a generic train-underfloor experiment for cfd...

BBAA VI International Colloquium on:Bluff Bodies Aerodynamics & Applications

Milano, Italy, July, 20–24 2008

A GENERIC TRAIN-UNDERFLOOR EXPERIMENT FOR CFDVALIDATION

Hans-Jakob Kaltenbach?, Igor Alonso Portillo‡, and Martin Schober∀

?Deutsche Bahn AG, DB Systemtechnik, Aerodynamics and Air conditioningVolckerstraße 5, 80939 Munchen, Germany

e-mail: [email protected]

‡ work carried out when affiliated with CAF (Construcciones y Auxiliar de Ferrocarriles),Departamento de Investigacion, J. M. Iturrioz, 26, 20200 Beasain, Spain

now with UNIFE, 221 Avenue Louise, B-1050 Brussels, Belgiume-mail: [email protected]

∀ Bombardier Transportation MLN/TSSA, Am Rathenaupark, 16761 Hennigsdorf, Germanye-mail: [email protected]

Keywords: Underfloor aerodynamics, bogie cavity, CFD validation, LDA measurements

Abstract: Within the DEUFRAKO research cooperation “Aerodynamics in Open Air” (AOA)a generic train underfloor geometry has been studied in the wind tunnel in scale 1:7 in orderto provide reference data for the assessment of the suitability of various turbulence modelingapproaches later to be used on full train geometries under 1:1 conditions.

The geometry consists of a duct connecting three cavities opposite to a flat wall representingthe trackbed. The first and the last cavities are equipped with realistic models of ICE 3 bogies inscale 1:7 whereas the central cavity is empty. It represents the intercargap. The inlet boundaryconditions consist in steady air stream with 25 m/s and low turbulence intensity.

Various profiles of all components of the mean velocity vector and of the turbulence in-tensities (normal components of the Reynolds stress tensor) have been collected using a two-component LDA. A sufficient accuracy was reached for the use of the data for validation of CFDpredictions both on the level of mean flow and of turbulence intensities.

Flow visualizations helped to identify flow features such as a strong flux out of the funnel-shaped rearward end of the first bogie cavity and the existence of strong secondary flow in thecentral cavity. Downstream of the first bogie cavity the irregularity of the underfloor geometryhad a noticeable effect on the flow near the trackbed. There, an increase of the axial speed by30 % and of the turbulence intensity by 200 % was observed.

Results can not directly be mapped to the real, full-scale situation of a passing train. Never-theless, the generic configuration seems to pose sufficient challenges to allow for a meaningfulcomparison for different turbulence modeling approaches such as RANS, DES, and LES. Simu-lation results obtained are presented in an accompanying paper.

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Hans-Jakob Kaltenbach, Igor Alonso Portillo, Martin Schober

1 INTRODUCTION

The investigation of the underfloor flow field of high-speed trains is motivated by severalaspects which affect system safety and performance: cruising speeds are approaching valueswhere ballast projection becomes a serious issue, requiring the optimization of the underbellydesign in order to reduce the aerodynamic load on the track bed. With the increase in energycost the reduction of the drag by use of bogie fairings becomes attractive as well as for noisereduction purposes. Since both full-scale tests and wind-tunnel tests over moving belts or withmoving model rigs are costly the interest in CFD as a tool for the flow assessment and investi-gation of the effects of design changes has increased.

Commercial solvers have reached a state where technical issues such as meshing for com-plex geometries, convergence rate, memory requirements and computational resources can behandled. Nevertheless, the flow region in the gap between the underbelly of the vehicle and thetrackbed poses a challenge to turbulence modeling since the highly turbulent, non-equilibriumflow is characterized by features which have shown to be difficult to capture within the classicalsteady RANS approach: the Couette type flow is regularly interrupted by the passing bogiesand the cross-sectional changes at the inter-coach connections. It is characterized by flow sep-aration and formation of vortices at sharp edges and behind bluff bodied geometry details, bylarge-scale unsteadiness, and by intense secondary flow [6]. Despite intense research none ofthe many concepts for transient flow simulations such as URANS, DES, or (V)LES, - see [11]for some clarification with respect to the terminology - has prooven to be applicable in a generalmanner for flow prediction.

Thus, it is necessary to validate turbulence modeling approaches by comparison of flow fieldpredictions with measurements either from the track side or from the laboratory. Within theresearch cooperation Aerodynamics in Open Air - as part of the French-German DEUFRAKOprogramme - the four partners DB AG, Bombardier, Siemens and CAF launched a laboratoryinvestigation of a generic underfloor geometry in scale 1:7 that was carried out in 2006 at theISTA at the University of Technology, Berlin (TU Berlin). The data was used for validation ofturbulence modeling approaches which is reported in an accompanying publication [12].

