CN115510710A - Pneumatic resistance calculation method and system for tail blowing/air suction drag reduction type train - Google Patents

Pneumatic resistance calculation method and system for tail blowing/air suction drag reduction type train Download PDF

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CN115510710A
CN115510710A CN202211193683.8A CN202211193683A CN115510710A CN 115510710 A CN115510710 A CN 115510710A CN 202211193683 A CN202211193683 A CN 202211193683A CN 115510710 A CN115510710 A CN 115510710A
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blowing
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杨明智
张雷
周丹
王田天
伍钒
钱博森
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Central South University
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Abstract

The invention discloses a pneumatic resistance calculation method and a system of a tail blowing/sucking drag reduction type train, wherein a geometric model and a calculation domain of the tail blowing/sucking drag reduction type train are constructed, and mixed grid dispersion is carried out on the geometric model and the calculation domain of the train; and then constructing a pneumatic characteristic numerical model when the train runs the blowing/sucking drag reduction assembly based on a train geometric model after grid dispersion and a calculation domain, wherein the pneumatic characteristic numerical model simulates turbulent flow at the tail of the train when the train runs the blowing/sucking drag reduction assembly by adopting a DDES method based on a k-epsilon turbulent flow model. And iteratively solving the pneumatic characteristic numerical model to obtain the pneumatic resistance of the train. The invention achieves the purposes of accurately simulating the phenomena of flow separation, turbulence vortex shedding, boundary layer thickness change and the like of the tail part of the train under the action of blowing and sucking air by using a mixed grid technology and combining a higher-precision DDES turbulence simulation method, thereby obtaining a more accurate resistance value calculation result.

Description

Pneumatic resistance calculation method and system for tail blowing/air suction resistance reduction type train
Technical Field
The invention relates to the technical field of train pneumatic resistance numerical simulation, in particular to a method and a system for calculating the pneumatic resistance of a tail blowing/sucking drag reduction type train.
Background
The method ensures that the pneumatic resistance of the train is reduced as much as possible on the premise of high-speed running, and has important basic research value and engineering application significance for saving running energy and reducing the later-stage design cost of the high-speed train. At present, subway trains and intercity motor train units with large passenger load requirements in China use shorter streamline lengths to improve space utilization rate and meet the requirement of high passenger load, which means that the trains face larger aerodynamic resistance in the running process. Generally speaking, by regulating and controlling the flow phenomena of transition, separation, vortex and the like of the flow field around the train, the local flow can be changed so as to achieve the aim of reducing the drag. The tail blowing and sucking drag reduction method is based on the flow control theory. When incoming flow flows to a train equal-section train body and a streamline tail transition part, due to the sudden change of the train section area, the air flow is accelerated, the pressure is reduced, the flow structure in the boundary layer is suddenly changed, a large velocity gradient is formed, large flow separation is generated, and the resistance borne by the train is increased. Proper blowing and sucking air is set in the position to control the flow field, and the flow separation strength is changed by changing the pressure distribution on the surface of the trailer and the thickness change of the boundary layer, so that the aim of pneumatic drag reduction is fulfilled.
Researches show that the pneumatic resistance can be effectively reduced by using the train tail blowing and sucking method, the resistance reduction effect can reach more than 10%, but the method brings great challenges to resistance measurement.
