Vehicle drag coefficient testing method and related device

Abstract

The invention discloses a vehicle drag coefficient testing method and a related device. The method comprises the following steps: acquiring air velocity distribution of a wake flow section at a preset distance from the tail of a to-be-tested vehicle and relative static pressure distribution of the wake flow section relative to an automobile aerodynamic wind tunnel nozzle; and based on the air velocity distribution and the relative static pressure distribution, obtaining the acting force of the to-be-tested vehicle on the air, and based on the acting force of the to-be-tested vehicle on the air and a wind resistance coefficient formula, obtaining a vehicle wind resistance coefficient corresponding to the to-be-tested vehicle. The air velocity distribution of the wake flow section comprises a plurality of air velocity test quantities, and the relative static pressure distribution of the wake flow section relative to the automobile aerodynamic wind tunnel nozzle comprises a plurality of static pressure difference test quantities, which is equivalent to that a single test quantity in a traditional scheme is decomposed into the sum of a plurality of test quantities. According to the invention, each test quantity can be measured more accurately, and compared with a traditional single test quantity, the test resolution of the vehicle drag coefficient can be greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle testing, and more particularly to a vehicle drag coefficient testing method and related devices. Background Art

[0002] Air resistance is an important component of vehicle driving resistance and a major factor affecting vehicle energy consumption. Reducing air resistance helps reduce vehicle fuel and electricity consumption and increase vehicle range. The vehicle drag coefficient is a key indicator for evaluating the air resistance of a vehicle. It is related to vehicle styling design and chassis structure. Therefore, testing the vehicle drag coefficient has become an important part of vehicle design and development.

[0003] The existing vehicle drag coefficient test is completed in the automobile aerodynamic wind tunnel using a force balance. The force balance mainly tests the single test quantity of the resultant force on the vehicle. The force test resolution directly affects the vehicle drag coefficient test resolution. However, the force test resolution in the existing technology is not high, which leads to the corresponding vehicle drag coefficient test resolution is not high. Summary of the invention

[0004] In view of this, the present invention discloses a vehicle drag coefficient testing method and related devices to improve the test resolution of the vehicle drag coefficient.

[0005] A method for testing a vehicle drag coefficient, comprising:

[0006] Obtaining the air velocity distribution of the wake cross section at a preset distance from the rear of the vehicle to be tested and the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel;

[0007] Obtaining a force exerted by the vehicle to be tested on the air based on the air flow velocity distribution and the relative static pressure distribution;

[0008] The vehicle drag coefficient corresponding to the vehicle to be tested is obtained based on the force exerted by the vehicle to be tested on the air and the drag coefficient formula.

[0009] Optionally, the step of obtaining the air velocity distribution of a wake cross section at a preset distance from the rear of the vehicle to be tested and the relative static pressure distribution of the wake cross section relative to the nozzle of an automobile aerodynamic wind tunnel comprises:

[0010] Dividing the wake cross section into a plurality of grids according to a preset spacing;

[0011] Obtaining the relative static pressure at the center of each grid relative to the nozzle of the automobile aerodynamic wind tunnel to obtain the relative static pressure distribution;

[0012] The air flow velocity at the center of each grid in the rearward direction of the vehicle is obtained to obtain the air flow velocity distribution.

[0013] Optionally, obtaining the air flow velocity of each grid center in the rearward direction of the vehicle to obtain the air flow velocity distribution includes:

[0014] Obtaining the dynamic pressure at the center of each of the grids;

[0015] Based on each of the dynamic pressure and air flow rate calculation formulas, the air flow rate of each of the grid centers in the rearward direction of the vehicle is obtained;

[0016] Based on the air flow velocity magnitudes corresponding to all the grid centers, the air flow velocity distribution is obtained.

[0017] Optionally, it is characterized in that the obtaining the force exerted by the vehicle to be tested on the air based on the air flow velocity distribution and the relative static pressure distribution comprises:

[0018] Obtaining air density, distances between adjacent grid points on the wake cross section in the y-axis direction of the aerodynamic coordinate system, and distances between adjacent grid points in the z-axis direction of the aerodynamic coordinate system;

[0019] The air velocity distribution, the relative static pressure distribution, the air density, the distance between adjacent grid points on the wake cross section in the y-axis direction of the aerodynamic coordinate system, and the distance in the z-axis direction of the aerodynamic coordinate system are substituted into the calculation formula of the force exerted by the vehicle to be tested on the air to obtain the force exerted by the vehicle to be tested on the air.

[0020] Optionally, obtaining the vehicle drag coefficient corresponding to the vehicle to be tested based on the force exerted by the vehicle to be tested on the air and the drag coefficient formula includes:

[0021] Determine the reaction force of the test vehicle on the force of the air to obtain the vehicle air resistance;

[0022] The vehicle drag coefficient is obtained according to the vehicle air resistance and the drag coefficient calculation formula.

[0023] Optionally, the process of determining the wake cross section includes:

[0024] An aerodynamic coordinate system is established with the midpoint of the centerline of the front wheel of the vehicle to be tested as the origin, the rearward direction of the vehicle as the positive direction of the x-axis, the rightward direction of the vehicle as the positive direction of the y-axis, and the upward direction of the vehicle as the positive direction of the z-axis;

[0025] In the aerodynamic coordinate system, a section whose distance from the rear of the vehicle to be tested is a preset distance, whose normal is the positive direction of the x-axis, whose boundary in the y-axis direction is a first distance range, and whose boundary in the z-axis direction is a second distance range is determined as the wake cross section.

[0026] A vehicle drag coefficient testing device, comprising:

[0027] An acquisition unit, used to acquire the air velocity distribution of the wake cross section at a preset distance from the rear of the vehicle to be tested and the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel;

[0028] a force determination unit, configured to obtain a force exerted by the vehicle to be tested on the air based on the air flow velocity distribution and the relative static pressure distribution;

[0029] The vehicle drag coefficient determination unit is used to obtain the vehicle drag coefficient corresponding to the vehicle to be tested based on the force exerted by the vehicle to be tested on the air and the drag coefficient formula.

