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Numerical evaluation of the scale problem on the wind flow of a windbreak.

Liu B, Qu J, Zhang W, Tan L, Gao Y - Sci Rep (2014)

Bottom Line: In this study, we perform a numerical comparison between a scaled wind-fence experimental model and an actual-sized fence via computational fluid dynamics simulations.The results show that although the general field pattern can be captured in a reduced-scale wind tunnel or numerical model, several flow characteristics near obstacles are not proportional to the size of the model and thus cannot be extrapolated directly.For example, the small vortex behind a low-porosity fence with a scale of 1:50 is approximately 4 times larger than that behind a full-scale fence.

View Article: PubMed Central - PubMed

Affiliation: Dunhuang Gobi Desert Ecological and Engineering Research Station, Key Laboratory of Desert and Desertification, Chinese Academy of Sciences, Lanzhou 730000, China.

ABSTRACT
The airflow field around wind fences with different porosities, which are important in determining the efficiency of fences as a windbreak, is typically studied via scaled wind tunnel experiments and numerical simulations. However, the scale problem in wind tunnels or numerical models is rarely researched. In this study, we perform a numerical comparison between a scaled wind-fence experimental model and an actual-sized fence via computational fluid dynamics simulations. The results show that although the general field pattern can be captured in a reduced-scale wind tunnel or numerical model, several flow characteristics near obstacles are not proportional to the size of the model and thus cannot be extrapolated directly. For example, the small vortex behind a low-porosity fence with a scale of 1:50 is approximately 4 times larger than that behind a full-scale fence.

No MeSH data available.


Related in: MedlinePlus

Comparison of the small vortex behind a solid fence at the two scales; wind speed = 10 m/s and η = 0.
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f3: Comparison of the small vortex behind a solid fence at the two scales; wind speed = 10 m/s and η = 0.

Mentions: A small vortex behind a solid or low-porosity fence was observed in the wind tunnel13 and in both numerical simulations in the present study. A direct comparison of the vortex in the two scale simulations reveals the difference caused by the scale effect (Fig. 3). Under a 10 m/s wind condition, the vortex behind the solid wind tunnel model fence was well developed to approximately a 0.6 H height and 1 H distance, whereas the vortex behind the actual size solid fence had a height and distance of only approximately 0.15 H and 0.25 H, respectively; the relatively small vortex in the latter led to the short convergence length of the actual-sized simulation in Fig. 2. If the measured wind tunnel and CFD-simulated data were extrapolated 50 times to their actual size, then the height and length of the vortex would be 4 times larger than those of the vortex in the actual-sized model. This scale-affected difference indicates that although the general flow characteristics can be captured using scale models in a wind tunnel or same-scale CFD simulations, as tested by many previous works, the results of these methods will not be proportional to the model size and can be deformed if applied directly to a unique area, particularly near obstacles.


Numerical evaluation of the scale problem on the wind flow of a windbreak.

Liu B, Qu J, Zhang W, Tan L, Gao Y - Sci Rep (2014)

Comparison of the small vortex behind a solid fence at the two scales; wind speed = 10 m/s and η = 0.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4196098&req=5

f3: Comparison of the small vortex behind a solid fence at the two scales; wind speed = 10 m/s and η = 0.
Mentions: A small vortex behind a solid or low-porosity fence was observed in the wind tunnel13 and in both numerical simulations in the present study. A direct comparison of the vortex in the two scale simulations reveals the difference caused by the scale effect (Fig. 3). Under a 10 m/s wind condition, the vortex behind the solid wind tunnel model fence was well developed to approximately a 0.6 H height and 1 H distance, whereas the vortex behind the actual size solid fence had a height and distance of only approximately 0.15 H and 0.25 H, respectively; the relatively small vortex in the latter led to the short convergence length of the actual-sized simulation in Fig. 2. If the measured wind tunnel and CFD-simulated data were extrapolated 50 times to their actual size, then the height and length of the vortex would be 4 times larger than those of the vortex in the actual-sized model. This scale-affected difference indicates that although the general flow characteristics can be captured using scale models in a wind tunnel or same-scale CFD simulations, as tested by many previous works, the results of these methods will not be proportional to the model size and can be deformed if applied directly to a unique area, particularly near obstacles.

Bottom Line: In this study, we perform a numerical comparison between a scaled wind-fence experimental model and an actual-sized fence via computational fluid dynamics simulations.The results show that although the general field pattern can be captured in a reduced-scale wind tunnel or numerical model, several flow characteristics near obstacles are not proportional to the size of the model and thus cannot be extrapolated directly.For example, the small vortex behind a low-porosity fence with a scale of 1:50 is approximately 4 times larger than that behind a full-scale fence.

View Article: PubMed Central - PubMed

Affiliation: Dunhuang Gobi Desert Ecological and Engineering Research Station, Key Laboratory of Desert and Desertification, Chinese Academy of Sciences, Lanzhou 730000, China.

ABSTRACT
The airflow field around wind fences with different porosities, which are important in determining the efficiency of fences as a windbreak, is typically studied via scaled wind tunnel experiments and numerical simulations. However, the scale problem in wind tunnels or numerical models is rarely researched. In this study, we perform a numerical comparison between a scaled wind-fence experimental model and an actual-sized fence via computational fluid dynamics simulations. The results show that although the general field pattern can be captured in a reduced-scale wind tunnel or numerical model, several flow characteristics near obstacles are not proportional to the size of the model and thus cannot be extrapolated directly. For example, the small vortex behind a low-porosity fence with a scale of 1:50 is approximately 4 times larger than that behind a full-scale fence.

No MeSH data available.


Related in: MedlinePlus