Cheli F.

Orellano A.

Rocchi D.

Schober M.

Tomasini G.

ROCCHI, DANIELE

CHELI, FEDERICO

TOMASINI, GISELLA MARITA

Archivio istituzionale della ricerca - Politecnico di Milano

 1 EUROMECH COLLOQUIUM 509    Vehicle Aerodynamics     External Aerodynamics of Railway Vehicles, Trucks, Buses and Cars     Berlin, Germany, March 24--25, 2009 COMPARISON OF WIND TUNNEL TESTS RESULTS ON THE ATM TRAIN Daniele Rocchi†, Martin Schober, Federico Cheli†, Alexander Orellano and Gisella Tomasini†  Centre of Competence for aerodynamics and thermodynamics Bombardier Am Rathenaupark, 16761 - Hennigsdorf - Germany e-mail: Mar-tin.Schober@de.transport.bombardier.com,Alexander.orellano@de.transport.bombardier.com † Mechanical Department – Politecnico di Milano Campus Bovisa, Via La Masa 1, 20158 Milano, Italy e-mails: Federico.Cheli@polimi.it, Daniele.Rocchi@polimi.it, Gisel-la.Tomasini@polimi.it Keywords: Wind tunnel, Cross Wind, Aerodynamic coefficients, Pressure distribution.  Abstract. The paper presents a comparison of the results obtained by experimental cam-paigns, performed in different wind tunnel plants on the same train model. The comparison will be presented in terms of global forces and pressure distribution on the first vehicle of the train model. Tests have been performed on a flat ground configuration and allow to investi-gate the effects related to the Reynolds number on the different components of the global aerodynamic force, to the blockage ratio, and to the adoption of open or closed wind tunnel test section. The sharing of the same scaled model and the availability of detailed data re-garding the pressure distribution in the different test conditions allow a good insight in the modeling of the train aerodynamics in wind tunnel.. Comparison of wind tunnel testsresults on the ATM trainby Daniele Rocchi , Martin Schober ,Federico Cheli , Alexander Orellano,Gisella Tomasiniwordword word240M. Schober , A. Orellano , F. Cheli, D. Rocchi, and G. Tomasini  2 1 INTRODUCTION One of the not yet answered questions on the assessment of the aerodynamic behavior of trains concerns the reliability of the aerodynamic coefficients measured in wind tunnel with respect to the full scale behavior. Wind tunnel tests are commonly performed in different ex-perimental laboratories with different flow qualities, different performances, different equip-ments and different techniques using scaled models and scaled representation of the ground scenarios. These differences may insert uncertainties in the definition of the aero-dynamic performances of trains and a deeper understanding of the physics of the flow around the ve-hicle should be reached to assess the importance of each single term on the experimental re-sult. In this paper a comparison of the results obtained by three experimental campaigns, performed in the 2 test sections of the Politecnico di Milano wind tunnel (PMWT) and at the wind tunnel T103 of the Central Aerodynamic Institute TsAGI (TsAGI) on the same train model is provided. The model is a 1:10 power car and it represents a reference train built by Bombardier, called “Aerodynamic Train Model ” (ATM) for comparison purposes [1]. The model shape is similar to an ICE2 train and it shows all the interesting aerodynamic features of high speed trains. The tests have been performed using, not only the same model of the power car but also the same end car. The model allows to measure the global forces using both internal and external force balances and it is also equipped by pressure taps to measure the pressure distribution on the carbody. Tests have been performed on a flat ground configu-ration trying to reproduce the same boundary condition by means of splitter planes. The dif-ferent characteristics of the used wind tunnel plants allows to investigate the effects related to the Reynolds number on the different components of the global aerodynamic force, to the blockage ratio, and to the adoption of open or closed wind tunnel test section. The sharing of the same scaled model and the availability of detailed data regarding the pressure distribution in the different test conditions allow a good insight in the modeling of the train aerodynamics in wind tunnel.  