[0030] A control device, comprising: a memory and a processor;

[0031] The memory is used to store at least one instruction;

[0032] The processor is used to execute the at least one instruction to implement the vehicle drag coefficient testing method described above.

[0033] A vehicle drag coefficient test system, comprising: an automobile aerodynamic wind tunnel mobile test frame, a pressure test device, a wind speed test device and the control device described above;

[0034] The pressure testing device is arranged on the automobile aerodynamic wind tunnel mobile test frame, and is used to obtain the static pressure of each grid center divided on the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel by moving on the automobile aerodynamic wind tunnel mobile test frame, so as to obtain the relative static pressure distribution of the wake cross section;

[0035] The wind speed test device is arranged on the automobile aerodynamic wind tunnel mobile test frame, and is used to obtain the air flow velocity of each grid center in the rearward direction of the vehicle by moving on the automobile aerodynamic wind tunnel mobile test frame, and obtain the air flow velocity distribution of the wake cross section;

[0036] The control device is respectively connected to the automobile aerodynamic wind tunnel mobile test frame, the pressure testing device and the wind speed testing device, and is used to control the automobile aerodynamic wind tunnel mobile test frame to move to the wake cross section and obtain the relative static pressure distribution and the air flow velocity distribution.

[0037] Preferably, the pressure testing device comprises: a pressure scanning valve;

[0038] The wind speed testing device comprises: any one of a hot wire anemometer, a laser anemometer, a particle image anemometer, and an anemometer consisting of the pressure scanning valve and a porous probe.

[0039] As can be seen from the above technical solutions, the present invention discloses a vehicle drag coefficient test method and related devices, which obtain the air velocity distribution of the wake cross section at a preset distance from the rear of the vehicle to be tested and the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel, obtain the force of the vehicle to be tested on the air based on the air velocity distribution and the relative static pressure distribution, and obtain the vehicle drag coefficient corresponding to the vehicle to be tested based on the force of the vehicle to be tested on the air and the drag coefficient formula. In the present application, the air velocity distribution of the wake cross section includes multiple air velocity test quantities, and the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel includes multiple static pressure difference test quantities, which is equivalent to decomposing a single test quantity in the traditional solution into the sum of multiple test quantities. Since the present application can perform more accurate measurements for each test quantity, the present application can greatly improve the test resolution of the vehicle drag coefficient compared with the traditional single test quantity. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the disclosed drawings without paying creative work.

[0041] Figure 1 A flow chart of a vehicle drag coefficient testing method disclosed in an embodiment of the present invention;

[0042] Figure 2 A schematic diagram of a wake cross section with a normal direction being the positive direction of the x-axis disclosed in an embodiment of the present invention;

[0043] Figure 3 A schematic diagram of grid division of a wake flow cross section disclosed in an embodiment of the present invention;

[0044] Figure 4 A flow chart of a method for obtaining the air flow velocity of each grid center in the rearward direction of the vehicle to obtain the air flow velocity distribution disclosed in an embodiment of the present invention;

[0045] Figure 5 A schematic diagram of the structure of a vehicle drag coefficient testing device disclosed in an embodiment of the present invention;

[0046] Figure 6 A schematic diagram of the structure of a control device disclosed in an embodiment of the present invention;

[0047] Figure 7 The present invention is a schematic structural diagram of a vehicle drag coefficient testing system disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] The embodiment of the present invention discloses a vehicle drag coefficient test method and related device, which obtains the air velocity distribution of the wake cross section at a preset distance from the rear of the vehicle to be tested and the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel, obtains the force of the vehicle to be tested on the air based on the air velocity distribution and the relative static pressure distribution, and obtains the vehicle drag coefficient corresponding to the vehicle to be tested based on the force of the vehicle to be tested on the air and the drag coefficient formula. In the present application, the air velocity distribution of the wake cross section includes multiple air velocity test quantities, and the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel includes multiple static pressure difference test quantities, which is equivalent to decomposing a single test quantity in the traditional scheme into the sum of multiple test quantities. Since the present application can perform more accurate measurements for each test quantity, the present application can greatly improve the test resolution of the vehicle drag coefficient compared with the traditional single test quantity.

[0050] See also Figure 1 , a flow chart of a vehicle drag coefficient testing method disclosed in an embodiment of the present invention, the method comprising:

[0051] Step S101, obtaining the air velocity distribution of the wake cross section at a preset distance from the rear of the vehicle to be tested and the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel.

[0052] Wake refers to the air or fluid disturbance formed behind a vehicle when it is moving.

[0053] The wake cross section refers to the cross section of the wake at a specific position or plane, which reflects the shape, size, velocity distribution and other characteristics of the wake at that position. The wake cross section in this application refers to the wake cross section at a preset distance from the rear of the vehicle to be tested, where the value of the preset distance is determined according to actual needs.

[0054] The study found that the flow velocity in the x-direction on the wake section needs to be greater than -5m / s, otherwise it will affect the accuracy of the test results. Based on this, the preset distance between the wake section and the rear of the vehicle can be limited to more than 0.5m; at the same time, in order to reduce the impact of the ground, the wake section is required to be more than 1m away from the end of the central moving belt of the wind tunnel ground. Based on this, the preset distance between the wake section and the rear of the vehicle can be limited to no more than 2m. Therefore, the optimal value of the preset distance can be a value in the range of 0.5m~2m, and the preferred preset distance is 1.5m.

[0055] The air velocity distribution in this application refers to the distribution of air velocity on the wake cross section during the flow process. That is, the air velocity distribution includes multiple air velocity test quantities. In practical applications, the air velocity distribution may be affected by many factors, including the shape of the vehicle to be tested, the state of motion, the characteristics of the fluid, and environmental conditions.

