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Most of the works in the literature agree to attribute the generation of wheel/rail squeal noise in curves to the important lateral slip imposed in the curve and the resulting instabilities. In models, the occurrence of the phenomenon is thus generally studied through a stability analysis based on the linearization of the contact forces. Despite its undeniable interest, the stability analysis does not allow the prediction of the amplitudes of the nonlinear self-sustained vibrations resulting from the instabilities. These nonlinear vibrations are most often calculated using a numerical integration of the dynamic equations of the system in the time domain. Some authors have proposed simplified methods allowing a direct calculation of stationary regimes, but limited to a reduced modal description of the system dynamics. In this presentation, an original method is proposed to determine approximate limit cycles from the wheel/rail contact mobilities expressed in the frequency domain. The contact condensation allows to be both more general and more functional to describe the dynamics of structures, in particular the one of the rail. Assuming a mono-harmonic vibratory cycle, the corresponding amplitude is determined from a power balance and the squeal level at the considered pulsation is obtained from analytical radiation factors.

Aerodynamic noise is generated by interaction of the air flow with an object and within the turbulent flow itself. In railways it becomes an important noise source for speeds above 250 kph and major areas of noise generation on trains, in particular high speed trains, are the train head, the leading and second bogie, the pantograph and the gaps between trailers. In this presentation a numerical simulation approach based on CFD/CAA techniques aiming to predict aerodynamic noise of different components of SNCF's TGV high speed trains. The approach is based on an unsteady DES flow simulation combined with the Ffowcs-Williams and Hawkins (FW-H) analogy for the acoustic part. In order to develop the method different models are implemented and the leading bogie was selected as an application case. A simplified symmetric model will be compared against a full, higher resolved model in order to see if computation time gains are feasible. Results of this simulation, in terms of sound power and directivity, are already used by SNCF noise experts in order to estimate pass-by noise levels of TGV high speed trains. Furthermore, noise mitigation solutions can be tested virtually with the suggested approach before being tested with a prototype.

[EN] The noise inside railway vehicles is transmitted by both structure-borne and airborne paths and, although there are many sources, the rolling noise is often the most important. This paper focuses on the structure-borne transmission of rolling noise in a metro vehicle. Measurements are presented first of the vertical and lateral dynamic stiffness of a primary suspension element consisting of conical rubber/metal elements. Results are presented for various constant preloads over the frequency range 60600 Hz. An analytical model of the suspension element is also developed, based on a mass-spring system and including wave motion within the rubber elements. The dynamic stiffness results are used in a finite element model of the running gear, consisting of the bogie frame, wheelsets and suspension elements. The excitation is provided by the combined wheel/rail roughness at the contact point. This model is used to calculate the blocked forces at the connection points between the secondary suspension elements and the car body. The blocked forces are combined with measured vibro-acoustic transfer functions from these mounting points to the vehicle interior to determine the structure-borne noise inside the vehicle. The proposed methodology is validated against measurements during operation in terms of acceleration levels, blocked forces and structure-borne noise levels inside the vehicle, showing reasonably good agreement. Including the dynamic stiffness for the primary suspension leads to improved agreement between 100 and 500 Hz compared with using a constant stiffness., The work presented in this paper has received funding from the Shift2Rail Joint Undertaking under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 777564). The contents of this publication only reflect the authors' views and the Joint Undertaking is not responsible for any use that may be made of the information contained in the paper.

[EN] A framework is described for predicting the airborne noise inside railway vehicles which is applied to rolling noise sources. Statistical energy analysis (SEA) is used to predict the interior noise by subdividing the train cabin into several subsystems. The dissipation loss factors are obtained from the measured reverberation time in the train cabin. The power input to the interior SEA model is obtained from the external noise sources by multiplying the incident sound power on the external surfaces with measured transmission coefficients of the train floor and sidewalls. The sound power incident on the train floor is calculated by using an equivalent source model for the wheels and track together with an SEA model of the region below the floor. The incident sound power on the sides is obtained by using a waveguide boundary element (2.5D BE) method. The procedure is applied to a Spanish metro train vehicle running in the open field for which rolling noise is the main external noise source. The procedure is verified by field measurements of sound pressure beneath the carriage, on the sidewalls and inside the vehicle. The sensitivity of the results to changes in interior absorption is also studied, including the effect of passengers., This work has been funded by the China Scholarship Council and the RUN2Rail H2020/Shift2Rail project (Grant agreement No: 777564). The contents of this publication only reflect the authors' views and the Shift2Rail Joint Undertaking is not responsible for any use that may be made of the information contained in the pape

