RESEARCH ON THE AERODYNAMICS OF HIGH-SPEED TRAINS

ABSTRACT

In this article, the impact of high-speed electric train “Afrasiab” on the transfer of freight trains at the Stations of JSC “Uzbek Railways” is defined as a topical issue. In particular, in order to increase the tourist attractiveness of our country, to provide modern transport services to passengers, the expansion of the scale of the future “Afrosiab” high-speed electropoiesis flights, as well as the study of the interaction of these trains in conditions of increasing flow of cargo on Railways, has been identified as an extremely important issue of ensuring the As a result of this study, the possibilities of carrying cargo trains in one direction or in the opposite direction are determined by ensuring the safety of movement on two-way parcels in which high-speed “Afrasiab” high-speed electric trains travel. This makes it possible to develop recommendations for more effective use of the ability of parcels to conduct trains.

АННОТАЦИЯ

В данной статье в качестве актуального вопроса определено влияние скоростного электропоезда “Афросиёб” на процесс пропуска грузовых поездов на участках АО “Ўзбекистон темир йўллари”. В условиях дальнейшего расширения масштабов движения скоростных электропоездов "Афросиёб" в целях повышения туристической привлекательности нашей страны, оказания современных услуг пассажирам, а также дальнейшего роста объемов грузовых перевозок на железных дорогах, изучение взаимного аэродинамического воздействия этих поездов в процессе движения, считается важнейшим вопросом обеспечения безопасности перевозок. Результатом данного исследования является определение возможности движения грузовых поездов в одном направлении или в противоположном направлении при обеспечениим безопасности движения на двухпутных участках, по которым курсируют высокоскоростные электропоезда “Афросиёб”. Это дает возможность выработать рекомендации по более эффективному использованию пропускной способности участков.

Keywords: Section, passenger train, capacity, Afrasiab electric train, high speed, aerodynamic forces.

Ключевые слова: Участок, пассажирский поезд, вместимость, Афросиёб электропоезд, высокая скорость, аэродинамические силы.

Introduction. At present, modern technologies with all-round conveniences are used in the Republic for the purpose of passenger transportation and quality service. In particular, in November 2009, Spain's Patentes Talgo S.L. Under the agreement signed between the company and Uzbekistan Railways, two high-speed electric trains Talgo 250 were delivered. In order to organize the movement of these trains, by March 2011 the railway section from Tashkent to Samarkand was completely reconstructed, in particular, the technical structure of modern signaling devices and contact networks of about 600 km was improved;

4 metal bridges with a length of 400 meters were built, providing a speed of up to 200 km / h; The existing 409 artificial structures and 154 bridges on the Tashkent-Samarkand section were reconsidered, new guarded crossings and stations were reconstructed [2, 12, 18, 19]. 189 man-made structures were built on the site, including 148 culverts, 40 culverts and 1 tunnel with a length of 142 meters. [2, 12, 18, 19].

On August 26, 2011, the first walking test of the Afrosiyob electric train was carried out and it covered a distance of 344 km from Tashkent to Samarkand in 120 minutes and reached a maximum speed of 254 km / h on the section [2, 12, 18, 19].

On September 5, 2015, the Afrosiyob train was launched to Karshi and on September 15, 2016 to Bukhara [18, 19, 22].

In turn, the movement of high-speed passenger trains leads to a decrease in the capacity of freight trains on the section. For example, the capacity of a freight train on a one-track section not equipped with an auto-blocking system can be increased to 6-7 pairs of trains per day, and an increase in the speed of passenger trains from 160 km / h to 250 km / h leads to an average 7.1% increase in train displacement. [9, 10, 11, 13]. This leads to inefficient maintenance of freight trains and an increase in many technical and economic costs.

To date, modern, high-quality transportation services have been provided to about 1.5 million passengers on Afrosiyob trains. In order to further increase the tourist attractiveness of the country, it is planned to further expand the Afrosiyob train. This, in turn, requires the study of the aerodynamic effects of high-speed passenger train traffic on the environment, railway equipment and structures, the road structure on the adjacent track, as well as passengers.

The aerodynamic effect of high-speed Afrosiyob trains on the roadside object and passengers depends on their actual speed. Traffic speed is limited in accordance with the plan and profile of the roads, the structure of the sections in order to ensure traffic safety [12]. For example, the Afrosiyob train will reach a height of 155 meters in the Syrdarya region and 699 meters in the Jizzakh region on the Tashkent-Samarkand route [2, 18, 19].

Taking into account the above considerations, the limited speeds of the Afrosiyob train are set for each section [1, 18, 21]:

• Between Tashkent and Yangier stations - up to 160 km / h;
• Between Yangier and Jizzakh stations - up to 230 km / h;
• Between Jizzakh and Gallaorol stations - from 120 km / h to 160 km / h;
• Between Gallaorol and Bulungur stations - up to 200 km / h;
• Between Bulungur and Samarkand stations - up to 160 km / h;
• Between Samarkand and Karshi stations - up to 165 km / h;
• Between Samarkand and Navoi stations - up to 230 km / h;
• Between Navoi and Bukhara stations - up to 160 km / h;

Discussion. Let’s take a look at the airflows that form around a high-speed moving train and its key performance indicators. The main parameters that indicate the state of air include its temperature (Т), pressure (Р) and density (ρ). We use the Mendeleev-Clayperon equation to correlate these figures:

                                                                             (1)

Viscosity and compressibility are the main properties of air. It is known that the train cuts off the air as it moves. When the airflow at the beginning of the content is short, it gradually increases, creating a turbulent flow. The flow velocity profile near the surface has the following appearance (Figure 1):

Figure 1. Flow velocity profile near the surface

As a result of this effect of the layers, an experimental voltage τ occurs between them. This voltage depends on the product of the flow rate normally falling to the surface [3, 4, 5, 6]:

     ,                                                                        (2)

Where is µ- dynamic viscosity coefficient, [Па·c];

   - approaching flow rate, [m/h];

To find the coefficient of kinematic viscosity, it is sufficient to divide the coefficient of dynamic viscosity by the density of air:

 .                                                                               (3)

As the temperature increases, the speed of chaotic motion of air molecules also increases. This, in turn, leads to an increase in dynamic viscosity.