The assessment of the quality of model and simulation output is a topic in many disciplines.For example, a standardization for the assessment of the quality of fire prediction methods isunder way [1]. There, the relevant technical terminology and useful definitions can be foundand mathematical measures of error for various quantities are proposed. In a recent CFD inves-tigation of a cooling tower drift [9] some useful definitions and references are given such as:Validation is defined as the process of determining the degree to which a model is an accuraterepresentation of the real world from the perspective of the intended uses of the model.

Continued verification and validation is required at almost every level of CFD predic-tion [4, 3]. Various criteria for measuring agreement between predictions and full or model-scale measurements are available. Several organizations have established committees andgroups to focus on the quality of and trust in CFD applied to practical applications (e.g.[5, 2, 10, 7]).

The experiment was tailored around existing 1:7 scale wooden models of two typical ICE 3bogies. The generic underfloor geometry consisting of two bogie cavities connected by a ductwas chosen with the following criteria in mind:

• it should include typical flow features of the underfloor region of a train,

• the boundary conditions should be well-defined and easily to be realized in a CFD model,

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• it should allow for easy access for LDA from different sides and the dimensions of themeasuring volume should be small compared to typical geometrical features,

• the experiment should provide detailed profiles of mean velocity and turbulence statis-tics, allowing for a validation of CFD predictions on the level of second-order moments(Reynolds stresses)

Clearly, the channel situation differs strongly from the one under the real train due to thepresence of an axial pressure gradient and because of the lateral obstruction of the flow by theside walls. Nevertheless, some features such as the formation of shear-layers at sharp edges, theflow around obstacles such as the wheels, the formation of vortices at the slanted cavity edges,the presence of strong secondary flow, and the existence of flow from the trackbed side in anout of the cavities should be qualitatively similar. Thus, measurement results can not be directlycarried over to the train. However, the flow should have some typical features and thereforepose the proper challenge to CFD modeling. One can probably make the following statement:if a turbulence modeling approach gives good agreement with measurements in this geometrythen it is probably appropriate for a full train simulation, too.

The purpose of this paper is to document the experimental set-up, to assess the measurementuncertainties, and to give an overview over flow features and the type of results obtained.

The paper is organized in the following way: in section 2 the rig and the measurement systemare described and the uncertainty is assessed. Results are presented in section 3, including theinlet boundary conditions, pdfs of the velocity field at selected points, profiles of mean andturbulence intensities and some flow visualizations.

2 SET-UP OF THE EXPERIMENT

2.1 Test facility

Fig. 1 shows the setup used to investigate the flow through the generic underfloor configu-ration called BIAC (bogies in a channel). The rig consists of a centrifugal blower with a rect-angular outlet cross section which is followed by a diffuser equipped with screens and porousmats. The axisymmetric settling chamber of length of 1000 mm ends with a contraction whichhas a rectangular outlet cross section of 70 mm×530 mm. The flow in the vicinity of the semi-circular corners of the contraction is cut off by splitter plates connected to the side walls of thetest section.

The idealized underfloor geometry consisting of two bogie cavities with one blunt and onefunnel-shaped end is shown in Fig. 2. Between the bogie cavities is another cavity representingthe intercargap. A circular cylinder with a diameter of 30 mm models the rod (the coupling)connecting two coaches. In the lateral direction the test section is wider than the underbody ofthe real vehicle. In the BIAC geometry the bogie cavities are 22 mm (in 1:1) shallower thanat the real train. Thus, the bogie obstructs the 68 mm (in 1:7) wide gap between trackside andunderbelly by an additional 3 mm (in 1:7). Also, the shape of the trapezoidal end of the cavitydeviates from its counterpart on the real train.

Photographs of the rig are shown in Fig. 3. The transparent test section made out of perspexis placed such that the bogies are attached to one of the vertical sidewalls by screws. Theopposite flat wall of the test section represents the trackbed. Since there are currently no tracksin the model there is a gap of 27 mm (in 1:7 scale) between the rim of the wheel and the wall.

The two bogie models in scale 1:7 are made out of wood. Fig. 4 shows some details. Insidethe first bogie cavity the asymmetrical motor bogie with a pair of engines and gear boxes is

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Figure 1: Wind tunnel set up.

