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Physical experiments have difficulties to thoroughly investigate the full structure of air flow behind a porous fence. Physical measurement sensors have their limitations of data acquisitions in turbulent air flow. Computational Fluid Dynamics (CFD) technique provides an infinite number of virtual sensors that allows producing quantitative CFD base...
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... CFD simulation, as the time averaged bed shear stress reflects the velocity in the cell next to the boundary, then the reattachment is defined as the point where the near-wall velocity is zero. Therefore it can conveniently allocate the position of reattachment point in the domain. Fig. 9 displays the red-cross is the position of the reattachment point, which is at x, y, z = 3.1e-5, 0, -1668 mm. ...
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One main disadvantage that has consistently remained for CFD is the chaotic nature of
turbulent flow. To tackle the task of modelling turbulence, various models have been devised,
including the K-epsilon model, the K-omega model, and the Reynolds Stress Model. To
compare the accuracy of the three models, a wind tunnel simulation was created using t...
Citations
... The low recirculating wind created in the recirculation region behind the porous wind fence traps the eroded particles and controls the material loss. (Xu and Mustafa 2015) In recent years, many investigators focused on the efficacy of fences by evaluating the reduction in wind velocity in the wake region behind the fence. There are numerous experimental studies and numerical simulations to study the shelter effect of porous fences. ...
The wind blowing at high velocity in an open storage yard leads to wind erosion and loss of material. Fence structures can be constructed around the periphery of the storage yard to reduce the erosion. The fence will cause turbulence and recirculation behind it which can be utilized to reduce the wind erosion and loss of material. A properly designed fence system will produce lesser turbulence and longer shelter effect. This paper aims to show the applicability of Support Vector Machine (SVM) to predict the recirculation length. A SVM model was built, trained and tested using the experimental data gathered from the literature. The newly developed model is compared with numerical turbulence model, in particular, modified k-e model along with the experimental results. From the results, it was observed that the SVM model has a better capability in predicting the recirculation length. The SVM model was able to predict the recirculation length at a lesser time as compared to modified k-e model. All the results are analyzed in terms of statistical measures, such as root mean square error, correlation coefficient, and scatter index. These examinations demonstrate that SVM has a strong potential as a feasible tool for predicting recirculation length.
... Airflow through a porous fence is a dynamic process that involves interactions between the fence and the air, which the oncoming air velocity does not simply decrease after passing though the fence. Figure 1 illustrates the difference of airflow profiles leeward of porous fences with different porosities [1]. When the porosity is above a critical level, the bleed flow dominates and the airflow in the leeward side of the fence is generally in the same direction as the windward flow shown in Figure 1 (top). ...
... When the porosity is below the critical level, the leeward airflow directly behind the fence reverses, resulting in a region of recirculating air shown in Figure 1 (bottom). The researchers [1][2][3][4] have found that the presence of both the bleed flow passing through the porous holes and the displaced flow diverted over the fence formed a complex airflow field behind. A high velocity region was A c c e p t e d M a n u s c r i p t formed above the fence. ...
This paper presents using the computational fluid dynamics (CFD) modelling to analyze the flow around porous fences. The feasibility of applying two- and three-dimensional models was assessed with respect to corresponding wind tunnel experiments. Comparisons between the flow structures on leeward of the fence as predicted by CFD models and the wind tunnel measurements were discussed. Velocity values for the two modelling approaches were in good agreement. However, there is a noticeable discrepancy in predicting the turbulence structure. Both two- and three-dimensional model have demonstrated the capability to predict flow characteristics necessary for the design of porous fences. However, the selection between two- and three-dimensional model is dependent on, design stage and the extent of accuracy required by the application. The presented CFD models are potentially applicable to heat transfer issues.
... Further detail about numerical procedure and validation of the model are presented in another paper [6]. ...
This paper presents a numerical simulation of non-normal wind loads on a porous fence. It was found that non-normal wind load has significant impact on the performance of the fence in terms. The performance of the fence was measured as the effective fence zone behind the fence where flow characteristics and normal drag coefficients were maintained within safe level. It is recommended the incidental angle between the most prevalent wind direction and the fence position is preferably less than 15° but and no more than 30°.
... Four types of shape of pores were selected, namely circle, rectangular, triangular and trimmed triangular shaped pores. The detail about numerical procedure and model validation were presented in a previous paper [21]. ...
This paper presents an application of Computational Fluid Dynamics (CFD) technique for designing of protective fences for shelter from snow and winds commonly used on offshore rigs and other facilities in cold regions. The CFD simulation of real situations provided detailed information about the flow characteristics behind the fence and the effective shelter zone. Such flow details are usually very expensive, time consuming and difficult to obtain by physical experiments. The numerical simulations found that the shape of pores and surface shear stress has significant impact on the reattachment length and the size of effective fence zone. The effective shelter distance can be increased by avoiding sharp angular corners in the porous pores and reducing surface shear stress. The 3D modelling and CFD simulation provide detailed aerodynamics flow characteristics and stress distributions that allow evaluating a number of designs cost effectively. The technique can be integrated with small-scale intelligent manufacturing system (SIMS) for flexible design and manufacturing of fences.
... Fig.1. shows a comparison of flow regimes behind porous fences for porosities above and under critical porosity, where β is porosity of fence, and βcrit is critical porosity of fence [1,3]. [1] Critical porosity, β crit is defined as the maximum fence porosity below which flow separation and reversal occurs [3]. ...
... shows a comparison of flow regimes behind porous fences for porosities above and under critical porosity, where β is porosity of fence, and βcrit is critical porosity of fence [1,3]. [1] Critical porosity, β crit is defined as the maximum fence porosity below which flow separation and reversal occurs [3]. Above the critical porosity, the airflow in the leeward is dominant by bleed flow and there is no flow separation; (Fig.1, a). ...
Efficiency of wind fences is evaluated by the reduction of wind velocity and the effective shelter area behind the fence. Fence porosity is the most influential structural parameters in the porous fence design, and has significant impact on the structure of wind velocity and turbulence leeward. In this work, three fences with porosity of 23%, 35% and 45% have been tested under 10m/s inlet velocity in an environmental wind tunnel. An ultrasonic anemometer was used to measure three dimensional velocity vectors and the fluctuations of velocity vectors with a designed spatial resolution. The obtained data were used to calculate velocity magnitudes, turbulence intensities and turbulent kinetic energies in the test domain. Porosity influencing the structure of turbulence intensity and effective fence zone were discussed in this paper. Neither the distribution of wind velocities nor the structure of turbulence alone can provide sufficient information to assess the performance of porous fences. Consideration of the targeted reduction rate of wind velocity needs to be taken for optimal fence design.