Another important feature of air is its ability to compress. The compressive capacity of the environment is the process of changing its volume under the influence of pressure. The speed of propagation of sound waves is called the speed of sound and is defined as follows [3, 5, 7, 8]:

                                                                              (4)

(2) Substituting formula (4) into the first-order product of pressure in density, we obtain the following equation:

                                                                         (5)

If we put in this formula the universal gas constant and the molecular masses of air,

                                                                      (6)

(6) the formula shows that the speed of sound in air is directly proportional to the temperature through the square root, if the air temperature increases the resistance of the air to compression increases and conversely the degree of compression increases with decreasing temperature. The Max number is used to measure the degree of compression of the air,as:

                                                                        (7)

Basic parameters of air in standard condition T_c= 288,15 K; P_c= 101300 Па; ρ_с= 1,225 кг/м³; a_c= 340,29 м/с; _с= 1,46·10^-5 м²/ we accept that [3, 6, 14, 15].

Previous studies [4, 5] have highlighted the expressions of aerodynamic force and pressure resulting from the movement of high-speed passenger trains, i.e.:

                                                        (8)

We determine the aerodynamic forces that occur under the influence of air flow from the following expression:

 ,                                                              (9)

Where is - aerodynamic coefficient of resistance (1,21,3);

S- projection of a body on a plane perpendicular to the direction of flow

 by equating formula (9) with  we create an equation, accordingly =  equality is appropriate. Instead of the generated expression = 1 and coefficient k = 0,052÷0.068 in the transverse direction, k= 0,029÷0,038 in the longitudinal direction, in the transverse direction , in the longitudinal direction  we find the aerodynamic impact force, pressure, and present the result in Table 1 [5, 8, 9, 20].

Table 1.

Calculation of aerodynamic pressure depending on train speed

The two components of aerodynamic force and pressure acting on a stationary vehicle on an adjacent road are transverse and longitudinal (Figure 2).

Results. Calculations show that when a high-speed train is traveling at 160 km / h, the force on the adjacent track is affected by a force of 73.6 Kn and 96 Kn at a speed of 180 km / h. It can be seen that the longitudinal component of this force is unable to move the movement structure standing on the adjacent road. But a wagon standing alone on an adjacent road could move [16, 17, 20].

Figure 2. Organizer of transverse and longitudinal aerodynamic forces

                                                                                     (10)

Where is:

F_a – the aerodynamic force acting on the moving structure on the adjacent road, Kn;

F_x, F_y, F_z - projection of aerodynamic force on the x, y, z axes, Kn;

φ – the angle between the aerodynamic force and the horizontal plane caused by the win.

Aerodynamic forces, as above, affect the rolling stock on the adjacent road and the roadside device structures. When calculating aerodynamic forces, pressures and safe distances (distance from the axis) affecting passengers standing, moving or standing on a platform on the side of the road, the pressure(Па), specified in sanitary norms, the distance from the object axis S(м) and the speed of the trainV (km/h) is expressed by the function.

Despite the scientific research of many scientists in this field, the above issue remains open. The solution to these problems will be to increase the capacity of the section to ensure train safety and eliminate the problem of freight trains on sections where high-speed passenger trains run. In solving the problem, we learn that the speed of a train depends on the speed and distance of the air flow, based on the sanitary norms of the pressure on the passenger standing on the platform and on the construction sites located on the side of the road.

According to the formula (8)-the wind speed at any point of the plane
(x, y, z) in space around the train:

.                                                                       (11)

(10) Based on the formula and the laws of hydromechanics, hydrogasodynamics, we find the safe distance as a result of solving the expressions (11-13), ie:

                                     (12)

We also write down the laws of gas state and mass conservation:

                                                            (13)

Where is: ,, - projections of the velocity vector on the x, y, z axes;

- pressure, - density, - temperature, - coefficient of dynamic viscosity of air [16, 17].

Through the above conclusions, we can determine and analyze the interaction aerodynamic forces and pressures of trains.

Conclusion. In the conditions of high-speed passenger trains in Uzbekistan, the organization of freight trains remains one of the most pressing issues. In particular, it is very important to substantiate the possibility of combining freight trains in the same direction and in the opposite direction with the train "Afrosiyob" on the designated two-way sections, ensuring traffic safety [13, 14]. In this case, it is necessary to create a mathematical program model for calculating the mutual aerodynamic forces and pressures of passenger-freight, freight-passenger, passenger-passenger trains, to obtain and analyze the results, or to achieve the result using existing programming languages [18, 19].

There is also a need to organize the movement of freight trains while improving the schedule of the train "Afrasiab", ie to re-determine the speed of certain trains without changing the total travel time on the section, to balance the speed of the section by increasing the speed on sections. In addition, there is a need to develop scientifically based proposals to improve train conduction and capacity by improving the technology of freight trains, taking full advantage of the existing opportunities on mixed sections of train traffic.

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