| 1. |
- Braunbehrens, Robert, et al.
(author)
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A statistical model for wake meandering behind wind turbines
- 2019
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : ELSEVIER. - 0167-6105 .- 1872-8197. ; 193
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Journal article (peer-reviewed)abstract
- A new wake model is proposed to account for wake meandering in simulations of wind-turbine wakes performed on steady solvers, through a wake-meandering description based on the dispersion theory of Taylor (1921, P. Lond. Math Soc., vol. 20, pp. 196-211). Single-turbine simulations were performed by means of the linearised solver ORFEUS. By analysing the steady wake behind a turbine, a set of parameters describing the wake was first obtained and synthesised into a look-up table. The proposed meandering model extended the simulation results by superimposing the lateral and vertical meandering motions to the steady wake. As a result, the time-averaged velocity distribution of the wake was increased in width and reduced in intensity. Through this combination, the model provides rationale for the wake-deficit decrease and for the power underestimation effects of several wake models. The new wake model is validated against the Lillgrund and Horns Rev data sets.
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| 2. |
- Buccolieri, Riccardo, et al.
(author)
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The drag force distribution within regular arrays of cubes and its relation to cross ventilation – Theoretical and experimental analyses
- 2019
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier. - 0167-6105 .- 1872-8197. ; 189, s. 91-103
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Journal article (peer-reviewed)abstract
- A novel set of wind tunnel measurements of the drag force and its spatial distribution along aligned arrays of cubes of height H and planar area index λ p (air gap between cubes) equal to 0.028 (5H) to 0.69 (0.2H) is presented and analysed. Two different types of measurements are compared: one type where the drag force is obtained using the standard load cell method, another type where the drag force is estimated by measuring the pressure difference between windward and the leeward façades. Results show that the drag force is nearly uniformly distributed for lower λ p (0.028 and 0.0625), it decreases up to 50% at the second row for λ p = 0.11, and it sharply decreases for larger λ p (from 0.25 to 0.69) where the force mostly acts on the first row. It follows that for the lowest λ p the drag force typically formulated as a drag area corresponds to the total frontal area of the array, whereas for large λ p the drag area corresponds to the area of the first row. By assessing the driving pressure for ventilation from the drag force, the analysis is extended to estimate the cross ventilation as an example of application of this type of measurements.
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| 3. |
- Chen, Guang, et al.
(author)
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Dynamic analysis of the effect of nose length on train aerodynamic performance
- 2019
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 184, s. 198-208
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Journal article (peer-reviewed)abstract
- The improved delayed detached eddy simulation (IDDES) was used to study the influence of the train’s nose length on its aerodynamic performance. Both the time-averaged and instantaneous near-wake structures and the associated distribution of slipstream velocity are compared for three nose lengths. As the nose length increases, the mean and Std values of the drag and lift force are decreased. The shorter nose-length case results in a higher slipstream velocity. In particular, at the TSI track-side position, the TSI value U_2δ for the 5-m nose length case is 30% and 32% higher than the corresponding values for the 7.5-m and 10-m nose length cases, respectively. The dynamical flow topology in the wake reveals that the flow structures of the 5-m nose length are different from those of the other two cases in the tail streamline surface. As nose length increases, the longitudinal vortices are weaker, and the angle and distance between the longitudinal vortices are smaller. The shear production from the P_xy caused by the separation of the boundary layer at the lateral wall of the tail train is greater than that of the P_xz caused by the separation of the boundary layer at the top and bottom of the tail train.
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| 4. |
- Dong, Tianyun, et al.
(author)
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Effects of simplifying train bogies on surrounding flow and aerodynamic forces
- 2019
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 191, s. 170-182
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Journal article (peer-reviewed)abstract
- © 2019 Elsevier Ltd In this study, the numerical solution of a high-speed train with several simplified bogies is investigated. The time-averaged flow field around the train, the surface pressure, and the aerodynamic forces on the train are discussed. The results reveal that a simpler bogie structure can achieve a higher underbody flow velocity and change fluctuations beneath the train owing to the resulting turbulence level. The simplification of bogies has a smaller effect on the side slipstream velocity and pressure compare to which in underbody, and at 3 m away from the centre of the track, the simplified bogie with wheels and a simple side frame used in this study obtains similar results to cases wherein more complex bogies are used. The surface pressure under the train is affected by bogie simplification, especially in the bogie cabin end area, resulting in aerodynamic drag and lift variations. If underbody flow or aerodynamic drag and lift forces are the focus of study, then the geometry of the centre region of the bogie, i.e. its main structures features, should be maintained in simplified models.