Figure 2: Test section with dimensions in mm in scale 1:1 and 1:7 (in brackets).

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Figure 3: Views of the experimental facility. Top left: Blower and axisymmetric settling chamber. Top right: testsection with trailer bogie in second bogie cavity. Bottom left: view through the contraction into the test section.Bottom right: view from the outlet duct into the test section.

placed whereas the second cavity holds the symmetrical trailer bogie with three disk brakes oneach axle. In addition it is equipped with the eddy-current brake in lifted position.

Fig. 1 and 2 also show the orientation and the origin of the coordinate system used in thisreport. The coordinate x denotes the axial direction (along tunnel axis), the coordinate y isaligned with the spanwise or lateral direction (between the sidewalls of the channel) and zdenotes the wall-normal coordinate pointing from the vehicle underbody towards the channelwall representing the trackbed. The origin of the coordinate system is defined at the center planeof the idealized intercargap between the two bogie cavities with z = 0 located at the undersideof the coach. For the model scale 1:7 the opposite wall (trackbed) is located at z = 68 mm.In 1:1 the origin z = 0 represents a point which is 286.5 mm above top of rail. The distancebetween the rim of the wheel and the trackbed surface would correspond to 189.5 mm in 1:1.All coordinates will be normalized by the gap width h = 68 mm.

2.2 The measurement equipment

A two-component LDA system of Dantec Systems with a 300 mW air cooled argon ionlaser was used in backscatter mode. The signals were processed by the BSA F60 flow pro-cessor. Version 4 of the BSA Flow software was used to control the recording of data and the

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Figure 4: Original bogies placed in the test section. Top: motor bogie. Bottom: trailer bogie.

traverse system. The LDA and the 3D-traverse were operated in two different orientations. Inorientation (i) the beams enter through the wall representing the trackbed and point in the neg-ative z-direction. The LDA is then measuring the components u and v. In orientation (ii) thebeams enter from below through a lateral wall of the test section and the LDA is measuring thecomponents u and w. As a consequence, there is some redundancy in the measurements (withrespect to u) which is exploited for quality checks.

The beams had wavelengths of 488 nm and 514.4 nm. Two different lenses were used. Fororientation (i) the focal length was 310 mm and for orientation (ii) 600 mm. For orientation (i)the size of the measurement volume was ∆x = ∆y = 0.047 mm and ∆z = 0.39 mm.

The flow was seeded with a spray of DEHS which was produced in a cyclone seeder (PallasAGF10) operated by compressed air. This spray was directed into the inlet orifice of the blower.In order to reduce the amount of seeding required the windows of the laboratory were alwaysclosed. Thus, after a couple of minutes the room was filled with the spray. Measurement timefor a single data point varied between 5 s and 180 s. Data rates up to 14 kHz were obtained.

An air condition system was used in order to keep the room temperature approximatelyconstant between 27◦ and 30◦.

The optical access was limited by several factors: most of the time in the orientation (ii)the LDA system was not inclined when approaching a wall. Thus, depending on the distanceof the measurement volume from the wall where the beam entered only a small region in the

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center of the duct existed where both beams were undisturbed. This limitation affects the wall-normal velocity component only. The optical access for the wall-parallel velocity componentwas sometimes hindered by the presence of screws in the wall where the beam entered. Impuri-ties, scratches, and residues from the seeding led occasionally to a reduction of beam intensity.At certain locations (e.g. when the beam pointing towards the coupling rod in the intercar gap)the photo detector was disturbed by reflections.

2.3 Assessment of the measurement accuracy

The mean axial flow speed undergoes significant changes, taking much smaller values insidethe cavities than in the gap between coach underbody and trackbed. This poses some difficultiesfor the proper choice of the primary parameters of the measuring system: the center frequencyand the bandwidth. With the given constraints in time and budget it was not possible to selectoptimal settings for each measurement location since this can only be done in an iterative way.

In order to be able to automatically take measurements on a predetermined grid of locationsit was necessary to often operate the system using a rather wide bandwith of 64 m/s for theaxial flow component. As a consequence, the resulting frequency distributions for the velocitysignals suffer from a large bin width and look somewhat jagged. Despite the large band widththe pdfs were sometimes cut off at one side due to an improper setting of the center frequency.

Data quality was checked in a heuristic way: examination of the tails of the pdfs - if available- revealed whether the full range of velocity fluctuations was covered. In addition, a minimumnumber of samples was required (in the order of 1000 counts) and the confidence for the meanhad to be below 0.25 m/s in order for a recording to be considered as valid.

