9 49 49 49 49 4 QR of RTRI, Vol. 42, No. 2, May. 2001

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WWWWWind Tind Tind Tind Tind Tunnel Tunnel Tunnel Tunnel Tunnel Tests to Reduce Aerodynamic Drag of Tests to Reduce Aerodynamic Drag of Tests to Reduce Aerodynamic Drag of Tests to Reduce Aerodynamic Drag of Tests to Reduce Aerodynamic Drag of Trainsrainsrainsrainsrainsby Smoothing the Under-floor Constructionby Smoothing the Under-floor Constructionby Smoothing the Under-floor Constructionby Smoothing the Under-floor Constructionby Smoothing the Under-floor Construction

1. Introduction1. Introduction1. Introduction1. Introduction1. Introduction

As a train runs at a higher speed, the rate of the aero-dynamic drag to the running resistance becomes largerand the aerodynamic drag reduction becomes important.On long train-sets such as Shinkansen trains, the aero-dynamic drag is mainly caused by intermediate vehicles,and in order to reduce this, it is necessary to reduce theaerodynamic drag of intermediate vehicles. In previousresearches, we proved that smoothing the under-floorconstruction reduces the aerodynamic drag. However, themechanism of this effect has not been solved sufficiently.In this research, we investigate the effect of the aerody-namic drag reduction by smoothing the under-floor con-

struction, by measuring in detail the aerodynamic dragand the pressure distribution on the intermediate vehicle.

2. Experimental equipment and method2. Experimental equipment and method2. Experimental equipment and method2. Experimental equipment and method2. Experimental equipment and method

Wind tunnel tests were carried out by using a closedtype test section of the Large-Scale Low- Noise Wind Tun-nel of Railway Technical Research Institute. Figure 1shows the test section arrangement. The size of the testsection is 5 m wide, 3 m high and 20 m long. The maxi-mum speed of the wind is 83 m/s. We used moving-beltand boundary layer suction equipment to simulate theairflow between train models and the ground under the

Atsushi IDOAtsushi IDOAtsushi IDOAtsushi IDOAtsushi IDOSenior Researcher,

Heat & Air Flow, Environmental Engineering Div.

TTTTTsuyoshi MAsuyoshi MAsuyoshi MAsuyoshi MAsuyoshi MATSUMURATSUMURATSUMURATSUMURATSUMURADeputy Manager,

Minoru SUZUKIMinoru SUZUKIMinoru SUZUKIMinoru SUZUKIMinoru SUZUKIAssistant Manager,

Wind Tunnel Technical Center, Administration Div.

TTTTTatsuo MAEDAatsuo MAEDAatsuo MAEDAatsuo MAEDAatsuo MAEDAGeneral Manager,

Environmental Engineering Div.

As a train runs at a higher speed, aerodynamic drag increases. On long train-sets such asShinkansen trains, the aerodynamic drag is mainly generated by intermediate vehicles. Inthe previous researches, we proved that smoothing the under-floor construction reduces theaerodynamic drag. To investigate the mechanism of this effect, we performed wind tunneltests with train models consisting of three vehicles (representing head, intermediate and tailvehicles) and measured the aerodynamic drag and the pressure distribution on the intermedi-ate vehicle. Test results show that the reduced aerodynamic drag is mainly the effect ofdecreases in the pressure drag around bogies.

KeywordsKeywordsKeywordsKeywordsKeywords : aerodynamic drag, running resistance, pressure drag, wind tunnel test, under-floor construction

YYYYYoshihiko KONDOoshihiko KONDOoshihiko KONDOoshihiko KONDOoshihiko KONDOGeneral Manager,

Fig. 1 TFig. 1 TFig. 1 TFig. 1 TFig. 1 Test section arrangementest section arrangementest section arrangementest section arrangementest section arrangement

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actual condition. The size of moving-belt is 2.7 m wideand 6 m long and maximum speed is 60 m/s.

