气动力 气动噪声

E-mail address:kimhd@andong.ac.kr(H.-D.Kim).0376-0421/02/$-see front matter r2002Elsevier Science Ltd.All rights reserved.PII:S0376-0421(02)00029-55.1.Wind tunneltest .....................................4825.2.Train-induced flows ...................................4835.3.Aerodynamic forces due to trains passing each other ..................4855.4.Cross-wind effects ....................................4886.Aeroacoustic problems of railway train ............................4886.1.Aerodynamic noise due to train .............................4886.2.Wind tunneltest .....................................4896.3.Reduction of aerodynamic noise .............................4907.Vibration of railway train ...................................4918.Aerodynamics of railway train/tunnel systems .........................4918.1.Aerodynamic analysis of train/tunnel systems ......................4918.2.Pressure wave due to the train entering into tunnel...................4938.3.Pressure variation and aerodynamic drag inside tunnel.................4938.4.Pressure variation inside train ..............................495R.S.Raghunathan et al./Progress in Aerospace Sciences 38(2002)469–5144701.IntroductionDuring the past60decades,a great dealof attention has been concentrated on the development of airplanes. Fluid dynamics,structural mechanics and automatic controlengineering have made l arge contributions to the present aerospace technologies.Of them,fluid dynamics mainly dealing with aerodynamic drag has played the most important role in the development of airplanes and flight vehicles.Relatively,there have been only a few studies of the full train system.This has been attributed to the fact that train has run at very low speeds along afixed track, compared with airplanes.Thus,aerodynamic problems on the train system could not have attracted much attention fromfluid dynamists.Recently,the train speed exceeded over300km/h,being nearly comparable with the past airplane speeds.Furthermore,the train system is playing much more roles in transport than the airplane.Systematic work is needed in the development of the train system.Aerodynamic and aeroacoustic problems accompa-nied by the speed-up of train system are,at present, receiving a considerable attention as practical engineer-ing issues that should be urgently resolved.With the speed-up of train,many engineering problems which have been reasonably neglected at low speeds,are being raised with regard to aerodynamic noise and vibrations, impulse forces occurring as two trains intersect each other,impulse wave at the exit of tunnel,ear discomfort of passengers inside train,etc.These are of major limiting factors to the speed-up of the train system. Such aerodynamic problems mentioned above are closely associated with theflows occurring around the railway train.However,much effort to speed up the train system has been paid,to date,on the improvement of electric motor power rather than understanding the flow physics around the train and therebyfinding a proper control method.This has led to larger energy losses and performance deterioration of the train,since theflows around train are more disturbed due to turbulence of the increased speed;consequently,the flow energies are being converted to aerodynamic drag, noise and vibrations.Now,many countries are operating the high-speed railway trains,such as German Inter City Express(ICE), Japanese Shinkansen and French Train de Grande Vitesse(TGV);moreover,some countries like South Korea and China are trying to construct the high-speed railway train.Systematic work is highly needed to understand the aerodynamics of high-speed railway train,and to improve the existing conventionalrail way trains and to develop a new generation of high-speed train(HST)system.This article deals with the aerodynamic phenomena with regard to the high-speed railway trains,with a view to understand practicalengineering probl ems of the present high-speed railway trains and with an emphasis on proper controlmethods for the aerodynamic problems.2.Speed-up tendency of train2.1.Requirement for the speed-up of trainSince1960s,the speed-up of transportation vehicles has been made with the timely requirements for a safe and bulk volume of transportation.This has led to the advent of a large tanker,a high-speed railway train,a jumbo jet,and a supersonic transportation(SST) vehicle.The speed-up of transportation engine always leads to the shortness of an economic distance asso-ciated with the shortness of time–distance,resulting in an increased value of time.The speed of a transportation vehicle should be determined from the point of view of the energy efficiency of the