| 1. |
- Burman, Jan
(författare)
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An evaluation of topographical effects on neutral and heavy-gas dispersion with a CFD model
- 1998
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - 0167-6105 .- 1872-8197. ; 74:6, s. 315-325
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Tidskriftsartikel (refereegranskat)abstract
- Three different scenarios are studied to estimate how different structures at the side of a road, influence concentration levels. A solid fence gives the strongest effect on concentration. It forces the mean flow to move vertically which promotes mixing in the wake behind the fence. A hedge reduces the level of turbulence and the level of concentration becomes higher due to less turbulent dispersion. A road-valley generates turbulence in an intermediate regime. It captures a part of the plume in the valley which gives high concentrations locally. Atmospheric stability increases the concentration levels at a distance from the topographical disturbance. A heavy gasplume encountering a solid fence is broadened in front of the fence depending on the height of the fence and internal stability in the plume. The relation between these parameters, wind speed and the source rate will also affect the level of concentration downwind the fence.
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| 2. |
- Brandt, Adam, 1993, et al.
(författare)
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Base wake dynamics and its influence on driving stability of passenger vehicles in crosswind
- 2022
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 230
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Tidskriftsartikel (refereegranskat)abstract
- The unsteady flow around a travelling vehicle induces fluctuating aerodynamic loads. Automotive manufacturers usually set targets on the time-averaged lift forces to ensure good straight-line stability performance at high speeds. These targets are generally sufficient in preventing unstable vehicle designs. Yet, small changes in averaged values occasionally yield unexpectedly large differences in the stability performance, indicating that the changes in averaged normal loads cannot solely explain these differences. The unsteady aerodynamic effects on driving stability are, therefore, an interesting topic to study. The objective of the present work is to investigate the differences in wake dynamics and fluctuating aerodynamic loads for two variants of a roof spoiler on a sports utility vehicle: a baseline that was known to cause stability issues and an improved design which resolved them. The vehicle designs were investigated using accurate time-resolved CFD simulations for a set of crosswind conditions. The unsteady aerodynamic response was coupled to a vehicle dynamics model to analyse the resulting impact on driving stability. It was shown that in crosswinds the baseline spoiler, contrary to the improved spoiler, has bi-stable wake dynamics that induce lift force fluctuations at frequencies close to the 1st natural frequency of the rear suspension.
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| 3. |
- Braunbehrens, Robert, et al.
(författare)
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A statistical model for wake meandering behind wind turbines
- 2019
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : ELSEVIER. - 0167-6105 .- 1872-8197. ; 193
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Buccolieri, Riccardo, et al.
(författare)
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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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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier. - 0167-6105 .- 1872-8197. ; 189, s. 91-103
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Buscariolo, Filipe F., et al.
(författare)
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Spectral/hp element simulation of flow past a Formula One front wing : Validation against experiments
- 2022
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105 .- 1872-8197. ; 221
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Tidskriftsartikel (refereegranskat)abstract
- Emerging commercial and academic tools are regularly being applied to the design of road and race cars, but there currently are no well-established benchmark cases to study the aerodynamics of race car wings in ground effect. In this paper we propose a new test case, with a relatively complex geometry, supported by the availability of CAD model and experimental results. We refer to the test case as the Imperial Front Wing, originally based on the front wing and endplate design of the McLaren 17D race car. A comparison of different resolutions of a high fidelity spectral/hp element simulation using under-resolved DNS/implicit LES approach with fourth and fifth polynomial order is presented. The results demonstrate good correlation to both the wall-bounded streaklines obtained by oil flow visualization and experimental PIV results, correctly predicting key characteristics of the time-averaged flow structures, namely intensity, contours and locations. This study highlights the resolution requirements in capturing salient flow features arising from this type of challenging geometry, providing an interesting test case for both traditional and emerging high-fidelity simulations.
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| 6. |
- Chen, Guang, et al.
(författare)
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Dynamic analysis of the effect of nose length on train aerodynamic performance
- 2019
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 184, s. 198-208
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Chen, Zheng wei, et al.
(författare)
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Reducing the aerodynamic drag of high-speed trains by air blowing from the nose part: Effect of blowing speed
- 2023
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - 0167-6105. ; 238
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Tidskriftsartikel (refereegranskat)abstract
- To reduce the aerodynamic drag of high-speed trains, this work proposes an air blowing configuration on the head and tail cars of high-speed trains. The variation in the aerodynamic drag and slipstream velocity is analyzed under different blowing velocities, and the flow mechanism for train aerodynamic performance alteration is explained. The results show that under the blowing speeds of Ub = 0.05Ut, 0.10Ut, 0.15Ut, and 0.20Ut, where Ut is the train speed, the total drag coefficient (Cd) decreases by 5.81%, 10.78%, 13.70%, and 15.43% compared to the without-blowing case, respectively. However, with the increase in the blowing speed, the reduction trend of Cd tends to be smoother; namely, the decrement ratio compared to the previous blowing speed for the head car is 9.08%, 0.11%, 0.60%, and 1.14% for Ub = 0.05Ut, 0.10Ut, 0.15Ut, and 0.20Ut, respectively. The blowing measure generates an air gap between the coming flow and train surface, consequently causing a reduction in the viscous and pressure drag. In addition, the structure size and strength of the wake flow under different blowing cases show a decreasing trend from Ub = 0.00Ut to 0.10Ut and then an increasing trend from Ub = 0.10Ut to 0.20Ut. Thus, considering the blowing cost, efficiency, and flow structure evolution comprehensively, the case of Ub = 0.10Ut is recommended. Under this blowing speed, the reduction ratio of the aerodynamic drag is 9.18%, 12.77%, 10.90%, and 10.78% for the head, middle, tail car, and total train, respectively.