[0056] The automotive aerodynamic wind tunnel is a large-scale experimental facility designed specifically for automotive aerodynamic research. It uses artificial airflow to create an area of ​​uniform airflow in the pipe to simulate the air flow characteristics encountered by the car when driving on the actual road. The automotive aerodynamic wind tunnel is mainly composed of a tunnel, a drive system and a measurement and control system. The tunnel is a pipe that produces artificial airflow, and its shape and size are designed according to the experimental requirements. The drive system is used to provide power for the airflow so that the airflow forms a uniform flow in the tunnel. The measurement and control system is used to monitor and control the airflow velocity, temperature, humidity and other parameters to ensure the accuracy and reliability of the experiment.

[0057] The automobile aerodynamic wind tunnel nozzle is located at the exit of the wind tunnel. Its main function is to adjust and control the velocity, direction and flow of the airflow to simulate the air flow characteristics encountered when the car is driving on the actual road. By adjusting the size and shape of the nozzle, the velocity distribution and turbulence of the airflow can be changed to meet different experimental needs.

[0058] In the present application, the relative static pressure distribution of the wake cross section relative to the automobile aerodynamic wind tunnel nozzle includes multiple static pressure difference test quantities, each static pressure difference test quantity being the static pressure difference of the grid center on the wake cross section relative to the automobile aerodynamic wind tunnel nozzle.

[0059] The relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel can reflect the characteristics of the airflow at the rear of the automobile. By measuring the relative static pressure at the wake cross section, we can understand how the airflow is distributed at the rear of the automobile, including key parameters such as the airflow speed, direction and turbulence.

[0060] In practical applications, after determining the location of the wake section according to the rear position of the vehicle to be tested, the automobile aerodynamic wind tunnel mobile test frame is moved to the wake section. The automobile aerodynamic wind tunnel mobile test frame can be used to obtain the air velocity distribution of the wake section and the relative static pressure distribution of the wake section relative to the automobile aerodynamic wind tunnel nozzle.

[0061] Step S102: Obtaining the force exerted by the vehicle to be tested on the air based on the air flow velocity distribution and the relative static pressure distribution.

[0062] The air velocity distribution reflects the distribution of air velocity in the wake cross section during the flow process. The relative static pressure distribution reflects the characteristics of the airflow at the rear of the car. The combined air velocity distribution and relative static pressure distribution can determine the force exerted by the vehicle under test on the air, that is, the various forces generated when the vehicle under test interacts with the air during driving.

[0063] Step S103: obtaining the vehicle drag coefficient corresponding to the vehicle to be tested based on the force exerted by the vehicle to be tested on the air and the drag coefficient formula.

[0064] In practical applications, according to Newton's third law, the force exerted by the vehicle to be tested on the air and the force exerted by the air on the vehicle to be tested (that is, the vehicle's air resistance) are in the relationship of action and reaction. Therefore, the vehicle's air resistance can be determined based on the force exerted by the vehicle to be tested on the air, and then the vehicle's air resistance can be substituted into the drag coefficient formula to obtain the vehicle's drag coefficient corresponding to the vehicle to be tested.

[0065] In summary, the present application discloses a vehicle drag coefficient test method, which obtains the air velocity distribution of the wake cross section at a preset distance from the rear of the vehicle to be tested and the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel, obtains the force of the vehicle to be tested on the air based on the air velocity distribution and the relative static pressure distribution, and obtains the vehicle drag coefficient corresponding to the vehicle to be tested based on the force of the vehicle to be tested on the air and the drag coefficient formula. In the present application, the air velocity distribution of the wake cross section includes multiple air velocity test quantities, and the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel includes multiple static pressure difference test quantities, which is equivalent to decomposing a single test quantity in the traditional scheme into the sum of multiple test quantities. Since the present application can perform more accurate measurements for each test quantity, the present application can greatly improve the test resolution of the vehicle drag coefficient compared to the traditional single test quantity.

[0066] It should be noted that in the traditional solution, when the force measuring balance is used to test a single physical quantity, the force test resolution is the test resolution of the vehicle's drag coefficient. The force test resolution obtained by existing technical means can only reach 0.4N, and the corresponding test resolution of the vehicle's drag coefficient is 0.2 counts. In this way, the optimization scheme with an effect lower than 0.2 counts will not be recognized, resulting in a low test resolution of the vehicle's drag coefficient. To solve this problem, this application decomposes a single test quantity into the sum of multiple test quantities. Since this application can perform more accurate measurements on each test quantity, compared with the traditional single test quantity, this application can greatly improve the test resolution of the vehicle's drag coefficient. After verification, this application can increase the test resolution of the vehicle's drag coefficient to within 0.01 counts.

[0067] In one embodiment, step S101 may specifically include:

[0068] (1) Divide the wake cross section into multiple grids according to the preset spacing.

[0069] The value of the preset spacing is determined according to actual needs, for example, the preset spacing is 0.1m.

[0070] In practical applications, the wake cross section in the present application may be a cross section with a normal direction of +x in an aerodynamic coordinate system, that is, the wake cross section is a cross section in the positive direction of the x-axis.

[0071] Assumptions, see Figure 2 The normal direction is the schematic diagram of the wake cross section in the positive direction of the x-axis. The wake cross section is 1.5m away from the rear of the vehicle to be tested. In the aerodynamic coordinate system, the y-direction boundary is -1.2m to 1.2m, and the z-direction boundary is 0.2m to 2m from the ground. With a preset spacing of 0.1m, the wake cross section is divided into 24*18=432 grids, such as Figure 3 shown.

[0072] Research has found that the y-direction boundary needs to be 2m away from the wind tunnel nozzle boundary. Usually, the wind tunnel nozzle is 7 meters wide, so the y-direction range is not recommended to be greater than 3m. At the same time, to ensure that the impact of the vehicle can be covered, the y-direction range needs to be greater than the vehicle width, that is, it needs to be greater than 2m. Based on this, the y-direction boundary in this application is preferably -1.2m to 1.2m.