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| 5. |
- Gullbrekken, Lars, et al.
(author)
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Wind pressure coefficients for roof ventilation purposes
- 2018
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 175, s. 144-152
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Journal article (peer-reviewed)abstract
- Wind pressure coefficients (c p ) are important inputs for analytical calculations of wind load. The aim of this research is to investigate wind pressure coefficients on a test house located in Norway in order to pave the way for improved analysis of wind-driven roofing ventilation. The large-scale test measurements show that the wind pressure coefficient along the eaves of the house varies with different wind approach angles. Assuming wind-driven air flow through the air cavity beneath the roofing, an average Δc p ¯ value of 0.7 is derived for practical engineering purposes. The results from the study are applicable for single or two-storey houses with pitched roofs at different roof angles.
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| 6. |
- Hobeika, Teddy, 1988, et al.
(author)
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CFD investigation on wheel rotation modelling
- 2018
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 174, s. 241-251
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Journal article (peer-reviewed)abstract
- It is well understood in the automotive community that wheels are a major contributor to the aerodynamic drag of passenger vehicles. The flow around rotating wheels is very complex due to the many separation regions created by very small tyre features and by the contact area of the tyre with the ground. Correct modelling of wheel rotation requires accuracy in the representation of the tyre geometry and proper boundary conditions to simulate the rotation. This paper proposes a hybrid approach for simulating tyre rotation which is simple to implement and does not suffer from the limitations of a sliding mesh approach, at the region where the tyre meets the ground. The method is first evaluated on a single wheel that is free standing and the results are compared to a full sliding mesh computation, which is considered to be the best possible numerical solution. The technique is then implemented on a complete vehicle model simulation and the results are compared against wind tunnel force measurements. The good agreement obtained in these test cases shows that the proposed approach is a promising solution to a more accurate numerical simulation of rotating wheels.
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| 7. |
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| 8. |
- Minelli, Guglielmo, 1988, et al.
(author)
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Aerodynamic flow control for a generic truck cabin using synthetic jets
- 2017
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 168, s. 81-90
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Journal article (peer-reviewed)abstract
- This experimental work presents the achievement in drag reduction with the use of active flow control (AFC) for a generic bluff body. Experiments were done in the Chalmers University closed loop wind-tunnel at Reynolds number . The is based on the undisturbed velocity m/s and the width of the model m. The model consists of a simplified truck cabin, characterized by sharp edge separation on top and bottom edges and pressure induced separation on the rounded vertical side edges. The pressure induced separation reproduces the flow detachment occurring at the front A-pillar of a real truck. The investigation of the unactuated and actuated flow was conducted by means of time-resolved particle image velocimetry (PIV). Loudspeakers were used as the actuation device. These were characterized before the actuation study, highlighting an interesting analogy between actuation frequency and jet vortex pair size. The effects of different actuations were evaluated with hot wire anemometry. The effect of the actuation was studied using phase averaging and modal analysis. A notable reduction of the side recirculation bubble was observed. The nature of the separation mechanism was investigated and related to different actuation frequencies spanning the range . As for the , the non-dimensional frequency is based on the undisturbed velocity and the width of the model W.
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| 9. |
- Minelli, Guglielmo, 1988, et al.