Comparison of measurements with the most reliable available CFD results - from DES andLES, see [12] - gives an idea of the plausibility of the results. Overall, it is estimated that themean flow has been measured with a relative error of 5% and the turbulence intensity withan error of 20% which seems to be sufficient for comparison of different turbulence modelingapproaches. However, no formal analysis of error propgation for the entire measurement systemhas been attempted.

3 RESULTS

3.1 Flow in the inlet duct of the test rig

Fig. 5 shows that the flow in the inlet duct is fairly uniform both with respect to mean flowand turbulence level. With respect to the wall-normal coordinate z the non-uniformity of thecore flow is about 0.2 m/s (0.7 %) and with respect to the lateral direction y it is approximately0.3 m/s (1.2%). Boundary layers along the walls seem to be fairly thin keeping in mind thatthese measurements did not try to resolve the near wall region.

The investigations were carried out in two campaigns in 2006, each lasting for about twoweeks. Under the given constraints in budget and time some compromises had to be made.For technical reasons it was not possible to fix the volume flow rate which made the definitionof a reference speed more difficult. During the first campaign all measurements were takensupplying a constant voltage of Sblow = 6.5 V to the blower. In the second campaign it wasattempted to reach the same nominal value of the axial speed at a reference location by adjustingthe blower voltage. An a posteriori analysis revealed that this procedure was not reliable. Afterchecking the data consistency using the redundancy in the u-component it was concluded thatthe safest way for a consistent normalization of data is to deduce the reference speed Uref from

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0

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24 24.5 25 25.5 26

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-3.46-1.76-0.07 1.62 3.31

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y/h=

-3.46-1.76-0.07 1.62 3.31

Figure 5: Profiles of mean U(z) and intensity urms(z) of the axial flow speed in the inlet duct at several lateralpositions y/h given in the legend.

the characteristic of the blower which follows closely the relation

Uref = 3.89 Sblowm

sV −1 . (1)

Here, Uref is the mean flow speed in the center of the inlet duct at an axial position about 50 mmahead of the first bogie cavity.

3.2 Pdfs of the axial flow speed

Fig. 6 shows histograms or pdfs of the axial velocity at different positions.

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Figure 6: Histograms of the axial flow speed at different positions as indicated in the legend.

These plots demonstrate the wide variety of flow states encountered in this configuration. Forexample, in the upper half of the duct (middle subfigure of top row) the velocity oscillates in a

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narrow band around a mean in the order of 27 m/s. Closer to the underside of the coach locatedat z = 0 the range of fluctuation increases and the pdf becomes wider (top left subfigure).Finally, over the intercargap (top right subfigure) the width of the pdf approaches about 20 m/sand is thus comparable to the mean, indicating a high turbulence intensity.

The bottom row of Fig. 6 shows some pdfs from the first bogie cavity which deviate stronglyfrom a Gaussian shape. The histogram for a position close to the wheel at x/h = −9.9 - lowerleft subfigure - exhibits a pronounced bimodal shape. This is typical for flows around obstacleswhere the flow oscillates between different states possibly in connection with vortex shedding.Often steady RANS methods have difficulties in obtaining converged solutions for this type offlow configurations. It is also evident that statistical moments such as U and urms computedfrom such a pdf are rather mathematical constructs which do not represent an average physicalflow state. In this case more meaningful averages might be defined from phase averaging. Sofar, bimodal pdf shapes have only be observed in isolated flow regions near the bogies. Thus,not the entire flow field is dominated by oscillating flow behaviour.

3.3 Profiles of mean and turbulence intensities

Mean flow and turbulence intensity profiles along z have been measured at the nodes of a50 mm by 50 mm grid in the x, y-plane as sketched in Fig. 7.

Figure 7: Grid of locations in the x, y-plane where profiles along z were measured.

Profiles obtained over the funnel-shaped rear part of the first bogie cavity are shown in Figs. 8to 11. Note that for clarity the measurement positions inside the cavity (z < 0) are not includedin these plots. Thus, the location z = 0 does not necessarily corresponds to a location at thewall. Fig. 7 shows whether a certain position (x, y) falls into the cavity or into the small ductconnecting the bogie cavity with the intercar gap.

In Figs. 8 and 10 measurements from the two different LDA orientations are included forthe axial component u which gives some idea of the consistency and accuracy. In general, dataacquired from beam orientations (i) and (ii) are in very good agreement. However, at certainlocations noticeable differences exist. Part of this might be contributed to positioning errorswith respect to the x, y-grid of measurement locations, especially at positions in the vicinity ofthe swept rearward edges of the cavity or near the wheels. On the other hand, the quality ofcertain measurements close to the walls might deteriorate due to beam reflexions. Thus, whendata are used for validation one should always carefully check whether the measurements areplausible.