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| 8. |
- Dong, Tianyun, et al.
(författare)
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Effects of simplifying train bogies on surrounding flow and aerodynamic forces
- 2019
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 191, s. 170-182
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Dong, Tianyun, et al.
(författare)
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The effect of reducing the underbody clearance on the aerodynamics of a high-speed train
- 2020
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 204
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Tidskriftsartikel (refereegranskat)abstract
- The effect of lowering the ground clearance, on train aerodynamics is investigated using IDDES. The high speed train geometry with its full underbody complexity is used in the investigation. The clearance is reduced by installing extra panels on the track. The numerical results are verified and validated by a grid independence study and experimental data. This work shows that, when lowered the clearance, the underbody velocity at the head car decreases, while the underbody velocity at the middle and tail car increases. The reduced clearance barely affects the time-averaged slipstream at 3 m away from the center of track. However, at a closer distance to the train body, the difference in velocity is observed to reach up to 50% between the two clearance configurations and the clearance has an opposite effect on the trackside and platform slipstream. Based on the analysis of ensemble-averaged slipstream, lowering the underbody clearance, the characteristic air speed at the trackside and platform height increases by 2.0% and 6.7%, respectively. The total drag is almost unaffected by the clearance, but the changed distribution of the drag indicates a larger drag depends on the bogie structure if longer grouped train is used. The total lift decreases 25.9% after the clearance is reduced. Specifically, 4.1% of the negative lift is increased at the head car, while the positive lift decreases 92.7% and 1.8% for the middle and tail car, respectively. Overall it is shown that reducing the underbody clearance barely affect the slipstream at standard positions, but affects more aerodynamic loads of the train.
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| 10. |
- Ekman, Petter, 1988-, et al.
(författare)
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Assessment of hybrid RANS-LES methods for accurate automotive aerodynamic simulations
- 2020
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105 .- 1872-8197. ; 206
-
Tidskriftsartikel (refereegranskat)abstract
- The introduction of the Harmonized Light Vehicles Test Procedure causes a significant challenge for the automotive industry, as it increases the importance of efficient aerodynamics and demands how variations of optional extras affect the car’s fuel consumption and emissions. This may lead to a huge number of combinations of optional extras that may need to be aerodynamically analyzed and possibly optimized, being to resource-consuming to be done with wind tunnel testing merely. Reynolds Average Navier-Stoles (RANS) coupled with Large Eddy Simulations (LES) have shown potential for accurate simulation for automotive applications for reasonable computational cost. In this paper, three hybrid RANS-LES models are investigated on the DrivAer notchback and fastback car bodies and compared to wind tunnel measurements. Several yaw angles are investigated to see the model’s ability to capture small and large changes of the flow field. It is seen that the models generally are in good agreement with the measurement, but only one model is able to capture the behavior seen in the measurements consistently. This is connected to the complex flow over the rear window, which is important to capture for accurate force predictions.
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| 11. |
- Gullbrekken, Lars, et al.
(författare)
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Wind pressure coefficients for roof ventilation purposes
- 2018
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 175, s. 144-152
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Tidskriftsartikel (refereegranskat)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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| 12. |
- Hang, Jian, et al.
(författare)
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Experimental and numerical studies of flows through and within high-rise building arrays and their link to ventilation strategy
- 2011
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105 .- 1872-8197. ; 99:10, s. 1036-1055
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Tidskriftsartikel (refereegranskat)abstract
- Urban ventilation implies that wind from rural areas may supply relatively clean air into urban canopies and distribute rural air within them to help air exchange and pollutant dilution. This paper experimentally and numerically studied such flows through high-rise square building arrays as the approaching rural wind is parallel to the main streets. The street aspect ratio (building height/street width, H/W) is from 2 to 5.3 and the building area (or packing) density (lambda(p)) is 0.25 or 0.4. Wind speed is found to decrease quickly through high-rise building arrays. For neighbourhood-scale building arrays (1-2 km at full scale), the velocity may stop decreasing near leeward street entries due to vertical downward mixing induced by the wake. Strong shear layer exists near canopy roof levels producing three-dimensional (3D) vortexes in the secondary streets and considerable air exchanges across the boundaries with their surroundings. Building height variations may destroy or deviate 3D canyon vortexes and induced downward mean flow in front of taller buildings and upward flow behind taller buildings. With a power-law approaching wind profile, taller building arrays capture more rural air and experience a stronger wind within the urban canopy if the total street length is effectively limited. Wider streets (or smaller lambda(p)), and suitable arrangements of building height variations may be good choices to improve the ventilation in high-rise urban areas.
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| 13. |
- He, Kan, et al.
(författare)
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Assessment of LES, IDDES and RANS approaches for prediction of wakes behind notchback road vehicles
- 2021
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 217
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Tidskriftsartikel (refereegranskat)abstract
- The capability of Large Eddy Simulations (LES), Improved Delayed Detached Eddy Simulations (IDDES) and Reynolds-Averaged Navier–Stokes Equations (RANS) to predict the flow behind notchback Ahmed body is investigated in the present paper. Simulations consider two specific models, with effective backlight angles of β1=17.8° and β2=21.0°, respectively. The focus of the study is on the prediction of the expected lateral asymmetry or symmetry of the near-wake flows. Results show that IDDES using coarse computational grids predicts the flow in agreement with LES using finer computational grids. RANS results in inaccurate flow predictions, attributed to its steady formulation relying on turbulence modelling being incapable of dealing with the studied flow. Modal analysis applying Proper Orthogonal Decomposition (POD) suggests the consistency of the wake dynamics between IDDES and LES. The presence of the wake bi-stability is validated by the wind tunnel experiment.
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| 14. |
- He, Kan, et al.
