Q2. What future works have the authors mentioned in the paper "Flow behaviour and aeroacoustic characteristics of a simplified high-speed train bogie" ?
Such factors need to be accounted for in future work.
Flow behaviour and aeroacoustic characteristics of a simplified high-speed train bogie
01 Sep 2016-Vol. 230, Iss: 7, pp 1642-1658
TL;DR: In this paper, the aerodynamic and aeroacoustic behavior of the flow past a simplified high-speed train bogie at scale 1:10 is studied using a two-stage hybrid method comprising computational fluid dynamics and acoustic analogy.
Abstract: Aerodynamic noise becomes significant for high-speed trains and its prediction in an industrial context is difficult to achieve. The aerodynamic and aeroacoustic behaviour of the flow past a simplified high-speed train bogie at scale 1:10 is studied using a two-stage hybrid method comprising computational fluid dynamics and acoustic analogy. The near-field unsteady flow is obtained by solving the Navier-Stokes equations numerically with the delayed detached-eddy model and the results are used to predict the far-field noise through the Ffowcs Williams-Hawkings method. The sound radiated from the same scaled bogie model is measured in an anechoic open-jet wind tunnel. The aeroacoustic characteristics of tandem wheelsets are also investigated for comparison. It is found that the unsteady flow past the bogie is characterized by coherently alternating vortex shedding from the axles and more randomly distributed vortices of various scales and orientations from the wheels and frame. The vortices formed behind the upstream geometries are convected downstream and impinge on the downstream bodies, generating a highly turbulent wake behind the bogie. The noise predictions correspond fairly well with the experimental measurements for the dominant frequency of tonal noise and the shape of spectra. Vortex shedding from the axles generates the tonal noise with the dominant peak corresponding to the vortex shedding frequency. The directivity exhibits a dipole shape for the noise radiated from the bogie. Compared to the wheelsets of the bogie, the noise contribution from the bogie frame is relatively weaker.
Summary (2 min read)
Jump to: [1. Introduction] – [4.1. Flow field] – [4.3. Wall pressure fluctuations] – [5.1. Acoustic spectra computation] and [6. Conclusions]
1. Introduction
- Over the last few decades, researches have been conducted regarding the source mechanisms of flow-induced noise, particularly in aerospace engineering for landing gears and airframes [1,2].
- In contrast, modelling numerically some simplified geometries can reveal more details of the flow behaviour and the corresponding aeroacoustic mechanisms for some main noise-generating components of high-speed trains.
- 4 DDES is an extension of the detached-eddy simulation (DES) method which combines the large-eddy simulation (LES) in the main flow region with the Reynolds-averaged Navier-Stokes (RANS) approach in the boundary layer region close to the solid objects.
- The cell size on the axle surface is implemented as 0.42 mm around the perimeter and 0.88 mm in the spanwise direction.
4.1. Flow field
- Fig. 3 visualizes the iso-surfaces of the second invariant of the velocity gradient 𝑄 to get an overview of the unsteady flow developed around the bogie.
- Distinct features are observed in different regions of the flow field.
- The flow separates from the upstream wheel front edges and interferes with the flow separated on the wheel tread; therefore, the coherent vortex shedding, seen behind the front axle, cannot be formed behind the front wheel and the wake developed there becomes fully three-dimensional.
- For the point one axle radius above and behind the front axle in the mid-plane between the wheel inner surface and axle mid-span, a tonal peak appears in the spectrum at 324 Hz, as seen in Fig. 5(a).
- A peak appears in the drag coefficient of the bogie and the front wheelset at 641 Hz, which is twice the frequency of the tonal peak in the lift coefficient while at a much lower amplitude.
4.3. Wall pressure fluctuations
- Fig. 8 displays the wall fluctuating pressure level in decibels (𝐿! = 10log 𝑝!"/𝑝!"#! , where 𝑝!" is mean-square fluctuating pressure and 𝑝!"# is reference acoustic pressure 20𝜇𝑃𝑎) on the bogie surface, which can be used to identify the potentially significant noise source regions.
- This also indicates that the massive vortex shedding generated from the front axle may potentially be a major contributor to the noise radiated from the bogie.
- Furthermore, the high pressure fluctuations can be seen around the downstream wheelset due to the flow impingement by the incoming vortex convected from the upstream geometry as well as the flow separation developed from the rear wheel front edges and the vortex shedding formed behind the rear axle.
- Based on the near-field unsteady flow data obtained from the CFD calculations, the far-field noise signals can be predicted by the FW-H acoustic analogy using equivalent acoustic sources.