2 THE ATM TRAIN MODEL The ATM train model is a 1:10 simplified version of an ICE2 train shape (see Figure 1a), that is used by Bombardier for research and benchmark purposes. It is made by an instru-mented locomotive vehicle and by an endcar model with the same nose geometry of the leed-ing car that is used for the boundary condition reproduction. A gap of 5mm is left between the leading car and the end car to grant that they are mechanically disconnected. The basic dimensions of the wind tunnel model are: length=3.557m, width=0.299m and height=0.385m. The model can be equipped with bogies and with a spoiler under the train head, in the present research the model without bogies and without spoiler is considered. In this version the bogie cavities are closed by covers (Figure 1b). The model has an internal aluminum frame allowing for the connection with the supporting system in the central part. The model is also instrumented with 91 pressure taps distributed along 8 transversal sec-tions along the train axis (Figure 1c). The position of the instrumented sections is reported in the following table while an example of pressure taps distribution in the section is reported in Figure 1c for section 6:  Section n.  1  2  3  4  5  6  7  8  Distance from the train head [mm] 100  175  250 500 700 1500 2000 2500  Table 1: position of the instrumented sections along the train. wordword word241M. Schober , A. Orellano , F. Cheli, D. Rocchi, and G. Tomasini  3 a  b  c    1  2  3       4      5                               6                  7                   8  Figure 1: ATM model geometry (a); ATM model without bogies and without spoiler in the PMWT (b); position, along the train axis, of the sections instrumented with pressure taps (c) 3 WIND TUNNEL TESTS The results of three wind tunnel campaigns will be compared in this papers, two of them was performed at the Politecnico di Milano Wind Tunnel (PMWT) and another one at the TsAGI T103 wind tunnel (TsAGI). Wind tunnel tests have been performed on a true flat ground scenario (flat plate without rails). A splitter plate was used in all the considered wind tunnel campaigns in order to grant similar incoming flow conditions on the model. Aerodynamic forces were measured by external force balances while the pressure distribu-tion was measured through pressure scanners positioned inside the train model. 3.1 TsAGI wind tunnel tests TsAGI T103 wind tunnel tests were performed in an open test section with a wind speed range between 30 and 70m/s, which corresponds to Re-numbers of Rel = 0.6~1.4·106. Tests were performed at different yaw angles between 0 and 60 deg. The blockage ratio varies be-tween 4% and 8% for yaw angles between 10° and 30°. A sketch of the wind tunnel plant is reported in Figure 2a. The flat ground consists of an elliptical shaped floor which contains a turntable (Figure 2b). The model is fixed on the turntable which can be automatically rotated during the wind tunnel measurements. Figure 2b shows the whole set up of the experiment including the ATM model and the elliptic splitter plate. An external six-component force balance was used to measure the aerodynamic forces and moments on the leading car. Data averaging was per-formed over 4s for each angle with a sampling frequency of 100Hz.  wordword word242M. Schober , A. Orellano , F. Cheli, D. Rocchi, and G. Tomasini  4 a    b  Figure 2: TsAGI wind tunnel plant scheme (a), ATM model in the TsAGI test section (b) 3.2 PMWT wind tunnel tests The PMWT plant is a closed circuit wind tunnel with two test sections: a larger one (14m x 4m) where tests can be carried on with a wind speed up to 15 m/s (PMWT LS tests section) and a nominal turbulence intensity IT<2% and a smaller one (4m x 4m) where tests can be carried on with a wind speed up to 50 m/s (PMWT HS tests section) and a nominal turbulence intensity IT<0.2%. A sketch of the wind tunnel plant is reported in Figure 3.  