transportation.Fig.1shows Bouladon’s criterion for the speed of a transportation vehicle[1],in which the speed required for a transportation vehicle is given by a function of9.Impulse wave at the exit of tunnel (496)9.1.State-of-the-art of impulse wave (498)9.2.Theory of impulse wave (498)9.3.Slab and ballast track tunnels (500)9.4.Short and long tunnels (502)9.5.Control methodologies of impulse wave (503)9.5.1.Train body (503)9.5.2.Tunnelentrance (504)9.5.3.Inside tunnel (506)9.5.4.Tunnelexit (508)10.Concluding remarks (511)Acknowledgements (512)References (512)R.S.Raghunathan et al./Progress in Aerospace Sciences38(2002)469–514471distance.The solid line indicates the required speed according to the transportation distance,showing a generaltendency that the l onger the transportation distance,the higher the speed required.This line also indicates an increased gradient with time,thus leading to more increasing requirement for the speed-up of a transportation vehicle.An ideal speed required for transportation vehicle in the21st century is also indicated as the thick solid line.The present realizable speed to meet the speed-up requirement for a transpor-tation vehicle is also indicated in Fig.1.There are severalregions between the distance–speed curves of each transportation and the solid line,which are,at present,not able to meet the requirement for the speed of transportation.Region1indicates too long distance for walking,but too short distance for driving. Region2is between train and airplane.Region3 indicates the speed lack of subsonic airplane for inter-continentaltransportation.Region4indicates too l ong a distance for boat on sea,but too short a distance for airplane.To meet the speeds required for each region, new-generation traffic system,high-speed railway train, SST,and speedboat are under development,respec-tively.2.2.Transportation energy efficiencyIn general,energy efficiency of a transportation vehicle can be estimated based upon the fuel consump-tion used.In the case of cargo transport,the energy E necessary to carry unit weight per unit distance is expressed as[2]E¼consumed energyðkcalÞtransport capacityðtonÞÂtransport distanceðkmÞ:ð1ÞIn the case of passenger transport,Eq.(1)is changed toE¼consumed energyðkcalÞpersonðone personÞÂtransport distanceðkmÞ:ð2ÞMeanwhile,the efficiency of a transportation engine canbe obtained from the economic aspects of the fuelused:economic efficiency of fuel¼lower calorific value of fuelðkcal=gÞÂconsumption rate of fuelðg=hp hÞÂhorse powerðhpÞÂtimeðhÞpayloadðtonÞÂdistanceðkmÞ:ð3ÞFor a given lower calorific value and consumptionrate of fuel,Eq.(3)reduces toeconomic efficiency of fuelphorse powerÂtimepayloadÂdistance¼horse powerpayloadÂspeed¼H pW p V:ð4ÞThe economic efficiency of fuelused can be an indexindicating the transportation energy,and is,thus,expressed by an inverse of the transportation efficiency:transport efficiency pW p VH p¼W VH pW pW;ð5Þwhere W is the totalpayl oad,V the speed,and H p thehorse power.Using the equations above,Fig.2shows a comparisonbetween the transportation energies necessary to carryone person up to1km[2].For three different types ofvehicles,i.e.,train,bus and car,the number on the rightside indicates the transportation energy relative to thetrain,in which the transportation energy of the train isSpeed(km/h)Distance (km)Supersonic planeFig.1.Relationship between speed and distance required for transportation vehicle.R.S.Raghunathan et al./Progress in Aerospace Sciences38(2002)469–514472assumed to be 100kcal.It is found that the transporta-tion energy of a car amounts to 6times that of a train.F rom the economic point of view of the fuelused,Fig.3shows a comparison between each transportation engine [3].The solid line indicates the well-known Karman–Gabrielli’s limiting line (KG line).The KG line increases with the speed of transportation vehicle.It is noted that the economic efficiency of the fuelused in transportation engine is improved as the transportation vehicle approaches the KG line.Each transportation vehicle has different speed ranges.For instance,the boat is in the range below 50km/h,the ground vehicles are in between 50and 200km/h,the airplane in between 500and 800km/h.These speed ranges can be classified,depending on whether the vehicle is driven by the buoyancy force,the reaction force,or the lift force.The KG line indicates the lower limits of each speed range.For the range of the buoyancy force support,the energy consumption in low-speed ranges is comparatively low.However,with the speed-up of the boat,the transportation efficiency becomes remarkably low due to the increased wave drag on the boat.For instance,the value of P =ðW p V