RU242599U1 - VERTICAL WIND TUNNEL FOR VEHICLE WIND TESTING - Google Patents

Abstract

The utility model relates to the field of automotive engineering, in particular to testing of vehicles (TV), and can be used in determining the aerodynamic parameters of a vehicle, such as the drag force (Pb) and the aerodynamic drag coefficient (Cx). A vertical wind tunnel (VWT) for aerodynamic testing of a vehicle (TV) comprises a transparent vertical chamber, a pipeline connected to its lower part, a fan providing an air flow through the pipeline into the lower part of said vertical chamber, two guides located inside said vertical chamber along its entire length, a vertical suspension located in the center of said vertical chamber, intended for connecting the tested vehicle through an upper mount, and two pulleys configured to rotate freely with one end of an adjustable mass counterweight located outside said vertical chamber, as well as an elastic element of a given rigidity connected to the other end of said counterweight, configured to move relative to a device for measuring linear displacement. The utility model provides increased visibility and accuracy in determining air resistance using direct measurement.

Description

The field of technology to which the utility model belongs

The proposed utility model relates to the field of automotive engineering, in particular to testing of vehicles (V), and can be used in determining the aerodynamic parameters of V, such as the drag force (P _в ) and the aerodynamic drag coefficient (С _x ).

State of the art

A wind tunnel for testing vehicles is known, installed at the Dmitrov testing ground of NAMI, containing a horizontal measuring chamber in which the vehicle being tested is installed, vehicle mounts to a support, sensors for determining the air resistance force acting on the vehicle, fans that create a powerful air flow simulating the movement of the vehicle at high speed (see A.M. Ivanov et al. Textbook "Testing of Wheeled Vehicles", Moscow, MADI, 2018, pp. 69-70).

The well-known wind tunnel has the following disadvantages:

- very high power of fans to create the required air flow to determine the drag force P _in ;

- the air resistance force P _in is determined not by direct measurements, but by data from sensors installed in the vehicle's mounts to the support, which record the force tending to move the vehicle under the action of the oncoming air flow.

This occurs for the following reason. The air resistance force _P (along the X-axis) is a component of the total aerodynamic force. It is applied to the center of the windage—the center of the frontal area—and is determined by the following expression:

where С _Х is the aerodynamic drag coefficient along the X axis;

ρ _in – air density (1.22 kg/ ^m3 under normal atmospheric conditions: temperature - 15°C, pressure - 760 mm Hg, relative air humidity - 50%);

F – frontal area, i.e. the area of the frontal projection of the vehicle;

V – air flow velocity around the vehicle (m/s).

Approximately, the frontal area of passenger cars and trucks does not exceed 2-5 ^m2 , the aerodynamic drag coefficient C _x for trucks is approximately 1, for passenger cars it is about 0.2-0.4.

If we use these data to calculate the air resistance force P _b at a speed of 30 m/s (108 km/h), we obtain P b _of no more than 500 N for a passenger car and 2700 N for a truck. The force of gravity (G _a ) for a typical unladen passenger car is approximately 10,000-15,000 N, while for a truck it is 50,000-150,000 N. In other words, at this speed, the force of gravity is several times greater than the force of air resistance. Therefore, the weight of the vehicle on the support is much greater than the force tending to move it. As a result, obtaining accurate data from the sensors is very difficult, and the air pressure on the vehicle must be increased to obtain higher values of air resistance (a schematic representation of a well-known wind tunnel is shown in Fig. 1).

For example, at a speed of 50 m/s (180 km/h): P _b = 1200 N for a passenger car, P _b = 7500 N for a truck.

However, even by increasing the airflow power and indirectly obtaining the air resistance force, it is very difficult to accurately calculate small changes in the aerodynamic drag coefficient _Cx . For modern vehicles, especially passenger cars, even a 0.01 change in _Cx yields significant fuel savings and an increase in traction and speed performance, but the change in _Pb at an airflow speed of 50 m/s is only 10-15 N, which is very difficult to determine given the very large mass of the vehicle itself.