The measuring means of the train resistance mainly comprises two measuring means, namely wind tunnel test and numerical calculation. For the wind tunnel test, it is very difficult to realize the simulation of tail blowing and sucking air, and the main difficulties are as follows: the method is limited by the size of the wind tunnel, a model used in the wind tunnel test is generally small, and the difficulty in installing a blowing and sucking air duct in a narrow space is high; in the test, the air blowing and sucking quantity provided by the fan is interfered by the external environment of the air blowing and sucking port to generate violent fluctuation, and the real-time air blowing and sucking quantity is limited by space and is difficult to measure, so that an accurate change relation between the air blowing and sucking quantity and the resistance reduction effect cannot be established. Therefore, the resistance reduction effect of the blowing and suction drag reduction method is only studied by numerical calculation. The train resistance consists of two parts, namely differential pressure resistance and friction resistance. In the numerical calculation, the accurate differential pressure resistance needs to be obtained through accurate simulation of a flow field at the tail of the train; the frictional resistance requires accurate calculation of the flow velocity distribution of the train near the wall surface. The original flow field at the tail of the train can be seriously changed in the air blowing and sucking process at the tail of the train, so that the precision of the train resistance calculated by using a conventional method is reduced.
Disclosure of Invention
The invention provides a method and a system for calculating the pneumatic resistance of a tail blowing/sucking drag reduction type train, which are used for solving the technical problem that the pneumatic resistance of the tail blowing/sucking drag reduction type train cannot be accurately calculated by the conventional pneumatic resistance calculation method.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a method for calculating the aerodynamic resistance of a tail blowing/air suction drag reduction type train is characterized by comprising the following steps:
constructing a geometric model of the tail blowing/sucking drag reduction train, wherein the geometric model comprises a blowing/sucking drag reduction assembly of the train;
constructing a calculation domain of the pneumatic characteristic numerical simulation when the geometric model of the train operates the blowing/sucking drag reduction assembly, and carrying out grid dispersion on the geometric model of the train and the calculation domain; the region of the complex geometric shape of the computational domain adopts unstructured tetrahedral mesh dispersion, and other regions in the computational domain adopt structured mesh dispersion;
constructing a pneumatic characteristic numerical model of the train when the geometric model of the train runs the blowing/sucking drag reduction assembly based on a grid-dispersed train geometric model and a calculation domain, wherein variables of the pneumatic characteristic numerical model further comprise tail blowing/sucking air volume and wind speed, and the pneumatic characteristic numerical model simulates turbulent flow at the tail of the train when the train runs the blowing/sucking drag reduction assembly by adopting a DDES method based on a k-epsilon turbulent flow model;
setting boundary conditions of a calculation domain, initializing the aerodynamic characteristic numerical model, and iteratively solving the aerodynamic characteristic numerical model to obtain the aerodynamic resistance of the train when the blowing/sucking drag reduction assembly runs.
Preferably, the train blow/suction drag reduction assembly comprises a blow/suction inlet arranged at the tail of the train, the blow/suction inlet is arranged in a streamline area between an air separation line and an air reattachment line at the tail of the train and is arranged in an annular mode, and the blow/suction inlet is connected with an air outlet of an exhaust fan of each train, is used for collecting waste gas of each carriage and discharges the waste gas outwards from the tail.
Preferably, the region of complex geometry comprises: bogies, pantographs; the calculation domain carries out encryption processing on grids in a train near-wall area, and N layers of boundary layer grids are arranged on the surface of the train; wherein the first boundary layer mesh thickness Δ s is estimated by the following formula:
Figure BDA0003869977360000021
wherein y + is a dimensionless wall surface distance and is used for measuring the adaptability of the wall surface normal grid dimension to the turbulence model; μ is the fluid viscosity; rho is the fluid density U fric The near-wall friction speed is given by:
Figure BDA0003869977360000022
in the formula, τ wall Wall shear stress; the wall shear stress is influenced by the normal velocity gradient of the wall and is difficult to directly calculate to obtain an accurate value, the flow is usually simplified into flat plate flow in engineering application, and according to the theory of a flat plate boundary layer, the wall friction coefficient C is used f And estimating the speed of the incoming flow at infinity:
Figure BDA0003869977360000023
Figure BDA0003869977360000024
in the formula of U ∞ Taking the maximum speed for the infinite incoming flow speed; re is Reynolds number.
Preferably, the difference format of the aerodynamic characteristic numerical model adopts a QUICK format with second-order precision, and the speed-pressure coupling solving method of the aerodynamic characteristic numerical model is a SIMPLEC algorithm.