This paper presents computational methods that are used by rolling stock manufacturers to predict noise inside vehicles. For airborne transmission, which dominates in the medium-high frequency range, a four-step procedure is applied: source description by their emitted sound power level, propagation of noise to the train’s exterior surface, panel transmission loss and acoustic response of the interior cavity. Reasonable agreement between computations and measurements is usually obtained, and the method makes it possible to rank the different source contributions and airborne transmission paths. Structure borne noise dominates in low frequencies. Finite Element models are used to improve car body design (dynamic stiffness at input points and carbody vibroacoustic transfers), but they do not cover the whole problem since the modelling of excitation from the bogie is not included. Recent research allowing the computation of blocked forces at car body input points and starting with wheel/rail interaction is briefly presented. Concerning source modelling, a focus is made on traction noise, including electromagnetic excitations in electric motors and mechanical excitations due to the meshing process inside gearboxes. Efficient computational methods and validation examples are presented. The coupling of these methods with optimization methods has great potential for improvement of motor noise and vibration design.

[EN] An approach is presented for modelling the noise propagation beneath the train floor and this is applied to rolling noise sources. It is assumed that the sound incident on the train floor is made up of a direct and a reverberant component. A combination of two numerical modelling approaches is considered to deal with these: an equivalent source model, to represent the direct component, and statistical energy analysis (SEA) for the reverberant part. In the equivalent source model, the wheel is replaced by monopole and dipole sources, which represent its radial and axial radiation. The rail vertical vibration and the sleepers are replaced by arrays of monopole sources while the rail lateral vibration is replaced by an array of lateral dipoles. The sound power of the rolling noise is obtained by using the TWINS model. In the SEA model, the region beneath the train floor is divided into several volumes and the power input to these subsystems is assumed to be due to the first reflections from the train floor and the ground. The reverberant and direct sound have very similar contributions to the total sound power incident on the train floor although this depends on how the equipment is arranged beneath the train. The modelling approach is verified by comparing the predicted sound pressure levels with laboratory measurements and with field tests., This work has been funded by the China Scholarship Council and the RUN2Rail H2020/Shift2Rail project (Grant agreement No: 777564). The contents of this publication only reflect the authors' views and the Shift2Rail Joint Undertaking is not responsible for any use that may be made of the information contained in the paper. The authors would also like to thank Dr. Hongseok Jeong for his assistance in the laboratory measurements and Metro de Madrid for assistance in the field tests. All data published in this paper are openly available from the University of Southampton repository at 10.5258/SOTON/D1552.

In this paper, a wavenumber-domain boundary element (2.5D BE) approach is adopted to predict the transmission of noise from the wheels, the rails and the sleepers to the train external surfaces. In the 2.5D models, only the cross-section of the vehicle is created by using boundary elements, while the third direction is taken into account in terms of wavenumbers. After the sound pressure on the train cross-section is obtained, an inverse Fourier transform is applied to obtain the spatial distribution of the sound on the train surfaces. To validate this approach, the 2.5D boundary element method was used to predict the sound distribution on the train surfaces due to a point source below the vehicle, and due to the vibration of the track. The prediction of the sound distribution from the 2.5D method shows the sound pressure levels on the train floor are 20 dB higher than the pressure on the sides, and the pressure on the train roof caused by the sources below the vehicle is negligible. The 2.5D boundary element method was also used to predict the sound pressure spectrum on the train sides when the train was in running operation. Reasonable agreement was found with measurements.

[EN] In order to be able to predict train interior noise, it is first important to calculate the external sound pressure distribution on the floor, sidewalls and roof. This can then be combined with the transmission loss of the train panels to determine the interior noise. Traditional techniques such as the finite element and boundary element (FE/BE) methods in three dimensions (3D) can achieve this result but are computationally very expensive. In this paper, a wavenumber-domain boundary element (2.5D BE) approach is instead adopted to predict the propagation of rolling noise from the wheels, rails and sleepers to the train external surfaces. In the 2.5D models, only the cross-section of the vehicle is represented by using boundary elements, while the third direction is considered in terms of a spectrum of wavenumbers. The rail is treated directly in the wavenumber domain but, to include the wheel, a method of representing point sources in a 2.5D approach is developed. An inverse Fourier transform is applied to obtain the spatial distribution of the sound pressure on the train surfaces. The validity of this approach has been verified by comparison with experimental data. The 2.5D BE method was first used to predict the sound distribution on a 1:5 scale train surfaces due to a point source below the vehicle, and later it was used to predict the sound pressure on a full-scale metro vehicle due to a loudspeaker. Comparisons of predictions with measurements on the scale model and on the metro vehicle showed good agreements. For a point source below the vehicle, the sound pressure levels on the train floor were found to be around 20 dB higher than on the sides, and the sound pressure on the train roof was negligible. The 2.5D BE method was also used to predict the sound pressure on the metro vehicle surfaces in running operation, in which the predicted sound pressure levels on the train external surfaces agreed with measurements to within 3 dB and similar trends were found in terms of spectra and longitudinal distribution of pressure., The work presented in this paper has received funding from China Scholarship Council and the Shift2Rail Joint Undertaking under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 777564). The contents of this publication only reflect the authors' view and the Joint Undertaking is not responsible for any use that may be made of the information contained in the paper. The authors would also like to thank Dr. Hongseok Jeong for his assistance in the laboratory measurements and Metro de Madrid for assistance in the field tests. The authors are grateful to Dr. Xianying Zhang for providing the measured vibration of the 1:5 scale rail. All data published in this paper are openly available from the University of Southampton repository at 10.5258/SOTON/D1483