For the tests, we used train models consisting of threevehicles (representing head, intermediate and tail ve-hicles) and measured the aerodynamic drag and the pres-sure distribution on the intermediate vehicle. Figure 2shows four types of the intermediate vehicle model (types1, 2, 3 and 4) and holes for pressure measurement. Thescale of the models is 1/7 in consideration of a blockageratio to the cross section of the wind tunnel and the sizeof the moving belt. The under-floor construction of thehead and tail vehicle is the same as that of the interme-diate vehicle. We measured the aerodynamic drag actingon the intermediate vehicle by a load cell built in thehead vehicle. The four types of under-floor constructionare shown below.TTTTType 1:ype 1:ype 1:ype 1:ype 1: Equipment coversEquipment coversEquipment coversEquipment coversEquipment coversTTTTType 2:ype 2:ype 2:ype 2:ype 2: Body mount except at bogiesBody mount except at bogiesBody mount except at bogiesBody mount except at bogiesBody mount except at bogiesTTTTType 3:ype 3:ype 3:ype 3:ype 3: Body mount except at bogies + bogie skirtsBody mount except at bogies + bogie skirtsBody mount except at bogies + bogie skirtsBody mount except at bogies + bogie skirtsBody mount except at bogies + bogie skirtsTTTTType 4:ype 4:ype 4:ype 4:ype 4: Body mount except at bogies + bogie skirtsBody mount except at bogies + bogie skirtsBody mount except at bogies + bogie skirtsBody mount except at bogies + bogie skirtsBody mount except at bogies + bogie skirts

+ under-bogie covers+ under-bogie covers+ under-bogie covers+ under-bogie covers+ under-bogie coversWhere the body mount means the cover shrouding thebogies and the equipment, which consists of the curvedside surface and the plane bottom surface.

We measured the pressure on the following six sur-faces of the vehicle.Surface A:Surface A:Surface A:Surface A:Surface A: Front surface in the inter-vehicle gapFront surface in the inter-vehicle gapFront surface in the inter-vehicle gapFront surface in the inter-vehicle gapFront surface in the inter-vehicle gapSurface B:Surface B:Surface B:Surface B:Surface B: Back surface in the front bogie gapBack surface in the front bogie gapBack surface in the front bogie gapBack surface in the front bogie gapBack surface in the front bogie gapSurface C:Surface C:Surface C:Surface C:Surface C: Front surface in the front bogie gapFront surface in the front bogie gapFront surface in the front bogie gapFront surface in the front bogie gapFront surface in the front bogie gapSurface D:Surface D:Surface D:Surface D:Surface D: Back surface in the rear bogie gapBack surface in the rear bogie gapBack surface in the rear bogie gapBack surface in the rear bogie gapBack surface in the rear bogie gapSurface E:Surface E:Surface E:Surface E:Surface E: Front surface in the rear bogie gapFront surface in the rear bogie gapFront surface in the rear bogie gapFront surface in the rear bogie gapFront surface in the rear bogie gapSurface F:Surface F:Surface F:Surface F:Surface F: Back surface in the inter-vehicle gapBack surface in the inter-vehicle gapBack surface in the inter-vehicle gapBack surface in the inter-vehicle gapBack surface in the inter-vehicle gapWhere “the inter-vehicle gap” means the space betweenthe vehicles and “bogie gap” means the space where bo-gies exist.

Since the pressure distribution on each surface wasexpected to be symmetrical, we measured the pressureon only one side. When we measured the pressure, thereference pressure (the standard pressure) was the staticpressure of the pitot tube for wind velocity control.

By a load cell built in the head vehicle, we measured thetotal of the aerodynamic drag acting on the train body andthe aerodynamic drag acting on bogies. Improvement of theunder-floor construction should reduce the aerodynamic dragof the train body and the bogies. In order to separate theaerodynamic drag of the train body and that of the bogies,simultaneously with drag measurement of the intermedi-ate vehicle, we also measured the aerodynamic drag of bo-gies with balances built in the intermediate vehicle.

3. Results and discussion3. Results and discussion3. Results and discussion3. Results and discussion3. Results and discussion

The flow velocity of the wind tunnel is 50 m/s. Weshow the test results with Cp and Cd, where “Cp” is thepressure coefficient and “Cd” is the drag coefficient (Cp= p/q, Cd=D/(q*S) where p: surface pressure, q: dynamicpressure, D: drag, S: c-c' cross section area of type 2).

3.1 Pressure acting on train body surface3.1 Pressure acting on train body surface3.1 Pressure acting on train body surface3.1 Pressure acting on train body surface3.1 Pressure acting on train body surface

In the inter-vehicle gap and the bogie-gap, there arefront surfaces (Surface A, C, E) where airflow hits andback surfaces (Surface B, D, F) where airflow rolls up.The positive pressure on the front surface and the nega-tive pressure on the back surface cause the aerodynamicdrag. Figure 3 shows the pressure measurement pointsindicated in the graphs of measurement results.