Preferably, the boundary conditions of the computation domain include: setting an inflow end face of a calculation domain as a speed inlet boundary condition, and setting a speed opposite to the speed direction of the train at a speed inlet; calculating the boundary condition of a given pressure outlet on the downstream end surface of the domain, wherein the static pressure is 0; giving a non-slip fixed wall boundary condition on the surface of the train; if the air blowing and suction is actively controlled on the surface of the train, the control surface gives a speed inlet boundary; the ground gives a slip ground boundary condition to eliminate the influence of a ground boundary layer, and the slip speed is consistent with the vehicle speed; and adopting a gliding wall surface boundary condition for the top surface and the two side surfaces of the calculation domain.
Preferably, the blowing/suction air volume and the air speed at the tail of the train are obtained by the following formula: v = Q/S, Q = Q 1 +Q 2 +Q 3 +...+Q n Wherein v is the blowing/sucking air quantity and the air speed of the tail part of the train, S is the size of a blowing/sucking opening of the tail part of the train, and Q 1 、Q 2 、Q 3 ……Q n Are respectively a rowThe fresh air/waste air exhaust volume of the carriage at the nth section is n, wherein n is the total number of carriages of the train.
A computer system comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the steps of the above method when executing the computer program.
The invention has the following beneficial effects:
according to the method and the system for calculating the aerodynamic resistance of the tail blowing/air suction drag reduction type train, the geometric model and the calculation domain of the tail blowing/air suction drag reduction type train are constructed, and mixed grid dispersion is carried out on the geometric model and the calculation domain of the train; and then constructing a pneumatic characteristic numerical model when the train runs the blowing/sucking drag reduction assembly based on a train geometric model after grid dispersion and a calculation domain, wherein the pneumatic characteristic numerical model simulates turbulent flow at the tail of the train when the train runs the blowing/sucking drag reduction assembly by adopting a DDES method based on a k-epsilon turbulent flow model. And iteratively solving the pneumatic characteristic numerical model to obtain the pneumatic resistance of the train. The invention achieves the purposes of accurately simulating the phenomena of flow separation at the tail part of the train, turbulence vortex shedding, boundary layer thickness change and the like under the action of blowing and sucking air by using a mixed grid technology and combining a higher-precision DDES turbulence simulation method, thereby obtaining a more accurate resistance numerical value calculation result.
In addition to the objects, features and advantages described above, other objects, features and advantages of the present invention are also provided. The present invention will be described in further detail below with reference to the accompanying drawings.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a schematic diagram of a geometric model of a train in a preferred embodiment of the present invention, wherein (A) is an aerial view of the train and (B) is a schematic diagram of a model of the bottom of the train;
FIG. 2 is a schematic view showing the position of a blowing/suctioning surface in a preferred embodiment of the present invention, wherein (A) is a front view of the blowing/suctioning surface and (B) is a side view of the blowing/suctioning surface;
FIG. 3 is a schematic diagram of a compute domain in a preferred embodiment of the invention;
FIG. 4 is a grid discretization graph of a computational domain and train in accordance with a preferred embodiment of the present invention, wherein (A) is a grid longitudinal section of a computational domain of a head car and (B) is a grid map of a surface of the head car; (C) is a grid diagram of a boundary layer on the surface of the train;
fig. 5 is a comparison graph of flow field velocity distribution obtained by the train aerodynamic resistance calculation method in the preferred embodiment of the present invention and the train aerodynamic resistance calculation method in the prior art, wherein (a) is a flow field velocity cloud graph obtained by the train aerodynamic resistance calculation method in the prior art, and (B) is a flow field velocity cloud graph obtained by the train aerodynamic resistance calculation method in the present invention;
fig. 6 is a flowchart of a method for calculating the aerodynamic resistance of the tail-blowing/suction drag reduction train in the present invention.