- Additionally, equivalent circular-shaped receiver positions are defined in the horizontal x-z plane (the coordinates referred to Fig. 1).
5.1. Acoustic spectra computation
- Flow statistics on lift and drag coefficients in Section 4.2 suggest that the flow transient is washed out after 0.1 s.
- Moreover, compared with the experimental data, the tonal peak has a higher amplitude from the calculations in both cases.
- The directivity of the noise radiated to far-field is calculated based on the OASPL determined from the PSD in the frequency range below 2 kHz.
- Note that the similar directivity pattern of sound radiation occurs from the two cases with the slight difference of noise amplitudes between them, which also demonstrates that the wheelsets are the dominant noise sources of the bogie and the noise contribution from the bogie frame is relatively small.
6. Conclusions
- The aerodynamic and aeroacoustic behaviour of the flow past a simplified bogie has been studied using the DDES model and FW-H acoustic analogy.
- It is found that both streamwise and spanwise vortices are generated due to flow separation and vortex shedding around the bogie.
- Furthermore, a vertical dipole pattern of noise radiation is predicted for the upstream wheelset; whereas the downstream wheelset has a multi-directional directivity pattern due to the lift and drag dipoles being aligned perpendicular to each other and its sound generation is relatively weaker.
- These findings are helpful to understand the aerodynamic noise generating mechanisms from the bogie at full scale.
- The turbulent inflow and the complex geometry will lead to complex flow structures and these will also affect the noise generation.
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Figures (19)
Fig. 9. Sketch of receiver locations 
Fig. 2. Structured mesh topology around the bogie 
Fig. 5. Power spectral densities of pressure at bogie wake positions 
Fig. 16. Noise directivity of whole geometry in vertical x-y plane 
Fig. 15. Three-dimensional noise directivity for simplified bogie 
Fig. 7. Power spectral densities of drag coefficients 
Fig. 17. Spectra comparisons of the radiated noise from a circular cylinder case 
Fig. 12. Comparisons of far-field noise spectra between simulation and experiment 5.3. Acoustic directivity 
Fig. 6. Power spectral densities of lift coefficients 
Fig. 10. Spectra of acoustic pressure on far-field receivers (𝑈!=30 m/s) 
Fig. 13. Three-dimensional noise directivity for front and rear wheelsets of simplified bogie 
Table 2. Overview of the mesh size and timestep size for grid independence study 
Table 1. Root-mean-square and mean values of lift and drag coefficients 
Fig. 3. Iso-surface of the instantaneous normalized 𝑄-criterion (at value of 25) 
Fig. 14. Noise directivity of front and rear half-bogies in vertical z-y plane 
Fig. 4. Contours of the instantaneous spanwise vorticity field in a vertical plane (side views) 
Fig. 11. Experimental setup in the anechoic chamber 
Fig. 1. Simplified bogie model (1:10 scale, dimensions in millimetres) 
Fig. 8. Wall pressure fluctuation level of the simplified bogie
Citations
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TL;DR: In this article, a numerical simulation method based on the Realizable k - e turbulence model and Discrete Phase Model (DPM) was used to investigate the mechanism of snow accumulation on the bogie by analysing the characteristics of movement of snow particles.
Abstract: The operation of high-speed trains in ice and snow weather results in a large amount of snow accumulation with ice on the bogies, which will pose a risk to the safety of high-speed trains. In this paper, the snow accumulating on the bogie has been investigated using a numerical simulation method based on the Realizable k - e turbulence model and Discrete Phase Model (DPM). The accuracy of mesh resolution and methodology of CFD was validated by the experimental results of wind tunnel tests. The DPM was used to investigate the mechanism of snow accumulation on the bogie by analysing the characteristics of movement of snow particles. Based on this analysis, two deflectors with the angles of 2.58° and 5.14° were designed, and the anti-snow effect of deflectors for the bogies was compared with numerical results. The results show that lots of snow particles underneath the bogie have direct impacts on the equipment of the bogie, causing massive snow accumulation on the bottom surface. A small amount of snow particles turn back to the region above the bogie from the rear cabin cover, which leads to little snow accumulation on the upper surface of the bogie. The number of particles accumulating on the bottom surface of the bogie is much more than that on the top. Application of deflectors with different angles can improve the anti-snow performance in the bogie region of high-speed trains. The deflector with an angle of 5.14° has the better anti-snow performance. It can reduce the snow accumulation on the whole bogie surfaces by 49.34%, while on the primary heat-producing devices, such as calipers and motors, by 42.47% and 47.40%, respectively.
37 citations
TL;DR: In this paper, the effects of the shape of the bogie cut outs, the running speed of high speed trains and the snow particle density and diameter on the snow accumulation and particle movement characteristics were investigated.