[0073] The z-direction boundary also needs to be 2m away from the wind tunnel nozzle boundary. Usually the wind tunnel nozzle is 4 meters high. Based on this, the z-direction boundary is preferably at most 2m away from the ground. According to the requirement that the porous probe needs to be at least 0.2m away from the ground for measurement, this application prefers that the z-direction boundary is at least 0.2m away from the ground.

[0074] (2) Obtain the relative static pressure at the center of each grid relative to the nozzle of the automobile aerodynamic wind tunnel to obtain the relative static pressure distribution.

[0075] In practical applications, the automobile aerodynamic wind tunnel mobile test frame can be moved to the wake section, and the static pressure of each grid center relative to the automobile aerodynamic wind tunnel nozzle can be measured using a pressure testing device arranged on the automobile aerodynamic wind tunnel mobile test frame.

[0076] The pressure testing device can be moved on the automobile aerodynamic wind tunnel moving frame under the control of the control device to measure the relative static pressure of each grid center relative to the automobile aerodynamic wind tunnel nozzle one by one.

[0077] Preferably, the pressure test device can be a pressure scanning valve, which can directly measure the relative static pressure of each grid center relative to the nozzle of the automobile aerodynamic wind tunnel. When the relative static pressure of all grid centers on the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel is measured, the relative static pressure distribution of the wake cross section can be obtained.

[0078] (3) Obtain the air flow velocity at the center of each grid in the rearward direction of the vehicle to obtain the air flow velocity distribution.

[0079] In practical applications, when the automobile aerodynamic wind tunnel mobile test frame moves to the wake section, the wind speed test device set on the automobile aerodynamic wind tunnel mobile test frame can be used to measure the air flow velocity of each grid center in the rear direction of the vehicle.

[0080] The wind speed testing device may be a hot wire anemometer, a laser velocimeter, a PIV (Particle Image Velocimetry) device, or a wind speed testing device composed of a pressure scanning valve and a porous probe.

[0081] In practical applications, hot wire anemometers, laser anemometers, and PIV devices can directly measure the air velocity at the center of each grid in the rearward direction of the vehicle. When the wind speed test device is composed of a pressure scanning valve and a multi-hole probe, it is necessary to first measure the dynamic pressure at the center of each grid, and then convert the dynamic pressure into the corresponding air velocity.

[0082] Specifically, in one embodiment, when the wind speed test device is composed of a pressure scanning valve and a multi-hole probe (preferably a five-hole probe), see Figure 4 , a flow chart of a method for obtaining the air flow velocity size of each grid center in the rearward direction of the vehicle to obtain the air flow velocity distribution is disclosed in an embodiment of the present invention, the method comprising:

[0083] Step S201: Obtain the dynamic pressure at the center of each grid.

[0084] Pressure Scanning Valve (PSV) is a sensor for measuring aerodynamic forces. It is mainly used for measuring dynamic pressure in industrial fields such as aircraft, automobiles and rockets. Its working principle is to measure the gas flow through an annular pipe through an array of pressure sensors. These sensors can capture the pressure difference generated when the fluid flows through the annular pipe, including dynamic pressure and static pressure. Dynamic pressure is the pressure drop caused by the change in airflow velocity, which is proportional to the square of the airflow velocity and directly reflects the magnitude of the airflow kinetic energy. Static pressure refers to the pressure generated when the gas is not disturbed by the flow conditions. By measuring these two pressures, the pressure scanning valve can calculate parameters such as fluid velocity, density and pressure distribution.

[0085] When measuring the dynamic pressure at the center of each grid on the wake cross section, the pressure scanning valve can monitor the changes of multiple pressure points simultaneously and continuously, thus providing comprehensive flow field information.

[0086] Multi-hole probes (such as five-hole probes) are precision measuring devices commonly used in fluid mechanics testing. They accurately obtain airflow pressure distribution information at different spatial locations by arranging multiple small holes (usually five) on the probe. These small holes are used to measure the static pressure and total pressure (including static pressure and dynamic pressure) of the fluid.

[0087] During the measurement process, the five-hole probe is placed perpendicular to the fluid flow direction to ensure accurate perception of pressure changes at each point. The center hole is usually used to measure the total pressure of the fluid, while the four side holes are used to measure the static pressure value of the relatively static fluid. By comparing the pressure values ​​measured by the center hole and the side holes, the velocity vector at a certain point in front of the probe and parameters such as turbulence intensity can be calculated.

[0088] When the pressure scanning valve and the multi-hole probe are used together to measure the dynamic pressure at the center of each grid on the wake cross section, the advantages of both can be fully utilized. The pressure scanning valve can provide comprehensive flow field information, including the dynamic changes of multiple pressure points; while the multi-hole probe can accurately measure the static pressure and total pressure at a specific location, thereby calculating key parameters such as flow velocity. By combining the measurement results of the two, the dynamic pressure distribution and flow velocity changes on the wake cross section can be understood more accurately.

[0089] Step S202: Based on each of the dynamic pressure and air flow rate calculation formulas, obtain the air flow rate of each of the grid centers in the rearward direction of the vehicle.

[0090] The air velocity calculation formula is as follows:

[0091] ;

[0092] In the formula, Indicates the air velocity at the center of each grid in the rearward direction of the vehicle. represents the dynamic pressure at the center of each grid, Indicates the air density.

[0093] Step S203: obtaining air flow velocity distribution based on the air flow velocity corresponding to all the grid centers.

[0094] After determining the air velocity magnitude corresponding to each grid center in the wake cross section, the air velocity magnitudes corresponding to all grid centers can constitute the air velocity distribution of the wake cross section.