Detailed Description
The embodiments of the invention will be described in detail below with reference to the drawings, but the invention can be implemented in many different ways as defined and covered by the claims.
The first embodiment is as follows:
as shown in fig. 6, in this embodiment, a method for calculating the aerodynamic resistance of a tail blowing/sucking drag reduction type train is disclosed, which includes the following steps:
constructing a geometric model of the tail blowing/sucking drag reduction train, the geometric model including a blowing/sucking drag reduction assembly of the train;
constructing a calculation domain of aerodynamic characteristic numerical simulation when the geometric model of the train operates the blowing/sucking drag reduction assembly, and performing grid dispersion on the geometric model of the train and the calculation domain; wherein, the region of the complex geometric shape of the computational domain adopts unstructured tetrahedral mesh dispersion, and other regions in the computational domain all adopt structured mesh dispersion;
constructing a pneumatic characteristic numerical model when the geometric model of the train runs the blowing/sucking drag reduction assembly based on a grid-dispersed train geometric model and a calculation domain, wherein variables of the pneumatic characteristic numerical model further comprise tail blowing/sucking air volume and wind speed, and the pneumatic characteristic numerical model simulates turbulent flow at the tail of the train when the train runs the blowing/sucking drag reduction assembly by adopting a DDES method based on a k-epsilon turbulent flow model;
setting boundary conditions of a calculation domain, initializing the aerodynamic characteristic numerical model, and iteratively solving the aerodynamic characteristic numerical model to obtain the aerodynamic resistance of the train when the blowing/sucking drag reduction assembly runs.
In addition, in the embodiment, a computer system is also disclosed, which includes a memory, a processor, and a computer program stored on the memory and executable on the processor, and when the processor executes the computer program, the steps of the method are implemented.
The invention achieves the purposes of accurately simulating the phenomena of flow separation, turbulence vortex shedding, boundary layer thickness change and the like of the tail part of the train under the action of blowing and sucking air by using a mixed grid technology and combining a higher-precision DDES turbulence simulation method, thereby obtaining a more accurate resistance value calculation result.
The second embodiment:
the second embodiment is the preferred embodiment of the first embodiment, and the difference between the first embodiment and the second embodiment is that the specific steps of the method for calculating the aerodynamic resistance of the tail blowing/suction drag reduction type train are optimized:
the invention designs a numerical calculation method for the drag reduction of the blowing and suction gas at the tail part of a train based on a numerical simulation method, generates a refined discrete grid by constructing a train model, sets boundary conditions, and adopts a finite volume or finite difference method for simulation; judging whether the flow field is completely developed or not according to the iteration time history curves of the aerodynamic resistance coefficients of the head car, the middle car and the tail car obtained by simulation; carrying out research and analysis on a completely developed flow field, carrying out detailed exploration on a flow equalizing field structure surrounding the periphery of the train, establishing cognition on the distribution characteristic of the flow field around the blunt-nose train, analyzing a flow separation phenomenon and a transient wake vortex structure at the tail of the train, and exploring the correlation of a tail pulsation flow field; according to the research, the distribution characteristic of aerodynamic resistance and the generation reason thereof are obtained, a blowing/sucking boundary condition is established between a main area causing resistance increase, namely a flow separation and reattachment area at the tail of the train, and reasonable blowing/sucking strength is set, and the numerical calculation method for the blowing and sucking drag reduction at the tail of the train comprises the following steps:
1) Building a geometric computation model
As shown in fig. 1, a train model with a real scale is established by using geometric modeling software (such as Rhino) to select a blunt-end-shaped subway train as a geometric model for calculation. For the comparison and verification with the test result, the calculation model is set to be consistent with the wind tunnel model, and key parts such as an embankment, a bogie, equipment under a cabin, a roof air conditioner, a windshield and the like are reserved. The height H =3.822m, the width W =2.92m, the length L =71.12m and the running speed of the train in calculation is 140km/H.