Also known are vertical wind tunnels (hereinafter referred to as VAT) for parachutists and simulating long jumps (see, for example, RU 2693106 C1, RU 162175 U1, RU 2435624 C1).

A distinctive feature of the known VATs is that the objects in them are in free fall on a rising air flow, in conditions close to natural ones.

The disadvantages of such VATs are:

- very high power of fans pumping air from below to support heavy objects in free flight (the average weight of an adult is 80-100 kg or approximately 800-1000 N);

- free movement of the object inside the pipe, which makes it impossible to determine the aerodynamic parameters.

The above mentioned shortcomings lead, in turn, to:

- too much energy expenditure on testing to determine the aerodynamic parameters of the vehicle;

- the impossibility of determining the aerodynamic drag coefficient with high accuracy;

- lack of clarity of tests;

- the need to equip the wind tunnel with additional sensors.

However, additional equipment is required to visualize the tests.

A known VAT comprises a transparent vertical chamber, a pipeline connected to its lower portion, and a fan providing airflow through the pipeline into the lower portion of the vertical chamber (see RU 2394726 C2, IPC B64D 23/00, published 15.12.2006). This known VAT enables research on aircraft capable of taking off, i.e., maintaining them in a hovering state with visual demonstration of the results.

The known VAT is accepted as the closest analogue to the declared VAT.

The main disadvantages of the well-known VAI are the very high power required from the fans to maintain the test objects in the air in a hovering state and the difficulty in finding the air resistance force due to the presence of three degrees of freedom of the test object when it hovers in the vertical part of the VAT.

Disclosure of the essence of the utility model

The technical problem solved by the claimed utility model consists of creating a VAT that ensures a significant reduction in the air flow power during testing.

This achieves a technical result that consists of increasing the visibility and accuracy of determining the air resistance force using the direct measurement method, which is achieved by compensating for up to 99.99% of the mass of the object being studied and visualizing the movement under the action of this force.

The technical problem is solved, and the specified technical result is achieved as a result of creating a VAT for aerodynamic testing of a vehicle, containing a transparent vertical chamber, a pipeline connected to its lower part, and a fan that provides an air flow through the pipeline into the lower part of said vertical chamber, which is equipped with two guides located inside said vertical chamber along its entire length, a vertical suspension located in the center of said vertical chamber, intended for connecting the tested vehicle through an upper mount and two pulleys, made with the possibility of free rotation, with one of the ends of a counterweight adjustable by mass located outside of said vertical chamber, as well as an elastic element of a given rigidity, connected to the other end of said counterweight, made with the possibility of movement relative to a device for measuring linear displacement.

Brief description of the drawings

The claimed utility model is explained by graphic materials, where:

- Fig. 1 shows a schematic representation of a known horizontal wind tunnel for aerodynamic testing of vehicles, from the side;

- Fig. 2 shows a schematic representation of the declared VAT for aerodynamic testing of vehicles, in the initial state (without air supply), side view;

- Fig. 3 shows a schematic representation of the declared VAT for aerodynamic testing of the vehicle during testing (with air supply), side view.

Implementation of a utility model

The aerodynamic test apparatus for vehicles shown in Fig. 2 comprises a transparent vertical chamber 1, a pipeline 2 connected to its lower part, a fan 3 with a drive from a corresponding electric motor, providing air supply through the pipeline 2 into the lower part of the vertical chamber 1, two guides 4 located inside the vertical chamber 1 along its entire length, a vertical suspension 5 located in the center of the vertical chamber 1, intended for connecting the vehicle being tested through an upper mount 6 and two pulleys 7, made with the possibility of free rotation, with one of the ends of a counterweight 8, adjustable by weight, located outside the vertical chamber 1, as well as an elastic element 9 of a given rigidity, connected to the other end of the counterweight 8, made with the possibility of movement relative to the device for measuring linear displacement 10 (and, accordingly, movement of the indicator 11 associated with it).

