ASHRAE OR-10-002-2010 Natural Ventilation in London Underground Sub-Surface Lines-Modelling for Normal Operations《伦敦地下次地表线路的自然通风 标准操作的建模》.pdf
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1、2010 ASHRAE 11ABSTRACTPlanned increases in train frequency and the use of airconditioned rolling stock on the London Underground Sub-Surface lines will increase the energy dissipated in the tunnelsand an assessment has been made of the potential impacts ofthis on tunnel temperatures. The Cooling the
2、 Tube Programmein London has been established to help manage thermal condi-tions on the network. An important early step is to identify thehot spots in the existing system, and predict the future envi-ronment in light of changes to train operations and expectedpassenger numbers. Aero-thermodynamic m
3、odelling of theindividual lines was considered to be essential in this process.This paper discusses the tunnel ventilation modelling ofthe southern portion of the sub-surface lines (District andCircle) during normal train operations. The line has severalnatural ventilation openings of various sizes
4、and orientations.The modelling is particularly challenging due to the bi-direc-tional nature of the tunnels. Important considerations whenbuilding datasets, modelling sensitivities, collecting and inter-preting temperature data, the effect of ground water migration,validation approaches and the perf
5、ormance of the model ispresented.INTRODUCTIONARUP has provided Cooling the Tube Programme (CTP)with tunnel ventilation modelling for the Sub-Surface Line(SSL) section of the London Underground. The modelincludes about 8.3 km (13.3 miles) of double-track Districtand Circle line tunnels and eleven sta
6、tions from west of SloaneSquare to east of Whitechapel Stations.London Undergrounds Circle line runs along the align-ment of the oldest underground railway in the world. Builtwith steam trains in mind, the tunnels have historically beenquite cool and well ventilated by the blow holes used to relieve
7、the steam. These blow holes now function as natural ventopenings to reduce tunnel temperatures.A Subway Environment Simulation (SES) model wasdeveloped for the existing trains and future upgraded rollingstock running on the southern portion of the SSL to estimatethermal conditions under normal and c
8、ongested operations.The model was validated by comparison to present dayconditions. The benchmarked model could then be applied tofuture train operations to estimate the air temperatures infuture, identify the warmer sections, and if needed, proposecooling measures to mitigate the high temperatures
9、encoun-tered.The simulations were aimed at predicting the peak airtemperatures at 5 P.M. peak operation on a relatively hot Julyafternoon in the selected portion of SSL.This paper presents selected key modelling issues relatingto the SSL and the specific techniques applied to tackle these.A validati
10、on or benchmarking process matching results totemperature monitoring data was used to tune these techniquesfor the current case. This gave more confidence in the predic-tions of the modelling for future train operations. The mainissues on the SSL are:Bi-directional tunnelsGround water movementFuture
11、 air-conditioned rolling stockThe paper discusses the benchmarking process andsome key sensitivities, but does not cover the modelling ofthe system upgrades except for the impact of air-condition-ing.Natural Ventilation in London Underground Sub-Surface LinesModelling for Normal OperationsJohn Alexa
12、nder Mohammad Tabarra, PhD, DIC, CEngMember ASHRAEJohn Alexander is an engineer and Mohammad Tabarra is an associate at ARUP, England.OR-10-002 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Par
13、t 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. 12 ASHRAE TransactionsMODELLING BI-DIRECTIONAL TUNNELSThe SSL is a double-track or bi-directional tunnel, serv-ing both the ea
14、stbound and westbound trains. This results incomplex patterns of airflows and pressure peaks as trains passeach other, and poses the difficulty of modelling a three-dimensional airflow field using a one dimensional model.Several approaches were investigated for the SSL.Any one dimensional network mo
15、del can be challenged inproviding accurate temperature predictions with bi-direc-tional tunnels, where the passing trains can cause a cancella-tion (partial or complete) of train piston effects, and generatelow or null flow regions in the tunnels of the model. Therunning of trains “like clockwork” i
16、n an SES model can resultin trains passing each other at exactly the same point for theduration of a simulation, creating an enduring low flow regionin which heat can build up. The heat transfer in a one dimen-sional model is based on bulk airflow movement, and will beminimal in low flow sections. I
17、n reality, turbulent eddies andchurning of the air by the passage of trains could give rise tomore heat transfer to the walls than would necessarily bepredicted by SES. The low blockage ratio of the trains in theSSL also contributes to low bulk airflow velocities. This limi-tation can cause numerica
18、l instabilities and/or result in artifi-cially high temperature predictions. This is not usually anissue for unidirectional tunnels where trains travel in onedirection and higher blockage ratios result in higher bulkairflow velocities and heat transfer.This effect was noted early on and steps were t
19、aken toavoid this from happening with the SSL model. Differentheadways or time delays were used for the eastbound andwestbound routes to compensate for piston effect cancellationand avoid trains repeatedly crossing at the same point in thesimulation.This method has been used with both weekly average
20、(long-term) train operations and peak (short-term) train oper-ations to ensure reasonable temperatures and avoid “hot spots”in the model. It should be noted that in SES 4.1 it is usual torun “long-term” simulations in which wall temperatures arecalculated with peak train operations. The default heat
21、 sinkattenuation factor of 0.5 accounts for off-peak operationsallowing an overall daily average of 50% of peak-hour heattransfer into the walls. In SES SI an improved approach isavailable. Long-term simulations are run with average trainoperations and a heat sink attenuation factor set to 1. Wallte
22、mperatures from this simulation are then fixed and used in ashort-term model with peak train operations. This allows heattransfer to be more accurately based on actual average trainoperations but also provides flexible inputting for futurechanges in both peak and off-peak operations.Several compensa
23、tion methods were identified and arediscussed below.Staggering MethodIn this method the simulation for the long-term walltemperature calculation is repeated several times and averaged.In each repetition, the starting time of the routes in one of thedirections, say westbound, is delayed by a fraction
24、 of the head-way. This is repeated until a full set of headways are coverede.g., 0 delay, 1/4, 1/2, and 3/4 headway delay. The resultingwall temperatures are averaged to smooth out any hot/coldspots. The method is repeated for the short-term air tempera-ture simulations to give the result.Unequal He
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