(author)
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Validation of PANS and active flow control for a generic truck cabin
- 2017
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 171, s. 148-160
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Journal article (peer-reviewed)abstract
- This paper presents a drag reduction study using active flow control (AFC) on a generic bluff body. The model consists of a simplified truck cabin, characterized by sharp edge separation on top and bottom edges and pressure induced separation on the two other rounded vertical front corners. The pressure induced separation reproduces the flow detachment occurring at the front A-pillar of a real truck (Schuetz, 2015). The prediction of the flow field by partially averaged Navier-Stokes (PANS) simulations, conducted on a relatively coarse mesh, is validated against wind tunnel data (pressure measurements and particle image velocimetry (PIV)) and resolved large eddy simulations (LES) data. The Reynolds number for both simulations and experiments is Re=5×10^5 (which corresponds to 1/6 of a full scale truck Re) based on the inlet velocity Uinf and the width of the model W=0.4m. A validation of PANS results is followed by a CFD study on the actuation frequency that minimizes the aerodynamic drag and suppresses the side recirculation bubbles. PANS accurately predicts the flow field measured in experiments and predicted by a resolved LES. The side recirculation bubble of a simplified truck cabin model is suppressed almost completely and a notable drag reduction by means of AFC is observed.
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| 10. |
- Rao, Anirudh Narayan, 1985, et al.
(author)
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Investigation of the near-wake flow topology of a simplified heavy vehicle using PANS simulations
- 2018
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 183, s. 243-272
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Journal article (peer-reviewed)abstract
- The near-wake flow topology of a ground transportation system (GTS) is investigated using partially-averaged Navier–Stokes (PANS) simulations at Re=2.7×104. Recent numerical investigations for the GTS model using large eddy simulations (LES) showed an anti-symmetric flow topology (flow state II) in the vertical midplane compared to that observed in previous experimental studies (flow state I). The geometrical configuration of the GTS permits bi-stable behaviour, and the realisation of each of the two flow states, which are characterised by an asymmetrical flow topology, is achieved by varying the differencing scheme for the convective flux in the PANS simulations; AVL SMART schemes predict flow state I, while central differencing scheme (CDS) predicts flow state II. When the GTS model was placed away from the ground plane, the AVL SMART scheme fails to predict the flow asymmetry resulting in a pair of symmetrical vortices in the vertical midplane, while flow state II topology is observed when CDS is used. The switch from flow state I (II) to flow state II (I) is achieved by changing the numerical scheme from AVL SMART (CDS) to CDS (AVL SMART), with an intermediate transient-symmetric (TS) state being observed during the switching process. The numerical scheme in the PANS simulations thus plays a critical role in determining the initial flow topology in the near wake of the GTS.
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| 11. |
- Rao, Anirudh Narayan, 1985, et al.
(author)
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On the two flow states in the wake of a hatchback Ahmed body
- 2018
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 173:February 2018, s. 262-278
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Journal article (peer-reviewed)abstract
- Recent experimental investigations in the wake of an idealised car model – the Ahmed body showed the existence of two stable wake states: flow state I, where the flow is fully separated over the back slant of the Ahmed body, and flow state II, where the flow initially separates and then reattaches further along the back slant. The existence of the two flow states is confirmed numerically by using the partially-averaged Navier–Stokes (PANS) turbulence model for various configurations of the Ahmed body. The two flow states can also be distinguished by the instantaneous values of the force coefficients. In flow state I, values of both the lift and drag coefficient are lower compared to flow state II. The influence of the aspect ratio, defined as the ratio of the width of the model to that of a standard Ahmed body, on the two flow states is investigated for the 25deg back slant Ahmed body. For low aspect ratios, flow state II is observed, while for larger aspect ratios, flow state I is observed. Next, the influence of the yaw angle (β) on the occurrence of the two flow states is investigated for the 35deg back slant Ahmed body. For β
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| 12. |
- Rao, Anirudh Narayan, 1985, et al.
(author)
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Qualitative assessment of the bi-stable states in the wake of a finite-width double backward facing step
- 2019
-
In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 186, s. 241-249
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Journal article (peer-reviewed)abstract
- The flow past a simplified frigate shape model which is analogous to a finite-width double backward facing step is investigated numerically using well-resolved large eddy simulations at Re≃8×104. The geometric configuration of this model permits the occurrence of bi-stable flow states, with an asymmetrical flow topology being observed in the lateral midplane behind each step. In each flow state, the flow at the top step is anti-symmetrical to that observed on the bottom step, and the two flow states are anti-symmetrical to each other. Furthermore, incorporating a base cavity on the top step leads to the suppression of the asymmetrical flow topology on both the steps. The recirculation bubble formed by the downwash at each step is elongated when the base cavity is used, as compared to that observed in either of the two flow states, resulting in a decrease of the drag coefficient. In each of the two flow states, the unequal strength of the streamwise vortices close to the lateral edgeson the top step has been identified as the likely cause of the asymmetrical flow on the bottom step.
