Research On The Long Tunnel And Tunnel Group's Aerodynamic Algorithm And Its Application

Both the pressure waves inside the tunnel and the microwaves at theexit, which are aroused by high speed trains running through the tunnel,will leave an adverse effect on the safety of train operation, theeconomical efficiency, passengers' comfort as well as the environmentsurrounding of the tunnel. Decreasing the tunnel aerodynamic problem isa technical key for the development of high-speed rails. So the worldwideresearch of tunnel aerodynamic is full swing. Our country will makegreat efforts to develop high speed special passenger line including largenumbers of long tunnels which are most slab track, in which a train canrun at a high speed. It is highly necessary to study the mechanism ofaerodynamic effect of long tunnel and tunnel group and the measures toreduce it deeply. Obtaining the change amplitude of airpressure andmicro-pressure quatificationally in all sorts of tunnels is very significant.This paper combined three dimensional compressible SIMPLEmethod and one dimensional characteristics method organically,proposed the one dimensional and three dimensional coupled calculationmethod which had taken both efficiency and accuracy into considerationand developed a corresponding software. And relying on a number of keyprojects by the Ministry of Railways, this paper carried out a series ofresearches on the aerodynamic effect of long tunnel and tunnel groupcombining with dynamic model and actual experiments(1) A new method had been proposed to solve the problem of tunnel aerodynamic effect: changes in pressure wave inside the tunnel would be solved through one dimensional characteristics method; the 3-D effect at the exit of tunnel would be solved through three dimensional compressible simple method; data switching faces for the two methods would be established on the place where the 3-D effect at the exit of tunnel could be ignored in order to make the data exchanges between one dimension and three dimensions.(2) A software named "TRAIN-TUNNEL " had been developed to correspond to the one dimensional and three dimensional coupled calculation method, some key technologies had been adopted in the software as follows: firstly, by the means of quadratic interpolation with several intercepted cross section's real area , the area parameter of the streamlined head had been got; secondly, by adopting linear impedance and porous model , the basic equation of the compression wave propagation considering the condition of slab and ballasted track had been established and the goal of solving the aerodynamic effect for tunnels with ballasted track or without achieved; thirdly, by using the method of local mesh mobile encryption and frequent update, the changing curve of train's surface pressure had been solved steadily.(3) The result out of numerical method and from the dynamic model and full-scale experiments had been compared and validated. And it showed that under corresponding condition, the pressure's curve on tunnel's wall, train's surface and micro air pressure at the exit of tunnel from each results matched well under corresponding condition, the amplitude differences from each other nearly below 5%, at the most of 10%, which indicated that the newly-developed method was right, with the computational accuracy meeting the requirement of technical application.(4) According to waves' propagation and superposition principle, the extreme amplitude point of the pressure changes inside the tunnel, when tunnel length was certain, had been deduced for the first time . It was when the train with common configuration length high-speed ran through the long tunnel, the extreme amplitude point was at L_d:This provided a theoretical basis for the selection of monitor point in full-scale test, model test and numerical simulation.(5) When the single train passed through the tunnel at high speed, the pressure variation rules inside tunnel and micro-air pressure at the exit of tunnel were as follows: the utmost pressure variation took place when the train ran though mid-long tunnel from 0.8 km to 1.5 km and the rain set's configuration length is 200 m, then the pressure decreased gradually as the tunnel length increased, there is a turning point of pressure change took place with the change of tunnel length, it related to he rain set's configuration length and the turning point's tunnel length decreased as the train's running speed development. The rules of micro-air pressure changing with tunnel length related to the type of plate road bed nearly. The micro-air pressure at the exit of tunnel with gravel ballast would decline as its length increased; and the micro-air pressure at the exit of tunnel with plate road bed would rise first and fall later, with the extreme amplitude point appearing when the tunnel length was between 4.0km and 8.0 km.(6) A certain tunnel length corresponded to a most dangerous train set's configuration length. The longer the tunnel is, the larger the corresponding most dangerous train set's length is, and the more noticeable the influence of the length on the inside tunnel's pressure variation is, but the train set's configuration length had no influence on micro-air pressure at the exit of tunnel.(7) When two trains met in the tunnel at the same speed, the variation of pressure on tunnel's wall and train's surface would not be simply intensified as the result of tunnel length increasing. The utmost pressure variation took place when the relationship between tunnel length,train set's configuration length and train's velocity reached the conditionthat M L_TU/L_TR = 0.21, 0.34 or 0.88. Morever, there would be two worst position for trains' crossing when two trains met in the tunnel at the same speed .One was positioned at 0.5L_TU and the other at 0.33L_TU.(8) The aerodynamic effect, which was caused by high-speed trains running through the tunnel group, had been studied also for the first time. The relationship within inside-tunnel air-pressure variation, the micro-air pressure at the exit of tunnel and the spacing between adjacent tunnels had been clarified. And tunnel group had been defined in the view of aerodynamics: tow adjacent tunnels which spacing distance is below 100m. As to long tunnel group which the total length of tow tunnels of tunnel group in series is below 9 km, tow tunnels could be connected when considering the elevation of micro-air pressure at the exit of tunnel.(9) As to the tunnel with plate road bed, when the train's operating speed, the tunnel length and the cross-sectional area were determined, both the two basic hood and various hood length corresponded to a best entrance hood area. Vice versa, there is a fixed best proportion between the both; On the basis of best match, the air pressure amplitude at the exit of tunnel couldn't be reduced significantly through increasing hood's cross section's area or structure's length individually...