[0095] In summary, the air velocity distribution of the wake cross section of the present application includes multiple air velocity test quantities. The present application can perform more accurate measurements on each air velocity test quantity. Therefore, compared with the traditional single test quantity, the present application can greatly improve the test resolution of the vehicle drag coefficient.

[0096] In one embodiment, step S102 may specifically include:

[0097] (1) Obtain the air density, the distance between adjacent grid points on the wake cross section in the y-axis direction of the aerodynamic coordinate system, and the distance between adjacent grid points in the z-axis direction of the aerodynamic coordinate system.

[0098] (2) Substitute the air velocity distribution, the relative static pressure distribution, the air density, the distance between adjacent grid points on the wake cross section in the y-axis direction of the aerodynamic coordinate system, and the distance between adjacent grid points in the z-axis direction of the aerodynamic coordinate system into the calculation formula of the force exerted by the vehicle to be tested on the air to obtain the force exerted by the vehicle to be tested on the air.

[0099] Specifically, the force exerted by the vehicle to be tested on the air The calculation formula is as follows:

[0100] ;

[0101] In the formula, represents the air density, -L represents the minimum coordinate value of all grids on the wake cross section in the y-axis direction of the aerodynamic coordinate system, +L represents the maximum coordinate value of all grids on the wake cross section in the y-axis direction, H represents the maximum coordinate value of all grids on the wake cross section in the z-axis direction of the aerodynamic coordinate system, H0 represents the minimum coordinate value of all grids on the wake cross section in the z-axis direction of the aerodynamic coordinate system, It represents the static pressure at the nozzle of the automobile aerodynamic wind tunnel. represents the static pressure at the center of each grid on the wake cross section, represents the air flow velocity, It represents the air velocity in the +x direction at the center of the grid with coordinates (y,z) on the wake cross section. represents the distance between adjacent grid points on the wake cross section in the y-axis direction, represents the distance between adjacent grid points on the wake cross section in the z-axis direction of the aerodynamic coordinate system, It represents the static pressure difference of each grid center with coordinates (y, z) relative to the nozzle of the aerodynamic wind tunnel of the automobile.

[0102] by Figure 2 and Figure 3 For example, the force exerted by the vehicle on the air to be tested In the calculation formula, the reference values ​​are: L=1.15m, H=1.75m, dL= dH=0.1m.

[0103] In one embodiment, step S103 may specifically include:

[0104] (1) Determine the reaction force of the test vehicle on the air and obtain the vehicle's air resistance.

[0105] According to Newton's third law, the vehicle air resistance is the reaction force of the force exerted by the vehicle to be tested on the air.

[0106] Therefore, the expression for the vehicle's air resistance is as follows:

[0107] ;

[0108] In the formula, is the air resistance of the vehicle, Represents the force exerted by the vehicle under test on the air.

[0109] (2) Obtaining the vehicle drag coefficient according to the vehicle air resistance and the drag coefficient calculation formula.

[0110] The expression of vehicle drag coefficient is as follows:

[0111] ;

[0112] In the formula, Represents the vehicle's drag coefficient, represents the air density, represents the air flow velocity, It represents the frontal area of ​​the vehicle. The frontal area of ​​the vehicle is related to the model of the vehicle to be tested. After the model of the vehicle to be tested is determined, the corresponding frontal area of ​​the vehicle is also determined accordingly.

[0113] In one embodiment, the present application also discloses a process for determining the wake cross section, which specifically includes:

[0114] (1) Establish an aerodynamic coordinate system with the midpoint of the front wheel centerline of the vehicle to be tested as the origin, the vehicle's rearward direction as the positive x-axis, the vehicle's rightward direction as the positive y-axis, and the vehicle's upward direction as the positive z-axis.

[0115] The aerodynamic coordinate system is a reference frame used to describe and analyze the aerodynamic forces and related characteristics of objects (such as cars, aircraft, etc.) in air flow. The purpose of the aerodynamic coordinate system is to facilitate the mathematical description and analysis of the motion state of objects in the air.

[0116] In this embodiment, an aerodynamic coordinate system is established with the midpoint of the centerline of the front wheel of the vehicle to be tested as the origin, the rearward direction of the vehicle, that is, the direction from the front to the rear of the vehicle as the positive direction of the x-axis, the rightward direction of the vehicle as the positive direction of the y-axis, and the upward direction of the vehicle as the positive direction of the z-axis, so that the wake cross section can be meshed in the aerodynamic coordinate system later.

[0117] (2) In the aerodynamic coordinate system, a section whose distance from the rear of the vehicle to be tested is a preset distance, whose normal is the positive direction of the x-axis, whose boundary in the y-axis direction is a first distance range, and whose boundary in the z-axis direction is a second distance range is determined as the wake cross section.

[0118] The value of the first distance range of the boundary in the y-axis direction is determined according to actual needs, for example Figure 3 The first distance range is [-1.2m, 1.2m], and the value of the second distance range of the z-axis boundary is determined according to actual needs, for example Figure 3 The second distance range is [0.2m, 2m].

[0119] Corresponding to the above method embodiment, the present invention also discloses a vehicle drag coefficient testing device.

[0120] See also Figure 5 , a schematic diagram of the structure of a vehicle drag coefficient testing device disclosed in an embodiment of the present invention, the device may include:

[0121] The acquisition unit 301 is used to acquire the air velocity distribution of the wake cross section at a preset distance from the rear of the vehicle to be tested and the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel.

[0122] The wake cross section refers to the cross section of the wake at a specific position or plane, which reflects the shape, size, velocity distribution and other characteristics of the wake at that position. The wake cross section in this application refers to the wake cross section at a preset distance from the rear of the vehicle to be tested, wherein the value of the preset distance is determined according to actual needs, for example, the value of the preset distance can be a value in the range of 0.5m~2m, and the preferred preset distance is 1.5m.