Figure 3: PMWT wind tunnel plant scheme Tests on the ATM model were performed in both the test sections using a RUAG 6 com-ponents external force balance. Tests in the PMWT LS test section were performed in a wind speed range between 7 and 15m/s, which corresponds to Re-numbers of Rel = 1.4·105~3.0·105, with a blockage ratio that varies between 0.9% and 4.7% for the considered yaw angles be-tween 5° and 90°. Tests in the PMWT HS test section were performed in closed arrangement at a wind speed range between 7 and 50m/s (Rel = 1.4·105~1.0·106), with a blockage ratio that varies between 3% and 10% for the considered yaw angles between 5° and 30°. wordword word243M. Schober , A. Orellano , F. Cheli, D. Rocchi, and G. Tomasini  5 a   b  Figure 4: ATM model in the PMWT LS test section (a) and in the PMWT HS test section (b) Pressure measurements have only been recorded at 14 m/s during the PMWT LS tests session using a PSI high frequency pressure scanner system. 4 WIND TUNNEL RESULTS The dependence of the aerodynamic coefficients on the yaw angle will be compared in the following paragraphs. Coefficients are computed according to the sign convention reported in Figure 5 and to the following formulation: 2 2 21 1 12 2 2i iFi Mi pF M pC C CU S U Sh U      (1) where Fi (i = x,y,z) are the aerodynamic force components in the train’s reference system (Figure 5), Mi (i = x,y,z) are the corresponding moments and p is the differential pressure measured on the generic pressure tap. In equation (1),  is the air density, U is wind speed, h is equal to 3m (full scale), and S is a standard reference surface which is equal to 10m2(full scale).  x z y                          Wind  Figure 5: Aerodynamic coefficients’ sign convention  wordword word244M. Schober , A. Orellano , F. Cheli, D. Rocchi, and G. Tomasini  6 4.1 Aerodynamic coefficients In the following figure a comparison between the aerodynamic coefficients measured at TsAGI and PMWT is reported for different mean wind speeds and different yaw angles  (expressed in deg). Results obtained at PMWT in the high speed (HS) test section and in the low speed (LS) one are overlapped in the figures on the right. Furthermore a comparison in terms of CMx,lee coefficient is reported in Figure 7. 0 20 40 60 80 100-1-0.500.511.52CFxATM Model (No bogies, No spoiler)   TsAGI FLAT v= 30 m/sTsAGI FLAT v= 50 m/sTsAGI FLAT v= 70 m/s0 20 40 60 80 100-1-0.500.511.52CFxATM Model (No bogies, No spoiler)   PMWT HS FLAT v=  7 m/sPMWT HS FLAT v= 15 m/sPMWT HS FLAT v= 30 m/sPMWT HS FLAT v= 40 m/sPMWT HS FLAT v= 50 m/sPMWT LS FLAT v=  7 m/sPMWT LS FLAT v= 14 m/s 0 20 40 60 80 100012345678910CFyATM Model (No bogies, No spoiler)   TsAGI FLAT v= 30 m/sTsAGI FLAT v= 50 m/sTsAGI FLAT v= 70 m/s0 20 40 60 80 100012345678910CFyATM Model (No bogies, No spoiler)   PMWT HS FLAT v=  7 m/sPMWT HS FLAT v= 15 m/sPMWT HS FLAT v= 30 m/sPMWT HS FLAT v= 40 m/sPMWT HS FLAT v= 50 m/sPMWT LS FLAT v=  7 m/sPMWT LS FLAT v= 14 m/s 0 20 40 60 80 100-10-9-8-7-6-5-4-3-2-101CFzATM Model (No bogies, No spoiler)   TsAGI FLAT v= 30 m/sTsAGI FLAT v= 50 m/sTsAGI FLAT v= 70 m/s0 20 40 60 80 100-10-9-8-7-6-5-4-3-2-101CFzATM Model (No bogies, No spoiler)   PMWT HS FLAT v=  7 m/sPMWT HS FLAT v= 15 m/sPMWT HS FLAT v= 30 m/sPMWT HS FLAT v= 40 m/sPMWT HS FLAT v= 50 m/sPMWT LS FLAT v=  7 m/sPMWT LS FLAT v= 14 m/s wordword word245M. Schober , A. Orellano , F. Cheli, D. Rocchi, and G. Tomasini  7 0 20 40 60 80 1000123456CMxATM Model (No bogies, No spoiler)   TsAGI FLAT v= 30 m/sTsAGI FLAT v= 50 m/sTsAGI FLAT v= 70 m/s0 20 40 60 80 1000123456CMxATM Model (No bogies, No spoiler)   PMWT HS FLAT v=  7 m/sPMWT HS FLAT v= 15 m/sPMWT HS FLAT v= 30 m/sPMWT HS FLAT v= 40 m/sPMWT HS FLAT v= 50 m/sPMWT LS FLAT v=  7 m/sPMWT LS FLAT v= 14 m/s 0 20 40 60 80 100-6-4-20246CMyATM Model (No bogies, No spoiler)   TsAGI FLAT v= 