(författare)
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Evaluation of LES, IDDES and URANS for prediction of flow around a streamlined high-speed train
- 2022
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 223
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Tidskriftsartikel (refereegranskat)abstract
- The turbulent flow past a simplified Intercity-Express 3 high-speed train at ReH=6×104 is investigated by a combination of wind tunnel experiments and numerical simulations using the large-eddy simulation (LES), the improved delayed detached eddy simulation (IDDES) and the unsteady Reynolds-averaged Navier-Stokes (URANS) simulation. This work aims to compare the predictive capabilities of LES, IDDES and URANS for the flow over a streamlined high-speed train. Numerical simulations are compared to experimental data for validation. Results show that the well-resolved LES is more accurate among the numerical methods used. Compared to the well-resolved LES, IDDES and URANS using the coarser mesh can produce similar mean flow, although IDDES and URANS are found to be slightly inaccurate for the coherent wake structures near the wall. However, for the near-wall flow instability concerning wake dynamics, Reynolds stresses, turbulence kinetic energy and the fluctuation of pressure, IDDES is found to be inapplicable. Overall, this study suggests that the well-resolved LES is appropriate to the flow of a streamlined high-speed train. Moreover, IDDES and URANS are proved to apply to the mean field of the studied flow.
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| 15. |
- Helvig, Sanne de Jong, et al.
(författare)
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A comparison of lab-scale free rotating wind turbines and actuator disks
- 2021
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105 .- 1872-8197. ; 209
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Tidskriftsartikel (refereegranskat)abstract
- Planar particle image velocimetry was conducted upstream and in the near-wake of a lab-scale free-rotating wind turbine model and compared to several actuator disks with the same dimensions. The Reynolds number of the incoming flow is order 10(4). Actuator disks with different designs and solidities were tested, and the process of actuator disk selection is explicitly shown. The drag, mean velocity and mean vorticity in the wake of the disks were compared to that of the rotating model. For the disk that was the best match, the Reynolds stresses and swirling strength are also presented. The instantaneous swirling strength illustrated that despite similar mean fields, the instantaneous phenomena were significantly different. Distinct tip vortices were present in the wake of the rotating model but were absent from the wake of the actuator disk. Proper orthogonal decomposition was used to further investigate the underlying phenomena in the two flows, again demonstrating the importance of tip vortices when studying the rotating model and the lack of such distinct vortices when using the actuator disk. Hence, despite well-matched mean characteristics, the instantaneous structures in the two flows remain distinct.
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| 16. |
- Hemida, Hassan, 1972, et al.
(författare)
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LES study of the influence of the nose shape and yaw angles on flow structures around trains
- 2010
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 98:1, s. 34-46
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Tidskriftsartikel (refereegranskat)abstract
- Large-eddy simulation (LES) is made of the flow around a generic train model at two different yaw angles of 90 {ring operator} and 35 {ring operator} . The Reynolds numbers, based on the freestream velocity and the height of the train, are 3 × 10 5 and 3.7 × 10 5 for the yaw angles of 90 {ring operator} and 35 {ring operator} , respectively. The primary objective is to investigate the influence of the nose shape and yaw angles on the flow structures and the train aerodynamics. Both the time-averaged and instantaneous flows are explored. In the case of the 90 {ring operator} yaw angle, the LES results show that the influence of the three-dimensional flow from the nose of the train on the time-averaged wake flow is limited to a region of a length of 3.5 train heights from the tip of the nose in the direction of the length of the train. The instantaneous flow shows an unsteady vortex shedding due to the shear layer instabilities on the periphery of the recirculation region and the exterior flow. In the case of the 35 {ring operator} yaw angle, weak vortex shedding is found in the wake. Instead, unstable vortices are found in the lower part of the recirculation region. These vortices detach from and reattach to the train surface in a regular fashion leaving disturbances on the train surface and hence affecting the aerodynamic coefficients. The influence of the shape of the nose on the flow structures is investigated by repeating the simulations at the 90 {ring operator} yaw angle on a short nose model. The short nose model is identical to the long nose model whilst the length of its nose is half that of the long nose. The short-nose simulation shows highly unsteady and three-dimensional flow around the nose yielding more vortex structures in the wake. These structures result in a surface flow that differs from that in the long-nose train flow. They also influence the dominating frequencies that arise due to the shear layer instabilities. © 2009.
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| 17. |
- Hobeika, Teddy, 1988, et al.
(författare)
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CFD investigation on wheel rotation modelling
- 2018
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 174, s. 241-251
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Tidskriftsartikel (refereegranskat)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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| 18. |
- Josefsson, Erik, 1995, et al.
(författare)
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Evaluation of wind tunnel interference on numerical prediction of wheel aerodynamics
- 2022
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 224
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Tidskriftsartikel (refereegranskat)abstract
- For a passenger vehicle, approximately 25% of the total aerodynamic drag originates from the wheels, making the aerodynamics of wheels a significant factor for the overall performance of a vehicle. To understand the complex flow field created by the rotational condition and geometry of these bluff-bodies, numerical simulations are often used. However, computations are frequently performed in domains that replicate open road conditions, differing from the conditions of wind tunnels. Therefore, to properly validate a CFD procedure and to correlate physical tests to numerical results, interference effects of the wind tunnel need to be investigated and their impact on the aerodynamics of wheels analysed and compared to that of open road calculations. In this study, numerical simulations on the DrivAer model were performed using different tyres and rims in both open road conditions and with the inclusion of a detailed model of a slotted walls wind tunnel. The results of the simulations are compared to experimental data, consisting of forces and flow field measurements. It was found that the inclusion of the wind tunnel in the computations improves the prediction of the flow fields, resulting in better prediction of both the absolute drag values and the drag deltas between configurations.
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| 19. |
- Krajnovic, Sinisa, 1970, et al.
