lines parallel to the length of the train; 2) Acquisition of bionic microstructure dimensions CFD numerical experiments were conducted based on the k-ωSST turbulence model and the numerical modeling boundary of the bionic microstructure. The flow characteristics of microstructure surfaces of different sizes on a high-speed train running at a speed of 400 km / h were analyzed, and the optimal cross-sectional dimensions of the bionic microstructure were obtained. 3) Bionic microstructure layout design By analyzing the flow field of a simplified high-speed train model that ignores the bogie, pantograph and windshield components, the flow characteristics of the flow around the high-speed train are summarized. Combined with the flow control characteristics of the bionic microstructure, the bionic microstructure is arranged in the straight section of the train, while the bionic microstructure is not arranged in the streamlined areas of the head and tail cars.

2. The microstructure control method for drag reduction of higher-speed trains according to claim 1, characterized in that: The cross-sectional shape of a single bionic microstructure unit of the micro-ridge-shaped two-dimensional structure in step 1) is an isosceles triangle with a vertex angle of 53.13°, that is, a V-shaped structure with an aspect ratio of 1.

3. The microstructure control method for drag reduction of higher speed trains according to claim 1, characterized in that: The specific process of performing CFD numerical experiments based on the k-ωSST turbulence model and the bionic microstructure numerical modeling boundary in step (2) is as follows: The Reynolds average method is used to decompose the mean and pulsating parts of the flow variables, velocity u and pressure p, and the time-averaged control equation is obtained: Where t is time, ρ is the fluid density, μ is the fluid dynamic viscosity, and are the average velocity and average pressure respectively, u' is the velocity pulsation term, is the Reynolds stress term introduced additionally to reflect the effect of turbulence on momentum transport; Used to solve Reynolds stress in flow field The transport equations for the turbulent kinetic energy k and the turbulent specific dissipation rate ω are as follows: Where ρ is the fluid density; x j is the spatial coordinate, j represents the direction index, j = 1, 2, 3 corresponds to the x, y, z directions respectively; u j is the velocity component, k is the turbulent kinetic energy; μ t is the turbulent viscosity, which reflects the additional viscous effect of turbulence on fluid motion; σ k is the turbulent Prandtl number of the turbulent kinetic energy transport equation, τ tij is the turbulent stress tensor, S ij is the strain rate tensor, β * is the empirical coefficient, ω is the specific turbulence dissipation rate; F1 is the mixing function; From the perspective of velocity field, the drag reduction mechanism of the microstructure causes the velocity profile in the logarithmic law region to shift. The boundary condition of the microstructure numerical simulation is modified based on the k-ωSST turbulence model to simulate the velocity profile in the logarithmic law region on the bionic microstructure surface: Wherein, the Karman constant κ = 0.41; the constant B is determined by smooth wall experiments; ΔU + The logarithmic velocity offset caused by the wall properties. A negative offset corresponds to an increase in wall friction, and a positive offset corresponds to a decrease in wall friction. + The superscript "+" indicates the dimensionless physical quantity in the inner region of the boundary layer.

4. The microstructure control method for drag reduction of higher speed trains according to claim 1, characterized in that: The cross-sectional dimensions of the bionic microstructure are: width 70.7 microns, height 70.7 microns.

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