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| 13. |
- Urquhart, Magnus, 1990, et al.
(author)
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Numerical analysis of a vehicle wake with tapered rear extensions under yaw conditions
- 2018
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 179, s. 308-318
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Journal article (peer-reviewed)abstract
- In recent years, governmental legislation and consumer demands are driving the development of more energy efficient road vehicles. One of the aspects considered when increasing efficiency is the aerodynamic performance of the vehicle. The focus of this paper is on wake effects for a vehicle with tapered rear extensions in side wind conditions. For this purpose, numerical simulations are analysed using post-processing techniques such as Proper Orthogonal Decomposition (POD) and Two-point correlation. The extensions protrude 150 mm from the perimeter of the base and are investigated in two configurations: with a smooth taper and with an added kick. The kick realigns the perimeter base flow to the vehicle's driving direction. As the oncoming flow angularity is increased, drag increases for the investigated angles. The smooth extensions provide the greatest drag improvement at 0° yaw while the extensions with a kick yield additional benefits at yaw, effectively reducing the vehicles drag sensitivity to side wind. A large scale twisting motion is present at yaw for the baseline and smooth extensions configurations which is reduced when adding a kick to the extension.
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| 14. |
- Vernet, Julie, et al.
(author)
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Separation control by means of plasma actuation on a half cylinder approached by a turbulent boundary layer.
- 2015
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier. - 0167-6105 .- 1872-8197. ; 145, s. 318-326
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Journal article (peer-reviewed)abstract
- The flow around a half cylinder (i.e. an immersed cylinder in a flat plate) approached by a turbulent boundary layer is studied, with the aim to control separation via steady Dielectric Barrier Discharge (DBD) plasma actuation. The electric wind induced by a single DBD plasma actuator is studied in quiescent air to understand the role of the different driving parameters and how the cylindrical shape influences the downstream development of the induced electric wind. A double DBD plasma actuator is then placed on the cylinder and the influence of the position of the actuator is studied in order to find the best achievable control. Comparison of the controlled and uncontrolled cases, using both hot-wire anemometry and pressure measurements, shows that a reduction of the separation bubble is possible. By optimizing the position of the double actuator, a reduction of up to 30% of the drag is achieved. The present geometry is chosen as a generic model of the flow around the front corners (A-pillars) of a truck cabin and the work is performed with the long-term vision to be able to reduce drag on trucks.
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| 15. |
- Wang, Jiabin, et al.
(author)
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Impact of bogie cavity shapes and operational environment on snow accumulating on the bogies of high-speed trains
- 2018
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 176, s. 211-224
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Journal article (peer-reviewed)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.
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| 16. |
- Wang, Jiabin, 1993, et al.
(author)
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The effect of bogie fairings on the slipstream and wake flow of a high-speed train. An IDDES study.
- 2019
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 191, s. 183-202
-
Journal article (peer-reviewed)abstract
- In this study, an improved delayed detached eddy simulation (IDDES) method based on shear-stress transport k-ω turbulence model has been used to investigate the slipstream and wake flow around a high-speed train with different bogie fairings at Re = 1.85 × 10^6. The accuracy of the numerical method has been validated by wind tunnel experiments and full-scale field tests. Further, the train slipstream, underbody flow and wake structures are compared for three cases. The results show that the bogies covered by full size bogie fairings significantly decrease the train slipstream velocity and weaken the pressure fluctuation around the high-speed train, especially near the bogie regions. Compared to the maximum slipstream velocity at trackside position in Case 2 (half size fairings), it increases by 15.2% in Case 1 (no fairing) and decreases by 16.1% in Case 3 (full size fairings), respectively. The larger size fairings are found to reduce the scale of longitudinal vortices and decrease the streamwise vorticity level in the wake region, thereby lowering the slipstream velocity distribution in the wake. Finally, the larger bogie fairings are recommended to improve the train aerodynamic performance as well as to improve the safety of trackside workers and passengers standing on the platform.