(författare)
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Influence of floor motions in wind tunnels on the aerodynamics of road vehicles
- 2005
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 93:9, s. 677-696
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Tidskriftsartikel (refereegranskat)abstract
- The effect of a moving floor on the flow around a simplified car with a typical fastback geometry is investigated. Two large-eddy simulations of the flows with stationary and moving floors are made and both instantaneous and time-averaged results are compared. It is found that the floor motion reduces drag by 8% and lift by 16%. Changes in the flow are found to be global but are largest close to the floor and on the rear slanted surface of the vehicle. The wake flow is found to be relatively insensitive to the floor movement, in agreement with previous experimental observations. The periodicity of the flow events is found to be dependent on whether the floor is moving. Power spectral density of both the lift and the drag contain only one dominant frequency peak when the moving floor is adopted as compared to scattered spectra in the stationary floor case. Changes in the qualitative picture of the flow are limited to the flow near the floor and on the slanted surface of the body. However, changes in the surface pressure on the body and the history of the flow show the need of a moving floor in experimental and numerical simulations.
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| 20. |
- Krajnovic, Sinisa, 1970, et al.
(författare)
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Large eddy simulation of the flow around a simplified train moving through a crosswind flow
- 2012
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 110, s. 86-99
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Tidskriftsartikel (refereegranskat)abstract
- Results of large eddy simulation of the flow around a simplified train model moving through a crosswind are presented. These results are compared with the experimental data and show good agreement. The Reynolds number based on the inlet velocity and the height of the model is 22 615. In addition to the simulation of the flow around the moving model, another simulation was made of the flow around a stationary model influenced by the maximum crosswind from the moving case and the results are compared with the moving case. Overshoots were observed in several aerodynamic coefficients of the moving case over the stationary case. The yawing moment coefficient displayed an overshoot of some 30% indicating the importance of performing the dynamic tests for the purpose of fulfilling safety standards.
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| 21. |
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| 22. |
- Liang, Xifeng, et al.
(författare)
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On the aerodynamic loads when a high speed train passes under an overhead bridge
- 2020
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 202
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Tidskriftsartikel (refereegranskat)abstract
- The aerodynamic loads on the overhead bridge bottom surface induced by train passage are reported in this paper. Both moving model test and numerical simulation approaches at the 1:20 scale are used. The numerical work is validated through both mesh independence tests and comparison with experimental data. Typical pressure variation curves are plotted and compared with previous studies. The peak pressure values’ dependence on the Reynolds number is considered through four sets of experiments with different train running speeds. The peak pressure coefficient distribution law for the bridge bottom surface is presented. Differences in the pressure distribution in different bridge bottom areas are explained based on more detailed flow field information. The influence of the bridge height on the aerodynamic load magnitude and time interval is presented. Moreover, the application of the CEN Standard to practical engineering issues is discussed.
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| 23. |
- Liu, Dongyun, et al.
(författare)
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A review on aerodynamic load and dynamic behavior of railway noise barriers when high-speed trains pass
- 2023
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier. - 0167-6105 .- 1872-8197. ; 239
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Tidskriftsartikel (refereegranskat)abstract
- Noise barriers need to be installed along high-speed railway lines to protect nearby inhabitants from the noise pollution caused by the running of high-speed trains (HSTs). The vertical noise barrier is the main structural type. However, when an HST passes through the noise barriers sited along the track, significant and transient aerodynamic pressure will act on the surface of the noise barriers, resulting in strong dynamic responses and even fatigue damage. Therefore, it is important to determine the train-induced aerodynamic load on the barrier surface and analyze the dynamic behaviors of the noise barriers under such a load for its structural design and to guarantee its safety and durability. This paper is a systematic review of the current literature on the aerodynamic load and dynamic behavior of vertical noise barriers; it includes (1) a summary and analysis of characteristics of such aerodynamic pressure and relevant influencing factors, (2) an introduction to measurement methods of aerodynamic load and relevant pressure models on the surface of noise barriers, and (3) a description of the dynamic response and fatigue analysis of noise barriers under such loads. Finally, potential further studies on this topic are discussed, and conclusions are drawn.
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| 24. |
- Liu, Dongyun, et al.
(författare)
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Modified calculation model of train-induced aerodynamic pressure on vertical noise barriers considering the train geometry effect
- 2024
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier. - 0167-6105 .- 1872-8197. ; 249
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Tidskriftsartikel (refereegranskat)abstract
- High-speed trains (HSTs) generate air disturbance, leading to significant aerodynamic pressure on the noise barriers. Differences in train geometry result in variations in the aerodynamic pressure on noise barriers, implying that existing European standard calculation models may not necessarily be suitable for all types of HSTs. In this paper, the influence of the width, height, and nose length of the train on the aerodynamic pressure on vertical noise barriers was studied using computational fluid dynamics (CFD) simulations. Results showed that taller and wider trains result in greater aerodynamic loads on noise barriers. Conversely, an increase in the nose length of a train leads to a reduction in such pressure. Using grey relational analysis, correlation of various factors with the train-induced aerodynamic pressure is, from strong to weak: distance to the track center, width, height, and nose length of the train. Building upon the EN 14067-4 calculation model, the shape coefficients of trains with varying geometric characteristics were derived using the simulation data obtained in this study. A modified pressure calculation model was established accounting for the differences in geometric features of HSTs and pressure distribution in the vertical direction of noise barriers and validated using relevant data from the literature.
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| 25. |
- Liu, Mingyang, et al.