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Figure 8: Profiles of axial mean speed U(z)/Uref at the lateral position y = −150 mm, −100 mm, −50 mm,0 mm (from top to bottom) from LDA orientation i (◦) and ii (4). The ticmark spacing is 0.1.

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z/h

Figure 9: Profiles of the lateral speed V (z)/Uref (4) and of the wall-normal component W (z)/Uref (+) at thelateral position y = −150 mm, −100 mm, −50 mm, 0 mm (from top to bottom). The ticmark spacing is 0.05.

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Figure 10: Profiles of axial turbulence intensity urms(z)/Uref at the lateral position y = −150 mm, −100 mm,−50 mm, 0 mm (from top to bottom) from LDA orientation i (◦) and ii (4). The ticmark spacing is 0.1.

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Figure 11: Profiles of the lateral intensity vrms(z)/Uref (4) and of the wall-normal intensity wrms(z)/Uref (+)at the lateral position y = −150 mm, −100 mm, −50 mm, 0 mm (from top to bottom). The ticmark spacing is0.05.

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Fig. 8 shows that the flow separates at the rearward blunt face of the first bogie cavity and asmall separation bubble forms along the “train” underside downstream of the funnel, see profilesfor y = 0 mm,x = −175 mm. In this region, a considerable lateral flow component exists, seeFig. 9. Near the separation region the r.m.s. of the axial velocity component - shown in Fig. 10- exceeds 40% of the bulk velocity Uref . Profiles of the lateral intensity vrms show two peaks, asmaller one near the flat “trackbed” wall and a larger one over the cavity. Maximum intensities(r.m.s.) reach 30 % of Uref , see Fig. 11.

Fig. 12 shows part of the flow evolution along the trackbed. The vectoring of the outflowfrom the funnel-shaped end of the bogie cavity causes a 30% increase of the near-wall meanflow (in a distance of 6 mm from the flat wall) in the region −100 mm < y < 100 mm. Inaddition, the fluctuation intensity urms more than triples along the centerline of the duct. Thismight be relevant for the assessment of the aerodynamic load on the trackbed with respectto ballast projection since usually an increase of the near-wall turbulence intensity is closelycoupled to the wall shear stress which in turn governs the onset of particle dislodgement [8].

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ref

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-0mm

Figure 12: Profiles (along x) of the mean (left) U and the intensity urms (right) of the axial velocity component atseveral lateral positions close to the flat wall of the rig (z/h = 0.91) representing the trackbed.

Profiles measured in the central cavity representing the intercoach gap are shown in Fig. 13.From the curves of U(z) it is evident that a free shear layer forms at the upstream edge of thecavity and that the flow recirculates at the bottom of this cavity. At the same time a considerablesecondary flow evolves in the lower part of the cavity with the lateral mean flow component Wreaching up to 20% of Uref . In this region, the turbulence intensity reaches its maximum ofup to 30% of Uref in the free shear layer. A clear trend with respect to the lateral position isobserved: the intensity increases towards the central region of the channel. The increase of theintensity near the upper wall (for z/h > 0.5) affects the near-wall flow and thus the skin frictionas previously concluded from Fig. 12.

The profiles of U(z) nicely demonstrate the well-known fact that the local skin-friction -represented by the near-wall turbulence intensity - is only weakly coupled with the mean axialflow profile. In fact, for a position around z/h = 0.7 the lateral trend of the U -profiles is theopposite as for urms. This has to be considered in the definition of a full-scale measurementprocedure for the determination of the aerodynamic load on the trackbed [8, 6]: one might bemisled when trying to estimate the local wall shear stress based on the measurement of the axialmean speed in a certain wall distance. However, presently it is not clear to what degree the localvariation of the skin friction is relevant for the dislodgement of ballast particles. Since the wallshear strees can be hardly measured directly one might think of assessment of the near-wallturbulence intensity instead since it is closely correlated to the wall stress [13].

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Figure 13: From top to bottom: profiles of axial and lateral mean flow components U/Uref ,W/Uref and of axialand lateral intensities urms(z)/Uref , wrms(z)/Uref at three lateral positions y = −150 mm (◦), y = −100 mm(4), and y = −50 mm (+) over the intercar gap cavity

3.4 Flow visualization

Surface streamline visualization obtained by the China-clay method are shown in Fig. 14. Itdemonstrates the presence of intense secondary flow. A vortex with the axis aligned normal tothe car body forms in the funnel-shaped end of the first bogie cavity. Inside of the intercoachgap three major “cells” form which have approximately equal lateral extent.

