Numerical Analysis of the Tunnel-Train-Air Interaction Problem in a Tunnel with a Double-Hat Oblique Hood

The tunnel-train-air interaction problem is investigated by using a numerical method able to provide relevant information about pressure fluctuations,aerodynamic drag characteristics and the“piston wind”effect.The method relies on a RNG k-εtwo-equation turbulence model.It is shown that although reducing the oblique slope can alleviate the pressure gradient resulting from initial compression waves at the tunnel entrance,the pressure fluctuations in the tunnel are barely affected;however,a large reduction of micro-pressure wave amplitudes is found outside the tunnel.In comparison to the case where no tunnel hood is present,the amplitudes of micro-pressure waves at 40 m from the tunnel reach an acceptable range.The aerodynamic drag of the head and tail fluctuates greatly while that of the intermediate region undergoes only limited variations when the high-speed train passes through the double-hat oblique tunnel.It is shown that the effects of the oblique slope of the portal on the aerodynamic drag can almost be ignored while the train speed plays an important role.

Cooling System Design Optimization of an Enclosed PM Traction Motor for Subway Propulsion Systems

This paper presents the design optimization of a self-circulated ventilation system for an enclosed permanent magnet(PM)traction motor utilized in the propulsion systems for subway trains.In order to analyze accurately the machine's inherent cooling capacity when the train is running,the ambient airflow and the related heat transfer coefficient(HTC)are numerically investigated considering synchronously the bogie installation structure.The machine is preliminary cooled with air ducts set on the motor shell,and the fluidic-thermal field distributions with only the shell air duct cooling are numerically calculated.During simulations,the HTC obtained in the former steps is applied to the external surface of the machine to model the inherent cooling characteristic caused by the train movement.To reduce the temperature rise and thus guarantee the motor's working reliability,an internal self-circulated air cooling system is proposed according to the machine temperature distribution.The air enclosed in the end-caps is driven by the blades mounted on both sides of the rotor core and forms two air circuits to bring the excessive power losses generated in the heating components to cool regions.The fluid flow and temperature rise distributions of the cooling system's structural parameters are further improved by the Taguchi method in order to confirm the efficacy of the internal air cooling system.

The Feature of Weak Shock Wave Propagated in a Overlong Tunnel

Many experiment researches have been developed before. But most of them were carried out with the condition that the tunnel’s ratio of length and diameter (x/D) is under 1000. Recently, the process that compression wave convents into shock wave in the overlong tunnel has also been paid attention. In this paper, features of shock wave as it propagates through a overlong tunnel is investigated, rupturing thin films at the entrance to obtain three kinds of shock wave with different intensities. Then study their features respectively during they propagates through a overlong tunnel with x/D over 6000 at most. Comprehend shock wave more deeply by comparing the results of experiments.

Effects of Optimized Operating Parameters on Combustion Characteristics and NO_(x)Emissions of a Burner based on Orthogonal Analysis

To optimize the structure of the burner,improve the combustion performance,and reduce the emission of NO_(x),a self-circulating low NO_(x)combustion technology was used to design a new type of flue gas self-circulating low NO_(x)burner.Based on previous research on the numerical model of combustion and the composition of mixed gas on combustion and NO_(x)emissions,the effect of various factors on the ejection coefficient of the flue gas self-circulating structure was analyzed using the orthogonal test method,and the burner operating parameters,such as preheating temperature and excess air coefficient,were deeply studied through the three-dimensional finite element numerical model in this paper.The results show that the diameter ratio of the nozzle and the length of the cylindrical section of the flue gas self-circulating structure have great influence on its ejection and mixing ability.The optimal ejection coefficient was 0.4829.Overall,the amount of NO_(x)emissions greatly increased from 6.23×10^(-6)(volume fraction)at the preheating temperature 973 K to 3.5×10^(-3)at preheating temperature 1573 K.When the excess air coefficient decreased from 1.2 to 1,the maximum combustion temperature decreased from 2036.3 K to 1954.22 K,and the NO_(x)emissions decreased from 352.29×10^(-6)to 159.73×10^(-6).