(författare)
-
A numerical study on water spray from wheel of high-speed train
- 2020
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 197
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of water spray from wheels on the ice accumulation in the bogie regions of high-speed train has been studied using the coupling numerical methods of improved delayed detached eddy simulation (IDDES) and Lagrangian Model. The rotation of the wheels was simulated using the moving overset grid technique. The flow field, spatial distribution and surface distribution of droplets on the bogies have been analysed to identify the effect of various speed on the movement of droplets. The results show that the inlet speed between 160 km/h and 250 km/h will lead to the most severe influence on water spray from wheel in the whole bogie regions. A large amount of water droplets gathering on the surface of the bogies and bogie cavities is likely to cause severe ice accretion. The influence of water spray for high-speed train decreases rapidly at the speed of 300 km/h and changes a little as the speed continues to increase. Among all the components of the bogie, the brake clamp is most affected by droplets. Furthermore, the droplets were found to have a severe effect on the draft sill and air spring.
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| 26. |
- Ljungskog, Emil, 1990, et al.
(författare)
-
Inclusion of the physical wind tunnel in vehicle CFD simulations for improved prediction quality
- 2020
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 197
-
Tidskriftsartikel (refereegranskat)abstract
- When performing numerical simulations of the aerodynamic properties of vehicles, the simulation domain used is often a large box with a very low blockage ratio and a fully moving ground plane, replicating open road conditions. However, the physical measurements to which the simulation results are usually compared are typically performed in wind tunnels, with deficiencies concerning blockage, ground modeling, and other boundary interference effects. Some of these effects can be corrected for, but such corrections are usually performed on a global level and thus fail to correct for local effects that might influence different configurations of the vehicle in different ways. In this work, the typical open road numerical setup is compared to simulations where the computational domain is a virtual model of the complete slotted wall wind tunnel test section geometry. A vehicle of sedan type is simulated in different configurations, and the simulation results are compared to forces and pressure measurements from physical tests. The results show that the absolute drag coefficient can be predicted with very good accuracy by simulating the car inside the wind tunnel if compared to uncorrected measurement data. However, despite the good agreement for drag, the prediction of lift is not as satisfactory.
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| 27. |
- Lv, Dazhou, et al.
(författare)
-
Numerical study on transient aerodynamic characteristics of high-speed trains during the opening of braking plates based on dynamic-overset-grid technology
- 2023
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 233
-
Tidskriftsartikel (refereegranskat)abstract
- The safety of high-speed trains is considerably compromised by increasing speed trends. Thus, braking plate technology has been applied to high-speed trains. The purpose of this study is to clarify the evolution law of the flow field of the vehicle during the opening of the braking plate and analyze the influence of the plate movement on the aerodynamic performance of the train. In this study, the flow field was computed using incompressible Navier–Stokes equations and the shear-stress transport (SST) k–ω turbulence model, and the unsteady flow over the opening brake plates was simulated using moving overlapping grids and dual time-stepping. The numerical method was verified through comparison with wind tunnel data (error <8%). The results reveal that the upstream braking plate significantly decreases the aerodynamic forces of the downstream plate during opening of the plates and causes the aerodynamic drag of the downstream braking plate to fluctuate significantly when it increases. The operation of the braking plate produces a small increase in the drag force of the train body (2.6%), but it significantly decreases the lift force of the train body (by up to 94%), especially during the opening of the braking plates. The flow field in the upper part of the train is significantly changed by the opening of the braking plate. In particular, the pressure in the cavity of the braking device changes sharply, and the surface is subjected to a large pulse pressure.
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| 28. |
- Magnusson, M, et al.
(författare)
-
Air flow behind wind turbines
- 1999
-
Ingår i: JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS. - : ELSEVIER SCIENCE BV. - 0167-6105. ; 80:1-2, s. 169-189
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Wind turbine wakes have been studied by analysing a large set of atomospheric data, from a wind farm with four turbines sited on a flat coastal area. The results obtained have been generalized to allow tests against data from other full scale wind turbine
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| 29. |
- Magnusson, M
(författare)
-
Near-wake behaviour of wind turbines
- 1999
-
Ingår i: JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS. - : ELSEVIER SCIENCE BV. - 0167-6105. ; 80:1-2, s. 147-167
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- For studies of the flow downstream wind turbines, the initial state of the how is of importance. In this study the flow generated by a wind turbine has been calculated. The purpose is to study how a logarithmic wind profile and yaw, modifies the initial s
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| 30. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
Aerodynamic flow control for a generic truck cabin using synthetic jets
- 2017
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 168, s. 81-90
-
Tidskriftsartikel (refereegranskat)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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| 31. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
Validation of PANS and active flow control for a generic truck cabin
- 2017
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 171, s. 148-160
-
Tidskriftsartikel (refereegranskat)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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| 32. |
- Nguyen, Minh-Thao, et al.
(författare)
-
Evaluation of the unsteady aerodynamic forces acting on a vertical-axis turbine by means of numerical simulations and open site experiments
- 2020
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : ELSEVIER. - 0167-6105 .- 1872-8197. ; 198
-
Tidskriftsartikel (refereegranskat)abstract
- An increasing number of vertical-axis wind turbine prototypes have reached the step in which the theoretically predicted performance needs to be validated in order to move to the next steps of a real commercial project. This step often faces the significant challenges posed by their airfoil aerodynamics that are more complex than those of conventional horizontal-axis wind turbines, and it has also to deal with the lack of fundamental experimental data for robust validation. In this context, an accurate prediction of the real turbine operation is important and the use of computational fluid dynamics (CFD) is imposing itself as the most suitable tool to characterize the unsteady phenomena that are difficult to detect by means of experimental measurements. In the current work, two-dimensional numerical simulations of an H-type three-blade Darrieus turbine have been performed in a wide range of tip-speed ratios (TSRs) from TSR = 1.8 to TSR = 5.0. Unsteady CFD simulations were compared with unique experimental data collected in the field in terms of normal aerodynamic forces acing on the blades during the revolution. Generally, nice agreement was found between simulations and experiments, especially at medium-high tip-speed ratios. The influence of operating conditions on the performance prediction capability of the numerical model was also discussed. This is one of the key points of study since the lack of detailed experimental data often makes numerical analyses doubtful or scarcely effective. Finally, the simulation results were exploited in order to analyze the phenomena occurring during the revolution and to correlate them with the experimental findings.