30 m/sTsAGI FLAT v= 50 m/sTsAGI FLAT v= 70 m/s0 20 40 60 80 100-6-4-20246CMyATM Model (No bogies, No spoiler)   PMWT HS FLAT v=  7 m/sPMWT HS FLAT v= 15 m/sPMWT HS FLAT v= 30 m/sPMWT HS FLAT v= 40 m/sPMWT HS FLAT v= 50 m/sPMWT LS FLAT v=  7 m/sPMWT LS FLAT v= 14 m/s  0 20 40 60 80 100-1012345678910CMzATM Model (No bogies, No spoiler)   TsAGI FLAT v= 30 m/sTsAGI FLAT v= 50 m/sTsAGI FLAT v= 70 m/s0 20 40 60 80 100-1012345678910CMzATM Model (No bogies, No spoiler)   PMWT HS FLAT v=  7 m/sPMWT HS FLAT v= 15 m/sPMWT HS FLAT v= 30 m/sPMWT HS FLAT v= 40 m/sPMWT HS FLAT v= 50 m/sPMWT LS FLAT v=  7 m/sPMWT LS FLAT v= 14 m/s Figure 6: Aerodynamic coefficients vs yaw angle A very good agreement is visible by the comparison of the TsAGI and the PMWT LS re-sults for all the aerodynamic coefficients apart from CMy.where a similar trend is visible only up to 20 deg. For higher yaw angles, the TsAGI results show a double sign change from nega-tive to positive CMy values at 35 deg and from positive to negative values at 50 deg, while PMWT LS results show the same slope changes, they never reach positive CMy values. A CMy trend closer to the TsAGi results is highlighted by the PMWT HS data even if they seem to anticipate the minimum (=15 deg) and the crossing of the x-axis (=30 deg) to low-er yaw angles. wordword word246M. Schober , A. Orellano , F. Cheli, D. Rocchi, and G. Tomasini  8 PMWT HS results differ significantly from the PMWT LS results for the CFz and CMz coef-ficients where HS data overestimate the consistent values of the PMWT LS and TsAGI results. Differences in the CFz and CMy coefficients indicate, for the PMWT HS data, a higher ver-tical lifting force positioned in the forepart of the train. It is difficult to explain this experi-mental evidence starting from the global force measurement, since, even if the model and the measurement system are the same, tests are performed with different turbulence intensity le-vels and different splitter plates. Similar considerations hold also for the CMz coefficient. TsAGI results show a small Reynolds number dependency for the CFx coefficient that in-creases the slope at yaw angles higher than 20 if the wind speed is increased. The same aero-dynamic coefficient seems to be not affected by Reynold number effect in the PMWT data where only the 7 m/s LS coefficient shows some differences from 0 to 30 deg. CFy and CMx coefficients don’t have any Reynolds number dependency both for TsAGI and PMWT results up to 60 deg. A different maximum value is reached by the PMWT LS data, being the lower wind speed the more conservative. Reynolds number effects are negligible also comparing the TsAGI and the PMWT HS re-sults for the CFz and CMz coefficients even if the best agreement is shown between the TsAGI and the PMWT LS data for these coefficients. Another discrepancy between TsAGI and PMWT LS results is present at =60 deg that represents the largest yaw angle tested at TsAGI due to the test section/model dimensions. CFy and CMx seem to change the slope passing from 50 to 60 deg in the TsAGI results while they continue with a different trend in the PMWT LS results. Also looking at the comparison on the CFx and CMz coefficients a difference appears at 60 deg while a very good agreement is present on the other yaw angles. This could be explained considering that, at 60 deg, the mod-el in the TsAGI open tests section is too close to the boundaries of the flow while in the large PMWT LS test section results are less affected by the boundary conditions and wind tunnel tests may be extended up to 90 deg. Figure 7 reports the comparison between TsAGI and PMWT data in terms of CMx, lee representing the overturning moment computed around the leeward rail axis that is a key pa-rameter for the evaluation of the overturning effects induced by cross-wind. From the compar-ison it is visible the complete agreement up to 50 deg and the negligibility of the Reynolds number effects on this coefficient.  