2) Blow and suction air position determination
When the incoming flow flows to the equal-section train body and the streamline tail transition part of the train, the air flow is accelerated and the pressure is reduced due to the sudden change of the sectional area of the train, so that the boundary layer is suddenly changed, a large speed gradient is formed, large flow separation is generated, and the resistance borne by the train is increased. The blowing/suction position needs to be determined by the end-of-train flow structure: the speed of the roof air flow continuously increases when the roof air flow passes through the transition position of the vehicle body and the tail part, the pressure is further reduced, in the process of developing towards the tail part of the tail vehicle, the roof air flow and the side surface of the tail vehicle are in counter pressure gradient distribution, then the flow of the two sides of the tail vehicle is promoted to converge towards the center of the tail part, the flow of the two sides is generated, and the key position for forming the vortex is the shoulder transition area of the two sides of the tail part of the tail vehicle. Therefore, proper air suction control is arranged at the position, and the strength of flow separation is changed by changing the pressure distribution of the surface of the trailer and the thickness change of the boundary layer, so that the aim of pneumatic drag reduction is fulfilled. The blow and suction gas position for the final use of the present invention is shown in figure 2. Namely, the blowing/suction inlet of the blowing/suction drag reduction assembly of the train is arranged in the tail streamline area, replaces the wall surface condition of the original train surface and is annularly arranged.
3) Air volume and speed estimation and setting of blowing and sucking air
The air suction quantity is estimated according to the fresh air/exhaust air quantity of the subway train. For the calculation example of any multi-section train marshalling, the fresh air/waste exhaust air volume of each section of train is Q 1 、Q 2 、Q 3 ……Q n The total air volume of the blowing and the suction is set as Q = Q 1 +Q 2 +Q 3 +...+Q n . According to the area S of the blowing and sucking port, the wind speed v = Q/S of the blowing and sucking port can be obtained through calculation, and finally the boundary condition of the blowing and sucking port is set as a speed inlet, and the speed is set as the wind speed v.
For the three-vehicle marshalling used in the calculation example, the fresh air/exhaust air volume of each vehicle is 14000m respectively 3 The total air volume of the blowing and suction air is 42000m 3 H is used as the reference value. Further, according to the invention, the area of the blowing inlet is 2m 2 The blowing port wind speed v =23.3m/s can be calculated.
4) Setting a computing Domain
The train resistance was calculated using the air blowing method. The calculation domain is set to be consistent with that of a conventional wind blowing method, and a large enough calculation domain needs to be set in order to ensure that the flow field around the train is fully developed and the boundary does not interfere with the flow field calculation result. FIG. 3 is a schematic diagram of a calculation domain used in the method, in which a train is located at the transverse center of a calculation region, an upstream entrance is not less than 10 times of the train height from the head of the train, a wake outlet is not less than 3 times of the train length from the tail of the train, and the width and height of the calculation region are not less than 10 times of the train height.
In this embodiment, the train upstream entrance is 80m from the head of the embankment, the wake exit is 210m from the tail of the embankment, and the calculated zone width and height are 64m and 48m respectively.
5) Numerical calculation method
The DES method is beneficial to solving the problems of high Reynolds number and large-scale flow separation, can ensure enough calculation precision and capture vortex pulsation characteristics, and the calculation amount is far LESs than that of the LES method. The present invention chooses to simulate turbulent flow using a DDES method based on a k-epsilon turbulence model.