The operation of the declared VAT is carried out as follows.

In the initial position (without air supply inside the VAT), the tested vehicle weighing G _a [N] is suspended (along guides 4 on vertical hanger 5) in the center of transparent vertical chamber 1 (see Fig. 2). Outside vertical chamber 1, the same hanger 5, thrown over upper mount 6 and two pulleys 7, is connected to one end of adjustable counterweight 8 weighing m _k [kg], i.e. weighing G _k = 9.81 _{m k} [N].

The difference between the weight of the vehicle and the weight of the counterweight 8 is:

Δ = G _a – G _k

Under the action of this difference, the elastic element 9, connected to the other end of the counterweight 8, will stretch to a length l = Δ/C _p [m], where C _p is the rigidity of the elastic element [N/m].

The rigidity of the elastic element 9 is selected depending on Δ in such a way that the movement of the pointer 11 is sufficiently large and informative, and the change in its position is recorded even at small values of P _in .

The pointer 11 records the displacement l under the action of the difference in the weights of the vehicle and the counterweight 8 on the device for measuring linear displacement 10.

By selecting the counterweight 8 mass, it is possible to compensate for up to 99.99% of the test vehicle's mass. For example, from a 1000 kg vehicle mass, Δ = 100 N, or approximately 10.2 kg, can be retained. With the elastic element 9 having a stiffness of C _n = 100 N/m, the resulting displacement of pointer 11 relative to linear displacement measuring device 10 is l = 1 m.

Fan 3 creates an air flow supplied to the lower part of vertical chamber 1. After fan 3 is turned on and air is supplied through pipeline 2 to the lower part of vertical transparent chamber 1, the air flow resistance force acting from below on the tested vehicle is obtained, which can be replaced by the resultant air resistance force P _in [N] (see Fig. 3). Guides 4 ensure the movement of the vehicle under the action of P _in along them.

As shown earlier, P _in depends on the frontal area raised to the first power and the squared wind speed, while the aerodynamic drag coefficient C _x of a passenger vehicle is approximately 0.2-0.25, and the frontal area is approximately 2-3 m ² .

If we take as an example a TS with an area of 2 ^m2 and C _x = 0.2, then at a wind speed of 15 m/s (a completely achievable result with a low-power fan (5-10 kW)) we get P _b = 54.9 N.

In this case, the force P _in acts against the weight of the vehicle G _a and, consequently, will reduce the tensile force of the elastic element 9, which will be reflected in the displacement of the pointer 11 relative to the device for measuring the linear displacement 10; it will take a new position: l' = (Δ-P _in )/C _n = 0.45 m. And it will be possible to very accurately determine P _in by measuring l and l':

R _in = (l-l')⋅С _п

In contrast to the declared VAT, in the wind tunnel, adopted as the closest analogue, fans with a capacity of several thousand kW are used to create a significant air resistance force.

As a result of the implementation of the claimed utility model, if we change C _x of the tested vehicle by 0.01, with the same air flow parameters, the change in the air resistance force P _in will be 2.7 N, that is, the displacement of the pointer 11 along the device for measuring the linear displacement 10 will be 2.7 cm, which is quite clear and easy to measure.

The use of the declared VAT with the ability to compensate for up to 99.99% of the mass of the vehicle being tested allows for a clear and accurate determination of air resistance and the aerodynamic drag coefficient, down to 0.01, at low fan powers, which significantly simplifies and reduces the cost of conducting aerodynamic tests of vehicles.

Claims (1)

A device for aerodynamic testing of a vehicle in a vertical wind tunnel, comprising two guides located inside the wind tunnel along its entire length, a vertical suspension located in the center of the wind tunnel, designed to connect the test vehicle through an upper mount with two pulleys designed with the possibility of free rotation with one end of a counterweight located outside the vertical wind tunnel, which, in turn, is connected at the other end to an elastic element designed with the possibility of movement relative to the device for measuring linear displacement.