Figure 4 shows the pressure distribution on the trainbody. With types 2 and 3, the pressure distribution onthe front bogie gap (Surface B, C) and on the rear bogiegap (Surface D, E) is almost the same. This means thatthe airflow in the rear bogie gap is similar to that in thefront bogie gap. With types 2 and 3, the pressure of theback surface in the bogie gap is negative and the pres-sure of the front surface is positive, so the pressure act-ing on the front and back surfaces cause aerodynamicdrag. The absolute value of the pressure on the back sur-faces (Surface B, D) and the front surfaces (Surface C, E)with type 2 is larger than with type 3. This tendency

Fig. 2 VFig. 2 VFig. 2 VFig. 2 VFig. 2 Vehicle modelsehicle modelsehicle modelsehicle modelsehicle models

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Fig. 3 Pressure measurement points of graphsFig. 3 Pressure measurement points of graphsFig. 3 Pressure measurement points of graphsFig. 3 Pressure measurement points of graphsFig. 3 Pressure measurement points of graphs

Fig. 4 Pressure distribution in bogie gapFig. 4 Pressure distribution in bogie gapFig. 4 Pressure distribution in bogie gapFig. 4 Pressure distribution in bogie gapFig. 4 Pressure distribution in bogie gap

appears more remarkably in the areas near the side ofthe train body, because the airflow enters into the bogiegap from the train body side under the condition of nobogie skirts. We found that the absolute value of the nega-tive pressure on the back surface and the positive pres-sure on the front surface decrease, when the sides of thebogie are covered with the bogie skirts.

With type 1, the result shows a different tendencyfrom that of types 2 and 3. The airflow hits the frontbogie directly because there are no obstacles upstream ofthe front bogie of type 1. We thought that the pressureon the back surface of the front bogie (Surface B) is posi-tive because the influence of the strong airflow hittingthe front bogie reaches the back surface. With type 1 onback surface in the rear bogie gap (Surface D), the abso-lute value of the negative pressure is larger than that oftypes 2 and 3. Because the airflow becomes faster in the

larger space under the models, the airflow strongly rollsup and the negative pressure becomes larger.

With type 4, the pressure distribution in the bogiegap is roughly uniform because the airflow can not enterthe bogie gap.

Figure 5 shows the pressure distribution in the inter-vehicle gap. The influence of the modification of the un-der-floor construction appears in the area near the ve-hicle roof. This shows that modification of the under-floorconstruction changes the whole airflow around the vehicle.With types 2, 3 and 4, the pressure on the back surface inthe inter-vehicle gap (Surface F) is negative because of theroll up of the airflow. With type 1, the influence of thepositive pressure from the airflow hitting the front surface(Surface A) is larger than that of roll up, so the pressure onthe back surface in the inter-vehicle gap is positive.

3.2 Force in each surface3.2 Force in each surface3.2 Force in each surface3.2 Force in each surface3.2 Force in each surface

We obtained the force on each surface by integratingpressure measurement results. We defined that a posi-tive direction of force is in the same direction of the aero-dynamic drag. That is, the values of the force on SurfaceB, D and F are equal to the values that changed the signof the pressure integrating results. The force on eachsurface is shown in Fig.6. With type 1, large aerodynamicdrag acts on the front surface in the inter-vehicle gap;and with types 2 and 3, large aerodynamic drag acts onthe back surface in the inter-vehicle gap. With type 2,the force on the back surface in the bogie gap is largerthan that on the front surface. With type 3, the force inthe bogie gap shows the same tendency, though the valueof force is not larger than that of type 2. The negativepressure on the back surface and the positive pressure on

Fig. 5 Pressure distribution in inter-vehicle gapFig. 5 Pressure distribution in inter-vehicle gapFig. 5 Pressure distribution in inter-vehicle gapFig. 5 Pressure distribution in inter-vehicle gapFig. 5 Pressure distribution in inter-vehicle gap

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Fig. 6 Forces caused by pressure on surfaceFig. 6 Forces caused by pressure on surfaceFig. 6 Forces caused by pressure on surfaceFig. 6 Forces caused by pressure on surfaceFig. 6 Forces caused by pressure on surface

the front surface are aerodynamic drag, and we can de-crease the aerodynamic drag with bogie skirts, which de-crease the absolute value of this pressure. With types 2and 3, a negative force acts on the front surface in theinter-vehicle gap (Surface A) because of the negative pres-sure on the back surface of the front vehicle. With type 4,the force caused by the pressure distribution hardly acts,except for on the back surface in the inter-vehicle gap.