Common difference formats include a center difference of first order precisionMinutes, first order windward, and second order windward with second order accuracy, QUICK format, etc. The first-order precision has larger numerical diffusion errors, and the high-order format can obviously reduce the errors due to the fact that more adjacent nodes are introduced into calculation and the influence of flow directionality is considered. The method adopts a QUICK format with second-order precision for the differential format of the flow direction. The discrete problem of the pressure gradient is the problem of the velocity-pressure coupling method. The dominant method currently used for velocity-pressure coupling solutions is the pressure correction method. The basic idea of the pressure correction method is as follows: firstly, a pressure initial field p is set * Solving the velocity field v by the momentum equation * Then, a pressure correction p' is constructed through a continuity equation, and the pressure field and the speed field are corrected to obtain a new p * 、v * And continuously repeating the process to finally obtain the solution of the flow field. The essence of this is a process that is constantly iterative. The speed-pressure coupling solving method used by the method is a modified method of a pressure correction method, namely a SIMPLEC algorithm.
6) Spatial discretization of computational domains
As shown in fig. 4, the spatial discretization method in this embodiment is a hybrid mesh method, and regions with complex geometric shapes, such as a bogie and a pantograph, are discretized by using non-structural tetrahedral meshes; while all the remaining locations within the computational domain are discretized with a structured grid. By using the mixed grid method, the space discrete workload can be reduced, and meanwhile, the good near-wall flow calculation precision can be obtained, so that a more accurate resistance simulation value can be obtained. Because the flow velocity gradient of the train near-wall area is large, the grids in the area need to be subjected to grid encryption processing. The train surface is provided with 30 layers of boundary layer grids, so that enough nodes exist in the influence range of the viscosity effect. The first layer mesh thickness is estimated by y +. And y + is a dimensionless distance from the centroid of the first layer of grid to the wall surface, is related to speed, viscosity, shear stress and the like, and has important significance on solving the flow in the boundary layer according to the Plantt theory and an appropriate y + value. The first layer grid thickness deltas is estimated through y +, and the specific formula is as follows:
Figure BDA0003869977360000071
wherein y + is a dimensionless wall surface distance for measuring the adaptability of the wall surface normal grid scale to the turbulence model, and the k-epsilon model used in the invention requires y +<300, taking a target y + =250 to estimate the thickness of the first layer of grid; fluid viscosity μ =1.7894 × 10 -5 kg/(m.s); fluid density ρ =1.225kg/m 3 ；U fric The near-wall friction speed is given by:
Figure BDA0003869977360000072
in the formula, τ wall Is the wall shear stress. The wall shear stress is influenced by the normal velocity gradient of the wall and is difficult to directly calculate to obtain an accurate value, the flow is usually simplified into flat plate flow in engineering application, and according to the theory of a flat plate boundary layer, the wall friction coefficient C is used f And estimating the speed of the incoming flow at infinity:
Figure BDA0003869977360000073
Figure BDA0003869977360000074
in the formula of U ∞ Taking the maximum speed U for the infinite incoming flow speed ∞ =97.22m/s; reynolds number Re =2.62 × 10 7 . Calculating the estimated thickness delta s =1.12 multiplied by 10 of the first layer grid of the surface of the vehicle body -3 m, rounding as Δ s down to Δ s =1mm in the present invention.
The k-epsilon turbulence model adopted by the method requires that the value of y + is controlled to be between 30 and 300. The minimum distance between a mesh node and a wall surface within a boundary layer can be estimated by the following equation, based on the range of y + values to be controlled.
Figure BDA0003869977360000075
Wherein L is a characteristic length, R eL The characteristic length is the corresponding Reynolds number. And if the thickness of the first layer of grid is 1mm, the calculated y + value is about 95, and the requirement of the k-epsilon turbulence model on y + is met.
In this embodiment, the model is spatially discretized using meshing software (e.g., poitwise). Areas with complex geometric shapes such as a bogie and a pantograph are dispersed by adopting unstructured tetrahedral mesh, the minimum mesh size of an object plane is 30mm, and the mesh distortion rate is less than 0.8; all other positions in the calculation domain are dispersed by adopting structural grids, the minimum grid size of an object plane is 50mm, and the grid distortion rate is less than 0.7. 30 layers of boundary layer grids are arranged on the surface of the train, the thickness of the first layer of grids is 1mm, and the growth rate of each layer of grids is not more than 1.1.