Þincreases up to severalhundred times as the boat speed increases from about 15knot (28.7km/h)to 30knot (55.6km/h),resulting in an extremely low transportation efficiency.Therefore,a hydrofoilboat or a hovercraft of the lift force support can be one of the alternatives for higher speeds.For the range of the reaction force support,the value of P =ðW p V Þis low in the mid of the speed ranges.For the speeds over this range,a high-speed railway train is recommended.In this case,the value of P =ðW p V Þis on an extended line for the existing conventionaltrain593kcalTrainBusAutomobileFig.2.Energies necessary to carry one person up to 1km.Speed(km/h)P /W V (k h /t o k m )p parison of each transportation.R.S.Raghunathan et al./Progress in Aerospace Sciences 38(2002)469–514473system.Further extension of this line approaches the Magnetic levitation(Maglev)train system.For the range of the lift force support,the value of P=ðW p VÞis, in general,dependent on the lift-drag ratio,being independent of the speed of the transportation vehicle.2.3.Limiting factors to the speed-upIn general,the transportation vehicle connecting from city to city is required to meet the following conditions: high-speed transportation,bulk volume transportation, safe and comfortable transportation with less air pollution and noise,highly reliable transportation with low cost and maintenance,etc.The high-speed railway train can be one of the alternatives to meet these requirements.Since1940s,many countries have tried to speed-up the conventionaltrain system.F ig.4shows the progress of the speed-up of train[4].Symbol J refers to the TGV in France,&the ICE in Germany,K the Shinkansen in Japan and’the HST in UK.It is found that in over a half century,the train speed has increased more than two fold.Major limiting factors to the speed-up of train result from many different sources.Technicalfactors are associated with train/railsystems,whil e geographical factors are related to the tunnel system.For instance,in Japan,the portion of the tunnel to the total railway line amounts to about60%,while in France it is at most severalper cent.ig.5shows the technicall imiting factors to the speed-up of train and associated factors. These factors are mainly associated with the train body, the track line,the electric devices around the track,etc. For instance,the train speed along a curved track is limited by the traveling performance,passenger’s comfort and safety,which are again associated with the train body and track line.Thus,to be able to increase the maximum speed of trains,it is necessary to take account of these limiting factors.3.Aerodynamic problems of railway trainFor the purpose of development of a faster and more safe train system with lower air pollution and noise, many researchers are paying much attention on the aerodynamics of high-speed railway train.These works have attention to the development of new-generation train body,railand tunnelsystems.The aerodynamic phenomena with regard to high-speed railway train are strongly dependent on the train speed.Thus,the aerodynamic problems become more important as the train speed increases.In general,the train aerodynamics are related to aerodynamic drag,pressure variations inside train, train-inducedflows,cross-wind effects,ground effects,pressure waves inside tunnel,impulse waves at the exit of tunnel,noise and vibration,etc.The aerodynamic drag is dependent on the cross-sectionalarea of train body,train length,shape of train fore-and after-bodies, surface roughness of train body,and geographical conditions around the traveling train.The train-induced flows can influence passengers on the platform and is also associated with the cross-sectional area of train body,train length,shape of train fore-and after-bodies, surface roughness of train body,etc.The pressure variations,occurring as two trains intersecting each other,are related to passenger’s comfort and safe traveling of train.These are dependentSpeed(km/h)YearFig.4.Progress of railwaytrain.Speed typeTrainHardwareLimiting factorsFoundation Elementsof Railway system Fig.5.Factors limiting the speed-up and related factors.R.S.Raghunathan et al./Progress in Aerospace Sciences38(2002)469–514 474on the shape of train fore-and after-bodies,train width, and the distance between track lines.The cross-wind can also influence the safe traveling of the train,relating to train height and perimeter,bridge system,etc.The impulse wave at the exit of tunnel influences the surrounding area around the train track and is dependent on the cross-sectionalarea of train body, the cross-sectionalarea of tunnel,the shape of train fore-and after-bodies,the tunnell ength,the kind of