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| 17. |
- Zhang, Jie, 1987, et al.
(author)
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A study of the influence of bogie cut outs' angles on the aerodynamic performance of a high-speed train
- 2018
-
In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 175, s. 153-168
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Journal article (peer-reviewed)abstract
- The aerodynamic drag of a high-speed train can contribute significantly to its energy consumption. Hence, the purpose of this paper is to find out a new compound mode of bogie cut outs to achieve drag reduction for a Chinese high-speed train. In this paper, a Detached Eddy Simulation method based on the Realizable k-ε turbulence model was used to investigate the underbody flow features of high-speed trains with different compound modes in the angles of bogie cut outs at Re = 1.85 × 10 6 . The time-averaged aerodynamic drag was compared with experimental data from wind tunnel tests. The results show that the DES simulations present high accuracy in predicting this kind of flow underneath the train body, and those numerical results closely agree with the experimental data. The variations of bogie cut outs' angles only cause the changes of flow structures around the bogies and in the wake. As a result, obtain different aerodynamic drag forces. Most of drag of the train is experienced by the streamlined head and all bogie regions. A new compound mode of bogie cut outs is proposed in the present paper, achieving 2.92% drag reduction for a three-car model.
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| 18. |
- Zhang, Jie, 1987, et al.
(author)
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Detached eddy simulation of flow characteristics around railway embankments and the layout of anemometers
- 2019
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 193
-
Journal article (peer-reviewed)abstract
- Anemometers are usually set up along railway embankments to monitor wind speeds, and the layout for them has to be investigated. This work used an improved delayed detached eddy simulation (IDDES) approach to explore the flow properties around railway embankments, and then a proposal was put forward for the layout of anemometers. The numerical method was validated against previous wind tunnel tests on the speed-up ratios of the flow around a 1/300 scale two-dimensional embankment with the slope gradient of 1:2. The effects of inlet velocity profiles, i.e., uniform velocity and atmospheric boundary layer velocity profiles, on the speed-up ratios around a 5 m high railway embankment were compared. The study indicates that using a uniform velocity profile to assess the operational safety of trains running across strong wind regions could be favourable, especially when complex local terrains contribute to different wind characteristics. The anemometers should be set upstream, i.e., at a well defined distance in locations with sufficient extent of open ground and on the electrification masts along railway lines. This is not in line with the anemometer layout of the existing SWEWS (Strong Wind Early Warning Systems), the difference being due to the speed-up effect of the railway embankment, which is usually not considered explicitly. Formulas have been developed on the basis of regression of the simulation results to express the relationships between e.g. top wind speed over the embankment (located in an area where it is not possible to install anemometers) and measured wind speeds. In this way it is possible to take into account the speed-up effect encountered by the wind passing over the embankment, which needs to be considered in the operational rules in order to ensure safe operations.
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| 19. |
- Östh, Jan, 1985, et al.
(author)
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Cluster-based reduced-order modelling of the flow in the wake of a high speed train
- 2015
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 145, s. 327-338
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Journal article (peer-reviewed)abstract
- The flow field in the wake of a high-speed train is studied by cluster analysis and a cluster-based reduced-order model (CROM) is derived. The CROM strategy is a generalization of the Ulam-Galerkin method for the approximation of the finite-rank Perron-Frobenius operator and constitutes a data-driven approach to extract physical mechanisms in an unsupervised manner. Time-resolved data is first clustered into groups by using the k-means clustering algorithm to yield a small number of representative flow states, the cluster centroids. Then, the cluster transitions are modelled as a Markov process. A further analysis of the derived dynamic model provides information on the interaction of the dominant structures in the flow. The flow field around a generic high-speed train model, here the Aerodynamic Train Model, is obtained from a large-eddy simulation. This train model is designed to reproduce the geometrical features of the ICE2 train. The extracted flow structures can be associated with longitudinal vortices and vortex shedding. Furthermore, these structures are found to be associated with either states of low or high drag of the train.
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