[0123] In the present application, the relative static pressure distribution of the wake cross section relative to the automobile aerodynamic wind tunnel nozzle includes multiple static pressure difference test quantities, each static pressure difference test quantity being the static pressure difference of the grid center on the wake cross section relative to the automobile aerodynamic wind tunnel nozzle.

[0124] The relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel can reflect the characteristics of the airflow at the rear of the automobile. By measuring the relative static pressure at the wake cross section, we can understand how the airflow is distributed at the rear of the automobile, including key parameters such as the airflow speed, direction and turbulence.

[0125] In practical applications, after determining the location of the wake section according to the rear position of the vehicle to be tested, the automobile aerodynamic wind tunnel mobile test frame is moved to the wake section. The automobile aerodynamic wind tunnel mobile test frame can be used to obtain the air velocity distribution of the wake section and the relative static pressure distribution of the wake section relative to the automobile aerodynamic wind tunnel nozzle.

[0126] The force determination unit 302 is used to obtain the force of the vehicle to be tested on the air based on the air flow velocity distribution and the relative static pressure distribution.

[0127] The air velocity distribution reflects the distribution of air velocity in the wake cross section during the flow process. The relative static pressure distribution reflects the characteristics of the airflow at the rear of the car. The combined air velocity distribution and relative static pressure distribution can determine the force exerted by the vehicle under test on the air, that is, the various forces generated when the vehicle under test interacts with the air during driving.

[0128] The vehicle drag coefficient determination unit 303 is used to obtain the vehicle drag coefficient corresponding to the vehicle to be tested based on the force exerted by the vehicle to be tested on the air and the drag coefficient formula.

[0129] In practical applications, according to Newton's third law, the force exerted by the vehicle to be tested on the air and the force exerted by the air on the vehicle to be tested (that is, the vehicle's air resistance) are in the relationship of action and reaction. Therefore, the vehicle's air resistance can be determined based on the force exerted by the vehicle to be tested on the air, and then the vehicle's air resistance can be substituted into the drag coefficient formula to obtain the vehicle's drag coefficient corresponding to the vehicle to be tested.

[0130] In summary, the present application discloses a vehicle drag coefficient test device, which obtains the air velocity distribution of the wake cross section at a preset distance from the rear of the vehicle to be tested and the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel, obtains the force of the vehicle to be tested on the air based on the air velocity distribution and the relative static pressure distribution, and obtains the vehicle drag coefficient corresponding to the vehicle to be tested based on the force of the vehicle to be tested on the air and the drag coefficient formula. In the present application, the air velocity distribution of the wake cross section includes multiple air velocity test quantities, and the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel includes multiple static pressure difference test quantities, which is equivalent to decomposing a single test quantity in the traditional scheme into the sum of multiple test quantities. Since the present application can perform more accurate measurements for each test quantity, the present application can greatly improve the test resolution of the vehicle drag coefficient compared with the traditional single test quantity.

[0131] In one embodiment, the acquisition unit 301 may specifically include:

[0132] The grid division subunit is used to divide the wake cross section into multiple grids according to a preset spacing.

[0133] The value of the preset spacing is determined according to actual needs, for example, the preset spacing is 0.1m.

[0134] In practical applications, the wake cross section in the present application may be a cross section with a normal direction of +x in an aerodynamic coordinate system, that is, the wake cross section is a cross section in the positive direction of the x-axis.

[0135] The static pressure distribution determination subunit is used to obtain the relative static pressure of each grid center relative to the automobile aerodynamic wind tunnel nozzle to obtain the relative static pressure distribution.

[0136] The air velocity distribution determination subunit is used to obtain the air velocity size of each grid center in the rearward direction of the vehicle to obtain the air velocity distribution.

[0137] In one embodiment, the air velocity distribution determination subunit is specifically used for:

[0138] Obtaining the dynamic pressure at the center of each of the grids;

[0139] Based on each of the dynamic pressure and air flow rate calculation formulas, the air flow rate of each of the grid centers in the rearward direction of the vehicle is obtained;

[0140] Based on the air flow velocity magnitudes corresponding to all the grid centers, the air flow velocity distribution is obtained.

[0141] In one embodiment, the force determination unit 302 may be specifically used to:

[0142] Obtaining air density, a distance between adjacent grid points on the wake cross section in the y-axis direction of the aerodynamic coordinate system, and a distance between adjacent grid points in the z-axis direction of the aerodynamic coordinate system;

[0143] The air velocity distribution, the relative static pressure distribution, the air density, the distance between adjacent grid points on the wake cross section in the y-axis direction of the aerodynamic coordinate system, and the distance in the z-axis direction of the aerodynamic coordinate system are substituted into the calculation formula of the force exerted by the vehicle to be tested on the air to obtain the force exerted by the vehicle to be tested on the air.

[0144] Among them, the force exerted by the vehicle to be tested on the air The calculation formula is as follows:

[0145] ;

[0146] In the formula, represents the air density, -L represents the minimum coordinate value of all grids on the wake cross section in the y-axis direction of the aerodynamic coordinate system, +L represents the maximum coordinate value of all grids on the wake cross section in the y-axis direction, H represents the maximum coordinate value of all grids on the wake cross section in the z-axis direction of the aerodynamic coordinate system, H0 represents the minimum coordinate value of all grids on the wake cross section in the z-axis direction of the aerodynamic coordinate system, It represents the static pressure at the nozzle of the automobile aerodynamic wind tunnel. represents the static pressure at the center of each grid on the wake cross section, represents the air flow velocity, It represents the air velocity in the +x direction at the center of the grid with coordinates (y,z) on the wake cross section. represents the distance between adjacent grid points on the wake cross section in the y-axis direction, represents the distance between adjacent grid points on the wake cross section in the z-axis direction of the aerodynamic coordinate system, It represents the static pressure difference of each grid center with coordinates (y, z) relative to the nozzle of the aerodynamic wind tunnel of the automobile.