track,etc.The pressure variations influence the struc-turalstrength of the train body,passenger’s comfort, and are associated with the cross-sectionalarea of the train body,cross-sectional area of tunnel,train length, tunnel length,etc.Table1lists these major aerodynamic problems of HST and associated factors.All of these aerodynamic problems are closely related to the train shape,which is required to produce aerodynamically good characteristics.4.Aerodynamic forces on railway train4.1.Aerodynamic drag of trainThe aerodynamic characteristics of HST are quite different from those of airplane.There are many characteristic features in the aerodynamics of the high-speed railway train,in the points that the train length is, in general,very long,compared with the equivalent diameter of it,the train runs close to adjacent structures, passes through a confined tunnel,and intersecting with each other,the train runs along afixed railway track, always interacting with ground,and the train can be influenced by cross-winds.Thus,the aerodynamics, which has been applied to airplane,may not be of help for a detailed understanding of the HST aerodynamics.In general,a desirable train system should be aerodynamically stable and have low aerodynamic forces.These aerodynamic characteristics are closely associated with the aerodynamic drag of the running train.The aerodynamic drag on the traveling train is largely divided into mechanical and aerodynamic ones. Of both,the aerodynamic drag can influence the energy consumption of train.Thus,detailed understanding on the aerodynamic drag and its precise evaluation are of practicalimportance.It has been well known that the aerodynamic drag is proportionalto the square of speed,whil e the mechan-icaldrag is proportionalto the pared with the mechanicaldrag,the portion of the aerodynamic drag becomes larger as the train speed increases.Thus, reduction of the aerodynamic drag on high-speed railway train is one of the essential issues for the development of the desirable train system.In the open air without any cross-wind effects,the totaldrag on the travel ing train can be expressed by a sum of the aerodynamic and mechanicalones[5]:D¼D MþD A¼ðaþbVÞWþcV2;ð6Þwhere D A and D M are the aerodynamic and mechanical drags,respectively,a;b and c are the constants to be determined by the experiment,V the train speed and W the train weight.In Eq.(6),the mechanicaldrag,being proportional to the train weight,includes the sliding drag between rails and train wheels,and the rotating drag of the wheels.The measurement of the totaldrag on train and its precise prediction are not straightforward.The total drag can be obtained by using a deceleration speed of train or the consumed electric power,as will be described later.Fig.6shows a typical example of the measured totaldrag on train[5].Al lof the dataTable1Aerodynamic problems and their related mattersAerodynamic problems Related matters1Aerodynamic drag of train Maximum speed,energy consumption2Aerodynamic characteristics of train due to cross-winds Safety in strong cross-winds3Aerodynamic force due to passing-by of two trains Running stability,Quality of comfort for passengers4Winds induced by train Safety for passengers on platforms,Safety for maintenance workers5Pressure variations in tunnels Quality of comfort for passengers,(Ear discomfort)Airtightness of vehicle,Stress upon vehicle,Ventilating system of vehicle6Micro-pressure waves radiating from tunnelexit Environmentalprobl ems near tunnelexit 7Ventilation and heat transfer in underground station and tunnel Quality of comfort for passengers,Prevention of disaster(fire)8Aerodynamic noise Environmentalprobl emsR.S.Raghunathan et al./Progress in Aerospace Sciences38(2002)469–514475indicated refer to a given train with the same weight and length,and these collapse onto a single line,given by a curve fit,D ¼12:484þ0:04915þ0:001654V 2:In order to reasonably estimate the total drag on the trains with variable weight and length,it is necessary to divide it into the mechanicaland aerodynamic drags.For instance,the least-squares method can be used to correlate the data,and consequently the term propor-tionalto the square of speed can be considered as the aerodynamic drag.However,it is quite difficult to reasonably extract the aerodynamic drag from the total drag,since it can contain naturalwind effects,and additionally,it can depend on the methods of how to get the second-order polynomials for the correlation as well.4.2.Estimation of aerodynamic dragUnlike the aerodynamics of airplane,the train runs along a fixed track,strongly interacting with surround-ing structures,ground,tunnel,platform,etc.Especially,the presence of