Flame-wall interactions (FWI) of laminar premixed methane-air flames at atmospheric pressure are studied using various laser diagnostic methods. Velocity fields and flame front locations are measured simultaneously by two-component particle image velocimetry (PIV) and planar laser induced fluorescence (LIF) of the OH-radical. Coherent anti-Stokes Raman spectroscopy (CARS) and two-photon LIF of the CO molecule are used to determine temperatures and CO concentrations. The FWI process is investigated using a generic burner setup with well-defined boundary conditions, where one branch of a V-shaped flame interacts with a water-cooled stainless steel wall, corresponding to a sidewall quenching (SWQ) geometry. FWI is studied for equivalence ratios of ϕ = 0.83, 1.0 and 1.2. The quenching distance of the flames is determined using two different methods. Additionally, the near wall behavior of the flame consumption speed is analyzed and compared with that of a freely propagating laminar flame. Thermochemical properties are analyzed using CO/T-state diagrams. Comparison to one-dimensional laminar flame calculations undisturbed by the presence of a wall highlights the severe impact upon thermochemical states. Comparing characteristic time scales of heat transfer processes to chemical processes indicates that diffusion rather than chemical reaction processes is the reason for these observations.

The presence of a turbulent premixed flame strongly influences the properties of the adjacent velocity boundary layer. This influence is studied here using a generic configuration where at atmospheric pressure turbulent premixed methane/air flames interact with a temperature stabilized wall. The experiment is optimized for well-defined boundary conditions and optical accessibility in the zone where the flame impinges at the wall. Laser based diagnostic methods are used to measure two components of the velocity field by particle image velocimetry simultaneously with the flame front position using laser induced fluorescence of the OH molecule. Two measurement planes are selected that are aligned perpendicularly to the surface of the wall. Based on this data, the flow field near the wall is analyzed by different methodologies using laboratory-fixed and flame-conditioned statistics, a quadrant splitting analysis of the Reynolds stresses and an evaluation of the production term of the turbulent kinetic energy. The results of chemically reactive cases are compared to their corresponding non-reactive flows for otherwise identical inflow conditions. In the zone of flame-wall interactions the boundary layer structure and its turbulence are dominated by the turbulent flame. Important features are that the flame compresses the boundary layer already upstream the location where the flame is finally quenched and that ejection and sweeps are no longer the dominant mechanisms as in non-reactive boundary layers. This experimental data may serve additionally as a database for model development for near wall reactive flows.

Flame–wall interactions (FWI) of a turbulent side-wall quenching (SWQ) V-flame is characterized by planar laser diagnostics. Velocities and flame front positions are measured simultaneously by two-component particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) of the OH radical. Flame surface density and reactive flame surface density are derived from experimental data and evaluated in a physical and flame progress variable domain. The impact of the wall on flame structures is clearly observed. Additionally mean reaction rates are derived using both flame surface densities and a wall-influenced local consumption speed. Approaching walls reaction rates strongly decrease. Reaction rates are important for quantifying incomplete combustion near walls and impose a challenge for improved modeling approaches in numerical flame simulations. These experimental results are compared to previous direct numerical simulation (DNS) studies and flame surface density models from literature. Despite different Reynolds-numbers overall a good agreement between experimental data and modeling results is achieved. This is an indication that simplified chemical kinetic modeling in DNS is sufficient for representing kinematics of turbulent flames near walls.