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| 33. |
- Niu, Jiqiang, et al.
(författare)
-
Aerodynamic simulation of effects of one- and two-side windbreak walls on a moving train running on a double track railway line subjected to strong crosswind
- 2022
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 221
-
Tidskriftsartikel (refereegranskat)abstract
- High-speed railway lines are widely distributed worldwide. The surrounding wind environment of such railway lines is complex, which significantly affects the safety of high-speed train operations. Using a combination of the computational fluid dynamics method of improved delayed detached eddy simulation and sliding grid technology, the effects of one- and two-side windbreak walls on the unsteady aerodynamic performance of a high-speed train running under a crosswind on a double-track railway line with an embankment and the flow-field characteristics around the train were systematically studied. The grid independence and numerical methods used in this study were verified. The results showed that when the windbreak wall was absent, the aerodynamic performance of the train running on the upstream railway line was the poorest, while the train running on the downstream railway line exhibited large aerodynamic fluctuations. The windbreak wall significantly reduced the aerodynamic force and its fluctuation; the one- and two-side windbreak walls had different effects on the unsteady aerodynamic performance of trains running on the upstream and downstream railway lines under a crosswind. The one-side windbreak wall could restrain the aerodynamic fluctuation of the train more and is thus preferred from the perspective of construction effort and cost.
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| 34. |
- Otxoterena Af Drake, Paul, et al.
(författare)
-
Physical characteristics of splash and spray clouds produced by heavy vehicles (trucks and lorries) driven on wet asphalt
- 2021
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier B.V.. - 0167-6105 .- 1872-8197. ; 217
-
Tidskriftsartikel (refereegranskat)abstract
- Heavy vehicles rolling on wet roads produce splash and spray clouds. These aerosols reduce the visibility of other drivers, contribute to a small, but quantifiable proportion of road traffic accidents and affect the operational capabilities of autonomous vehicles travelling near them. Even though knowing the physical properties of these aerosols is essential for testing and validating sensors for environment perception and recognition of autonomous vehicles, there is little information about them. In this work the physical characteristics of spray clouds produced by heavy vehicles rolling on wet asphalt were measured by optical methods. Time resolved droplet size, mass concentration, number density, light extinction and contrast attenuation parallel and perpendicular to the travelling direction of the vehicle were measured. Vehicle velocity, vehicle configuration and water depth were varied during the tests. Results show that the average droplet diameter ranges between 100 and 400 μm with maximum diameters of almost 4 mm. Mass concentration gamuts between 0,2 and 0,7 kg/m3 with peaks surpassing 1 kg/m3 while number density spans between 20 and 40 cm−3 and occasionally exceeds 100 cm−3. Light extinction can reach levels as high as 0,2 m−1 and contrast, evaluated from images, can reach values under 0,1.
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| 35. |
- Pirooz, A. A. S., et al.
(författare)
-
Effects of sensor response and moving average filter duration on maximum wind gust measurements
- 2020
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 206
-
Tidskriftsartikel (refereegranskat)abstract
- The use of wind speed data recorded using different measuring equipment (i.e. anemometers with different response characteristics) and different signal-processing procedures can introduce errors in the characterisation of surface wind speeds. This study aims to assess the effects of a set of various moving average filter durations and turbulence intensities on the recorded maximum gust wind speeds. For this purpose, a series of wind-tunnel experiments was carried out on the widely-used Vaisala WAA151 cup anemometer. The variations of gust and peak factors, and turbulence intensities measured by the cup anemometer as a function of the averaging duration and turbulence intensity are presented. The wind-tunnel results are compared with values computed from a theoretical approach, namely random process and linear system theory, and the results were also validated against values reported in the literature where possible. The results show that the maximum gust wind speeds measured using large averaging durations (e.g. 3 s or 5 s) lead to up to 25%-30% negative biases compared to high frequency measurements (e.g. 4 Hz unfiltered gust measurements). This result can strongly impact subsequent meteorological, climatological and wind engineering studies, as different gust definitions have been adopted by National Weather Services and institutions around the world. Lastly, a set of correction factors (i.e. gust factor ratios) have been proposed that allows measurements at a specific gust duration to be converted to equivalent measurements at specified particular gust durations of interest.
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| 36. |
- Qiao, Zengxi, 1986, et al.
(författare)
-
Multi-frequency aerodynamic control of a yawed bluff body optimized with a genetic algorithm
- 2021
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 212
-
Tidskriftsartikel (refereegranskat)abstract
- This experimental work aims to investigate the manipulation of a bluff body flow with a yaw angle of 10° based on a genetic algorithm optimization. Two loudspeakers are used to generate zero-net mass-flux jets through streamwise slots, which span a large portion of the rounded A-pillars of the bluff body. The actuations produce a maximum drag reduction of 17% and 2% for the leeward and windward side control, respectively. The genetic algorithm has found two typical frequencies to separately drive the actuators on the windward and leeward sides. The drag reduction is 20% under the optimal control law, 3% larger than the 17% attained from the reference single frequency control. In addition, a beneficial effect is observed when considering energy efficiency, which increases by 30% in the optimal control compared to the single frequency control. The drag spectra and velocity mapping in the wake are measured with and without control, and, based on the measurement, the underlying flow mechanism behind the control is proposed.
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| 37. |
- Rao, Anirudh Narayan, 1985, et al.