an intersecting train makes the analysis of the train aerodynamics extremely difficult.In order to speed up the train,it is necessary that the electric motor power increases or the aerodynamic drag pared with the open air traveling,the aerodynamic drag can considerably increase as the train passes through a tunnel[6].This is because the train-induced flows do work to increase the pressure by interacting with the tunnel walls.A pantograph system may produce the aerodynamic drag corresponding to that caused by one train.In particular,the structures underneath the train may produce more drag.In the open air traveling,the aerodynamic drag on train can be divided into two contributions;one is dependent on train length and the other is independent of it.The drag independent of the train length is the pressure drag caused by the fore-and after-bodies of train.It is not easy to estimate the drag dependent onthe train length.This is because the friction drag on the train body should involve all kinds of the drags occurring in the connecting parts between trains,photographs,the structures under the train,etc.In this case,the aerodynamic drag can be expressed as [7]D ¼12r A 0V 2C dp þl 0d 0c;ð7Þwhere V is the train speed,r the density of air,A 0thecross-sectionalarea of train,C dp the coefficient of the pressure drag caused by the fore-and after-bodies of train,d 0the hydraulic diameter of train,l the train length,and l 0the hydraulic friction coefficient caused by the connecting parts between trains,photographs,the structures under the train,etc.In general,a wind tunnel test for measuring the aerodynamic drag on train,which is quite long compared with the equivalent diameter,is highly difficult.The use of a small model for the train wind tunnel test causes several problems associated with lower Reynolds numbers.In addition,ground effects on the aerodynamic drag should be considered in the wind tunneltest.In Eq.(7)C dp can be obtained by wind tunnel ing the realtrain entering into the tunnel ,Hara [8]reported that l 0could be obtained by the pressure rise on the train body,when it enters into tunnel.A train entering into the tunnel compresses the atmospheric air ahead of the train and the resulting compression waves will propagate nearly at the speed of sound towards the exit of the tunnel.Meanwhile,the air displaced by the train entering into the tunnelwil ldischarge back from the entrance of tunnel.In this case,the air flow should overcome the frictional drag on the train body and tunnel walls,resulting in a pressure gradient.Due to this fact,the pressure on the train body will increase as the train proceeds into the tunnel,as schematically shown in Fig.7.The compression waves propagating along tunnel will discharge from the exit of the tunnel,consequently forming an impulse wave,as will be described later.At the same instant as the compression waves dischargeSpeed (km/h)T r a v e l i n g d r a g (N )Fig.6.Traveling drag on Shinkansen (series 100).p Fig.7.Flow model for friction coefficient.R.S.Raghunathan et al./Progress in Aerospace Sciences 38(2002)469–514476from the exit of the tunnel,expansion waves will be formed to meet the mass conservation law,and then propagate back from the exit of the tunneltowards the entrance of tunnel.In Hara’s analysis,it is assumed that the expansion waves do not interact with the train body inside tunneland the after-body of the train is stil lin the open air.In Fig.7,the momentum equation can be applied to the controlvol ume between the cross-sections2and3, as belowðp2Àp0ÞðAÀA0ÞÀf0ÀF¼0;ð8Þwhere p2is the pressure on the train body,p0the atmospheric pressure,A the cross-sectionalarea of tunnel,A0the cross-sectionalarea of train,f the frictionalforce on train body,and F the frictionalforce on tunnel walls.Eq.(8)can be changed to[8]ðp2Àp0Þð1ÀRÞ¼12r V2c Rl0dcþv2V2þldv2V2;ð9Þwhere R is the ratio of cross-sectionalareas of train to tunnel,l the distance from the entrance of tunnelto train,l the hydraulic friction coefficient on tunnel walls, l0the hydraulic friction coefficient on the train body,d the hydraulic diameter of tunnel,d0the hydraulic diameter of train,V the train speed and v2the airflow velocity occurring between train and tunnel walls.For a known value of v2=V;the hydraulic friction coefficient l0 on the train body can be obtained by measuring the pressure rise(p2Àp0)parison of the drags on different trainsThe aerodynamic drag measurement results[9],which were conducted using a wind tunneltest in F rance,are summarized in Table2,where each of the contributions of the train body(TGV),the connecting part between trains and the structures under the train on the aerodynamic drag are indicated.The