In the embodiment, a fine structural grid within 50m behind the train tail and the tail is constructed to ensure accurate capture of the flow characteristics of the train tail; the whole vehicle model needs to be divided into a plurality of regions (such as a bogie, a vehicle body smoothing region, a vehicle body streamline region and the like), and each region independently monitors the resistance coefficient in the calculation process so as to carry out deep analysis on the whole vehicle resistance distribution condition.
7) Boundary condition
Setting boundary conditions as shown in FIG. 3, setting the inflow end surface of the calculation domain as a speed inlet boundary condition, and giving a speed which is equal to the vehicle speed and has an opposite direction; setting a pressure outlet boundary condition on the downstream end face, wherein the static pressure is 0; the surface of the train is given with a non-slip fixed wall boundary condition; if the blowing and suction air is actively controlled on the surface of the train, the control surface gives a speed inlet boundary; the ground gives a slip ground boundary condition to eliminate the influence of a ground boundary layer, and the slip speed is consistent with the vehicle speed; and adopting a gliding wall surface boundary condition for the top surface and the two side surfaces of the calculation domain.
8) Computation and result processing
The involved cases are subjected to unsteady state solution by using a pressure base solver of ANSYS Fluent, the time step length is calculated to be delta t =0.001s, and each residual error of each time step equation is lower than 10 -3 . The resistance is measured asAnd integrating all discrete grids on the train, and taking the average value of the final 7000 solving steps to obtain a resistance calculation result.
9) Comparison and verification of calculation results
And comparing the resistance value obtained by the method with the resistance value obtained in a wind tunnel test to verify the accuracy of the result obtained by the method. Fig. 5 shows a comparison of the velocity distribution of the flow field obtained by the present invention and the original method, which shows that the original method can only obtain an extremely fine flow field state, and especially the calculation result of the wake vortex, which has a great influence on the accuracy of the train differential pressure resistance, is too coarse, so that the deviation of the obtained result from the real result is large. The final calculated result differed by 5.7% from the result obtained without the method of the invention. Therefore, the mixed grid technology is combined with a DES turbulence simulation method with higher precision, so that the phenomena of flow separation, turbulence vortex shedding, boundary layer thickness change and the like at the tail part of the train under the blowing and sucking actions can be accurately simulated, and a more accurate resistance value calculation result can be obtained.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (7)

1. A method for calculating the aerodynamic resistance of a tail blowing/air suction drag reduction type train is characterized by comprising the following steps:
constructing a geometric model of the tail blowing/sucking drag reduction train, wherein the geometric model comprises a blowing/sucking drag reduction assembly of the train;
constructing a calculation domain of the pneumatic characteristic numerical simulation when the geometric model of the train operates the blowing/sucking drag reduction assembly, and carrying out grid dispersion on the geometric model of the train and the calculation domain; wherein, the region of the complex geometric shape of the computational domain adopts unstructured tetrahedral mesh dispersion, and other regions in the computational domain all adopt structured mesh dispersion;
constructing a pneumatic characteristic numerical model when the geometric model of the train runs the blowing/sucking drag reduction assembly based on a grid-dispersed train geometric model and a calculation domain, wherein variables of the pneumatic characteristic numerical model further comprise tail blowing/sucking air volume and wind speed, and the pneumatic characteristic numerical model simulates turbulent flow at the tail of the train when the train runs the blowing/sucking drag reduction assembly by adopting a DDES method based on a k-epsilon turbulent flow model;
setting boundary conditions of a calculation domain, initializing the aerodynamic characteristic numerical model, and iteratively solving the aerodynamic characteristic numerical model to obtain the aerodynamic resistance of the train when the blowing/sucking drag reduction assembly runs.