This paper reports on experimental investigations of turbulent flame-wall interaction (FWI) during transient head-on quenching (HOQ) of premixed flames. The entire process, including flame-wall approach and flame quenching, was analyzed using high repetition rate particle image velocimetry (PIV) and simultaneous flame front tracking based on laser-induced fluorescence (LIF) of the OH molecule. The influence of convection upon flame structures and flow fields was analyzed qualitatively and quantitatively for the fuels methane (CH4) and ethylene (C2H4) at ϕ = 1. For this transient FWI, flames were initialized by laser spark ignition 5 mm above the burner nozzle. Subsequently, flames propagated against a steel wall, located 32 mm above the burner nozzle, where they were eventually quenched in the HOQ regime due to enthalpy losses. Twenty ignition events were recorded and analyzed for each fuel. Quenching distances were 179 μm for CH4 and 159 μm for C2H4, which lead by nondimensionalization with flame thickness to Peclet numbers of 3.1 and 5.5, respectively. Flame wrinkling and fresh gas velocity fluctuations proved flame and flow laminarization during wall approach. Velocity fluctuations cause flame wrinkling, which is higher for CH4 than C2H4 despite lower velocity fluctuations. Lewis number effects explained this phenomenon. Results from flame propagation showed that convection dominates propagation far from the wall and differences in flame propagation are related to the different laminar flame speeds of the fuels. Close to the wall flames of both fuels propagate similarly, but experimental results clearly indicate a decrease in intrinsic flame speed. In general, the experimental results are in good agreement with other experimental studies and several numerical studies, which are mainly based on direct numerical simulations.

In the present paper, direct numerical simulation (DNS) and particle image velocimetry (PIV) have been applied complementarily in order to generate a database of near-wall turbulence properties of a highly turbulent jet impinging on a solid surface under different inclination angles. Thereby, the main focus is placed on an impingement angle of 45 ∘ , since it represents a good generic benchmark test case for a wide range of technical fluid flow applications. This specific configuration features very complex flow properties including the presence of a stagnation point, development of the shear boundary layer and strong streamline curvature. In particular, this database includes near-wall turbulence statistics along with mean and rms velocities, budget terms in the turbulent kinetic energy equation, anisotropy invariant maps, turbulent length/time scales and near-wall shear stresses. These properties are useful for the validation of near-wall modeling approaches in the context of Reynolds-averaged Navier–Stokes (RANS) and large-eddy simulations (LES). From this study, in which further impingement angles ( 0 ∘ , 90 ∘ ) have been considered in the experiments only, it turns out that (1) the production of turbulent kinetic energy appears negative at the stagnation point for an impingement angle other than 0 ∘ and is balanced predominantly by pressure-related diffusion, (2) quasi-coherent thin streaks with large characteristic time scales appear at the stagnation region, while the organization of the flow is predominantly toroidal further downstream, and (3) near-wall shear stresses are low at the stagnation region and intense in regions where the direction of the flow changes suddenly.

Die Entwicklung der Tatigkeitsfelder und der inneren Situation der gleichgeschalteten Ost-CDU hat in der DDR-Forschung bis zur deutschen Vereinigung nur geringe Aufmerksamkeit gefunden. Seit der erzwungenen Umformung zu einer stalinistischen Kaderpartei im Verlauf des Jahres 1950 galt die CDU in organisatorischer und programmatischer Hinsicht als eine Kopie der SED. Nach der Anerkennung der fuhrenden Rolle der SED im Juli 1952 zeichneten sich ihre politischen Erklarungen durch eine bedingungslose Gefolgschaft aus. Auf der anderen Seite vereinigte die CDU Angehorige einer Bevolkerungsgruppe, die aus verschiedenen Grunden nicht Mitglied der SED werden wollte und sich somit dem Hauptstrom parteipolitischer Betatigung in der DDR entzog. Die Mitglieder bekannten sich zu einer Weltanschauung, die von der SED als »unwissenschaftlich« und nicht selten auch als reaktionar betrachtet wurde. Inwieweit stellte die CDU eine Interessenvertretung fur christliche Belange im atheistischen Staat dar? Welche Erfolge und Schwierigkeiten ergaben sich beim Bemuhen, die kirchlich gebundenen Mitglieder in die sozialistische Gesellschaft zu integrieren? Wie auserte sich die innere Spannung zwischen der SED-horigen Fuhrung und der Parteibasis, die dem offiziellen Kurs nicht nur in den fruhen funfziger Jahren mit deutlicher innerer Distanz gegenuberstand? Der Zugang zu den Akten des ehemaligen Parteiarchivs der Ost-CDU, die Verfugbarkeit der Einschatzungen der SED sowie die Moglichkeit der Befragung von Mitgliedern und Funktionaren gewahren nun erstmals Einblicke hinter die Propagandafassade einer problemlosen Zusammenarbeit von Christen und Marxisten in der DDR.