(författare)
-
Investigation of the near-wake flow topology of a simplified heavy vehicle using PANS simulations
- 2018
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 183, s. 243-272
-
Tidskriftsartikel (refereegranskat)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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| 38. |
- Rao, Anirudh Narayan, 1985, et al.
(författare)
-
On the two flow states in the wake of a hatchback Ahmed body
- 2018
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 173:February 2018, s. 262-278
-
Tidskriftsartikel (refereegranskat)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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| 39. |
- Rao, Anirudh Narayan, 1985, et al.
(författare)
-
Qualitative assessment of the bi-stable states in the wake of a finite-width double backward facing step
- 2019
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 186, s. 241-249
-
Tidskriftsartikel (refereegranskat)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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| 40. |
- Reymert, Sebastian, et al.
(författare)
-
A characterisation of vehicle-driver response to lateral disturbances when passing through bridge tower wakes
- 2024
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105 .- 1872-8197. ; 246
-
Tidskriftsartikel (refereegranskat)abstract
- Some of the strongest wind -induced lateral perturbations of the vehicle -driver system on bridges are observed when passing the towers. Occupants may feel uncomfortable or unsafe as a result. The aims of this work are to characterise the wind velocity profile observed in the wakes of bridge towers and understand the mechanisms through which the vehicle -driver system responds. A test vehicle was repeatedly driven across 5 cable -supported bridges with towers, of which 4 have been studied. Observed changes in wind speed were between 7 and 20 m/s with reference wind speeds of 14 to 25 m/s. The spatial periods of the wind profiles varied between 1.0 and 3.5 vehicle lengths giving disturbances at frequencies of 0.7 to 3.2 Hz at 60 to 80 km/h. The results show that the driver overcompensates for the changes in aerodynamic loading at the towers and the handling response of the vehicle is dominated by steering input - rather than aerodynamic input - once the driver initiates steering compensation. It is also shown, in agreement with an existing conceptual model, that the amplitude of the driver's steering response is linearly related to the change in the vehicle's yaw rate immediately preceding the compensation attempt.
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| 41. |
- Sekulic, Dragan, 1976, et al.
(författare)
-
Analysis of vehicle path tracking ability and lateral stability on a floating bridge under a crosswind
- 2022
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 227
-
Tidskriftsartikel (refereegranskat)abstract
- The reconstructed route E39 along the west coast of Norway will provide efficient local and regional transportation for people and goods. Efficient transportation implies safety measures exist, e.g., driving speed limits for adverse weather condition. This is especially important for structures in open areas, such as long-span bridges. This paper investigates the path tracking ability and lateral stability of two vehicle types – a tractor-semitrailer (TS) and a sport utility vehicle (SUV) – on the Bjørnafjorden floating bridge considering a 1-year storm condition. At a speed of 108 km/h, the TS experiences a roll-over risk, and at a speed of 90 km/h, it frequently leaves the traffic lane. At the highest speed, the SUV wheels do not lose contact with the bridge deck, but the vehicle does leave the traffic lane. This implies that a TS driver requires more vehicle handling effort over the floating bridge than an SUV driver. Results suggest that a TS can safely enter the bridge at a low speed (36 km/h) and then accelerate to 72 km/h after travelling 2 km. An SUV entering at a speed of 90 km/h and accelerating to 108 km/h after travelling 0.5 km was found to be safe.
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| 42. |
- Sekulic, Dragan, 1976, et al.
(författare)
-
Effects of wind loads and floating bridge motion on intercity bus lateral stability
- 2021
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 212
-
Tidskriftsartikel (refereegranskat)abstract
- Efficient transportation is an important factor for regional socio-economic growth. Excitations from wind loads and road motions can influence vehicle-driver behaviour in a way that may impair transportation. This is especially true in open areas such as long-span bridges. This paper investigates the influence of wind loads and floating bridge motions on bus lateral stability for the straight concept solution across Bjørnafjorden in Norway. For this investigation, an 8-degree-of-freedom model of a two-axle coach is used. The defined driver model is based on the pure pursuit path tracking method. The vehicle deviation from the path is found to increase with increasing bus speed. This deviation is significant after the vehicle enters the bridge (e.g., over 0.5 m for a speed of 90 km/h). At 108 km/h, the windward rear wheel loses contact, indicating the potential risk of vehicle roll-over. The mean and root-mean-square values of the handwheel steering angle increase with increasing speed, which might cause difficulty for the driver to control the vehicle. Simulation results suggest that the bus can suitably enter the bridge at a lower speed (e.g., 72 km/h) with the possibility of increasing the speed (up to 90 km/h) after approximately 2 km of travelled distance.
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| 43. |
- Tunay, Tural, et al.
(författare)
-
On coupling methods used to simulate the dynamic characteristics of heavy ground vehicles subjected to crosswind
- 2020
-
Ingår i: Journal of Wind Engineering & Industrial Aerodynamics. - : Elsevier BV. - 0167-6105 .- 1872-8197. ; 201, s. 1-15
-
Tidskriftsartikel (refereegranskat)abstract
- Ground vehicles often encounter turbulent flows with wide range of scales, e.g. crosswind gusts, when moving on-road conditions. Crosswinds can be considered as an important factor in heavy vehicle’s roll-over accident due to their relatively high center of gravity and lateral surface area. However, there are few studies which investigate effects of crosswinds on heavy vehicles. Furthermore, existing studies have generally focused on lateral or yaw dynamics of heavy vehicles and neglected their roll dynamics. Therefore, effects of crosswinds on heavy ground vehicles should be understood in all aspects in order to design less wind-sensitive vehicles especially at early stages of their design processes. Inherently, crosswind studies require a multidisciplinary approach which involves coupling between aerodynamics and vehicle dynamics. In the present study, investigation of effects of the coupling methods, e.g. one-way and two-way couplings, between aerodynamics and vehicle dynamics simulations are aimed by considering both lateral and roll dynamics of heavy vehicles which are subjected to crosswind gust. Vehicle dynamics and aerodynamics results are presented. Results of the one-way coupled simulations, in general, overestimate the absolute maximum values of the vehicle dynamics results. However, differences in lateral displacement results Δymax are less than 0.2 m for the studied case.