2. The method for calculating the aerodynamic resistance of the tail-blowing/air-sucking drag reduction train according to claim 1, wherein the blowing/air-sucking drag reduction assembly of the train comprises a blowing/air-sucking port arranged at the tail of the train, the blowing/air-sucking port is arranged in a streamline area between an air separation line and an air reattachment line at the tail of the train and is arranged annularly, and the blowing/air-sucking port is connected with an air outlet of an exhaust fan of each train respectively and is used for collecting waste gas of each carriage and discharging the waste gas outwards from the tail.
3. The method for calculating the aerodynamic resistance of a tail-blowing/sucking drag reduction train according to claim 2, wherein the region of complex geometric shape comprises: bogies, pantographs; the calculation domain carries out encryption processing on grids in a near-wall area of the train, and N layers of boundary layer grids are arranged on the surface of the train; wherein the first boundary layer mesh thickness Δ s is estimated by the following formula:
Figure FDA0003869977350000011
wherein y + is a dimensionless wall surface distance and is used for measuring the adaptability of the wall surface normal grid dimension to the turbulence model; μ is the fluid viscosity; ρ is the fluid density U fric The near-wall friction speed is given by:
Figure FDA0003869977350000012
in the formula, τ wall Wall shear stress; the wall shear stress is influenced by the normal velocity gradient of the wall and is difficult to directly calculate to obtain an accurate value, the flow is usually simplified into flat plate flow in engineering application, and according to the theory of a flat plate boundary layer, the wall friction coefficient C is used f And estimating the speed of the incoming flow at infinity:
Figure FDA0003869977350000013
Figure FDA0003869977350000021
in the formula, U infinity incoming flow speed is selected as the maximum speed; re is Reynolds number.
4. The method for calculating the aerodynamic resistance of a tail-blowing/aspirating drag-reducing train according to claim 3, wherein the differential format of said aerodynamic numerical model adopts QUICK format with second order precision, and the velocity-pressure coupling solving method of said aerodynamic numerical model is SIMPLEC algorithm.
5. The method for calculating the aerodynamic resistance of a tail-blowing/sucking drag-reducing train according to claim 4, wherein the boundary conditions of the calculation domain include: setting an inflow end face of a calculation domain as a speed inlet boundary condition, and setting a speed opposite to the speed direction of the train at a speed inlet; calculating the boundary condition of a given pressure outlet on the downstream end face of the domain, wherein the static pressure is 0; giving a non-slip fixed wall boundary condition on the surface of the train; if the air blowing and suction is actively controlled on the surface of the train, the control surface gives a speed inlet boundary; the ground gives a slip ground boundary condition to eliminate the influence of a ground boundary layer, and the slip speed is consistent with the vehicle speed; and adopting a gliding wall surface boundary condition for the top surface and the two side surfaces of the calculation domain.
6. The method for calculating the aerodynamic resistance of the tail-blowing/sucking drag reduction train according to claim 5, wherein the blowing/sucking air volume wind speed at the tail of the train is obtained by the following formula: v = Q/S, Q = Q 1 +Q 2 +Q 3 +...+Q n Wherein v is the blowing/suction air quantity and the air speed of the tail part of the train, S is the blowing/suction opening size of the tail part of the train, and Q 1 、Q 2 、Q 3 ……Q n The fresh air/waste air exhaust volume of the nth compartment is the total number of the compartments of the train.
7. A computer system comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the steps of the method of any one of claims 1 to 6 when executing the computer program.
CN202211193683.8A 2022-09-28 2022-09-28 Pneumatic resistance calculation method and system for tail blowing/air suction drag reduction type train Pending CN115510710A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116992784A (en) * 2023-05-26 2023-11-03 中南大学 Dynamic sealing performance analysis method for high static pressure fan in high-speed train

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116992784A (en) * 2023-05-26 2023-11-03 中南大学 Dynamic sealing performance analysis method for high static pressure fan in high-speed train
CN116992784B (en) * 2023-05-26 2024-03-12 中南大学 Dynamic sealing performance analysis method for high static pressure fan in high-speed train

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