[0147] In one embodiment, the vehicle drag coefficient determination unit 303 may be specifically used for:

[0148] Determine the reaction force of the test vehicle on the force of the air to obtain the vehicle air resistance;

[0149] The vehicle drag coefficient is obtained according to the vehicle air resistance and the drag coefficient calculation formula.

[0150] In one embodiment, the vehicle drag coefficient test may further include:

[0151] The wake cross section determination unit is used to determine the wake cross section.

[0152] The wake cross section determination unit can be specifically used for:

[0153] An aerodynamic coordinate system is established with the midpoint of the centerline of the front wheel of the vehicle to be tested as the origin, the rearward direction of the vehicle as the positive direction of the x-axis, the rightward direction of the vehicle as the positive direction of the y-axis, and the upward direction of the vehicle as the positive direction of the z-axis;

[0154] In the aerodynamic coordinate system, a section whose distance from the rear of the vehicle to be tested is a preset distance, whose normal is the positive direction of the x-axis, whose boundary in the y-axis direction is a first distance range, and whose boundary in the z-axis direction is a second distance range is determined as the wake cross section.

[0155] It should be noted that, for the specific working principles of each component in the device embodiment, please refer to the corresponding part of the method embodiment, which will not be repeated here.

[0156] Corresponding to the above embodiment, Figure 6 As shown, the present invention also provides a structural schematic diagram of a control device, and the control device may include: a processor 1 and a memory 2;

[0157] The processor 1 and the memory 2 communicate with each other via a communication bus 3;

[0158] Processor 1, configured to execute at least one instruction;

[0159] Memory 2, used to store at least one instruction;

[0160] The processor 1 may be a central processing unit (CPU), or an application specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the embodiments of the present invention.

[0161] The memory 2 may include a high-speed RAM memory, and may also include a non-volatile memory (non-volatile memory), such as at least one disk memory.

[0162] The processor executes at least one instruction to implement the steps shown in the embodiment of the vehicle drag coefficient testing method.

[0163] Corresponding to the above embodiment, see Figure 7 , a schematic diagram of the structure of a vehicle drag coefficient testing system disclosed in an embodiment of the present invention, the vehicle drag coefficient testing system may include:

[0164] Automobile aerodynamic wind tunnel mobile test frame 401, pressure test device 402, wind speed test device 403 and Figure 6 The control device 404 in the illustrated embodiment.

[0165] Preferably, the pressure testing device 402 can pressure scan the valve.

[0166] The wind speed testing device 403 may be a hot wire anemometer, a laser anemometer, a PIV device, or a speed measuring device composed of a pressure scanning valve and a multi-hole probe.

[0167] The pressure testing device 402 is arranged on the automobile aerodynamic wind tunnel mobile test frame 401, and is used to obtain the static pressure of each grid center divided on the wake cross section relative to the automobile aerodynamic wind tunnel nozzle by moving on the automobile aerodynamic wind tunnel mobile test frame 401, so as to obtain the relative static pressure distribution of the wake cross section.

[0168] The wind speed testing device 403 is arranged on the automobile aerodynamic wind tunnel mobile test frame 401, and is used to obtain the air flow velocity of each grid center in the rear direction of the vehicle by moving on the automobile aerodynamic wind tunnel mobile test frame 401, and obtain the air flow velocity distribution of the wake cross section.

[0169] The control device 404 is respectively connected to the automobile aerodynamic wind tunnel mobile test frame 401, the pressure testing device 402 and the wind speed testing device 403, and is used to control the automobile aerodynamic wind tunnel mobile test frame 401 to move to the wake section and obtain the relative static pressure distribution and the air flow velocity distribution.

[0170] In practical applications, after determining the wake cross section, the control device 404 divides the wake cross section into multiple grids according to a preset spacing, controls the automobile aerodynamic wind tunnel mobile test frame 401 to move to the wake cross section, controls the pressure test device 402 to move on the automobile aerodynamic wind tunnel mobile test frame 401, obtains the static pressure of each grid center relative to the automobile aerodynamic wind tunnel nozzle one by one, and finally obtains the relative static pressure distribution of the wake cross section. The control device 404 controls the wind speed test device 403 to move on the automobile aerodynamic wind tunnel mobile test frame 401, obtains the air flow velocity of each grid center in the rear direction of the vehicle one by one, and finally obtains the air flow velocity distribution of the wake cross section. The control device 404 obtains the force of the vehicle to be tested on the air based on the air flow velocity distribution and the relative static pressure distribution, and then obtains the vehicle drag coefficient corresponding to the vehicle to be tested based on the force of the vehicle to be tested on the air and the drag coefficient formula.

[0171] In summary, the present invention discloses a vehicle drag coefficient testing system, comprising: an automobile aerodynamic wind tunnel mobile test frame 401, a pressure testing device 402, a wind speed testing device 403 and a control device 404. Since the air flow velocity distribution of the wake cross section in the present application includes multiple air flow velocity test quantities, the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel includes multiple static pressure difference test quantities, which is equivalent to decomposing a single test quantity in the traditional scheme into the sum of multiple test quantities. Since the present application can perform more accurate measurements on each test quantity, therefore, compared with the traditional single test quantity, the present application can greatly improve the test resolution of the vehicle drag coefficient.

[0172] In addition, compared with the traditional solution where the force balance is complex, bulky, not easy to carry, requires a special pit, is greatly affected by the environment, and must maintain a constant temperature and humidity, making it difficult for the automotive aerodynamic wind tunnel to simultaneously conduct thermal environment-related tests, the pressure testing device 402 and wind speed testing device 403 that replace the force balance in the present application are relatively lightweight, can be transported and compared between different automotive aerodynamic wind tunnels, and have low environmental requirements, making them suitable for thermal environment-related tests in wind tunnels.