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Both, the flow speed measurements and the visualizations indicate that the peculiar trape-zoidal shape of the ICE 3 bogie cavity has a strong effect on the downstream flow, causing aconsiderable lateral variation of the aerodynamic load imposed on the trackbed.

Figure 14: Visualization of surface streamlines. Top: forward facing wall of intercoach cavity. Lower left: bottomof funnel-shaped end of first bogie cavity. Lower right: intercoach cavity.

4 CONCLUSIONS

The flow in a generic underfloor geometry was investigated in a laboratory in scale 1:7 inorder to provide data for validation of numerical flow simulations by CFD. Examination ofthe underlying histograms and cross-comparison of measurements taken from different beamorientations suggests that the data quality is sufficient to allow for a meaningful comparisonwith simulation results both for mean flow components and turbulence intensities.

As a result of the ”funneling” of the flow in the rear part of the first bogie cavity a strong sec-ondary flow pattern evolves which affects the downstream flow. Subsequently the aerodynamicload imposed on the trackbed develops considerable variation in the lateral direction.

At the rear end of the bogie cavity and in the free shear layer which develops over the inter-car gap the turbulence intensity exceeds 30 % of the bulk velocity.

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Due to the lateral obstruction of the flow by the presence of side-walls the findings can not becarried over to the 1:1 scale situation of a passing train. Also, some of the flow features - for ex-ample the “funneling” - might be exaggerated due to the geometrical constraints. Furthermore,due to the reduced scale and the moderate bulk velocity the Reynolds number is an order ofmagnitude smaller than in the 1:1 case. Nevertheless, the configuration seems to pose sufficientchallenges to allow for a promising comparison of different turbulence modeling approaches.

Analysis of the highly disturbed near-wall flow over the intercoach cavity shows that one canbe mislead when trying to assess the local aerodynamic load on the trackbed by measurementof the mean axial speed in a certain distance from the wall. However, it remains to be seen towhat degree knowledge of the local variation of the skin friction is needed for the assessmentof the properties of a certain vehicle.

ACKNOWLEDGMENT

The financial support of Siemens AG for the design of the test section and for the completionof two measurement campaigns is appreciated. We thank the aerodynamic measurement teamof ISTA (formerly known as Hermann-Fottinger-Institut) from TU Berlin, headed by Dr. NavidNayeri, for setting up the experiment and for carrying out a substantial part of the measure-ments. Public funding under grants 19 S 5009 A and 19 S 5009 B from the German ministry ofeconomy (BMWi) under the auspices of S. Meuresch within the French-German DEUFRAKOprogramme is acknowledged.

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[7] ERCOFTAC. The ERCOFTAC best practice guidelines for industrial computational fluiddynamics, in: M. Casey, T. Wintergerste (Eds.), Ver. 1.0, ERCOFTAC Special Interest

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Group on Quality and Trust in Industrial CFD, ERCOFTAC Coordination Centre STI-LMF-EPFL, CH-1015 Lausanne, Switzerland, 95pp., 2000.

[8] H.-J. Kaltenbach, P.-E. Gautier, G. Agirre, A. Orellano, K. Schroeder-Bodenstein,M. Testa, and T. Tielkes. Assessment of the aerodynamic loads on the trackbed caus-ing ballast projection: results from the DEUFRAKO project Aerodynamics in Open Air(AOA). In Proceedings of the 8th World Congress on Railway Research, May 18-22, 2008in Seoul, Korea, page S. 2.3.4.1, 2008.

[9] R.N. Meroney. CFD prediction of cooling tower drift. Journal of Wind Engineering andIndustrial Aerodynamics, 94:463–289, 206.

[10] QNET CFD. Thematic Network on Quality and Trust for the industrial applications ofComputational Fluid Dynamics (CFD). European Union R&D program GROWTH, un-der contract number G1RT-CT-2000-05003, financed by the European Commission. (Seehttp://www.qnet-cfd-net), 2004.

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[12] M. Sima, A. Gurr, and A. Orellano. Validation of CFD for the flow under a train with1:7 scale wind tunnel measurements. In Proceedings of the BBAA VI, Milano, Italy, July20-24, 2008.

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a generic train-underfloor experiment for cfd...

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