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| 44. |
- Törnell, Johannes, 1991, et al.
(författare)
-
Effects of separation distance, lateral offset, and yaw on the drag of a truck and SUV platoon
- 2023
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - 0167-6105. ; 241
-
Tidskriftsartikel (refereegranskat)abstract
- The recent popularity of electric vehicles and upcoming governmental regulations on emissions are forcing automotive manufacturers to build more efficient vehicles. An approach to improve the efficiency of a road vehicle is by reducing its aerodynamic resistance. One way of achieving this is through platooning, vehicles drive in close-proximity. Despite of the extensive literature available on platooning of multiple vehicle types, most studies have focused on the drag and flow effects around the truck only. This work aims to increase the understanding and recognize the usefulness of a truck-SUV platoon system as a whole using wind tunnel measurements on two scale models and CFD simulations. From the results of this study, it was found that the effects on the SUV are large and contribute to a significant portion of the drag reduction of the system, especially at short inter-vehicle distances where the drag of the car can become negative. The drag reduction for the truck is generally limited as the truck is a much larger vehicle. For the system, the results show that for very short distances it is beneficial for the truck to lead the platoon, while at longer separations there is no preferable order.
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| 45. |
- Törnell, Johannes, 1991, et al.
(författare)
-
Experimental investigation of a two-truck platoon considering inter-vehicle distance, lateral offset and yaw
- 2021
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 213
-
Tidskriftsartikel (refereegranskat)abstract
- In recent years a renewed interest in platooning has emerged due to increasing pressure on vehicle manufacturers to reduce greenhouse gas emissions of their fleets. Vehicles traveling in close proximity have been studied in some depth, particularly simplified bodies and North American trucks. Still, there is a lack of understanding of the benefits of platooning for European style trucks. In this study, experiments were undertaken using two 1:6 scale detailed cab over engine tractor-trailer models in a wind tunnel with a moving ground. Surface pressures were measured on both trucks, while force measurements were taken on the model placed on the belt. Inter-vehicle distance, lateral offset, and yaw conditions were varied. Results show that a reduction of drag for the platoon is seen as the inter-vehicle distance decreases. For the leading truck, the reduction is due to an increased base pressure caused by the truck behind. The trailing truck has a more complex behavior and is sensitive to yaw changes. At short inter-vehicle distances, the leading truck loses in performance with a lateral offset, while the trailing truck gains in performance if under yaw conditions. To aid the flow analysis, numerical simulations were undertaken for some conditions studied experimentally.
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| 46. |
- Urquhart, Magnus, 1990, et al.
(författare)
-
Numerical analysis of a vehicle wake with tapered rear extensions under yaw conditions
- 2018
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 179, s. 308-318
-
Tidskriftsartikel (refereegranskat)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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| 47. |
- Uystepruyst, David, 1983, et al.
(författare)
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Numerical simulation of the transient aerodynamic phenomena induced by passing manoeuvres
- 2013
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 114, s. 62-71
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Tidskriftsartikel (refereegranskat)abstract
- Several three-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations of the passing generic vehicles (Ahmed bodies) are presented. The relative motion of vehicles was obtained using a combination of deforming and sliding computational grids. The vehicle studied is an Ahmed body with an angle of the rear end slanted surface of 30 degrees. Several different relative velocities and transversal distances between vehicles were studied. The aerodynamic influence of the passage on the overtaken vehicle was studied. The results of the simulations were found to agree well with the existing experimental data. Numerical results were used to explain effects of the overtaking manoeuvre on the main aerodynamic coefficients.
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| 48. |
- Vernet, Julie, et al.
(författare)
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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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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier. - 0167-6105 .- 1872-8197. ; 145, s. 318-326
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Tidskriftsartikel (refereegranskat)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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| 49. |
- Wang, Jiabin, et al.
(författare)
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An IDDES investigation of Jacobs bogie effects on the slipstream and wake flow of a high-speed train
- 2020
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 202
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Tidskriftsartikel (refereegranskat)abstract
- This study numerically investigates the effects of Jacobs bogies on the aerodynamic behaviors of a high-speed train using improved delayed detached eddy simulation (IDDES) at Re = 3.3 × 105. The results of the numerical simulations have been validated against the experimental data obtained from a previous reduced-scale moving model test and a wind tunnel test. The slipstream velocity, wake flow, underbody flow and aerodynamic drag of the HST are compared between the conventional bogie case and Jacobs bogie case. The results show that the use of Jacobs bogies can reduce the TSI values of the slipstream velocity at trackside and platform positions by 11.07% and 22.40%, respectively, which thereby shows a positive effect on improving the safety level of trackside workers and passengers standing on the platform. The Jacobs bogies are found to decrease the maximum values of the slipstream velocity and turbulence kinetic energy occurring at the intermediate bogie regions beneath the HST by 30.08% and 41.32%, respectively, which is beneficial for weakening the ballast flight phenomenon. The Jacobs bogies significantly narrow the scale of the longitudinal vortex structure in the wake propagation region. Additionally, the application of Jacobs bogies lowers the aerodynamic drag values of the vehicles and contributes to a 10% total drag reduction.
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| 50. |
- Wang, Jiabin, et al.
(författare)
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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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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 176, s. 211-224
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Tidskriftsartikel (refereegranskat)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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