[0173] Furthermore, compared with the traditional solution in which there are large systematic errors between different force balances, and because the force balance is large and cannot be moved over long distances, resulting in the inability to conduct comparative tests between different wind tunnels based on the same set of force balances, the pressure testing device 402 and the wind speed testing device 403 that replace the force balances in the present application are relatively light and easy to move, and comparative tests between different wind tunnels based on the same set of equipment can be achieved, thereby ensuring the consistency of the test results.

[0174] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0175] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0176] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A vehicle drag coefficient testing method, characterized in that: include: Obtaining the air velocity distribution of the wake cross section at a preset distance from the rear of the vehicle to be tested and the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel; Obtaining a force exerted by the vehicle to be tested on the air based on the air flow velocity distribution and the relative static pressure distribution; The vehicle drag coefficient corresponding to the vehicle to be tested is obtained based on the force exerted by the vehicle to be tested on the air and the drag coefficient formula.

2. The vehicle drag coefficient testing method according to claim 1, characterized in that: The step of obtaining the air velocity distribution of the wake cross section at a preset distance from the rear of the vehicle to be tested and the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel comprises: Dividing the wake cross section into a plurality of grids according to a preset spacing; Obtaining the relative static pressure at the center of each grid relative to the nozzle of the automobile aerodynamic wind tunnel to obtain the relative static pressure distribution; The air flow velocity magnitude at the center of each grid in the rearward direction of the vehicle is obtained to obtain the air flow velocity distribution.

3. The vehicle drag coefficient testing method according to claim 2, characterized in that: The step of obtaining the air flow velocity of each grid center in the rearward direction of the vehicle to obtain the air flow velocity distribution includes: Obtaining the dynamic pressure at the center of each of the grids; Based on each of the dynamic pressure and air flow rate calculation formulas, the air flow rate of each of the grid centers in the rearward direction of the vehicle is obtained; Based on the air flow velocity magnitudes corresponding to all the grid centers, the air flow velocity distribution is obtained.

4. The vehicle drag coefficient testing method according to any one of claims 1 to 3, characterized in that: The step of obtaining the force exerted by the vehicle to be tested on the air based on the air flow velocity distribution and the relative static pressure distribution includes: Obtaining air density, a distance between adjacent grid points on the wake cross section in the y-axis direction of the aerodynamic coordinate system, and a distance between adjacent grid points in the z-axis direction of the aerodynamic coordinate system; The air velocity distribution, the relative static pressure distribution, the air density, the distance between adjacent grid points on the wake cross section in the y-axis direction of the aerodynamic coordinate system, and the distance in the z-axis direction of the aerodynamic coordinate system are substituted into the calculation formula of the force exerted by the vehicle to be tested on the air to obtain the force exerted by the vehicle to be tested on the air.

5. The vehicle drag coefficient testing method according to claim 1, characterized in that: The method of obtaining the vehicle drag coefficient corresponding to the vehicle to be tested based on the force exerted by the vehicle to be tested on the air and the drag coefficient formula includes: Determine the reaction force of the test vehicle on the force of air to obtain the vehicle air resistance; The vehicle drag coefficient is obtained according to the vehicle air resistance and the drag coefficient calculation formula.

6. The vehicle drag coefficient testing method according to claim 1 or 5, characterized in that: The process of determining the wake cross section includes: An aerodynamic coordinate system is established with the midpoint of the centerline of the front wheel of the vehicle to be tested as the origin, the rearward direction of the vehicle as the positive direction of the x-axis, the rightward direction of the vehicle as the positive direction of the y-axis, and the upward direction of the vehicle as the positive direction of the z-axis; In the aerodynamic coordinate system, a section whose distance from the rear of the vehicle to be tested is a preset distance, whose normal is the positive direction of the x-axis, whose boundary in the y-axis direction is a first distance range, and whose boundary in the z-axis direction is a second distance range is determined as the wake cross section.

7. A vehicle drag coefficient testing device, characterized in that: include: An acquisition unit, used to acquire the air velocity distribution of the wake cross section at a preset distance from the rear of the vehicle to be tested and the relative static pressure distribution of the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel; a force determination unit, configured to obtain a force exerted by the vehicle to be tested on the air based on the air flow velocity distribution and the relative static pressure distribution; The vehicle drag coefficient determination unit is used to obtain the vehicle drag coefficient corresponding to the vehicle to be tested based on the force exerted by the vehicle to be tested on the air and the drag coefficient formula.

8. A control device, characterized in that: The control device comprises: a memory and a processor; The memory is used to store at least one instruction; The processor is used to execute the at least one instruction to implement the vehicle drag coefficient testing method as described in any one of claims 1 to 6.

9. A vehicle drag coefficient testing system, characterized in that: include: Automobile aerodynamic wind tunnel mobile test frame, pressure test device, wind speed test device and the control device as claimed in claim 8; The pressure testing device is arranged on the automobile aerodynamic wind tunnel mobile test frame, and is used to obtain the static pressure of each grid center divided on the wake cross section relative to the nozzle of the automobile aerodynamic wind tunnel by moving on the automobile aerodynamic wind tunnel mobile test frame, so as to obtain the relative static pressure distribution of the wake cross section; The wind speed test device is arranged on the automobile aerodynamic wind tunnel mobile test frame, and is used to obtain the air flow velocity of each grid center in the rearward direction of the vehicle by moving on the automobile aerodynamic wind tunnel mobile test frame, and obtain the air flow velocity distribution of the wake cross section; The control device is respectively connected to the automobile aerodynamic wind tunnel mobile test frame, the pressure testing device and the wind speed testing device, and is used to control the automobile aerodynamic wind tunnel mobile test frame to move to the wake cross section and obtain the relative static pressure distribution and the air flow velocity distribution.

10. The vehicle drag coefficient testing system according to claim 9, characterized in that: The pressure testing device comprises: a pressure scanning valve; The wind speed testing device comprises: any one of a hot wire anemometer, a laser anemometer, a particle image anemometer, and an anemometer consisting of the pressure scanning valve and a porous probe.

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