| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- Östh, Jan, 1985, et al.
(författare)
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The flow around a simplified tractor-trailer model studied by large eddy simulation
- 2012
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 102, s. 36-47
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Tidskriftsartikel (refereegranskat)abstract
- Large-eddy simulation (LES) is used to study the flow around a simplified tractor-trailer model. The model consists of two boxes placed in tandem. The front box represents the cab of a tractor-trailer road vehicle and the rear box represents the trailer. The LES was made at the Reynolds number of 0.51×106 based on the height of the rear box and the inlet air velocity. Two variants of the model were studied, one where the leading edges on the front box are sharp and one where the edges are rounded. One small and one large gap width between the two boxes were studied for both variants. Two computational grids were used in the LES simulations and a comparison was made with available experimental force measurements. The results of the LES simulations were used to analyze the flow field around the cab and in the gap between the two boxes of the tractor-trailer model. Large vortical structures around the front box and in the gap were identified. The flow field analysis showed how these large vortical structures are responsible for the difference in the drag force for the model that arises when the leading edges on the front box are rounded and the gap width is varied.
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