wind tunneltest was carried out at a train speed of260km/h under standard atmospheric conditions.The totaldrag is al so presented on the right side of Table2.Of the totaldrag,the aerodynamic drag onl y on the train body is about80%,the aerodynamic drag due to the pantograph system and other devices over the train is17%,the rest drag of3%is due to the mechanical drag caused by the brake system,etc.From the measured data above,the totaltravel ing drag D on train is given by D¼AþBVþCV2;where the constants A and B are experimentally given by250 and3.256,respectively.Note that these values are5% and17.1%of the aerodynamic drag on only the train body,respectively.Figs.8and9present the aerodynamic drag on the Germany ICE[9].The type of the ICE,its cross-sectionalarea and aerodynamic drag are al so indicated in Fig.8.For example,the train of type a has a cross-sectionalarea of14.61m2and is assumed that its aerodynamic drag is100%.For the trains of different types and cross-sectionalareas,rel ative aerodynamic drag is given based on the train of type a.In the case of the train of type k,the cross-sectionalarea of the train is 11.39m2and the aerodynamic drag relative to the type aTable2Wind tunnelexperiment for the travel ing drag on TGVComponents of traveling drag Drag coefficient(151C,1013mbar)TotaldragDrag in260km/h Power in260km/h(kW)N/(km/h)2(%)N(%)Aerodynamic component Drag of train0.0459580310662.52243Equipments on trainroof0.009651765213.1471Totalaerodynamiccomponents0.0556097375875.62714Disk brake0.001703115 2.383Total0.05730100387377.92797Rolling drag(train407ton)BV¼3:256V84717.1612A¼250250 5.0181 Totaldrag D¼AþBVþCV24970100.03590R.S.Raghunathan et al./Progress in Aerospace Sciences38(2002)469–514477is 78%.In Fig.8,note that the trains of different cross-sectionalareas have a train body mount system and a skirt system to smooth the structures underneath the train.For the trains shown in Fig.8,each portion of thecontributions of the fore-and after-bodies of train,the connecting part between trains,the train wall surfaces,the pantograph system,etc.to the totalaerodynamic drag is given in Fig.9[9].In the case of type a ,it is found that the aerodynamic drag caused in the connecting part between trains is about 4%,the surface friction drag 23%,the fore-and after-bodies 8%,the pantograph system 7%,and the underneath structures of train 58%.For type f ;the totalaerodynamic drag is about 50%of that of type a ;and each of the portions is quite different from that of type a .For reference,all these data refer to the same train length (200m).In the case of Japanese Shinkansen,the 0series have been known as l 0¼0:018;and C dp ¼0:2[10,11].An empiricalequation to predict the aerodynamic drag on the traveling train is given by the following equation:D ¼ð1:2þ0:022V ÞW þð0:013þ0:00029c ÞV 2;ð10Þwhere D is the totaldrag (kg f ),V the train speed (km/h),W the totalweight of train (ton),and l the train length (m).The term that is proportionalto the square of speed is the aerodynamic drag.For l ¼400m,corresponding to the length of 16trains,about 90%of the aerodynamic drag is attributed to the friction drag on the middle part of the train.Of the Japanese Shinkansen,series 100has a semi-body mount system for the underneath structures,and series 200has an underneath coverage to prevent snow accumulation on the train body.Table 3lists some major parameters influencing on the aerodynamic drag [10,11].It is found that smoothing the under-neath structures of train by using the body mount system or the skirt system reduces the hydraulic friction coefficient.4.4.Pressure dragOf the aerodynamic drag components,the pressure drag comes from the pressures on the fore-and after-bodies of train,and,in the case with a double deck in train series,it stems from the pressures due to the abrupt change in the cross-sectionalarea of the train.Assuming that the coefficient of the pressure drag is C dp and in the case of a double deck,it is C dpd ;a wind tunneltest [12]has been carried out to investigate the pressure drag.In the experiment,each of the models for the fore-and after-bodies of train and the middle part of train has been manufactured.Depending on the length of the middle part of the model,the model train experiment of different lengths could be done.F or a train modelwith a short l ength,the coefficient of the aerodynamic drag can be written as C ds ¼D s12r U 2A 0;ð11ÞTypeC r o s s -s e c t i o n a l a r e a (m 2)Fig.9.Aerodynamic drag components ofICE.Moving direction Fig.8.Aerodynamic drag on ICE (the hatching area is the device to smooth the structures underneath train).R.S.Raghunathan et al./Progress in Aerospace Sciences 38(2002)469–514478。