Abstract: In this paper, the snow accumulation on the bogies of high-speed trains has been investigated using a numerical simulation method based on the unsteady Reynolds-Averaged Navier-Stokes simulations (URANS) coupled with the Discrete Phase Model (DPM). The effects of bogie cut outs’ shape, running speed of high-speed trains and snow particle density and diameter on the snow accumulation and particle movement characteristics are discussed. The results show that the bogie installation region with inclined plates shows better anti-snow performance than the configuration with straight plates, which greatly affects the flow structure and snow concentration distribution in the upper space of bogie regions. The running speed of high-speed trains has dominant effect on the snow accumulation on the bogies, and the snow accumulation issue of bogie becomes more serious with increasing running speed. Furthermore, the snow particle density and diameter also have large influence on the snow accumulation on the bogies. With the increase of snow particle density and diameter, the flow range at height direction around bogie region of snow particles become lower and the quality of snow accumulation decrease significantly.
30 citations
TL;DR: In this paper, the aerodynamic behavior of flow past a simplified high-speed train bogie including the ground underneath with ballast particles at scale 1:10 is studied numerically, and it is found that the flow around the bogie is highly unsteady due to strong flow separations and flow interactions developed there.
Abstract: The aerodynamic behaviour of flow past a simplified high-speed train bogie including the ground underneath with ballast particles at scale 1:10 is studied numerically. It is found that the flow around the bogie is highly unsteady due to strong flow separations and flow interactions developed there. Generally, the ballast particles distributed inside the wheels are situated in the stronger turbulent flow and are subject to much higher aerodynamic forces than the particles located outside the wheels. Moreover, these aerodynamic forces increase when the ballast particles are located downstream of the bogie cavity and reach the peak values close to the bogie cavity trailing edge. The force time-series are produced based on the simulations of an array of the ballast particles in a wind-tunnel setup and it shows that the ballast flight is apt to happen as the rear part of the bogie cavity passing by the ballast bed. When the ballast particles become airborne, the fluctuating forces generated increase significantly. Therefore, the stronger unsteady flow developed around the bogie cavity, especially in the cavity trailing edge region, will produce larger fluctuating forces on the ballast particles, which will be more likely to cause ballast flights for high-speed railways.
23 citations
TL;DR: A numerical study using IDDES is carried out to investigate the aerodynamic and the aeroacoustic response of a simplified ICE3 high-speed train model, focusing on the front part of the train and, in particular, on the first bogie cavity.
Abstract: A numerical study using IDDES is carried out to investigate the aerodynamic and the aeroacoustic response of a simplified ICE3 high-speed train model. The work focuses on the front part of the train and, in particular, on the first bogie cavity. The choice is justified by a literature survey which shows that this part of the train is the principal contributor of critical noise pollution created at pass-by in populated areas. Detailed CFD can provide useful insight and be of great importance in the identification of noise generation mechanisms and their relation with the flow structures. Results show the formation of two main aerodynamic structures with a clear relation to the aeroacoustic response calculated on the train and ground surfaces. Simulations were made at Re = 1 . 8 × 10 5 and M = 0.058 to match the experimental observations found in literature and generate a set of benchmark data for future investigations.
21 citations
TL;DR: In this paper, the authors investigated the snow accumulation on the bogies of a three-car grouping high-speed train using unsteady Reynolds-Averaged Navier-Stokes simulations (URANS) coupled with Discrete Phase Model (DPM).
Abstract: The snow accumulation on bogies of a three-car grouping high-speed train has been investigated using unsteady Reynolds-Averaged Navier-Stokes simulations (URANS) coupled with Discrete Phase Model (DPM). The accuracy of mesh resolution and methodology of computational fluid dynamics (CFD) are validated against experimental results. The characteristics of flow fields around bogie regions, the snow particles' motion and snow accumulation are analysed herein. Also the computational costs of numerical simulations using URANS and detached eddy simulation (DES) in the present study are compared. The results show that snow particles begin to flow out from the high-speed train bottom as they come to the first bogie region. After that they whirl around, forming a wind-snow flow in the wake region. Bogie 2 experiences the most snow accumulation. Subsequently, the snow covering on the bogie regions decreases along the train length. A comparison of snow accumulation between URANS and DES methods is made, showing the URANS is sufficient to predict this snow accumulation, which only takes up 2/3 computational cost of the DES. The geometry model consisting of a leading vehicle and a 1/3 s vehicle is recommended to investigate the snow accumulation issue on the bogies of the train.
16 citations
References
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