3.3 Aerodynamic drag acting on bogies3.3 Aerodynamic drag acting on bogies3.3 Aerodynamic drag acting on bogies3.3 Aerodynamic drag acting on bogies3.3 Aerodynamic drag acting on bogies

Figure 7 shows the aerodynamic drag of bogies. Withtype 1, large aerodynamic drag acts on the bogies, be-cause there are only equipment covers and the airflowhits the front bogie directly. With the rear bogie, the bogiedoes not hide itself completely behind the equipment cov-ers. Therefore, the aerodynamic drag acting on the rearbogie is larger than that with types 2, 3 and 4. The aero-dynamic drag acting on the bogies of types 2, 3 and 4where the whole bogie is concealed under the train bodyis much smaller than that acting on the whole vehicle.With type 2, negative aerodynamic drag acts on the bo-gies, because the airflow enters into the bogie gap fromside and the integrated value of positive pressure behindthe bogie is larger than that with types 3 and 4.

3.4 Aerodynamic drag on intermediate vehicles3.4 Aerodynamic drag on intermediate vehicles3.4 Aerodynamic drag on intermediate vehicles3.4 Aerodynamic drag on intermediate vehicles3.4 Aerodynamic drag on intermediate vehicles

We divide the aerodynamic drag into four parts andshow the aerodynamic drag on each part of the intermedi-ate vehicle in Fig. 8.(1) Aerodynamic drag of front bogie and gap(1) Aerodynamic drag of front bogie and gap(1) Aerodynamic drag of front bogie and gap(1) Aerodynamic drag of front bogie and gap(1) Aerodynamic drag of front bogie and gap

The pressure drag caused by the pressure acting on

Fig. 7 Drag of bogiesFig. 7 Drag of bogiesFig. 7 Drag of bogiesFig. 7 Drag of bogiesFig. 7 Drag of bogies

surfaces B and C + the aerodynamic drag of the front bogie.(2) Aerodynamic drag of rear bogie and gap(2) Aerodynamic drag of rear bogie and gap(2) Aerodynamic drag of rear bogie and gap(2) Aerodynamic drag of rear bogie and gap(2) Aerodynamic drag of rear bogie and gap

The pressure drag caused by the pressure acting onsurfaces D and E + the aerodynamic drag of the rear bogie.(3) Aerodynamic drag of inter(3) Aerodynamic drag of inter(3) Aerodynamic drag of inter(3) Aerodynamic drag of inter(3) Aerodynamic drag of inter-vehicle gap-vehicle gap-vehicle gap-vehicle gap-vehicle gap

The pressure drag caused by the pressure acting onsurfaces A and F.(4) Other drag(4) Other drag(4) Other drag(4) Other drag(4) Other drag

Total drag - above-mentioned three drags.The results indicate aerodynamic drags all becomesmaller in the order of types 1, 2, 3 and 4. The smoothingof the under-floor construction and the under floor airflowreduce the aerodynamic drag. With types 2, 3 and 4, theaerodynamic drag in the bogie and gap decreases bysmoothing the airflow in the bogie gap. With type 4, wherethe train body covers the whole bogie completely, the aero-dynamic drag in the inter-vehicle gap becomes larger thanthe total aerodynamic drag of the bogie and the bogie gap.We can greatly reduce the aerodynamic drag of inter-ve-hicle gap by covering this gap.

4. Conclusions4. Conclusions4. Conclusions4. Conclusions4. Conclusions

The following conclusions are obtained from the tests.1) We showed the rate of the aerodynamic drags for each

part of the intermediate vehicle.2) The aerodynamic drag of a vehicle decreases when

bogies are covered.

5. Acknowledgements5. Acknowledgements5. Acknowledgements5. Acknowledgements5. Acknowledgements

This research had been financially supported by astate subsidy of Japan.

ReferencesReferencesReferencesReferencesReferences

1) Maeda et al.: “Aerodynamic Drag of Shinkansen Elec-tric Cars,” Railway Technical Research Report (inJapanese), Vol.1371, 1987

2) Ido, Fukuda and Tanemoto : “Aerodynamic Drag ofHigh Speed Train and Wind Tunnel Test to ReduceIt,” RTRI Report (in Japanese), Vol.9, No.1, 1995

Fig. 8 TFig. 8 TFig. 8 TFig. 8 TFig. 8 Total drag of intermediate vehicleotal drag of intermediate vehicleotal drag of intermediate vehicleotal drag of intermediate vehicleotal drag of intermediate vehicle