0 20 40 60 80 100012345678CMx, leeATM Model (No bogies, No spoiler)   TsAGI FLAT v= 30 m/sTsAGI FLAT v= 50 m/sTsAGI FLAT v= 70 m/s0 20 40 60 80 100012345678CMx, leeATM Model (No bogies, No spoiler)   PMWT HS FLAT v=  7 m/sPMWT HS FLAT v= 15 m/sPMWT HS FLAT v= 30 m/sPMWT HS FLAT v= 40 m/sPMWT HS FLAT v= 50 m/sPMWT LS FLAT v=  7 m/sPMWT LS FLAT v= 14 m/s Figure 7: Comparison of CMx,lee coefficient vs yaw angle  wordword word247M. Schober , A. Orellano , F. Cheli, D. Rocchi, and G. Tomasini  9 4.2 Pressure distribution  The comparison of the pressure distribution on all the 8 sections measured at TsAGI and at PMWT LS is reported in Figure 8 for the yaw angle =30 deg in terms of pressure coeffi-cients Cp. Arrows and points inside the section boundary represent positive values. Section 1  Section 2  Section 3  Section 4  Section 5  Section 6  → PMWT LS ●        TsAGI   Figure 8: Pressure coefficient distribution at =30 deg (blue arrows: PMWT; red points: TsAGI) wordword word248M. Schober , A. Orellano , F. Cheli, D. Rocchi, and G. Tomasini  10 A very good agreement is visible on all the 8 sections at the different pressure taps posi-tions. TsAGI values show a slightly higher suction zone in the upper leeward part of section 3 and section 4. This difference confined in the forepart of the train model could explain the negative value of the PMWT LS CMy coefficient compared to the almost null value of the TsAGI being the CFz coefficients equal for both the cases. Smaller discrepancies are visible in the lower leeward part of sections 3 and 5 where PMWT LS results present a higher suction. Similar differences appears also in the comparison between the TsAGI results and CFD re-sults presented in [2] and PMWT results seem to be closer to the numerical simulation data. 5 CONCLUSIONS   Good agreement is reached by the comparison of wind tunnel results performed at differ-ent wind tunnel plants on the same 1:10 scaled train model.  Results showed negligible Reynolds number effects especially for those coefficients in-volved in the cross wind analysis (CFy and CMx)  Differences in the results are present in CFz, CMy and CMz coefficients between PMWT HS and PMWT LS data while TsAGI (open section) and PMWT LS (large closed test section) data are in good agreement on all the coefficients apart from CMy for yaw angles higher than 20 deg.  Differences between PMWT HS and PMWT LS data may be due to different wind tunnel test conditions as turbulence intensity levels and splitter plate geometry being the model and the measurement set-up the same in both the wind tunnel campaigns.  The different CMy behavior, for yaw angles higher than 20 deg, between TsAGI and PMWT LS data, can be explained by analyzing the pressure distribution measured on the train model especially in the upper and lower leeward parts of the train in the forepart.  Benchmark tests and benchmark vehicles represent a good tool to compare and validate da-ta and wind tunnel procedures that is also included in standards [3]. Among all the parameters affecting the wind tunnel results analyzed in the present work, Reynolds number seems to be not critical for cross wind analysis while other parameters as turbulence intensity and boun-dary layer treatment affect only some aerodynamic coefficients.  REFERENCES  [1] A. Orellano and M. Schober. Aerodynamic performance of a typical high-speed train. WSEAS transactions on Fluid Mechanics, 1, 2006. [2] B. Diedrichs. Aerodynamic calculations of crosswind stability of a high-speed train us-ing control volumes of arbitrary polyhedral shape. Proceedings of the BBAA VI, Mila-no, Italy, July 20-24, 2008. [3] prEN 14067-6. Railway Applications – Aerodynamics – Part 6: Requirements and test procedures for cross wind assessment. European standard  wordword word249

Comparison of wind tunnel tests results on the ATM train

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Comparison of wind tunnel tests results on the ATM train

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